tess/

app.rs

use std::collections::HashMap;
use std::io::{self, Write};
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
use std::time::Duration;

use crossterm::cursor::MoveTo;
use crossterm::event::{poll, read, Event, KeyCode, KeyEvent, KeyModifiers};
use crossterm::style::{Print, ResetColor, SetAttribute, SetForegroundColor, SetBackgroundColor, Attribute};
use crossterm::terminal::{Clear, ClearType, size};
use crossterm::QueueableCommand;

use crate::error::Result;
use crate::input::{translate, Command};
use crate::marks::{mark_set, mark_jump, jump_previous, update_prev_position, is_valid_mark_name, MarkTarget};
use crate::line_index::LineIndex;
use crate::prettify::PrettifyMode;
use crate::render::Cell;
use crate::source::{find_tail_offset, Source};
use crate::viewport::{Frame, RowStyle, SearchDirection, Viewport};

/// Constraints to re-apply when the source content has been replaced wholesale
/// (`--live`). The line index is rebuilt from scratch each time, so caps that
/// were originally honored at startup need to be reasserted.
#[derive(Default, Clone, Copy)]
pub struct RebuildSpec {
    pub head: Option<usize>,
    pub tail: Option<usize>,
}

/// Per-keystroke modes the app event loop can be in.
#[derive(Debug, Clone)]
enum InputMode {
    Normal,
    /// User pressed `-`; the next keystroke selects an option to toggle.
    OptionPrefix,
    /// User pressed `-P`; the next keystroke chooses a prettify mode
    /// (`j`/`y`/`t`/`x`/`h`/`c`/`a`/`r`).
    PrettifyPrefix,
    /// User pressed `/` or `?`; subsequent characters accumulate into a
    /// search pattern until Enter (commit) or Esc (cancel).
    SearchPrompt {
        direction: SearchDirection,
        buffer: String,
        /// If a search compile error occurred, show this in place of the
        /// buffer until the next keystroke.
        error: Option<String>,
    },
    /// User pressed `!`. The next keystrokes build a shell command in
    /// `buffer`; Enter executes via shell::run_shell_command, Esc cancels.
    ShellPrompt { buffer: String, error: Option<String> },
    /// Set-mark prefix: the next keystroke names the mark to set.
    MarkSetPending,
    /// Jump-to-mark prefix: the next keystroke names the mark to jump to.
    MarkJumpPending,
    /// First half of the Ctrl-X Ctrl-X chord.
    CtrlXPending,
    /// User pressed `:`. The next keystrokes build a colon command in
    /// `buffer`; Enter dispatches, Esc cancels.
    ColonPrompt { buffer: String, error: Option<String> },
    /// User pressed Ctrl-]. The next keystrokes build a tag name in
    /// `buffer`; Enter dispatches, Esc cancels.
    /// `buffer` accumulates the tag name; `error` holds an error or hint
    /// message (e.g. "[3 matches]" after a second consecutive Tab).
    /// `last_tab_matches` carries the prefix-match list from the most
    /// recent Tab so a second Tab can show the count without re-querying.
    TagPrompt {
        buffer: String,
        error: Option<String>,
        last_tab_matches: Option<Vec<String>>,
    },
}

#[derive(Debug, Clone, PartialEq)]
enum ColonCommand {
    Next,
    Prev,
    Edit(std::path::PathBuf),
    ShowFile,
    Quit,
    Delete,
    First,
    Last,
    Tag(String),
    TagNext,
    TagPrev,
    /// `:tselect [NAME]` — open the tag picker overlay. With a name, look
    /// up matches; without, use the currently-active TagStack matches.
    TagSelect(Option<String>),
    OpenPicker,
    OpenHelp,
    /// `:hex N` — set hex group width to N hex characters (2/4/8/16/32).
    HexGroup(usize),
    /// `:color [strict|interpret|raw]` — set or cycle the ANSI render mode.
    Color(Option<crate::render::AnsiMode>),
    /// `:case [sensitive|smart|insensitive]` — set or cycle the search
    /// case-sensitivity policy.
    Case(Option<crate::viewport::CaseMode>),
    /// `:hlsearch` (true) / `:nohlsearch` (false) — toggle search-match
    /// highlighting at runtime.
    HlSearch(bool),
    /// `:incsearch` — toggle incremental search (preview-as-you-type in the
    /// `/`/`?` prompt) at runtime. Bare command; flips the current state.
    IncSearch,
    /// `:header L [C]` — pin top L source rows and left C cols.
    Header(usize, usize),
    /// `:yank` — copy the current top logical line to the system clipboard
    /// (only acts when `--clipboard` was passed).
    Yank,
}

#[derive(Debug, Clone, PartialEq)]
enum ColonParseError {
    UnknownCommand(String),
    MissingPath,
    TagRequiresName,
    HexGroupRequiresValue,
    HexGroupInvalid(String),
    ColorInvalid(String),
    CaseInvalid(String),
    HeaderInvalid(String),
}

impl std::fmt::Display for ColonParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ColonParseError::UnknownCommand(t) => write!(f, "unknown command: :{t}"),
            ColonParseError::MissingPath => write!(f, ":e requires a path"),
            ColonParseError::TagRequiresName => write!(f, ":tag requires a name"),
            ColonParseError::HexGroupRequiresValue => {
                write!(f, ":hex requires N (one of 2, 4, 8, 16, 32)")
            }
            ColonParseError::HexGroupInvalid(v) => {
                write!(f, ":hex N must be one of 2, 4, 8, 16, 32 (got {v})")
            }
            ColonParseError::ColorInvalid(v) => {
                write!(f, ":color mode must be strict, interpret, or raw (got {v})")
            }
            ColonParseError::CaseInvalid(v) => {
                write!(f, ":case mode must be sensitive, smart, or insensitive (got {v})")
            }
            ColonParseError::HeaderInvalid(v) => {
                write!(f, ":header expects `L` or `L C` (got {v})")
            }
        }
    }
}

fn parse_colon_command(buf: &str) -> std::result::Result<ColonCommand, ColonParseError> {
    let buf = buf.trim();
    if buf.is_empty() {
        return Err(ColonParseError::UnknownCommand(String::new()));
    }
    let mut parts = buf.splitn(2, char::is_whitespace);
    let cmd = parts.next().unwrap();
    let rest = parts.next().unwrap_or("").trim();
    match cmd {
        "n" | "next" => Ok(ColonCommand::Next),
        "p" | "prev" => Ok(ColonCommand::Prev),
        "e" | "edit" => {
            if rest.is_empty() {
                Err(ColonParseError::MissingPath)
            } else {
                // Tilde expansion.
                let expanded = if let Some(stripped) = rest.strip_prefix("~/") {
                    if let Some(home) = std::env::var_os("HOME") {
                        let mut p = std::path::PathBuf::from(home);
                        p.push(stripped);
                        p
                    } else {
                        std::path::PathBuf::from(rest)
                    }
                } else {
                    std::path::PathBuf::from(rest)
                };
                Ok(ColonCommand::Edit(expanded))
            }
        }
        "f" => Ok(ColonCommand::ShowFile),
        "q" | "quit" => Ok(ColonCommand::Quit),
        "d" | "delete" => Ok(ColonCommand::Delete),
        "x" | "first" => Ok(ColonCommand::First),
        "t" | "last" => Ok(ColonCommand::Last),
        "tag" => {
            if rest.is_empty() {
                Err(ColonParseError::TagRequiresName)
            } else {
                Ok(ColonCommand::Tag(rest.to_string()))
            }
        }
        "tnext" => Ok(ColonCommand::TagNext),
        "tprev" => Ok(ColonCommand::TagPrev),
        "tselect" => {
            if rest.is_empty() {
                Ok(ColonCommand::TagSelect(None))
            } else {
                Ok(ColonCommand::TagSelect(Some(rest.to_string())))
            }
        }
        "b" | "buffers" => Ok(ColonCommand::OpenPicker),
        "h" | "help"    => Ok(ColonCommand::OpenHelp),
        "hex" => {
            if rest.is_empty() {
                Err(ColonParseError::HexGroupRequiresValue)
            } else {
                match rest.parse::<usize>() {
                    Ok(n) if matches!(n, 2 | 4 | 8 | 16 | 32) => Ok(ColonCommand::HexGroup(n)),
                    _ => Err(ColonParseError::HexGroupInvalid(rest.to_string())),
                }
            }
        }
        "color" => {
            if rest.is_empty() {
                Ok(ColonCommand::Color(None))
            } else {
                match rest {
                    "strict" => Ok(ColonCommand::Color(Some(crate::render::AnsiMode::Strict))),
                    "interpret" => Ok(ColonCommand::Color(Some(crate::render::AnsiMode::Interpret))),
                    "raw" => Ok(ColonCommand::Color(Some(crate::render::AnsiMode::Raw))),
                    other => Err(ColonParseError::ColorInvalid(other.to_string())),
                }
            }
        }
        "hlsearch"   => Ok(ColonCommand::HlSearch(true)),
        "nohlsearch" => Ok(ColonCommand::HlSearch(false)),
        "incsearch"  => Ok(ColonCommand::IncSearch),
        "yank"       => Ok(ColonCommand::Yank),
        "header" => {
            let parts: Vec<&str> = rest.split_whitespace().collect();
            match parts.as_slice() {
                [l] => {
                    let n: usize = l.parse()
                        .map_err(|_| ColonParseError::HeaderInvalid(l.to_string()))?;
                    Ok(ColonCommand::Header(n, 0))
                }
                [l, c] => {
                    let nl: usize = l.parse()
                        .map_err(|_| ColonParseError::HeaderInvalid(l.to_string()))?;
                    let nc: usize = c.parse()
                        .map_err(|_| ColonParseError::HeaderInvalid(c.to_string()))?;
                    Ok(ColonCommand::Header(nl, nc))
                }
                _ => Err(ColonParseError::HeaderInvalid(rest.to_string())),
            }
        }
        "case" => {
            if rest.is_empty() {
                Ok(ColonCommand::Case(None))
            } else {
                match rest {
                    "sensitive" => Ok(ColonCommand::Case(Some(crate::viewport::CaseMode::Sensitive))),
                    "smart" => Ok(ColonCommand::Case(Some(crate::viewport::CaseMode::Smart))),
                    "insensitive" => Ok(ColonCommand::Case(Some(crate::viewport::CaseMode::Insensitive))),
                    other => Err(ColonParseError::CaseInvalid(other.to_string())),
                }
            }
        }
        other => Err(ColonParseError::UnknownCommand(other.to_string())),
    }
}

enum ColonOutcome {
    Continue(Option<String>),  // Some(msg) = transient status to show
    Quit,
    /// Hand a command to the outer dispatch loop. Used so colon commands
    /// like `:b` can install overlays via the same Command path as their
    /// keymap counterparts, without taking a `&mut overlay` argument.
    DispatchCommand(Command),
}

#[derive(Debug, Default)]
struct TagStack {
    /// Where we jumped FROM, in reverse-chronological order. Tuples are
    /// (file_index, top_line) at the time of the jump.
    history: Vec<(usize, usize)>,
    /// Currently-active match list, set when a tag has at least one match
    /// and cleared on Ctrl-T or on a fresh tag jump.
    active: Option<ActiveMatches>,
}

#[derive(Debug, Clone)]
struct ActiveMatches {
    name: String,
    matches: Vec<crate::tags::TagEntry>,
    cursor: usize,
}

#[derive(Debug, Clone, PartialEq, Eq)]
enum TagStepResult {
    /// Cursor moved; new index is `usize`.
    Moved(usize),
    /// Already at the boundary; show a transient message.
    AtBoundary,
    /// `active` was None — caller should show "no active tag".
    NoActive,
}

impl TagStack {
    fn push(&mut self, file_index: usize, top_line: usize) {
        self.history.push((file_index, top_line));
    }

    fn pop(&mut self) -> Option<(usize, usize)> {
        let popped = self.history.pop();
        if popped.is_some() {
            self.active = None;
        }
        popped
    }

    fn set_active(&mut self, name: String, matches: Vec<crate::tags::TagEntry>) {
        self.active = Some(ActiveMatches {
            name,
            matches,
            cursor: 0,
        });
    }

    fn next(&mut self) -> TagStepResult {
        let Some(a) = &mut self.active else {
            return TagStepResult::NoActive;
        };
        if a.cursor + 1 >= a.matches.len() {
            TagStepResult::AtBoundary
        } else {
            a.cursor += 1;
            TagStepResult::Moved(a.cursor)
        }
    }

    fn prev(&mut self) -> TagStepResult {
        let Some(a) = &mut self.active else {
            return TagStepResult::NoActive;
        };
        if a.cursor == 0 {
            TagStepResult::AtBoundary
        } else {
            a.cursor -= 1;
            TagStepResult::Moved(a.cursor)
        }
    }
}

/// Resolve a tag name to a list of matches, push the current position
/// onto the tag stack, set it as the active match list, and dispatch
/// Stat the tag file and reload it if its mtime moved. Returns a transient
/// status message when a reload happened so the caller can surface it.
/// Errors are swallowed (the previously-loaded state stays valid).
fn refresh_tag_file(tag_file: &mut Option<crate::tags::TagFile>) -> Option<String> {
    match tag_file.as_mut()?.reload_if_changed() {
        Ok(true) => Some("[tags reloaded]".into()),
        _ => None,
    }
}

/// Longest common prefix among a slice of strings. Returns "" for an empty
/// slice or when the items don't share any prefix. Used by Tab-completion
/// in the `:tag` / `Ctrl-]` prompt.
fn longest_common_prefix(items: &[String]) -> String {
    let mut iter = items.iter();
    let Some(first) = iter.next() else { return String::new() };
    let mut prefix = first.clone();
    for s in iter {
        while !s.starts_with(&prefix) {
            prefix.pop();
            if prefix.is_empty() {
                return prefix;
            }
        }
    }
    prefix
}

/// the first match. Returns a transient status string when something
/// goes wrong, or `None` on success.
#[allow(clippy::too_many_arguments)]
fn dispatch_tag_jump(
    name: &str,
    tag_file: Option<&crate::tags::TagFile>,
    tag_stack: &mut TagStack,
    file_set: &mut crate::file_set::FileSet,
    current_file_index: &mut usize,
    args: &crate::cli::Args,
    preprocessor: Option<&crate::preprocess::Preprocessor>,
    record_start_regex: Option<&regex::bytes::Regex>,
    viewport: &mut crate::viewport::Viewport,
    src: &mut Box<dyn crate::source::Source>,
    idx: &mut crate::line_index::LineIndex,
) -> Option<String> {
    let Some(tf) = tag_file else {
        return Some("[no tags file loaded]".into());
    };
    let matches = tf.lookup(name);
    if matches.is_empty() {
        return Some(format!("[tag not found: {name}]"));
    }
    let matches: Vec<crate::tags::TagEntry> = matches.to_vec();
    tag_stack.push(*current_file_index, viewport.top_line());
    tag_stack.set_active(name.to_string(), matches.clone());
    let msg = dispatch_match(
        &matches[0],
        file_set,
        current_file_index,
        args,
        preprocessor,
        record_start_regex,
        viewport,
        src,
        idx,
    );
    update_viewport_tag_indicator(tag_stack, viewport);
    msg
}

#[allow(clippy::too_many_arguments)]
fn dispatch_match(
    entry: &crate::tags::TagEntry,
    file_set: &mut crate::file_set::FileSet,
    current_file_index: &mut usize,
    args: &crate::cli::Args,
    preprocessor: Option<&crate::preprocess::Preprocessor>,
    record_start_regex: Option<&regex::bytes::Regex>,
    viewport: &mut crate::viewport::Viewport,
    src: &mut Box<dyn crate::source::Source>,
    idx: &mut crate::line_index::LineIndex,
) -> Option<String> {
    let target_file = entry.file.as_path();
    let already_current = file_set
        .current()
        .map(|p| p == target_file)
        .unwrap_or(false);

    if !already_current {
        let existing_idx = (0..file_set.len()).find(|i| {
            file_set
                .nth(*i)
                .map(|p| p == target_file)
                .unwrap_or(false)
        });
        match existing_idx {
            Some(i) => {
                file_set.set_current_index(i);
            }
            None => {
                file_set.append_and_switch(target_file.to_path_buf());
            }
        }
        let path = file_set.current().unwrap().to_path_buf();
        if let Err(e) = switch_file(
            &path,
            file_set.current_index(),
            file_set.len(),
            args,
            preprocessor,
            viewport,
            src,
            idx,
            record_start_regex,
        ) {
            return Some(format!("[open: {e}]"));
        }
        *current_file_index = file_set.current_index();
    }

    let (line, hint) = match resolve_tag_address(&entry.address, src.as_ref(), idx, 0) {
        AddressResult::Line(l) => (l, None),
        AddressResult::NotFound => (0, Some("[tag pattern not found]".into())),
        AddressResult::Unsupported(raw) => (
            0,
            Some(format!("[tag address not supported: {raw}]")),
        ),
    };

    let clamped = line.min(idx.line_count().saturating_sub(1));
    viewport.goto_line(clamped, src.as_ref(), idx);
    hint
}

enum AddressResult {
    Line(usize),
    NotFound,
    Unsupported(String),
}

/// Resolve a `TagAddress` to a 0-based line number, starting the search at
/// `from_line` (used for the chained-address case where the second step
/// resumes from the line matched by the first).
fn resolve_tag_address(
    addr: &crate::tags::TagAddress,
    src: &dyn crate::source::Source,
    idx: &mut crate::line_index::LineIndex,
    from_line: usize,
) -> AddressResult {
    match addr {
        crate::tags::TagAddress::Line(n) => AddressResult::Line(n.saturating_sub(1)),
        crate::tags::TagAddress::Pattern(p) => {
            let re_src = crate::tags::pattern_to_regex(p);
            let re = match regex::bytes::Regex::new(&re_src) {
                Ok(r) => r,
                Err(_) => return AddressResult::NotFound,
            };
            match find_pattern_line(src, idx, &re, from_line) {
                Some(l) => AddressResult::Line(l),
                None => AddressResult::NotFound,
            }
        }
        crate::tags::TagAddress::Chained(parts) => {
            let mut here = from_line;
            for step in parts {
                match resolve_tag_address(step, src, idx, here) {
                    AddressResult::Line(l) => here = l + 1,
                    other => return other,
                }
            }
            // Subtract 1 from the final "next-search start" to land on the
            // last matched line itself.
            AddressResult::Line(here.saturating_sub(1))
        }
        crate::tags::TagAddress::Unsupported(raw) => {
            AddressResult::Unsupported(raw.clone())
        }
    }
}

fn find_pattern_line(
    src: &dyn crate::source::Source,
    idx: &mut crate::line_index::LineIndex,
    re: &regex::bytes::Regex,
    from_line: usize,
) -> Option<usize> {
    idx.extend_to_end(src);
    for line_no in from_line..idx.line_count() {
        let bytes = idx.line_bytes_stripped(line_no, src);
        if re.is_match(&bytes) {
            return Some(line_no);
        }
    }
    None
}

fn update_viewport_tag_indicator(stack: &TagStack, viewport: &mut crate::viewport::Viewport) {
    viewport.set_tag_active(stack.active.as_ref().map(|a| {
        (a.name.clone(), a.cursor + 1, a.matches.len())
    }));
}

/// Open whatever file is at `file_set.current()`, updating viewport and
/// `current_file_index`. Returns `Some(msg)` if anything went wrong (for
/// transient status). The cursor in `file_set` must be set before calling.
#[allow(clippy::too_many_arguments)]
fn switch_to_current_file(
    file_set: &mut crate::file_set::FileSet,
    current_file_index: &mut usize,
    args: &crate::cli::Args,
    preprocessor: Option<&crate::preprocess::Preprocessor>,
    record_start_regex: Option<&regex::bytes::Regex>,
    viewport: &mut crate::viewport::Viewport,
    src: &mut Box<dyn crate::source::Source>,
    idx: &mut crate::line_index::LineIndex,
) -> Option<String> {
    let path = match file_set.current() {
        Some(p) => p.to_path_buf(),
        None => return Some("[empty file set]".into()),
    };
    let new_idx_val = file_set.current_index();
    match switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
        Ok(()) => {
            *current_file_index = new_idx_val;
            None
        }
        Err(e) => Some(format!("[open: {e}]")),
    }
}

#[allow(clippy::too_many_arguments)]
fn switch_file(
    new_path: &std::path::Path,
    new_file_index: usize,
    total_files: usize,
    args: &crate::cli::Args,
    preprocessor: Option<&crate::preprocess::Preprocessor>,
    viewport: &mut crate::viewport::Viewport,
    src: &mut Box<dyn crate::source::Source>,
    idx: &mut crate::line_index::LineIndex,
    record_start_regex: Option<&regex::bytes::Regex>,
) -> crate::error::Result<()> {
    let (new_src, new_label, new_failure) =
        crate::open::open_source_for_path(new_path, args, preprocessor)?;

    *src = new_src;
    let mut new_idx = crate::line_index::LineIndex::new();
    if let Some(re) = record_start_regex {
        new_idx.set_record_start(re.clone());
    }
    *idx = new_idx;

    viewport.set_source_label(new_label);
    viewport.set_file_index(new_file_index, total_files);
    viewport.set_preprocess_failure(new_failure);
    viewport.goto_top();
    viewport.reset_hscroll(); // new file: drop any horizontal scroll offset

    Ok(())
}

/// Copy the current top logical line's raw bytes (trailing newline already
/// stripped by `LineIndex::line_range`) to the system clipboard. Returns a
/// human-facing status string for the caller to flash. When `--clipboard`
/// wasn't passed, reports that and copies nothing.
fn yank_current_line(
    clipboard_enabled: bool,
    viewport: &crate::viewport::Viewport,
    src: &dyn crate::source::Source,
    idx: &mut crate::line_index::LineIndex,
) -> String {
    if !clipboard_enabled {
        return "[clipboard not enabled (pass --clipboard)]".to_string();
    }
    if idx.line_count() == 0 {
        return "[nothing to copy]".to_string();
    }
    let line = viewport.top_line();
    let bytes = current_line_bytes(idx, src, line);
    match crate::clipboard::write(&bytes) {
        Ok(()) => format!("[copied {} bytes]", bytes.len()),
        Err(e) => format!("[{e}]"),
    }
}

/// Raw bytes of the logical line at `line` (trailing newline already stripped
/// by `LineIndex::line_range`). Pulled out of `yank_current_line` so it can be
/// unit-tested without touching the OS clipboard.
fn current_line_bytes(
    idx: &crate::line_index::LineIndex,
    src: &dyn crate::source::Source,
    line: usize,
) -> Vec<u8> {
    let range = idx.line_range(line, src);
    src.bytes(range).into_owned()
}

#[allow(clippy::too_many_arguments)]
fn dispatch_colon_command(
    cmd: ColonCommand,
    file_set: &mut crate::file_set::FileSet,
    current_file_index: &mut usize,
    args: &crate::cli::Args,
    preprocessor: Option<&crate::preprocess::Preprocessor>,
    record_start_regex: Option<&regex::bytes::Regex>,
    viewport: &mut crate::viewport::Viewport,
    src: &mut Box<dyn crate::source::Source>,
    idx: &mut crate::line_index::LineIndex,
    tag_stack: &mut TagStack,
    tag_file: Option<&crate::tags::TagFile>,
) -> ColonOutcome {
    match cmd {
        ColonCommand::Next => {
            match file_set.next() {
                Ok(path) => {
                    let path = path.to_path_buf();
                    let new_idx_val = file_set.current_index();
                    if let Err(e) = switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                        ColonOutcome::Continue(Some(format!("[open: {e}]")))
                    } else {
                        *current_file_index = new_idx_val;
                        ColonOutcome::Continue(None)
                    }
                }
                Err(e) => ColonOutcome::Continue(Some(format!("[{e}]"))),
            }
        }
        ColonCommand::Prev => {
            match file_set.prev() {
                Ok(path) => {
                    let path = path.to_path_buf();
                    let new_idx_val = file_set.current_index();
                    if let Err(e) = switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                        ColonOutcome::Continue(Some(format!("[open: {e}]")))
                    } else {
                        *current_file_index = new_idx_val;
                        ColonOutcome::Continue(None)
                    }
                }
                Err(e) => ColonOutcome::Continue(Some(format!("[{e}]"))),
            }
        }
        ColonCommand::Edit(path) => {
            // Try to open first; if successful, append + switch.
            match crate::open::open_source_for_path(&path, args, preprocessor) {
                Ok(_) => {
                    // Successful open; commit to the FileSet.
                    let final_path = file_set.append_and_switch(path.clone()).to_path_buf();
                    let new_idx_val = file_set.current_index();
                    if let Err(e) = switch_file(&final_path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                        ColonOutcome::Continue(Some(format!("[open: {e}]")))
                    } else {
                        *current_file_index = new_idx_val;
                        ColonOutcome::Continue(None)
                    }
                }
                Err(e) => ColonOutcome::Continue(Some(format!("[open: {}: {e}]", path.display()))),
            }
        }
        ColonCommand::ShowFile => {
            let label = viewport.source_label_clone();
            let cur = file_set.current_index() + 1;
            let total = file_set.len();
            let top = viewport.top_line() + 1;
            let total_lines = idx.line_count();
            let msg = if total > 1 {
                format!("{label} (file {cur}/{total}): line {top}/{total_lines}")
            } else {
                format!("{label}: line {top}/{total_lines}")
            };
            ColonOutcome::Continue(Some(msg))
        }
        ColonCommand::Quit => ColonOutcome::Quit,
        ColonCommand::Delete => {
            match file_set.delete_current() {
                Ok(path) => {
                    let path = path.to_path_buf();
                    let new_idx_val = file_set.current_index();
                    if let Err(e) = switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                        ColonOutcome::Continue(Some(format!("[open: {e}]")))
                    } else {
                        *current_file_index = new_idx_val;
                        ColonOutcome::Continue(None)
                    }
                }
                Err(e) => ColonOutcome::Continue(Some(format!("[{e}]"))),
            }
        }
        ColonCommand::First => {
            if file_set.current_index() == 0 {
                ColonOutcome::Continue(None)  // silent no-op
            } else if let Some(path) = file_set.first() {
                let path = path.to_path_buf();
                let new_idx_val = file_set.current_index();
                if let Err(e) = switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                    ColonOutcome::Continue(Some(format!("[open: {e}]")))
                } else {
                    *current_file_index = new_idx_val;
                    ColonOutcome::Continue(None)
                }
            } else {
                ColonOutcome::Continue(None)
            }
        }
        ColonCommand::Last => {
            if file_set.current_index() + 1 == file_set.len() {
                ColonOutcome::Continue(None)
            } else if let Some(path) = file_set.last() {
                let path = path.to_path_buf();
                let new_idx_val = file_set.current_index();
                if let Err(e) = switch_file(&path, new_idx_val, file_set.len(), args, preprocessor, viewport, src, idx, record_start_regex) {
                    ColonOutcome::Continue(Some(format!("[open: {e}]")))
                } else {
                    *current_file_index = new_idx_val;
                    ColonOutcome::Continue(None)
                }
            } else {
                ColonOutcome::Continue(None)
            }
        }
        ColonCommand::Tag(name) => {
            match dispatch_tag_jump(
                &name,
                tag_file,
                tag_stack,
                file_set,
                current_file_index,
                args,
                preprocessor,
                record_start_regex,
                viewport,
                src,
                idx,
            ) {
                Some(msg) => ColonOutcome::Continue(Some(msg)),
                None => ColonOutcome::Continue(None),
            }
        }
        ColonCommand::TagNext => match tag_stack.next() {
            TagStepResult::NoActive => ColonOutcome::Continue(Some("[no active tag]".into())),
            TagStepResult::AtBoundary => ColonOutcome::Continue(Some("[no more matches]".into())),
            TagStepResult::Moved(cur) => {
                let entry = tag_stack.active.as_ref().unwrap().matches[cur].clone();
                let msg = dispatch_match(
                    &entry,
                    file_set,
                    current_file_index,
                    args,
                    preprocessor,
                    record_start_regex,
                    viewport,
                    src,
                    idx,
                );
                update_viewport_tag_indicator(tag_stack, viewport);
                ColonOutcome::Continue(msg)
            }
        },
        ColonCommand::TagSelect(name) => {
            let prepared = match name {
                Some(n) => {
                    let tf = match tag_file {
                        Some(t) => t,
                        None => {
                            return ColonOutcome::Continue(Some(
                                "[no tags file loaded]".into(),
                            ))
                        }
                    };
                    let matches: Vec<crate::tags::TagEntry> = tf.lookup(&n).to_vec();
                    if matches.is_empty() {
                        return ColonOutcome::Continue(Some(
                            format!("[no matches for `{n}`]"),
                        ));
                    }
                    tag_stack.set_active(n, matches);
                    true
                }
                None => tag_stack.active.is_some(),
            };
            if prepared {
                ColonOutcome::DispatchCommand(Command::OpenTagPicker)
            } else {
                ColonOutcome::Continue(Some("[no active tag]".into()))
            }
        }
        ColonCommand::TagPrev => match tag_stack.prev() {
            TagStepResult::NoActive => ColonOutcome::Continue(Some("[no active tag]".into())),
            TagStepResult::AtBoundary => ColonOutcome::Continue(Some("[at first match]".into())),
            TagStepResult::Moved(cur) => {
                let entry = tag_stack.active.as_ref().unwrap().matches[cur].clone();
                let msg = dispatch_match(
                    &entry,
                    file_set,
                    current_file_index,
                    args,
                    preprocessor,
                    record_start_regex,
                    viewport,
                    src,
                    idx,
                );
                update_viewport_tag_indicator(tag_stack, viewport);
                ColonOutcome::Continue(msg)
            }
        },
        // Hand off to the outer command dispatcher so the same install path
        // services both `:b` and the (future) F2 keybinding.
        ColonCommand::OpenPicker => ColonOutcome::DispatchCommand(Command::OpenPicker),
        ColonCommand::OpenHelp => ColonOutcome::DispatchCommand(Command::OpenHelp),
        ColonCommand::HexGroup(hex_chars) => {
            if !viewport.hex_mode() {
                return ColonOutcome::Continue(Some(
                    "[:hex requires --hex mode]".into(),
                ));
            }
            // Already validated in parse_colon_command, so unwrap is safe.
            let bpg = crate::hex::hex_chars_to_bytes_per_group(hex_chars).unwrap();
            viewport.set_hex_group_size(bpg);
            ColonOutcome::Continue(Some(format!("[hex group: {hex_chars} chars]")))
        }
        ColonCommand::Color(mode) => {
            use crate::render::AnsiMode;
            let next = mode.unwrap_or_else(|| match viewport.ansi_mode() {
                AnsiMode::Strict => AnsiMode::Interpret,
                AnsiMode::Interpret => AnsiMode::Raw,
                AnsiMode::Raw => AnsiMode::Strict,
            });
            viewport.set_ansi_mode(next);
            let label = match next {
                AnsiMode::Strict => "strict",
                AnsiMode::Interpret => "interpret",
                AnsiMode::Raw => "raw",
            };
            ColonOutcome::Continue(Some(format!("[color: {label}]")))
        }
        ColonCommand::Header(l, c) => {
            viewport.set_header(l, c);
            ColonOutcome::Continue(Some(format!("[header: {l} rows, {c} cols]")))
        }
        ColonCommand::HlSearch(on) => {
            viewport.set_hilite_search(on);
            let msg = if on { "[hlsearch on]" } else { "[hlsearch off]" };
            ColonOutcome::Continue(Some(msg.into()))
        }
        ColonCommand::IncSearch => {
            let on = !viewport.incsearch();
            viewport.set_incsearch(on);
            let msg = if on { "[incsearch on]" } else { "[incsearch off]" };
            ColonOutcome::Continue(Some(msg.into()))
        }
        ColonCommand::Yank => {
            ColonOutcome::Continue(Some(yank_current_line(args.clipboard, viewport, src.as_ref(), idx)))
        }
        ColonCommand::Case(mode) => {
            use crate::viewport::CaseMode;
            let next = mode.unwrap_or_else(|| match viewport.case_mode() {
                CaseMode::Sensitive => CaseMode::Smart,
                CaseMode::Smart => CaseMode::Insensitive,
                CaseMode::Insensitive => CaseMode::Sensitive,
            });
            viewport.set_case_mode(next);
            let label = match next {
                CaseMode::Sensitive => "sensitive",
                CaseMode::Smart => "smart",
                CaseMode::Insensitive => "insensitive",
            };
            ColonOutcome::Continue(Some(format!("[case: {label}]")))
        }
    }
}

#[allow(clippy::too_many_arguments, clippy::collapsible_match)]
pub fn run(
    mut src: Box<dyn Source>,
    mut viewport: Viewport,
    mut idx: LineIndex,
    sigterm: Arc<AtomicBool>,
    rebuild_spec: RebuildSpec,
    keymap: crate::keys::KeyMap,
    mut file_set: crate::file_set::FileSet,
    record_start_regex: Option<regex::bytes::Regex>,
    args: crate::cli::Args,
    preprocessor: Option<crate::preprocess::Preprocessor>,
    mut tag_file: Option<crate::tags::TagFile>,
) -> Result<()> {
    let (mut cols, mut rows) = size().unwrap_or((80, 24));
    viewport.resize(cols, rows);

    let truecolor = match args.truecolor.as_str() {
        "always" => true,
        "never" => false,
        _ => crate::render::TrueColor::Auto.resolve(),
    };

    let mut stdout = io::stdout();
    let timeout = Duration::from_millis(250);
    let mut last_revision = src.revision();

    // If hide-mode filtering is active (--filter or --grep without --dim),
    // we need to scan the whole source up front to find matching lines.
    // Without any predicate this is intentionally skipped — lazy indexing
    // keeps `tess` fast on huge files.
    if (viewport.filter_active() || viewport.grep_active()) && !viewport.dim_mode() {
        idx.extend_to_end(src.as_ref());
        viewport.extend_visible_lines(&idx, src.as_ref());
    }

    // If follow or live mode is on at startup, snap to the bottom of the
    // (possibly filtered) source so the user sees the newest content
    // (tail-style). Live mode tracks whole-file rewrites; starting at the end
    // keeps the latest content in view as the file is regenerated.
    if viewport.follow_mode() || viewport.live_mode() {
        src.pump();
        viewport.extend_visible_lines(&idx, src.as_ref());
        viewport.goto_bottom(src.as_ref(), &mut idx);
    }

    // Always draw the initial frame before entering the event loop.
    let mut needs_redraw = true;
    let mut mode = InputMode::Normal;
    let mut numeric_prefix: Option<usize> = None;
    let mut marks: HashMap<char, (usize, usize)> = HashMap::new();
    let mut previous_position: Option<(usize, usize)> = None;
    // Scroll position captured when an incremental-search prompt opens, so a
    // mid-type preview searches from there and Esc can restore it.
    let mut incsearch_origin: (usize, usize) = (0, 0);
    let mut current_file_index: usize = file_set.current_index();
    let mut transient_status: Option<String> = None;
    let mut tag_stack = TagStack::default();
    let mut overlay: Option<Box<dyn crate::overlay::Overlay>> = None;
    let mut overlay_flash: Option<(&'static str, std::time::Instant)> = None;
    let mouse_enabled = args.mouse;
    let clipboard_enabled = args.clipboard;
    let hscroll_shift = args.shift.unwrap_or(0);
    let wheel_lines = args.wheel_lines.unwrap_or(3).max(1);

    if let Some(tag_name) = args.tag.as_deref() {
        let _ = refresh_tag_file(&mut tag_file);
        if let Some(msg) = dispatch_tag_jump(
            tag_name,
            tag_file.as_ref(),
            &mut tag_stack,
            &mut file_set,
            &mut current_file_index,
            &args,
            preprocessor.as_ref(),
            record_start_regex.as_ref(),
            &mut viewport,
            &mut src,
            &mut idx,
        ) {
            return Err(crate::error::Error::Runtime(format!("startup tag jump failed: {msg}")));
        }
    }

    loop {
        if sigterm.load(Ordering::SeqCst) {
            break;
        }

        if needs_redraw {
            if let Some(ov) = overlay.as_ref() {
                let w = cols;
                let h = viewport.body_rows() + 1;
                let mut ovframe = ov.render(w, h);
                if let Some((msg, started)) = overlay_flash {
                    if started.elapsed() < std::time::Duration::from_millis(1500) {
                        ovframe.status = format!("[{msg}]");
                    } else {
                        overlay_flash = None;
                    }
                }
                render_overlay(&mut stdout, &ovframe, w, h)
                    .map_err(|e| crate::error::Error::Runtime(format!("stdout: {}", e)))?;
                needs_redraw = false;
                continue;
            }
            // `-J` status column: feed the current file's marks (line → letter)
            // into the viewport so it can render mark glyphs in the far-left
            // gutter. Empty when the feature is off.
            if viewport.status_column() {
                let status_marks: HashMap<usize, char> = marks
                    .iter()
                    .filter(|(_, (fi, _))| *fi == current_file_index)
                    .map(|(ch, (_, line))| (*line, *ch))
                    .collect();
                viewport.set_status_marks(status_marks);
            }
            let mut frame = viewport.frame(src.as_ref(), &mut idx);
            // Override the status row when we're in an interactive prompt OR
            // when a transient status message is pending.
            match &mode {
                InputMode::SearchPrompt { direction, buffer, error } => {
                    let prefix = if matches!(direction, SearchDirection::Forward) { "/" } else { "?" };
                    frame.status = match error {
                        Some(e) => format!("{prefix}{buffer}  [error: {e}]"),
                        None => format!("{prefix}{buffer}"),
                    };
                }
                InputMode::ShellPrompt { buffer, error } => {
                    frame.status = match error {
                        Some(e) => format!("!{buffer}  [error: {e}]"),
                        None => format!("!{buffer}"),
                    };
                }
                InputMode::ColonPrompt { buffer, error } => {
                    frame.status = match error {
                        Some(e) => format!(":{buffer}  [error: {e}]"),
                        None => format!(":{buffer}"),
                    };
                }
                InputMode::TagPrompt { buffer, error, .. } => {
                    frame.status = match error {
                        Some(e) => format!("tag: {buffer}  [error: {e}]"),
                        None => format!("tag: {buffer}"),
                    };
                }
                _ => {
                    if let Some(msg) = transient_status.take() {
                        frame.status = msg;
                    }
                }
            }
            write_frame(&mut stdout, &frame, cols, rows, truecolor)
                .map_err(|e| crate::error::Error::Runtime(format!("stdout: {}", e)))?;
            needs_redraw = false;
        }

        // Poll with timeout so stdin sources can be re-checked.
        match poll(timeout) {
            Ok(true) => {
                let event = read().map_err(|e| crate::error::Error::Runtime(format!("input: {}", e)))?;
                // Modal input handling: the search prompt and option prefix
                // intercept keys before they're translated to commands.
                match &mut mode {
                    InputMode::SearchPrompt { direction, buffer, error } => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            match code {
                                KeyCode::Esc => {
                                    if viewport.incsearch() {
                                        viewport.set_top(incsearch_origin.0, incsearch_origin.1);
                                    }
                                    mode = InputMode::Normal;
                                    needs_redraw = true;
                                }
                                KeyCode::Enter => {
                                    if viewport.incsearch() {
                                        viewport.set_top(incsearch_origin.0, incsearch_origin.1);
                                    }
                                    if buffer.is_empty() {
                                        // Empty buffer: repeat the last search in the
                                        // newly-typed direction (less compat). If no
                                        // prior search exists, just dismiss.
                                        if viewport.search_active() {
                                            let reverse = !matches!(
                                                (viewport.search_direction(), *direction),
                                                (SearchDirection::Forward, SearchDirection::Forward)
                                                | (SearchDirection::Backward, SearchDirection::Backward)
                                            );
                                            update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                                            viewport.search_repeat(src.as_ref(), &mut idx, reverse);
                                        }
                                        mode = InputMode::Normal;
                                    } else {
                                        match viewport.set_search(buffer.clone(), *direction) {
                                            Ok(()) => {
                                                update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                                                viewport.search_repeat(src.as_ref(), &mut idx, false);
                                                mode = InputMode::Normal;
                                            }
                                            Err(e) => { *error = Some(e); }
                                        }
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Backspace => {
                                    buffer.pop();
                                    *error = None;
                                    if viewport.incsearch() {
                                        viewport.incsearch_preview(
                                            src.as_ref(), &mut idx, buffer, *direction, incsearch_origin);
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Char(c) => {
                                    buffer.push(c);
                                    *error = None;
                                    if viewport.incsearch() {
                                        viewport.incsearch_preview(
                                            src.as_ref(), &mut idx, buffer, *direction, incsearch_origin);
                                    }
                                    needs_redraw = true;
                                }
                                _ => {}
                            }
                        }
                        continue;
                    }
                    InputMode::OptionPrefix => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            match code {
                                KeyCode::Char('N') | KeyCode::Char('n') => viewport.toggle_line_numbers(),
                                KeyCode::Char('S') | KeyCode::Char('s') => viewport.toggle_chop(),
                                KeyCode::Char('F') | KeyCode::Char('f') => viewport.toggle_follow(),
                                KeyCode::Char('P') | KeyCode::Char('p') => {
                                    // Two-key prefix: `-P` then a letter for the mode.
                                    mode = InputMode::PrettifyPrefix;
                                    needs_redraw = true;
                                    continue;
                                }
                                _ => {}
                            }
                        }
                        mode = InputMode::Normal;
                        needs_redraw = true;
                        continue;
                    }
                    InputMode::PrettifyPrefix => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            let target: Option<PrettifyTarget> = match code {
                                KeyCode::Char('j') | KeyCode::Char('J') => Some(PrettifyTarget::Mode(PrettifyMode::Json)),
                                KeyCode::Char('y') | KeyCode::Char('Y') => Some(PrettifyTarget::Mode(PrettifyMode::Yaml)),
                                KeyCode::Char('t') | KeyCode::Char('T') => Some(PrettifyTarget::Mode(PrettifyMode::Toml)),
                                KeyCode::Char('x') | KeyCode::Char('X') => Some(PrettifyTarget::Mode(PrettifyMode::Xml)),
                                KeyCode::Char('h') | KeyCode::Char('H') => Some(PrettifyTarget::Mode(PrettifyMode::Html)),
                                KeyCode::Char('c') | KeyCode::Char('C') => Some(PrettifyTarget::Mode(PrettifyMode::Csv)),
                                KeyCode::Char('r') | KeyCode::Char('R') => Some(PrettifyTarget::Mode(PrettifyMode::Off)),
                                KeyCode::Char('a') | KeyCode::Char('A') => Some(PrettifyTarget::Auto),
                                _ => None,
                            };
                            if let Some(t) = target {
                                apply_prettify(
                                    src.as_ref(),
                                    &mut viewport,
                                    &mut idx,
                                    rebuild_spec,
                                    t,
                                );
                                last_revision = src.revision();
                            }
                        }
                        mode = InputMode::Normal;
                        needs_redraw = true;
                        continue;
                    }
                    InputMode::MarkSetPending => {
                        if let Event::Key(KeyEvent { code: KeyCode::Char(c), .. }) = event {
                            if is_valid_mark_name(c) {
                                mark_set(&mut marks, c, current_file_index, viewport.top_line());
                            }
                        }
                        mode = InputMode::Normal;
                        continue;
                    }
                    InputMode::MarkJumpPending => {
                        if let Event::Key(KeyEvent { code: KeyCode::Char(c), .. }) = event {
                            if is_valid_mark_name(c) {
                                match mark_jump(&marks, c, current_file_index, &mut previous_position, viewport.top_line()) {
                                    Some(MarkTarget::SameFile { line }) => {
                                        let clamped = line.min(idx.line_count().saturating_sub(1));
                                        viewport.goto_line(clamped, src.as_ref(), &mut idx);
                                        needs_redraw = true;
                                    }
                                    Some(MarkTarget::OtherFile { file_index, line }) => {
                                        if file_index < file_set.len() {
                                            file_set.set_current_index(file_index);
                                            let path = file_set.current().unwrap().to_path_buf();
                                            if let Err(e) = switch_file(
                                                &path, file_index, file_set.len(),
                                                &args, preprocessor.as_ref(),
                                                &mut viewport, &mut src, &mut idx,
                                                record_start_regex.as_ref(),
                                            ) {
                                                transient_status = Some(format!("[open: {e}]"));
                                            } else {
                                                let clamped = line.min(idx.line_count().saturating_sub(1));
                                                viewport.goto_line(clamped, src.as_ref(), &mut idx);
                                                current_file_index = file_index;
                                                needs_redraw = true;
                                            }
                                        }
                                    }
                                    None => {}
                                }
                            }
                        }
                        mode = InputMode::Normal;
                        continue;
                    }
                    InputMode::ShellPrompt { buffer, error } => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            match code {
                                KeyCode::Esc => {
                                    mode = InputMode::Normal;
                                    needs_redraw = true;
                                }
                                KeyCode::Enter => {
                                    if buffer.is_empty() {
                                        mode = InputMode::Normal;
                                    } else {
                                        match crate::shell::run_shell_command(buffer) {
                                            Ok(()) => {
                                                mode = InputMode::Normal;
                                            }
                                            Err(e) => {
                                                *error = Some(e.to_string());
                                            }
                                        }
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Backspace => {
                                    buffer.pop();
                                    *error = None;
                                    needs_redraw = true;
                                }
                                KeyCode::Char(c) => {
                                    buffer.push(c);
                                    *error = None;
                                    needs_redraw = true;
                                }
                                _ => {}
                            }
                        }
                        continue;
                    }
                    InputMode::CtrlXPending => {
                        let is_ctrl_x = matches!(
                            event,
                            Event::Key(KeyEvent {
                                code: KeyCode::Char('x'),
                                modifiers: KeyModifiers::CONTROL,
                                ..
                            })
                        );
                        if is_ctrl_x {
                            match jump_previous(&mut previous_position, current_file_index, viewport.top_line()) {
                                Some(MarkTarget::SameFile { line }) => {
                                    let clamped = line.min(idx.line_count().saturating_sub(1));
                                    viewport.goto_line(clamped, src.as_ref(), &mut idx);
                                    needs_redraw = true;
                                }
                                Some(MarkTarget::OtherFile { file_index, line }) => {
                                    if file_index < file_set.len() {
                                        file_set.set_current_index(file_index);
                                        let path = file_set.current().unwrap().to_path_buf();
                                        if let Err(e) = switch_file(
                                            &path, file_index, file_set.len(),
                                            &args, preprocessor.as_ref(),
                                            &mut viewport, &mut src, &mut idx,
                                            record_start_regex.as_ref(),
                                        ) {
                                            transient_status = Some(format!("[open: {e}]"));
                                        } else {
                                            let clamped = line.min(idx.line_count().saturating_sub(1));
                                            viewport.goto_line(clamped, src.as_ref(), &mut idx);
                                            current_file_index = file_index;
                                            needs_redraw = true;
                                        }
                                    }
                                }
                                None => {}
                            }
                            mode = InputMode::Normal;
                            continue;
                        }
                        // Anything else: cancel and fall through to normal dispatch.
                        mode = InputMode::Normal;
                        // Don't `continue` — let the event fall through.
                    }
                    InputMode::ColonPrompt { buffer, error } => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            match code {
                                KeyCode::Esc => {
                                    mode = InputMode::Normal;
                                    needs_redraw = true;
                                }
                                KeyCode::Enter => {
                                    if buffer.is_empty() {
                                        mode = InputMode::Normal;
                                    } else {
                                        match parse_colon_command(buffer) {
                                            Ok(cmd) => {
                                                let is_tag_cmd = matches!(
                                                    &cmd,
                                                    ColonCommand::Tag(_)
                                                        | ColonCommand::TagNext
                                                        | ColonCommand::TagPrev
                                                        | ColonCommand::TagSelect(_),
                                                );
                                                let reload_msg = if is_tag_cmd {
                                                    refresh_tag_file(&mut tag_file)
                                                } else {
                                                    None
                                                };
                                                let outcome = dispatch_colon_command(
                                                    cmd,
                                                    &mut file_set,
                                                    &mut current_file_index,
                                                    &args,
                                                    preprocessor.as_ref(),
                                                    record_start_regex.as_ref(),
                                                    &mut viewport,
                                                    &mut src,
                                                    &mut idx,
                                                    &mut tag_stack,
                                                    tag_file.as_ref(),
                                                );
                                                match outcome {
                                                    ColonOutcome::Continue(msg) => {
                                                        transient_status = msg.or(reload_msg);
                                                    }
                                                    ColonOutcome::Quit => break,
                                                    ColonOutcome::DispatchCommand(Command::OpenPicker) => {
                                                        let saved = (0..file_set.len())
                                                            .map(|i| if i == current_file_index { viewport.top_line() } else { 0 })
                                                            .collect::<Vec<_>>();
                                                        overlay = Some(Box::new(
                                                            crate::overlay::picker::FilePicker::new(&file_set, saved)
                                                        ));
                                                    }
                                                    ColonOutcome::DispatchCommand(Command::OpenHelp) => {
                                                        let remaps = keymap.user_keys_by_command_name();
                                                        overlay = Some(Box::new(
                                                            crate::overlay::help::HelpOverlay::new(remaps)
                                                        ));
                                                    }
                                                    ColonOutcome::DispatchCommand(Command::OpenTagPicker) => {
                                                        if let Some(active) = tag_stack.active.as_ref() {
                                                            overlay = Some(Box::new(
                                                                crate::overlay::tag_picker::TagPicker::new(
                                                                    active.name.clone(),
                                                                    active.matches.clone(),
                                                                    active.cursor,
                                                                )
                                                            ));
                                                        }
                                                    }
                                                    ColonOutcome::DispatchCommand(cmd) => {
                                                        debug_assert!(false, "colon dispatcher emitted unexpected Command: {cmd:?}");
                                                        // In release builds, silently no-op.
                                                    }
                                                }
                                                mode = InputMode::Normal;
                                            }
                                            Err(e) => {
                                                *error = Some(e.to_string());
                                            }
                                        }
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Backspace => {
                                    buffer.pop();
                                    *error = None;
                                    needs_redraw = true;
                                }
                                KeyCode::Char(c) => {
                                    buffer.push(c);
                                    *error = None;
                                    needs_redraw = true;
                                }
                                _ => {}
                            }
                        }
                        continue;
                    }
                    InputMode::TagPrompt { buffer, error, last_tab_matches } => {
                        if let Event::Key(KeyEvent { code, .. }) = event {
                            match code {
                                KeyCode::Esc => {
                                    mode = InputMode::Normal;
                                    needs_redraw = true;
                                }
                                KeyCode::Enter => {
                                    if buffer.is_empty() {
                                        mode = InputMode::Normal;
                                    } else {
                                        let name = buffer.clone();
                                        let reload_msg = refresh_tag_file(&mut tag_file);
                                        let msg = dispatch_tag_jump(
                                            &name,
                                            tag_file.as_ref(),
                                            &mut tag_stack,
                                            &mut file_set,
                                            &mut current_file_index,
                                            &args,
                                            preprocessor.as_ref(),
                                            record_start_regex.as_ref(),
                                            &mut viewport,
                                            &mut src,
                                            &mut idx,
                                        );
                                        transient_status = msg.or(reload_msg);
                                        mode = InputMode::Normal;
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Backspace => {
                                    buffer.pop();
                                    *error = None;
                                    *last_tab_matches = None;
                                    needs_redraw = true;
                                }
                                KeyCode::Tab => {
                                    let _ = refresh_tag_file(&mut tag_file);
                                    let names: Vec<String> = match tag_file.as_ref() {
                                        Some(tf) => tf
                                            .names()
                                            .filter(|n| n.starts_with(buffer.as_str()))
                                            .map(String::from)
                                            .collect(),
                                        None => Vec::new(),
                                    };
                                    match (names.len(), last_tab_matches.as_ref()) {
                                        (0, _) => {
                                            *error = Some("no tags match".into());
                                            *last_tab_matches = None;
                                        }
                                        (1, _) => {
                                            *buffer = names.into_iter().next().unwrap();
                                            *error = None;
                                            *last_tab_matches = None;
                                        }
                                        (n, Some(prev)) if prev.len() == n => {
                                            *error = Some(format!("{n} matches"));
                                        }
                                        (n, _) => {
                                            let lcp = longest_common_prefix(&names);
                                            if lcp.len() > buffer.len() {
                                                *buffer = lcp;
                                                *error = None;
                                            } else {
                                                *error = Some(format!("{n} matches"));
                                            }
                                            *last_tab_matches = Some(names);
                                        }
                                    }
                                    needs_redraw = true;
                                }
                                KeyCode::Char(c) => {
                                    buffer.push(c);
                                    *error = None;
                                    *last_tab_matches = None;
                                    needs_redraw = true;
                                }
                                _ => {}
                            }
                        }
                        continue;
                    }
                    InputMode::Normal => {}
                }
                // Resize must update stored dims even when an overlay is active —
                // otherwise the overlay renders at stale dimensions until it closes.
                if let crossterm::event::Event::Resize(c, r) = event {
                    // Pin the bottom across resizes: a viewport sitting at the
                    // end (follow/live, or just scrolled to the bottom) must
                    // stay there when body height changes — otherwise the
                    // newest content drifts off-screen. Terminals/multiplexers
                    // often emit a resize right after startup, which is what
                    // made --follow/--live land short of the end.
                    let was_at_bottom = viewport.is_at_bottom(src.as_ref(), &idx);
                    cols = c;
                    rows = r;
                    viewport.resize(c, r);
                    if was_at_bottom {
                        viewport.goto_bottom(src.as_ref(), &mut idx);
                    }
                    needs_redraw = true;
                    if overlay.is_some() {
                        // Overlay still owns the screen; nothing else to do this tick.
                        continue;
                    }
                    // No overlay: fall through to normal handling so the
                    // existing Command::Resize path can do whatever else it does.
                }
                // Active overlay swallows input. Apply/Refuse/Close outcomes
                // are handled inline; CloseAnd defers to the normal command
                // dispatcher below.
                if let Some(ov) = overlay.as_mut() {
                    let outcome = match &event {
                        Event::Key(ke) => ov.handle_key(*ke),
                        Event::Mouse(me) => ov.handle_mouse(*me, viewport.body_rows()),
                        Event::Resize(_, _) => crate::overlay::OverlayOutcome::Stay,
                        _ => crate::overlay::OverlayOutcome::Stay,
                    };
                    match outcome {
                        crate::overlay::OverlayOutcome::Stay => {
                            needs_redraw = true;
                            continue;
                        }
                        crate::overlay::OverlayOutcome::Close => {
                            overlay = None;
                            overlay_flash = None;
                            needs_redraw = true;
                            continue;
                        }
                        crate::overlay::OverlayOutcome::CloseAnd(cmd) => {
                            overlay = None;
                            overlay_flash = None;
                            if let Command::SelectFile(i) = cmd {
                                if i < file_set.len() {
                                    file_set.set_current_index(i);
                                    if let Some(msg) = switch_to_current_file(
                                        &mut file_set, &mut current_file_index,
                                        &args, preprocessor.as_ref(),
                                        record_start_regex.as_ref(),
                                        &mut viewport, &mut src, &mut idx,
                                    ) {
                                        transient_status = Some(msg);
                                    }
                                }
                            } else if let Command::SelectTagMatch(idx_pick) = cmd {
                                if let Some(active) = tag_stack.active.as_mut() {
                                    if idx_pick < active.matches.len() {
                                        active.cursor = idx_pick;
                                        let entry = active.matches[idx_pick].clone();
                                        let msg = dispatch_match(
                                            &entry,
                                            &mut file_set,
                                            &mut current_file_index,
                                            &args,
                                            preprocessor.as_ref(),
                                            record_start_regex.as_ref(),
                                            &mut viewport,
                                            &mut src,
                                            &mut idx,
                                        );
                                        update_viewport_tag_indicator(&tag_stack, &mut viewport);
                                        if let Some(m) = msg {
                                            transient_status = Some(m);
                                        }
                                    }
                                }
                            }
                            needs_redraw = true;
                            continue;
                        }
                        crate::overlay::OverlayOutcome::Apply(cmd) => {
                            if let Command::DropFileAt(target) = cmd {
                                if file_set.len() > 1 && target < file_set.len() {
                                    let saved_cur = file_set.current_index();
                                    file_set.set_current_index(target);
                                    let _ = file_set.delete_current();
                                    // delete_current() moved the cursor itself; restore
                                    // the pre-drop position when the deletion was not OF
                                    // the saved cursor.
                                    if target < saved_cur {
                                        let restored = saved_cur.saturating_sub(1);
                                        file_set.set_current_index(restored);
                                    } else if target > saved_cur {
                                        file_set.set_current_index(saved_cur);
                                    }
                                    // (target == saved_cur: delete_current already landed on the nearest
                                    //  surviving file; nothing to restore.)
                                    if let Some(msg) = switch_to_current_file(
                                        &mut file_set, &mut current_file_index,
                                        &args, preprocessor.as_ref(),
                                        record_start_regex.as_ref(),
                                        &mut viewport, &mut src, &mut idx,
                                    ) {
                                        transient_status = Some(msg);
                                    }
                                    if let Some(ov) = overlay.as_mut() {
                                        ov.refresh(crate::overlay::OverlayContext { file_set: &file_set });
                                    }
                                }
                            }
                            needs_redraw = true;
                            continue;
                        }
                        crate::overlay::OverlayOutcome::Refuse(msg) => {
                            overlay_flash = Some((msg, std::time::Instant::now()));
                            needs_redraw = true;
                            continue;
                        }
                    }
                }
                // No-overlay mouse: scrollwheel scrolls the body. Other mouse
                // events are ignored to keep the body inert when --mouse is on
                // but no overlay is active.
                if let crossterm::event::Event::Mouse(me) = &event {
                    if mouse_enabled {
                        use crossterm::event::{KeyModifiers, MouseEventKind};
                        // Shift+wheel = horizontal scroll: the widely-supported
                        // convention for terminals that don't emit native
                        // ScrollLeft/ScrollRight (e.g. macOS Terminal.app). Only
                        // when there's a horizontal axis; otherwise fall through
                        // to normal vertical scroll.
                        let hshift = me.modifiers.contains(KeyModifiers::SHIFT)
                            && viewport.hscroll_active();
                        match me.kind {
                            MouseEventKind::ScrollDown if hshift => {
                                viewport.hscroll_right_step();
                                needs_redraw = true;
                            }
                            MouseEventKind::ScrollUp if hshift => {
                                viewport.hscroll_left_step();
                                needs_redraw = true;
                            }
                            MouseEventKind::ScrollDown => {
                                viewport.scroll_lines(wheel_lines as i64, src.as_ref(), &mut idx);
                                needs_redraw = true;
                            }
                            MouseEventKind::ScrollUp => {
                                viewport.scroll_lines(-(wheel_lines as i64), src.as_ref(), &mut idx);
                                needs_redraw = true;
                            }
                            MouseEventKind::ScrollLeft => {
                                viewport.hscroll_left_step();
                                needs_redraw = true;
                            }
                            MouseEventKind::ScrollRight => {
                                viewport.hscroll_right_step();
                                needs_redraw = true;
                            }
                            _ => {}
                        }
                    }
                    continue;
                }
                // Pre-translate keymap interception. Only consult the keymap
                // when in Normal mode (not inside a search/option/prettify/
                // shell prompt).
                let mut cmd: Option<Command> = None;
                if let InputMode::Normal = mode {
                    if let Event::Key(ke) = &event {
                        if let Some(target) = keymap.lookup(ke) {
                            match target {
                                crate::keys::BindingTarget::Shell(cmd_text) => {
                                    let cmd_text = cmd_text.clone();
                                    if let Err(e) = crate::shell::run_shell_command(&cmd_text) {
                                        let _ = writeln!(std::io::stderr(),
                                            "[shell: {e}]");
                                    }
                                    needs_redraw = true;
                                    continue;
                                }
                                crate::keys::BindingTarget::Command(c) => {
                                    cmd = Some(c.clone());
                                }
                            }
                        }
                    }
                }
                let cmd = cmd.unwrap_or_else(|| translate(event));
                // Consume the numeric prefix at the top of each dispatch so
                // commands that don't need it drop it implicitly.
                let prefix_at_cmd = numeric_prefix.take();
                match cmd {
                    Command::Digit(d) => {
                        let cur = prefix_at_cmd.unwrap_or(0);
                        let next = cur.saturating_mul(10).saturating_add(d as usize);
                        if next <= 99_999_999 {
                            numeric_prefix = Some(next);
                        } else {
                            // Overflow: keep previous prefix, ignore this digit.
                            numeric_prefix = prefix_at_cmd;
                        }
                        continue;
                    }
                    Command::Cancel => {
                        // prefix_at_cmd already consumed; nothing else to do.
                        continue;
                    }
                    Command::GotoLine => {
                        update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                        match prefix_at_cmd {
                            Some(line) if line > 0 => {
                                viewport.goto_line(line - 1, src.as_ref(), &mut idx);
                                viewport.suspend_follow_if(args.follow_suspend_on_motion);
                            }
                            _ => {
                                viewport.goto_top();
                                viewport.suspend_follow_if(args.follow_suspend_on_motion);
                            }
                        }
                        needs_redraw = true;
                    }
                    Command::GotoRecord => {
                        update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                        match prefix_at_cmd {
                            Some(rec) if rec > 0 => {
                                viewport.goto_record(rec - 1, src.as_ref(), &mut idx);
                                viewport.suspend_follow_if(args.follow_suspend_on_motion);
                            }
                            _ => viewport.goto_bottom(src.as_ref(), &mut idx),
                        }
                        needs_redraw = true;
                    }
                    Command::GotoPercent => {
                        update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                        match prefix_at_cmd {
                            Some(p) if p <= 100 => viewport.goto_percent(p as u8, src.as_ref(), &mut idx),
                            _ => viewport.goto_top(),
                        }
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        needs_redraw = true;
                    }
                    Command::Quit => break,
                    Command::Resize(c, r) => {
                        let was_at_bottom = viewport.is_at_bottom(src.as_ref(), &idx);
                        cols = c; rows = r;
                        viewport.resize(c, r);
                        if was_at_bottom {
                            viewport.goto_bottom(src.as_ref(), &mut idx);
                        }
                        needs_redraw = true;
                    }
                    Command::ScrollLines(n) => {
                        viewport.scroll_lines(n, src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        if viewport.note_motion_for_eof(n > 0, src.as_ref(), &idx) { break; }
                        needs_redraw = true;
                    }
                    Command::ScrollLogicalLines(n) => {
                        viewport.scroll_logical_lines(n, src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        if viewport.note_motion_for_eof(n > 0, src.as_ref(), &idx) { break; }
                        needs_redraw = true;
                    }
                    Command::PageDown => {
                        viewport.page_down(src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        if viewport.note_motion_for_eof(true, src.as_ref(), &idx) { break; }
                        needs_redraw = true;
                    }
                    Command::PageUp => {
                        viewport.page_up(src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        viewport.note_motion_for_eof(false, src.as_ref(), &idx);
                        needs_redraw = true;
                    }
                    Command::HalfPageDown => {
                        viewport.half_page_down(src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        if viewport.note_motion_for_eof(true, src.as_ref(), &idx) { break; }
                        needs_redraw = true;
                    }
                    Command::HalfPageUp => {
                        viewport.half_page_up(src.as_ref(), &mut idx);
                        viewport.suspend_follow_if(args.follow_suspend_on_motion);
                        viewport.note_motion_for_eof(false, src.as_ref(), &idx);
                        needs_redraw = true;
                    }
                    Command::Refresh => {
                        needs_redraw = true;
                    }
                    Command::Reload => {
                        // Force a stat+reread now (only meaningful for live
                        // sources; static FileSource::pump() is a no-op).
                        src.pump();
                        if src.revision() != last_revision {
                            rebuild_after_replace(
                                src.as_ref(), &mut viewport, &mut idx, rebuild_spec,
                            );
                            last_revision = src.revision();
                            needs_redraw = true;
                        }
                    }
                    Command::TogglePrettify => {
                        apply_prettify(
                            src.as_ref(), &mut viewport, &mut idx, rebuild_spec,
                            PrettifyTarget::Toggle,
                        );
                        last_revision = src.revision();
                        needs_redraw = true;
                    }
                    Command::SetPrettifyMode(m) => {
                        apply_prettify(
                            src.as_ref(), &mut viewport, &mut idx, rebuild_spec,
                            PrettifyTarget::Mode(m),
                        );
                        last_revision = src.revision();
                        needs_redraw = true;
                    }
                    Command::RedetectPrettify => {
                        apply_prettify(
                            src.as_ref(), &mut viewport, &mut idx, rebuild_spec,
                            PrettifyTarget::Auto,
                        );
                        last_revision = src.revision();
                        needs_redraw = true;
                    }
                    Command::ToggleLineNumbers => {
                        viewport.toggle_line_numbers();
                        needs_redraw = true;
                    }
                    Command::ToggleChop => {
                        viewport.toggle_chop();
                        needs_redraw = true;
                    }
                    Command::ToggleFollow => {
                        viewport.toggle_follow();
                        if viewport.follow_mode() {
                            // Re-engaging: pump any pending bytes and snap to bottom.
                            src.pump();
                            idx.notice_new_bytes(src.as_ref());
                            viewport.goto_bottom(src.as_ref(), &mut idx);
                        }
                        needs_redraw = true;
                    }
                    Command::SearchForward => {
                        incsearch_origin = (viewport.top_line(), viewport.top_row());
                        mode = InputMode::SearchPrompt {
                            direction: SearchDirection::Forward,
                            buffer: String::new(),
                            error: None,
                        };
                        needs_redraw = true;
                    }
                    Command::SearchBackward => {
                        incsearch_origin = (viewport.top_line(), viewport.top_row());
                        mode = InputMode::SearchPrompt {
                            direction: SearchDirection::Backward,
                            buffer: String::new(),
                            error: None,
                        };
                        needs_redraw = true;
                    }
                    Command::ShellEscape => {
                        mode = InputMode::ShellPrompt {
                            buffer: String::new(),
                            error: None,
                        };
                        needs_redraw = true;
                    }
                    Command::ColonPrompt => {
                        mode = InputMode::ColonPrompt {
                            buffer: String::new(),
                            error: None,
                        };
                        needs_redraw = true;
                    }
                    Command::NextMatch => {
                        update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                        if viewport.search_repeat(src.as_ref(), &mut idx, false) {
                            needs_redraw = true;
                        }
                    }
                    Command::PreviousMatch => {
                        update_prev_position(&mut previous_position, current_file_index, viewport.top_line());
                        if viewport.search_repeat(src.as_ref(), &mut idx, true) {
                            needs_redraw = true;
                        }
                    }
                    Command::OptionPrefix => {
                        mode = InputMode::OptionPrefix;
                    }
                    Command::MarkSet => {
                        mode = InputMode::MarkSetPending;
                    }
                    Command::MarkJump => {
                        mode = InputMode::MarkJumpPending;
                    }
                    Command::CtrlXPrefix => {
                        mode = InputMode::CtrlXPending;
                    }
                    Command::JumpPrevious => {
                        // Resolved inside the CtrlXPending mode intercept; this
                        // arm is defensive and should never fire.
                    }
                    Command::TagPrompt => {
                        if tag_file.is_none() {
                            transient_status = Some("[no tags file loaded]".into());
                            needs_redraw = true;
                        } else {
                            mode = InputMode::TagPrompt {
                                buffer: String::new(),
                                error: None,
                                last_tab_matches: None,
                            };
                            needs_redraw = true;
                        }
                    }
                    Command::TagPop => match tag_stack.pop() {
                        Some((file_index, line)) => {
                            if file_index != current_file_index && file_index < file_set.len() {
                                file_set.set_current_index(file_index);
                                let path = file_set.current().unwrap().to_path_buf();
                                if let Err(e) = switch_file(
                                    &path,
                                    file_index,
                                    file_set.len(),
                                    &args,
                                    preprocessor.as_ref(),
                                    &mut viewport,
                                    &mut src,
                                    &mut idx,
                                    record_start_regex.as_ref(),
                                ) {
                                    transient_status = Some(format!("[open: {e}]"));
                                } else {
                                    current_file_index = file_index;
                                }
                            }
                            let clamped = line.min(idx.line_count().saturating_sub(1));
                            viewport.goto_line(clamped, src.as_ref(), &mut idx);
                            update_viewport_tag_indicator(&tag_stack, &mut viewport);
                            needs_redraw = true;
                        }
                        None => {
                            transient_status = Some("[tag stack empty]".into());
                            needs_redraw = true;
                        }
                    },
                    Command::OpenPicker => {
                        let saved = (0..file_set.len())
                            .map(|i| if i == current_file_index { viewport.top_line() } else { 0 })
                            .collect::<Vec<_>>();
                        overlay = Some(Box::new(
                            crate::overlay::picker::FilePicker::new(&file_set, saved)
                        ));
                        needs_redraw = true;
                    }
                    Command::OpenHelp => {
                        let remaps = keymap.user_keys_by_command_name();
                        overlay = Some(Box::new(
                            crate::overlay::help::HelpOverlay::new(remaps)
                        ));
                        needs_redraw = true;
                    }
                    Command::SelectFile(_)
                    | Command::DropFileAt(_)
                    | Command::SelectTagMatch(_)
                    | Command::OpenTagPicker => {
                        // Overlay-only outcomes; consumed by the routing block above.
                    }
                    Command::MouseEvent(_) => {
                        // Mouse handling lives in the event-routing block, not here.
                    }
                    Command::HScrollLeft => {
                        if hscroll_shift != 0 {
                            viewport.hscroll_left_cols(hscroll_shift);
                        } else {
                            viewport.hscroll_left_half();
                        }
                        needs_redraw = true;
                    }
                    Command::HScrollRight => {
                        if hscroll_shift != 0 {
                            viewport.hscroll_right_cols(hscroll_shift);
                        } else {
                            viewport.hscroll_right_half();
                        }
                        needs_redraw = true;
                    }
                    Command::HScrollLeftStep => {
                        viewport.hscroll_left_step();
                        needs_redraw = true;
                    }
                    Command::HScrollRightStep => {
                        viewport.hscroll_right_step();
                        needs_redraw = true;
                    }
                    Command::YankLine => {
                        let msg = yank_current_line(clipboard_enabled, &viewport, src.as_ref(), &mut idx);
                        transient_status = Some(msg);
                        needs_redraw = true;
                    }
                    Command::Noop => {}
                }
            }
            Ok(false) => {
                // Timeout — check whether the source has grown or been rewritten.
                if viewport.live_mode() {
                    let was_at_bottom = viewport.is_at_bottom(src.as_ref(), &idx);
                    src.pump();
                    if src.revision() != last_revision {
                        rebuild_after_replace(
                            src.as_ref(), &mut viewport, &mut idx, rebuild_spec,
                        );
                        if was_at_bottom {
                            viewport.goto_bottom(src.as_ref(), &mut idx);
                        }
                        last_revision = src.revision();
                        needs_redraw = true;
                    }
                } else if viewport.follow_mode() {
                    let was_at_bottom = viewport.is_at_bottom(src.as_ref(), &idx);
                    src.pump();
                    if src.take_rotated() {
                        // File was rotated or truncated. Re-open from offset 0
                        // and reset the line index so we're not staring at
                        // stale mmap content. Snap to bottom of the fresh
                        // content (follow mode is on, so that's the natural
                        // place to land).
                        if let Some(path) = src.path().map(|p| p.to_path_buf()) {
                            match crate::open::open_source_for_path(
                                &path, &args, preprocessor.as_ref(),
                            ) {
                                Ok((new_src, _label, _err)) => {
                                    src = new_src;
                                    idx = LineIndex::new();
                                    if let Some(n) = rebuild_spec.head {
                                        idx.set_head_cap(n);
                                    }
                                    viewport.invalidate_filter_cache();
                                    idx.notice_new_bytes(src.as_ref());
                                    viewport.extend_visible_lines(&idx, src.as_ref());
                                    viewport.goto_bottom(src.as_ref(), &mut idx);
                                    viewport.flash("(F reopened)", 4);
                                    needs_redraw = true;
                                    continue;
                                }
                                Err(e) => {
                                    transient_status = Some(format!("[reopen failed: {e}]"));
                                    needs_redraw = true;
                                }
                            }
                        }
                    }
                    let lines_before = idx.line_count();
                    idx.notice_new_bytes(src.as_ref());
                    viewport.extend_visible_lines(&idx, src.as_ref());
                    if idx.line_count() != lines_before {
                        needs_redraw = true;
                        viewport.note_growth();
                        if was_at_bottom {
                            viewport.goto_bottom(src.as_ref(), &mut idx);
                        }
                    } else {
                        viewport.tick_idle();
                    }
                    viewport.tick_flash();
                    // `--exit-follow-on-close`: when the source signals
                    // that the upstream writer has finished (streaming
                    // stdin's reader thread exited), exit the pager.
                    // File sources are always complete from open, so this
                    // condition only fires for piped stdin.
                    if args.exit_follow_on_close && src.is_complete() {
                        break;
                    }
                } else if !src.is_complete() {
                    // Streaming stdin without follow mode: still keep the index
                    // up-to-date so line counts stay accurate, but don't auto-scroll.
                    let lines_before = idx.line_count();
                    idx.notice_new_bytes(src.as_ref());
                    viewport.extend_visible_lines(&idx, src.as_ref());
                    if idx.line_count() != lines_before {
                        needs_redraw = true;
                    }
                }
            }
            Err(_) => {
                // poll() error — sleep the timeout duration to avoid tight-spinning.
                std::thread::sleep(timeout);
            }
        }
    }
    Ok(())
}

/// What `apply_prettify` should do to the source's prettify state.
#[derive(Debug, Clone, Copy)]
enum PrettifyTarget {
    /// Set a specific mode (including `Off` for "raw").
    Mode(PrettifyMode),
    /// Flip between current mode and last-active mode.
    Toggle,
    /// Re-run byte-based content detection and apply the result.
    Auto,
}

/// Apply a prettify-state change to the source and propagate any visible
/// effects (line index rebuild, viewport label, scroll clamp). No-op if the
/// source isn't a `TransformingSource` (i.e. `prettify_mode()` is `None`).
fn apply_prettify(
    src: &dyn Source,
    viewport: &mut Viewport,
    idx: &mut LineIndex,
    spec: RebuildSpec,
    target: PrettifyTarget,
) {
    // Sources without a wrapper return None — nothing to do.
    if src.prettify_mode().is_none() {
        return;
    }
    match target {
        PrettifyTarget::Mode(m) => src.set_prettify_mode(m),
        PrettifyTarget::Toggle => src.toggle_prettify(),
        PrettifyTarget::Auto => src.redetect_prettify(),
    }
    rebuild_after_replace(src, viewport, idx, spec);
    viewport.set_prettify_label(src.prettify_label());
}

/// Rebuild line index and visible-line cache after the source content has
/// been replaced wholesale (e.g. an editor saved over the file). Re-applies
/// `--head`/`--tail` caps from the original CLI args; clamps `top_line` so the
/// user stays roughly where they were rather than jumping. Auto snap-to-bottom
/// (when the user *was* at the bottom) is the caller's responsibility.
fn rebuild_after_replace(
    src: &dyn Source,
    viewport: &mut Viewport,
    idx: &mut LineIndex,
    spec: RebuildSpec,
) {
    let new_off = match spec.tail {
        Some(n) => find_tail_offset(src, n),
        None => 0,
    };
    *idx = LineIndex::new_starting_at(new_off);
    if let Some(n) = spec.head {
        idx.set_head_cap(n);
    }
    viewport.invalidate_filter_cache();
    idx.notice_new_bytes(src);
    viewport.extend_visible_lines(idx, src);
    viewport.clamp_top_line(idx.line_count());
}

fn to_crossterm_color(c: crate::ansi::Color, truecolor: bool) -> crossterm::style::Color {
    use crossterm::style::Color as CC;
    use crate::ansi::Color;
    match c {
        Color::Ansi(0) => CC::Black,
        Color::Ansi(1) => CC::DarkRed,
        Color::Ansi(2) => CC::DarkGreen,
        Color::Ansi(3) => CC::DarkYellow,
        Color::Ansi(4) => CC::DarkBlue,
        Color::Ansi(5) => CC::DarkMagenta,
        Color::Ansi(6) => CC::DarkCyan,
        Color::Ansi(7) => CC::Grey,
        Color::Ansi(8) => CC::DarkGrey,
        Color::Ansi(9) => CC::Red,
        Color::Ansi(10) => CC::Green,
        Color::Ansi(11) => CC::Yellow,
        Color::Ansi(12) => CC::Blue,
        Color::Ansi(13) => CC::Magenta,
        Color::Ansi(14) => CC::Cyan,
        Color::Ansi(15) => CC::White,
        Color::Ansi(_) => CC::Reset,
        Color::Indexed(n) => CC::AnsiValue(n),
        Color::Rgb(r, g, b) => {
            if truecolor {
                CC::Rgb { r, g, b }
            } else {
                CC::AnsiValue(crate::render::rgb_to_256(r, g, b))
            }
        }
        Color::Default => CC::Reset,
    }
}

/// Emit crossterm commands to transition `prev` → `next`. Caller must
/// already have written prior cells using `prev`'s state.
fn emit_style_diff<W: Write>(
    out: &mut W,
    prev: &crate::ansi::Style,
    next: &crate::ansi::Style,
    truecolor: bool,
) -> io::Result<()> {
    // For attribute toggles, crossterm has individual on/off pairs.
    // `NormalIntensity` cancels both bold AND dim — handle them together
    // to avoid emitting it twice when only one changed.
    let intensity_changed = prev.bold != next.bold || prev.dim != next.dim;

    // Color changes. ResetColor clears BOTH fg and bg simultaneously, so
    // if either changed to None we emit ResetColor first and then re-emit
    // the other if it's Some.
    let fg_changed = prev.fg != next.fg;
    let bg_changed = prev.bg != next.bg;

    if (fg_changed && next.fg.is_none()) || (bg_changed && next.bg.is_none()) {
        out.queue(ResetColor)?;
        // After ResetColor, re-emit any color that should remain set.
        if let Some(c) = next.fg {
            out.queue(SetForegroundColor(to_crossterm_color(c, truecolor)))?;
        }
        if let Some(c) = next.bg {
            out.queue(SetBackgroundColor(to_crossterm_color(c, truecolor)))?;
        }
    } else {
        if fg_changed {
            if let Some(c) = next.fg {
                out.queue(SetForegroundColor(to_crossterm_color(c, truecolor)))?;
            }
        }
        if bg_changed {
            if let Some(c) = next.bg {
                out.queue(SetBackgroundColor(to_crossterm_color(c, truecolor)))?;
            }
        }
    }

    if intensity_changed {
        if next.bold {
            out.queue(SetAttribute(Attribute::Bold))?;
        } else if next.dim {
            out.queue(SetAttribute(Attribute::Dim))?;
        } else {
            out.queue(SetAttribute(Attribute::NormalIntensity))?;
        }
    }
    if prev.italic != next.italic {
        out.queue(SetAttribute(if next.italic { Attribute::Italic } else { Attribute::NoItalic }))?;
    }
    if prev.underline != next.underline {
        out.queue(SetAttribute(if next.underline { Attribute::Underlined } else { Attribute::NoUnderline }))?;
    }
    if prev.reverse != next.reverse {
        out.queue(SetAttribute(if next.reverse { Attribute::Reverse } else { Attribute::NoReverse }))?;
    }
    if prev.strike != next.strike {
        out.queue(SetAttribute(if next.strike { Attribute::CrossedOut } else { Attribute::NotCrossedOut }))?;
    }
    Ok(())
}

fn emit_hyperlink_diff<W: Write>(
    out: &mut W,
    prev: &Option<Arc<str>>,
    next: &Option<Arc<str>>,
) -> io::Result<()> {
    if prev == next {
        return Ok(());
    }
    if prev.is_some() {
        out.write_all(b"\x1b]8;;\x1b\\")?;
    }
    if let Some(uri) = next {
        out.write_all(b"\x1b]8;;")?;
        out.write_all(uri.as_bytes())?;
        out.write_all(b"\x1b\\")?;
    }
    Ok(())
}

/// DEC private mode 2026: synchronized output. Terminals that support it
/// (iTerm2, Kitty, WezTerm, Alacritty, Ghostty, foot, recent VTE,
/// Windows Terminal) buffer everything between `BEGIN` and `END` and
/// present the whole frame atomically; terminals that don't recognize the
/// sequence silently ignore it. This kills the flicker that would
/// otherwise appear during a frame's per-row repaint.
const SYNC_UPDATE_BEGIN: &[u8] = b"\x1b[?2026h";
const SYNC_UPDATE_END: &[u8] = b"\x1b[?2026l";

fn write_frame(out: &mut impl Write, frame: &Frame, cols: u16, rows: u16, truecolor: bool) -> io::Result<()> {
    // Raw mode (`-r` / `:color raw`) routes each visible body row through the
    // `frame.raw_rows` slot (populated by `Viewport::frame` when ansi_mode is
    // Raw). The writer below blasts those bytes to the terminal verbatim so
    // escape sequences like cursor moves and SGR pass through. Wrap math is
    // best-effort — terminal-driven wrapping may shift sub-rows under long
    // lines, matching `less -r`'s documented limitation.

    // Begin a synchronized update so the whole frame is presented atomically
    // (see SYNC_UPDATE_BEGIN). Paired with per-row `Clear(UntilNewLine)`
    // below, this replaces the previous global `Clear(All)` redraw and
    // eliminates the visible blank-frame flicker on every scroll keystroke.
    out.write_all(SYNC_UPDATE_BEGIN)?;

    // Reset attributes once before drawing so the first row starts clean.
    out.queue(SetAttribute(Attribute::Reset))?;
    out.queue(ResetColor)?;

    if let Some(blob) = &frame.image_blob {
        // Clear the body region once so a prior frame's cells don't bleed
        // around/under the image, then emit the graphics escape verbatim.
        for r in 0..frame.body.len() as u16 {
            out.queue(MoveTo(0, r))?;
            out.queue(Clear(ClearType::UntilNewLine))?;
        }
        out.queue(MoveTo(0, 0))?;
        out.write_all(blob)?;
        // Status row, mirroring the normal path's status handling.
        out.queue(MoveTo(0, rows.saturating_sub(1)))?;
        out.queue(Clear(ClearType::UntilNewLine))?;
        emit_style_diff(out, &crate::ansi::Style::default(), &frame.status_style, truecolor)?;
        let mut status = frame.status.clone();
        if status.len() > cols as usize { status.truncate(cols as usize); }
        else { let pad = cols as usize - status.len(); status.push_str(&" ".repeat(pad)); }
        out.queue(Print(status))?;
        out.queue(ResetColor)?;
        out.queue(SetAttribute(Attribute::Reset))?;
        out.write_all(SYNC_UPDATE_END)?;
        return out.flush();
    }

    for (i, row) in frame.body.iter().enumerate() {
        out.queue(MoveTo(0, i as u16))?;
        // Wipe whatever was on this row in the previous frame. Cursor is
        // at col 0 so UntilNewLine clears the full row width, which also
        // covers the shrink-on-resize case (old cells past the new edge).
        out.queue(Clear(ClearType::UntilNewLine))?;
        // Defensive: every row begins with a full attribute reset, so a
        // mis-handled reset on the previous row can't bleed forward.
        out.queue(SetAttribute(Attribute::Reset))?;

        // Raw passthrough: when the viewport set this row's `raw_rows` entry,
        // write the original source bytes directly to the terminal instead of
        // rendering cells. Empty Vec means "skip" (mid-line wrap continuation
        // whose first row already emitted the bytes).
        if let Some(Some(raw)) = frame.raw_rows.get(i) {
            if !raw.is_empty() {
                out.write_all(raw)?;
            }
            // Trailing reset so a bare `\x1b[31m` doesn't leak into the next row.
            out.queue(ResetColor)?;
            out.queue(SetAttribute(Attribute::Reset))?;
            continue;
        }

        let row_style = frame.row_styles.get(i).copied().unwrap_or(RowStyle::Normal);
        // Build the base style representing the terminal state after the
        // defensive reset above. Dim rows get a dim base so the style-diff
        // tracker inside write_row_with_highlights starts from the correct
        // live terminal state.
        let base_style = if matches!(row_style, RowStyle::Dim) {
            out.queue(SetAttribute(Attribute::Dim))?;
            crate::ansi::Style { dim: true, ..Default::default() }
        } else {
            crate::ansi::Style::default()
        };
        let no_highlights = Vec::new();
        let highlights = frame.highlights.get(i).unwrap_or(&no_highlights);
        write_row_with_highlights(out, row, cols, highlights, base_style, truecolor)?;
    }
    // Status row
    out.queue(MoveTo(0, rows.saturating_sub(1)))?;
    out.queue(Clear(ClearType::UntilNewLine))?;
    emit_style_diff(out, &crate::ansi::Style::default(), &frame.status_style, truecolor)?;
    let mut status = frame.status.clone();
    if status.len() > cols as usize {
        status.truncate(cols as usize);
    } else {
        let pad = cols as usize - status.len();
        status.push_str(&" ".repeat(pad));
    }
    out.queue(Print(status))?;
    out.queue(ResetColor)?;
    out.queue(SetAttribute(Attribute::Reset))?;

    // End the synchronized update. The terminal flushes the buffered frame
    // atomically on receipt of this sequence.
    out.write_all(SYNC_UPDATE_END)?;
    out.flush()
}


/// Emit a single row with per-cell color/attribute transitions and
/// reverse-video highlights. Walks each cell, diffing style and hyperlink
/// from the previous cell, emitting only the transitions needed.
///
/// `base_style` is the terminal's live style state when this function is
/// entered (reflects any row-level attribute the caller already emitted,
/// e.g. `Dim` for `--dim` rows).
///
/// Highlight ranges toggle each cell's `reverse` attribute so highlights
/// compose correctly with cells that are already reverse-video.
fn write_row_with_highlights(
    out: &mut impl Write,
    row: &[Cell],
    cols: u16,
    highlights: &[std::ops::Range<usize>],
    base_style: crate::ansi::Style,
    truecolor: bool,
) -> io::Result<()> {
    let cols_usize = cols as usize;

    let mut ranges: Vec<std::ops::Range<usize>> = highlights
        .iter()
        .filter_map(|r| {
            let s = r.start.min(cols_usize);
            let e = r.end.min(cols_usize);
            if e > s { Some(s..e) } else { None }
        })
        .collect();
    ranges.sort_by_key(|r| r.start);

    // Style register starts at `base_style` — what the terminal currently
    // has live after any row-level attribute the caller emitted.
    let mut prev_style = base_style;
    let mut prev_link: Option<Arc<str>> = None;

    let mut col = 0usize;
    let mut i = 0usize;
    while col < cols_usize && i < row.len() {
        let in_highlight = ranges.iter().any(|r| r.start <= col && col < r.end);

        match &row[i] {
            Cell::Char { ch, width, style, hyperlink } => {
                // Effective style: cell's style with reverse toggled when in
                // a highlight, so highlight composes with already-reverse content.
                // Row-level dim (from `--dim` non-matching rows) is OR'd into
                // each cell unless the cell explicitly sets bold (bold and dim
                // share the SGR intensity slot; bold wins).
                let mut eff = *style;
                if in_highlight {
                    eff.reverse = !eff.reverse;
                }
                if base_style.dim && !eff.bold {
                    eff.dim = true;
                }
                emit_style_diff(out, &prev_style, &eff, truecolor)?;
                emit_hyperlink_diff(out, &prev_link, hyperlink)?;
                out.queue(Print(*ch))?;
                prev_style = eff;
                prev_link = hyperlink.clone();
                col += *width as usize;
            }
            Cell::Continuation => {
                // Already accounted for by the preceding wide char.
            }
            Cell::Empty => {
                // Background padding. Reset style to default so we don't
                // paint the rest of the line in the last active color —
                // but preserve the row-level dim so trailing padding on a
                // dim row stays dim.
                let default = if base_style.dim {
                    crate::ansi::Style { dim: true, ..Default::default() }
                } else {
                    crate::ansi::Style::default()
                };
                emit_style_diff(out, &prev_style, &default, truecolor)?;
                emit_hyperlink_diff(out, &prev_link, &None)?;
                out.queue(Print(' '))?;
                prev_style = default;
                prev_link = None;
                col += 1;
            }
        }
        i += 1;
    }

    // End-of-row: close any open hyperlink and reset color/attrs so the
    // next row's defensive Reset is a true no-op.
    emit_hyperlink_diff(out, &prev_link, &None)?;
    out.queue(ResetColor)?;
    out.queue(SetAttribute(Attribute::Reset))?;

    Ok(())
}

fn render_overlay(
    out: &mut impl Write,
    frame: &crate::overlay::OverlayFrame,
    width: u16,
    height: u16,
) -> io::Result<()> {
    // Mirror write_frame's atomic-frame discipline: synchronized update +
    // per-row clear, with a reverse-video status row to match the regular
    // viewport's look.
    out.write_all(SYNC_UPDATE_BEGIN)?;
    out.queue(SetAttribute(Attribute::Reset))?;
    out.queue(ResetColor)?;
    for row in 0..height.saturating_sub(1) {
        out.queue(MoveTo(0, row))?;
        out.queue(Clear(ClearType::UntilNewLine))?;
        out.queue(SetAttribute(Attribute::Reset))?;
        if let Some(line) = frame.body.get(row as usize) {
            let mut written = 0usize;
            for ch in line.chars() {
                let w = unicode_width::UnicodeWidthChar::width(ch).unwrap_or(0);
                if written + w > width as usize { break; }
                write!(out, "{ch}")?;
                written += w;
            }
        }
    }
    out.queue(MoveTo(0, height.saturating_sub(1)))?;
    out.queue(Clear(ClearType::UntilNewLine))?;
    out.queue(SetAttribute(Attribute::Reverse))?;
    let mut status = frame.status.clone();
    // TODO: use display width (not byte count) — mirrors write_frame's latent limitation.
    if status.len() > width as usize {
        status.truncate(width as usize);
    } else {
        let pad = width as usize - status.len();
        status.push_str(&" ".repeat(pad));
    }
    out.queue(Print(status))?;
    out.queue(ResetColor)?;
    out.queue(SetAttribute(Attribute::Reset))?;
    out.write_all(SYNC_UPDATE_END)?;
    out.flush()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parse_colon_n() {
        assert_eq!(parse_colon_command("n").unwrap(), ColonCommand::Next);
        assert_eq!(parse_colon_command("next").unwrap(), ColonCommand::Next);
    }

    #[test]
    fn current_line_bytes_strips_trailing_newline() {
        use crate::line_index::LineIndex;
        use crate::source::MockSource;
        let m = MockSource::new();
        // Three lines; the last has no trailing newline.
        m.append(b"alpha\nbravo\ncharlie");
        let mut idx = LineIndex::new();
        idx.extend_to_end(&m);
        assert_eq!(idx.line_count(), 3);
        assert_eq!(current_line_bytes(&idx, &m, 0), b"alpha");
        assert_eq!(current_line_bytes(&idx, &m, 1), b"bravo");
        // Last line, no trailing newline, returned verbatim.
        assert_eq!(current_line_bytes(&idx, &m, 2), b"charlie");
    }

    #[test]
    fn write_frame_brackets_with_sync_update_and_no_full_clear() {
        // Locks in the flicker fix: every frame is wrapped in DEC mode 2026
        // begin/end escapes, and the previous global `Clear(All)` is gone
        // (replaced by per-row `Clear(UntilNewLine)`). If any of these
        // assumptions changes, flicker is likely to come back.
        use crate::ansi::Style;
        use crate::render::Cell;
        use crate::viewport::{Frame, RowStyle};

        let row: Vec<Cell> = (0..3)
            .map(|_| Cell::Char { ch: 'a', width: 1, style: Style::default(), hyperlink: None })
            .collect();
        let frame = Frame {
            body: vec![row.clone(), row],
            row_styles: vec![RowStyle::Normal, RowStyle::Normal],
            highlights: vec![Vec::new(), Vec::new()],
            status: "status".into(),
            status_style: crate::ansi::Style { reverse: true, ..Default::default() },
            raw_rows: vec![None, None],
            image_blob: None,
        };

        let mut buf: Vec<u8> = Vec::new();
        write_frame(&mut buf, &frame, 3, 3, true).unwrap();
        let s = std::str::from_utf8(&buf).expect("ascii");

        // Begin and end synchronized-update markers, in that order.
        let begin = s.find("\x1b[?2026h").expect("begin sync update");
        let end = s.find("\x1b[?2026l").expect("end sync update");
        assert!(begin < end, "begin must precede end");
        // Body content must sit between the markers.
        let first_a = s.find('a').expect("body char");
        assert!(begin < first_a && first_a < end, "body must be inside sync update");

        // Full-screen `Clear(All)` (`\x1b[2J`) must NOT appear — it was the
        // source of the flicker. Per-row clear-to-EOL (`\x1b[K`) is fine.
        assert!(
            !s.contains("\x1b[2J"),
            "full-screen Clear(All) reintroduced — flicker fix regressed: {s:?}",
        );
        assert!(s.contains("\x1b[K"), "expected at least one Clear(UntilNewLine)");
    }

    #[test]
    fn write_frame_emits_image_blob_verbatim_and_skips_cell_rows() {
        use crate::viewport::{Frame, RowStyle};
        let body_rows = 3usize;
        let cols = 10u16;
        let blob = b"\x1bPqDATA\x1b\\".to_vec();
        // Seed a body cell with a distinctive printable char; the image-blob
        // path must skip the per-row cell loop, so this char must NOT appear.
        let mut body = vec![vec![crate::render::Cell::Empty; cols as usize]; body_rows];
        body[0][0] = crate::render::Cell::Char { ch: 'Z', width: 1, style: crate::ansi::Style::default(), hyperlink: None };
        let frame = Frame {
            body,
            row_styles: vec![RowStyle::Normal; body_rows],
            highlights: vec![Vec::new(); body_rows],
            status: "img".to_string(),
            status_style: crate::ansi::Style::default(),
            raw_rows: vec![None; body_rows],
            image_blob: Some(blob.clone()),
        };
        let mut out: Vec<u8> = Vec::new();
        write_frame(&mut out, &frame, cols, (body_rows + 1) as u16, true).unwrap();
        let needle = b"\x1bPqDATA\x1b\\";
        assert!(out.windows(needle.len()).any(|w| w == needle), "image blob emitted verbatim");
        assert!(String::from_utf8_lossy(&out).contains("img"), "status still drawn");
        assert!(!String::from_utf8_lossy(&out).contains('Z'), "cell loop skipped: body cell not rendered");
    }

    #[test]
    fn raw_rows_passthrough_emits_original_bytes_and_skips_continuation() {
        use crate::ansi::Style;
        use crate::render::Cell;
        use crate::viewport::{Frame, RowStyle};

        // One body row (since rows=2 means body_rows=1).
        let placeholder_row: Vec<Cell> = (0..3)
            .map(|_| Cell::Char { ch: 'X', width: 1, style: Style::default(), hyperlink: None })
            .collect();
        let frame = Frame {
            body: vec![placeholder_row.clone(), placeholder_row],
            row_styles: vec![RowStyle::Normal, RowStyle::Normal],
            highlights: vec![Vec::new(), Vec::new()],
            status: "s".into(),
            status_style: Style { reverse: true, ..Default::default() },
            // Row 0 emits raw bytes (with an embedded ESC); row 1 is a
            // continuation and emits nothing.
            raw_rows: vec![Some(b"\x1b[31mABC\x1b[0m".to_vec()), Some(Vec::new())],
            image_blob: None,
        };

        let mut buf: Vec<u8> = Vec::new();
        write_frame(&mut buf, &frame, 3, 3, true).unwrap();
        let s = std::str::from_utf8(&buf).expect("ascii");

        // The original SGR bytes must appear (raw passthrough).
        assert!(s.contains("\x1b[31mABC\x1b[0m"), "raw bytes missing in output: {s:?}");
        // The placeholder cells must NOT appear — we bypassed the cell pipeline.
        assert!(!s.contains("XXX"), "cell content leaked through despite raw passthrough: {s:?}");
    }

    #[test]
    fn dim_row_keeps_dim_through_plain_cells_and_padding() {
        // Regression: a row with base_style.dim=true and Cell::Char carrying
        // Style::default() used to emit `\x1b[22m` (NormalIntensity) on the
        // first char, killing the row-level dim and rendering the whole
        // line at normal intensity. Same for Cell::Empty padding cells.
        use crate::ansi::Style;
        use crate::render::Cell;
        let row = vec![
            Cell::Char { ch: 'h', width: 1, style: Style::default(), hyperlink: None },
            Cell::Char { ch: 'i', width: 1, style: Style::default(), hyperlink: None },
            Cell::Empty,
            Cell::Empty,
        ];
        let mut buf: Vec<u8> = Vec::new();
        let base = Style { dim: true, ..Default::default() };
        write_row_with_highlights(&mut buf, &row, 4, &[], base, true).unwrap();
        let s = String::from_utf8_lossy(&buf);

        // Locate every emitted character; before any of them is printed, the
        // dim attribute must NOT have been cleared.
        for needle in ['h', 'i'] {
            let pos = s.find(needle).expect("char printed");
            let before = &s[..pos];
            assert!(
                !before.contains("\x1b[22m"),
                "dim cleared before {needle:?}: {before:?}",
            );
        }
        // The Cell::Empty padding shouldn't clear dim either. Look at the
        // bytes between 'i' and the end-of-row Reset.
        let after_i = s.find('i').unwrap() + 1;
        let eor = s[after_i..].find("\x1b[0m").unwrap_or(s.len() - after_i);
        let pad = &s[after_i..after_i + eor];
        assert!(
            !pad.contains("\x1b[22m"),
            "dim cleared in padding region: {pad:?}",
        );
    }

    #[test]
    fn dim_row_yields_to_explicit_bold_cell() {
        // If a cell carries bold=true from ANSI, that wins over row-level
        // dim (bold and dim share the SGR intensity slot).
        use crate::ansi::Style;
        use crate::render::Cell;
        let row = vec![
            Cell::Char {
                ch: 'B',
                width: 1,
                style: Style { bold: true, ..Default::default() },
                hyperlink: None,
            },
        ];
        let mut buf: Vec<u8> = Vec::new();
        let base = Style { dim: true, ..Default::default() };
        write_row_with_highlights(&mut buf, &row, 1, &[], base, true).unwrap();
        let s = String::from_utf8_lossy(&buf);
        // Bold should be emitted (\x1b[1m); dim should not re-appear.
        assert!(s.contains("\x1b[1m"), "expected Bold escape, got {s:?}");
    }

    #[test]
    fn parse_colon_p() {
        assert_eq!(parse_colon_command("p").unwrap(), ColonCommand::Prev);
        assert_eq!(parse_colon_command("prev").unwrap(), ColonCommand::Prev);
    }

    #[test]
    fn parse_colon_e_with_path() {
        match parse_colon_command("e /tmp/foo.log").unwrap() {
            ColonCommand::Edit(p) => assert_eq!(p, std::path::PathBuf::from("/tmp/foo.log")),
            other => panic!("expected Edit, got {other:?}"),
        }
    }

    #[test]
    fn parse_colon_e_with_tilde() {
        std::env::set_var("HOME", "/home/user");
        match parse_colon_command("e ~/foo.log").unwrap() {
            ColonCommand::Edit(p) => assert_eq!(p, std::path::PathBuf::from("/home/user/foo.log")),
            other => panic!("expected Edit, got {other:?}"),
        }
    }

    #[test]
    fn parse_colon_e_missing_path_errors() {
        assert_eq!(parse_colon_command("e").unwrap_err(), ColonParseError::MissingPath);
        assert_eq!(parse_colon_command("e ").unwrap_err(), ColonParseError::MissingPath);
    }

    #[test]
    fn parse_colon_f_q_d_x_t() {
        assert_eq!(parse_colon_command("f").unwrap(), ColonCommand::ShowFile);
        assert_eq!(parse_colon_command("q").unwrap(), ColonCommand::Quit);
        assert_eq!(parse_colon_command("d").unwrap(), ColonCommand::Delete);
        assert_eq!(parse_colon_command("x").unwrap(), ColonCommand::First);
        assert_eq!(parse_colon_command("t").unwrap(), ColonCommand::Last);
    }

    #[test]
    fn parse_unknown_command_errors() {
        let err = parse_colon_command("bogus").unwrap_err();
        match err {
            ColonParseError::UnknownCommand(name) => assert_eq!(name, "bogus"),
            other => panic!("expected UnknownCommand, got {other:?}"),
        }
    }

    #[test]
    fn parse_handles_whitespace() {
        // Trailing whitespace OK.
        assert_eq!(parse_colon_command("n  ").unwrap(), ColonCommand::Next);
        assert_eq!(parse_colon_command("  n").unwrap(), ColonCommand::Next);
    }

    #[test]
    fn parse_colon_tag_with_name() {
        assert_eq!(
            parse_colon_command("tag foo").unwrap(),
            ColonCommand::Tag("foo".into())
        );
    }

    #[test]
    fn parse_colon_tag_strips_trailing_whitespace() {
        assert_eq!(
            parse_colon_command("tag foo  ").unwrap(),
            ColonCommand::Tag("foo".into())
        );
    }

    #[test]
    fn parse_colon_tag_without_name_errors() {
        assert_eq!(
            parse_colon_command("tag").unwrap_err(),
            ColonParseError::TagRequiresName
        );
        assert_eq!(
            parse_colon_command("tag  ").unwrap_err(),
            ColonParseError::TagRequiresName
        );
    }

    #[test]
    fn parse_colon_tnext_and_tprev() {
        assert_eq!(parse_colon_command("tnext").unwrap(), ColonCommand::TagNext);
        assert_eq!(parse_colon_command("tprev").unwrap(), ColonCommand::TagPrev);
    }

    #[test]
    fn parse_colon_tselect_without_arg_uses_active() {
        assert_eq!(parse_colon_command("tselect").unwrap(), ColonCommand::TagSelect(None));
    }

    #[test]
    fn parse_colon_tselect_with_name() {
        assert_eq!(
            parse_colon_command("tselect foo").unwrap(),
            ColonCommand::TagSelect(Some("foo".into())),
        );
    }

    #[test]
    fn parse_colon_b_opens_picker() {
        assert_eq!(parse_colon_command("b").unwrap(), ColonCommand::OpenPicker);
        assert_eq!(parse_colon_command("buffers").unwrap(), ColonCommand::OpenPicker);
    }

    #[test]
    fn parse_colon_help_opens_help() {
        assert_eq!(parse_colon_command("h").unwrap(), ColonCommand::OpenHelp);
        assert_eq!(parse_colon_command("help").unwrap(), ColonCommand::OpenHelp);
    }

    #[test]
    fn parse_colon_hex_with_valid_widths() {
        for n in [2usize, 4, 8, 16, 32] {
            assert_eq!(
                parse_colon_command(&format!("hex {n}")).unwrap(),
                ColonCommand::HexGroup(n),
            );
        }
    }

    #[test]
    fn parse_colon_hex_without_value_errors() {
        assert_eq!(
            parse_colon_command("hex").unwrap_err(),
            ColonParseError::HexGroupRequiresValue,
        );
    }

    #[test]
    fn parse_colon_hex_with_invalid_value_errors() {
        match parse_colon_command("hex 3").unwrap_err() {
            ColonParseError::HexGroupInvalid(v) => assert_eq!(v, "3"),
            other => panic!("expected HexGroupInvalid, got {other:?}"),
        }
        match parse_colon_command("hex banana").unwrap_err() {
            ColonParseError::HexGroupInvalid(v) => assert_eq!(v, "banana"),
            other => panic!("expected HexGroupInvalid, got {other:?}"),
        }
    }

    #[test]
    fn parse_colon_color_without_arg_cycles() {
        assert_eq!(parse_colon_command("color").unwrap(), ColonCommand::Color(None));
    }

    #[test]
    fn parse_colon_color_with_named_mode() {
        use crate::render::AnsiMode;
        assert_eq!(
            parse_colon_command("color strict").unwrap(),
            ColonCommand::Color(Some(AnsiMode::Strict)),
        );
        assert_eq!(
            parse_colon_command("color interpret").unwrap(),
            ColonCommand::Color(Some(AnsiMode::Interpret)),
        );
        assert_eq!(
            parse_colon_command("color raw").unwrap(),
            ColonCommand::Color(Some(AnsiMode::Raw)),
        );
    }

    #[test]
    fn parse_colon_color_with_unknown_mode_errors() {
        match parse_colon_command("color rainbow").unwrap_err() {
            ColonParseError::ColorInvalid(v) => assert_eq!(v, "rainbow"),
            other => panic!("expected ColorInvalid, got {other:?}"),
        }
    }

    #[test]
    fn parse_colon_case_without_arg_cycles() {
        assert_eq!(parse_colon_command("case").unwrap(), ColonCommand::Case(None));
    }

    #[test]
    fn parse_colon_case_with_named_mode() {
        use crate::viewport::CaseMode;
        assert_eq!(parse_colon_command("case smart").unwrap(),
                   ColonCommand::Case(Some(CaseMode::Smart)));
        assert_eq!(parse_colon_command("case sensitive").unwrap(),
                   ColonCommand::Case(Some(CaseMode::Sensitive)));
        assert_eq!(parse_colon_command("case insensitive").unwrap(),
                   ColonCommand::Case(Some(CaseMode::Insensitive)));
    }

    #[test]
    fn parse_colon_case_unknown_errors() {
        match parse_colon_command("case rainbow").unwrap_err() {
            ColonParseError::CaseInvalid(v) => assert_eq!(v, "rainbow"),
            other => panic!("expected CaseInvalid, got {other:?}"),
        }
    }

    #[test]
    fn parse_colon_hlsearch_on_off() {
        assert_eq!(parse_colon_command("hlsearch").unwrap(), ColonCommand::HlSearch(true));
        assert_eq!(parse_colon_command("nohlsearch").unwrap(), ColonCommand::HlSearch(false));
    }

    #[test]
    fn parse_colon_incsearch_toggle() {
        assert_eq!(parse_colon_command("incsearch").unwrap(), ColonCommand::IncSearch);
    }

    #[test]
    fn lcp_empty_slice() {
        assert_eq!(longest_common_prefix(&[]), "");
    }

    #[test]
    fn lcp_single_item_returns_self() {
        assert_eq!(longest_common_prefix(&["foo".into()]), "foo");
    }

    #[test]
    fn lcp_finds_shared_prefix() {
        let v: Vec<String> = vec!["foobar".into(), "foobaz".into(), "fooqux".into()];
        assert_eq!(longest_common_prefix(&v), "foo");
    }

    #[test]
    fn lcp_no_shared_prefix_returns_empty() {
        let v: Vec<String> = vec!["abc".into(), "xyz".into()];
        assert_eq!(longest_common_prefix(&v), "");
    }

    #[test]
    fn lcp_one_item_is_prefix_of_others() {
        let v: Vec<String> = vec!["foo".into(), "foobar".into(), "foobaz".into()];
        assert_eq!(longest_common_prefix(&v), "foo");
    }

    #[test]
    fn tag_stack_push_pop_lifo() {
        let mut s = TagStack::default();
        s.push(0, 10);
        s.push(1, 20);
        assert_eq!(s.pop(), Some((1, 20)));
        assert_eq!(s.pop(), Some((0, 10)));
        assert_eq!(s.pop(), None);
    }

    #[test]
    fn tag_stack_pop_clears_active() {
        let mut s = TagStack::default();
        s.push(0, 10);
        s.set_active(
            "foo".into(),
            vec![crate::tags::TagEntry {
                file: std::path::PathBuf::from("/a"),
                address: crate::tags::TagAddress::Line(1),
            }],
        );
        assert!(s.active.is_some());
        let _ = s.pop();
        assert!(s.active.is_none());
    }

    #[test]
    fn tag_stack_next_advances_then_clamps() {
        let mut s = TagStack::default();
        s.set_active(
            "foo".into(),
            vec![
                crate::tags::TagEntry {
                    file: std::path::PathBuf::from("/a"),
                    address: crate::tags::TagAddress::Line(1),
                },
                crate::tags::TagEntry {
                    file: std::path::PathBuf::from("/b"),
                    address: crate::tags::TagAddress::Line(2),
                },
            ],
        );
        assert_eq!(s.next(), TagStepResult::Moved(1));
        assert_eq!(s.next(), TagStepResult::AtBoundary);
    }

    #[test]
    fn tag_stack_prev_clamps_at_zero() {
        let mut s = TagStack::default();
        s.set_active(
            "foo".into(),
            vec![crate::tags::TagEntry {
                file: std::path::PathBuf::from("/a"),
                address: crate::tags::TagAddress::Line(1),
            }],
        );
        assert_eq!(s.prev(), TagStepResult::AtBoundary);
    }

    #[test]
    fn tag_stack_next_with_no_active_returns_no_active() {
        let mut s = TagStack::default();
        assert_eq!(s.next(), TagStepResult::NoActive);
        assert_eq!(s.prev(), TagStepResult::NoActive);
    }

    #[test]
    fn tag_stack_set_active_replaces_previous_list() {
        let mut s = TagStack::default();
        s.set_active(
            "foo".into(),
            vec![crate::tags::TagEntry {
                file: std::path::PathBuf::from("/a"),
                address: crate::tags::TagAddress::Line(1),
            }],
        );
        s.set_active(
            "bar".into(),
            vec![
                crate::tags::TagEntry {
                    file: std::path::PathBuf::from("/x"),
                    address: crate::tags::TagAddress::Line(5),
                },
                crate::tags::TagEntry {
                    file: std::path::PathBuf::from("/y"),
                    address: crate::tags::TagAddress::Line(6),
                },
            ],
        );
        let active = s.active.as_ref().unwrap();
        assert_eq!(active.name, "bar");
        assert_eq!(active.matches.len(), 2);
        assert_eq!(active.cursor, 0);
    }

    #[test]
    fn writer_emits_color_for_red_cell() {
        let cells = vec![Cell::Char {
            ch: 'h',
            width: 1,
            style: crate::ansi::Style {
                fg: Some(crate::ansi::Color::Ansi(1)),
                ..Default::default()
            },
            hyperlink: None,
        }];
        let mut buf: Vec<u8> = Vec::new();
        write_row_with_highlights(&mut buf, &cells, 80, &[], crate::ansi::Style::default(), true).unwrap();
        let s = String::from_utf8_lossy(&buf);
        assert!(s.contains("\x1b["), "expected ANSI escape in output: {s:?}");
        assert!(s.contains('h'));
    }

    #[test]
    fn writer_emits_osc8_for_hyperlink_cell() {
        let link: std::sync::Arc<str> = std::sync::Arc::from("https://example.com");
        let cells = vec![Cell::Char {
            ch: 'c',
            width: 1,
            style: crate::ansi::Style::default(),
            hyperlink: Some(link),
        }];
        let mut buf: Vec<u8> = Vec::new();
        write_row_with_highlights(&mut buf, &cells, 80, &[], crate::ansi::Style::default(), true).unwrap();
        let s = String::from_utf8_lossy(&buf);
        assert!(s.contains("\x1b]8;;https://example.com\x1b\\"), "got: {s:?}");
    }
}