yosh 0.1.1

use std::io;
use crossterm::event::{Event, KeyEvent};
use unicode_width::UnicodeWidthChar;

use super::completion::{self, CompletionContext, CompletionUI, is_command_position, extract_completion_word};
use super::command_completion::CommandCompletionContext;
use super::display_width::display_width;
use super::edit_action::EditAction;
use super::fuzzy_search::FuzzySearchUI;
use super::highlight::{HighlightScanner, HighlightStyle, ColorSpan, CheckerEnv, apply_style};
use super::history::History;
use super::keymap::{BufferState, Keymap};
use super::kill_ring::KillRing;
use super::terminal::Terminal;
use super::undo::UndoManager;

/// A minimal line-editing buffer used by the interactive REPL.
///
/// The buffer stores characters as a `Vec<char>` so that cursor
/// movement and insertion work correctly with multi-byte UTF-8
/// characters.
pub struct LineEditor {
    buf: Vec<char>,
    pos: usize,
    suggestion: Option<String>,
    tab_count: u8,
    keymap: Keymap,
    kill_ring: KillRing,
    undo: UndoManager,
    yank_state: Option<YankState>,
    last_action: EditAction,
    last_was_insert: bool,
    prev_total_rows: usize,
}

#[derive(Debug, Clone)]
struct YankState {
    start: usize,
    len: usize,
}

impl LineEditor {
    /// Create an empty line editor.
    pub fn new() -> Self {
        Self {
            buf: Vec::new(),
            pos: 0,
            suggestion: None,
            tab_count: 0,
            keymap: Keymap::new(),
            kill_ring: KillRing::new(60),
            undo: UndoManager::new(256),
            yank_state: None,
            last_action: EditAction::Noop,
            last_was_insert: false,
            prev_total_rows: 0,
        }
    }

    /// Return the current buffer contents as a `String`.
    pub fn buffer(&self) -> String {
        self.buf.iter().collect()
    }

    /// Return the current cursor position (0-based character index).
    #[allow(dead_code)] // public API for interactive mode enhancements
    pub fn cursor(&self) -> usize {
        self.pos
    }

    /// Return `true` if the buffer is empty.
    pub fn is_empty(&self) -> bool {
        self.buf.is_empty()
    }

    /// Clear the buffer and reset the cursor to 0.
    pub fn clear(&mut self) {
        self.buf.clear();
        self.pos = 0;
        self.suggestion = None;
        self.tab_count = 0;
        self.yank_state = None;
        self.last_action = EditAction::Noop;
        self.last_was_insert = false;
        self.undo.clear();
        self.prev_total_rows = 0;
    }

    /// Insert a character at the current cursor position and advance
    /// the cursor by one.
    pub fn insert_char(&mut self, ch: char) {
        self.buf.insert(self.pos, ch);
        self.pos += 1;
    }

    /// Delete the character immediately before the cursor (like the
    /// Backspace key).  Does nothing when the cursor is at position 0.
    pub fn backspace(&mut self) {
        if self.pos > 0 {
            self.pos -= 1;
            self.buf.remove(self.pos);
        }
    }

    /// Delete the character at the current cursor position (like the
    /// Delete key).  Does nothing when the cursor is at the end of
    /// the buffer.
    pub fn delete(&mut self) {
        if self.pos < self.buf.len() {
            self.buf.remove(self.pos);
        }
    }

    /// Move the cursor one position to the left.  Does nothing when
    /// the cursor is already at position 0.
    pub fn move_cursor_left(&mut self) {
        if self.pos > 0 {
            self.pos -= 1;
        }
    }

    /// Move the cursor one position to the right.  Does nothing when
    /// the cursor is already at the end of the buffer.
    pub fn move_cursor_right(&mut self) {
        if self.pos < self.buf.len() {
            self.pos += 1;
        }
    }

    /// Move the cursor to the beginning of the buffer (position 0).
    pub fn move_to_start(&mut self) {
        self.pos = 0;
    }

    /// Move the cursor to the end of the buffer.
    pub fn move_to_end(&mut self) {
        self.pos = self.buf.len();
    }

    /// Returns true if `ch` is a word character (alphanumeric or underscore).
    fn is_word_char(ch: char) -> bool {
        ch.is_alphanumeric() || ch == '_'
    }

    /// Move cursor backward to the start of the previous word.
    pub fn move_backward_word(&mut self) {
        while self.pos > 0 && !Self::is_word_char(self.buf[self.pos - 1]) {
            self.pos -= 1;
        }
        while self.pos > 0 && Self::is_word_char(self.buf[self.pos - 1]) {
            self.pos -= 1;
        }
    }

    /// Move cursor forward to the end of the next word.
    pub fn move_forward_word(&mut self) {
        let len = self.buf.len();
        while self.pos < len && !Self::is_word_char(self.buf[self.pos]) {
            self.pos += 1;
        }
        while self.pos < len && Self::is_word_char(self.buf[self.pos]) {
            self.pos += 1;
        }
    }

    /// Kill from cursor to end of line. Returns the killed text.
    pub fn kill_to_end(&mut self) -> String {
        let killed: String = self.buf[self.pos..].iter().collect();
        self.buf.truncate(self.pos);
        killed
    }

    /// Kill from start of line to cursor. Returns the killed text.
    pub fn kill_to_start(&mut self) -> String {
        let killed: String = self.buf[..self.pos].iter().collect();
        self.buf.drain(..self.pos);
        self.pos = 0;
        killed
    }

    /// Kill the word behind the cursor. Returns the killed text.
    pub fn kill_backward_word(&mut self) -> String {
        let old_pos = self.pos;
        self.move_backward_word();
        let killed: String = self.buf[self.pos..old_pos].iter().collect();
        self.buf.drain(self.pos..old_pos);
        killed
    }

    /// Kill from cursor to end of the next word. Returns the killed text.
    pub fn kill_forward_word(&mut self) -> String {
        let old_pos = self.pos;
        let len = self.buf.len();
        let mut end = self.pos;
        while end < len && !Self::is_word_char(self.buf[end]) {
            end += 1;
        }
        while end < len && Self::is_word_char(self.buf[end]) {
            end += 1;
        }
        let killed: String = self.buf[old_pos..end].iter().collect();
        self.buf.drain(old_pos..end);
        killed
    }

    /// Transpose the two characters around the cursor (Ctrl+T).
    pub fn transpose_chars(&mut self) {
        if self.buf.len() < 2 {
            return;
        }
        if self.pos == 0 {
            return;
        }
        if self.pos == self.buf.len() {
            self.buf.swap(self.pos - 2, self.pos - 1);
        } else {
            self.buf.swap(self.pos - 1, self.pos);
            self.pos += 1;
        }
    }

    /// Transpose the two words around the cursor (Alt+T).
    pub fn transpose_words(&mut self) {
        let len = self.buf.len();
        if len == 0 { return; }

        let mut p = self.pos;
        if p == len || !Self::is_word_char(self.buf[p]) {
            while p > 0 && !Self::is_word_char(self.buf[p - 1]) {
                p -= 1;
            }
        }
        if p == 0 { return; }

        // Find end of word2
        let w2e = if self.pos < len && Self::is_word_char(self.buf[self.pos]) {
            let mut e = self.pos;
            while e < len && Self::is_word_char(self.buf[e]) { e += 1; }
            e
        } else {
            p
        };

        // Find start of word2
        let mut w2s = w2e;
        while w2s > 0 && Self::is_word_char(self.buf[w2s - 1]) {
            w2s -= 1;
        }
        if w2s == 0 { return; }

        // Find end of word1
        let mut w1e = w2s;
        while w1e > 0 && !Self::is_word_char(self.buf[w1e - 1]) {
            w1e -= 1;
        }
        if w1e == 0 { return; }

        // Find start of word1
        let mut w1s = w1e;
        while w1s > 0 && Self::is_word_char(self.buf[w1s - 1]) {
            w1s -= 1;
        }

        let word1: Vec<char> = self.buf[w1s..w1e].to_vec();
        let sep: Vec<char> = self.buf[w1e..w2s].to_vec();
        let word2: Vec<char> = self.buf[w2s..w2e].to_vec();

        let mut replacement = Vec::new();
        replacement.extend_from_slice(&word2);
        replacement.extend_from_slice(&sep);
        replacement.extend_from_slice(&word1);

        self.buf.splice(w1s..w2e, replacement);
        self.pos = w1s + word2.len() + sep.len() + word1.len();
    }

    /// Convert the next word to uppercase (Alt+U).
    pub fn upcase_word(&mut self) {
        let len = self.buf.len();
        while self.pos < len && !Self::is_word_char(self.buf[self.pos]) {
            self.pos += 1;
        }
        while self.pos < len && Self::is_word_char(self.buf[self.pos]) {
            self.buf[self.pos] = self.buf[self.pos].to_uppercase().next().unwrap_or(self.buf[self.pos]);
            self.pos += 1;
        }
    }

    /// Convert the next word to lowercase (Alt+L).
    pub fn downcase_word(&mut self) {
        let len = self.buf.len();
        while self.pos < len && !Self::is_word_char(self.buf[self.pos]) {
            self.pos += 1;
        }
        while self.pos < len && Self::is_word_char(self.buf[self.pos]) {
            self.buf[self.pos] = self.buf[self.pos].to_lowercase().next().unwrap_or(self.buf[self.pos]);
            self.pos += 1;
        }
    }

    /// Capitalize the next word: first char uppercase, rest lowercase (Alt+C).
    pub fn capitalize_word(&mut self) {
        let len = self.buf.len();
        while self.pos < len && !Self::is_word_char(self.buf[self.pos]) {
            self.pos += 1;
        }
        let mut first = true;
        while self.pos < len && Self::is_word_char(self.buf[self.pos]) {
            if first {
                self.buf[self.pos] = self.buf[self.pos].to_uppercase().next().unwrap_or(self.buf[self.pos]);
                first = false;
            } else {
                self.buf[self.pos] = self.buf[self.pos].to_lowercase().next().unwrap_or(self.buf[self.pos]);
            }
            self.pos += 1;
        }
    }

    /// Insert text at the current cursor position. Returns (start, len) for yank tracking.
    pub fn insert_str(&mut self, text: &str) -> (usize, usize) {
        let start = self.pos;
        let chars: Vec<char> = text.chars().collect();
        let len = chars.len();
        for (i, ch) in chars.into_iter().enumerate() {
            self.buf.insert(self.pos + i, ch);
        }
        self.pos += len;
        (start, len)
    }

    /// Remove `len` characters starting at `start`. Used by yank_pop to replace yanked text.
    pub fn remove_range(&mut self, start: usize, len: usize) {
        let end = (start + len).min(self.buf.len());
        self.buf.drain(start..end);
        if self.pos > start {
            self.pos = start;
        }
    }

    /// Return the current suggestion text, if any.
    #[allow(dead_code)]
    pub fn suggestion(&self) -> Option<&str> {
        self.suggestion.as_deref()
    }

    /// Accept the full autosuggestion, appending it to the buffer.
    fn accept_full_suggestion(&mut self) {
        if let Some(suggestion) = self.suggestion.take() {
            self.buf.extend(suggestion.chars());
            self.pos = self.buf.len();
        }
    }

    /// Accept the next word from the autosuggestion.
    /// A "word" is defined as: any leading spaces + non-space characters up to the next space.
    fn accept_word_suggestion(&mut self) {
        if let Some(suggestion) = self.suggestion.take() {
            let chars: Vec<char> = suggestion.chars().collect();
            let mut i = 0;
            // Skip leading spaces
            while i < chars.len() && chars[i] == ' ' {
                i += 1;
            }
            // Take non-space characters
            while i < chars.len() && chars[i] != ' ' {
                i += 1;
            }
            // Append the accepted portion to the buffer
            self.buf.extend(&chars[..i]);
            self.pos = self.buf.len();
            // Keep remaining suggestion, if any
            if i < chars.len() {
                self.suggestion = Some(chars[i..].iter().collect());
            }
        }
    }

    /// Update the autosuggestion based on the current buffer state.
    /// Only suggests when the cursor is at the end of a non-empty buffer.
    fn update_suggestion(&mut self, history: &History) {
        if self.pos == self.buf.len() && !self.buf.is_empty() {
            self.suggestion = history.suggest(&self.buffer());
        } else {
            self.suggestion = None;
        }
    }
}

impl std::fmt::Display for LineEditor {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.buffer())
    }
}

// ---------------------------------------------------------------------------
// Terminal I/O support (crossterm)
// ---------------------------------------------------------------------------

/// Result of processing a single key event.
enum KeyAction {
    Continue,
    Submit,
    Eof,
    Interrupt,
    FuzzySearch,
    TabComplete,
    ClearScreen,
}

impl LineEditor {
    /// Read a line of input from the terminal, handling cursor movement and
    /// editing keys.  Returns `Ok(Some(line))` on Enter, `Ok(None)` on
    /// Ctrl-D with an empty buffer (EOF), or `Ok(Some(""))` on Ctrl-C.
    #[allow(dead_code)] // Used by tests; production code uses read_line_with_completion
    pub fn read_line<T: Terminal>(&mut self, prompt: &str, upper_lines: &[String], history: &mut History, term: &mut T) -> io::Result<Option<String>> {
        self.clear();
        term.enable_raw_mode()?;
        let result = self.read_line_loop(prompt, upper_lines, history, term);
        let _ = term.disable_raw_mode();
        result
    }

    fn read_line_loop<T: Terminal>(&mut self, prompt: &str, upper_lines: &[String], history: &mut History, term: &mut T) -> io::Result<Option<String>> {
        let prompt_width = display_width(prompt);
        loop {
            term.flush()?;
            match term.read_event()? {
                Event::Key(key_event) => {
                    match self.handle_key(key_event, history) {
                        KeyAction::Submit => {
                            history.reset_cursor();
                            if self.prev_total_rows > 0 {
                                let buf_pos_width: usize = self.buf[..self.pos].iter()
                                    .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
                                    .sum();
                                let (tw, _) = term.size().unwrap_or((80, 24));
                                let tw = tw as usize;
                                let cursor_row = if tw > 0 { (prompt_width + buf_pos_width) / tw } else { 0 };
                                if self.prev_total_rows > cursor_row {
                                    term.move_down((self.prev_total_rows - cursor_row) as u16)?;
                                }
                            }
                            term.move_to_column(0)?;
                            term.write_str("\r\n")?;
                            term.flush()?;
                            return Ok(Some(self.buffer()));
                        }
                        KeyAction::Eof => {
                            return Ok(None);
                        }
                        KeyAction::Interrupt => {
                            history.reset_cursor();
                            if self.prev_total_rows > 0 {
                                let buf_pos_width: usize = self.buf[..self.pos].iter()
                                    .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
                                    .sum();
                                let (tw, _) = term.size().unwrap_or((80, 24));
                                let tw = tw as usize;
                                let cursor_row = if tw > 0 { (prompt_width + buf_pos_width) / tw } else { 0 };
                                if self.prev_total_rows > cursor_row {
                                    term.move_down((self.prev_total_rows - cursor_row) as u16)?;
                                }
                            }
                            term.move_to_column(0)?;
                            term.write_str("\r\n")?;
                            term.flush()?;
                            self.clear();
                            return Ok(Some(String::new()));
                        }
                        KeyAction::FuzzySearch => {
                            self.suggestion = None;
                            term.disable_raw_mode()?;
                            if let Ok(Some(line)) = FuzzySearchUI::run(history, term) {
                                self.buf = line.chars().collect();
                                self.pos = self.buf.len();
                            }
                            term.enable_raw_mode()?;
                            term.move_to_column(0)?;
                            term.clear_current_line()?;
                            for line in upper_lines {
                                term.write_str(line)?;
                                term.write_str("\r\n")?;
                            }
                            term.write_str(prompt)?;
                        }
                        KeyAction::ClearScreen => {
                            term.clear_all()?;
                            for line in upper_lines {
                                term.write_str(line)?;
                                term.write_str("\r\n")?;
                            }
                            term.write_str(prompt)?;
                        }
                        KeyAction::TabComplete | KeyAction::Continue => {}
                    }
                    self.update_suggestion(history);
                    let (tw, _) = term.size().unwrap_or((80, 24));
                    self.redraw(term, prompt, prompt_width, &[], tw)?;
                }
                Event::Resize(_cols, _rows) => {
                    let (tw, _) = term.size().unwrap_or((80, 24));
                    self.update_suggestion(history);
                    self.redraw(term, prompt, prompt_width, &[], tw)?;
                }
                _ => {}
            }
        }
    }

    /// Redraw the current buffer on screen, positioning the cursor correctly.
    /// Handles input that wraps past the terminal width.
    fn redraw<T: Terminal>(&mut self, term: &mut T, prompt: &str, prompt_width: usize, spans: &[ColorSpan], term_width: u16) -> io::Result<()> {
        let tw = term_width as usize;
        let col = |n: usize| -> u16 { n.min(u16::MAX as usize) as u16 };

        // Move cursor up to the prompt's last_line row (start of content)
        if self.prev_total_rows > 0 {
            term.move_up(self.prev_total_rows as u16)?;
        }
        term.move_to_column(0)?;

        // Clear all rows from previous render
        for i in 0..=self.prev_total_rows {
            if i > 0 {
                term.move_down(1)?;
            }
            term.clear_current_line()?;
        }
        // Move back up to start
        if self.prev_total_rows > 0 {
            term.move_up(self.prev_total_rows as u16)?;
        }

        // Repaint the prompt
        term.move_to_column(0)?;
        term.write_str(prompt)?;

        // Write the buffer with or without highlighting
        if spans.is_empty() {
            term.write_str(&self.buffer())?;
        } else {
            let mut current_style = HighlightStyle::Default;
            for (i, ch) in self.buf.iter().enumerate() {
                let new_style = spans.iter()
                    .find(|sp| sp.start <= i && i < sp.end)
                    .map(|sp| sp.style)
                    .unwrap_or(HighlightStyle::Default);
                if new_style != current_style {
                    if current_style != HighlightStyle::Default {
                        term.reset_style()?;
                    }
                    apply_style(term, new_style)?;
                    current_style = new_style;
                }
                term.write_char(*ch)?;
            }
            if current_style != HighlightStyle::Default {
                term.reset_style()?;
            }
        }

        // Draw suggestion
        let suggestion_width: usize;
        if let Some(ref suggestion) = self.suggestion
            && self.pos == self.buf.len()
        {
            term.set_dim(true)?;
            term.write_str(suggestion)?;
            term.set_dim(false)?;
            suggestion_width = suggestion.chars()
                .map(|c| UnicodeWidthChar::width(c).unwrap_or(0))
                .sum();
        } else {
            suggestion_width = 0;
        }

        // Calculate total display width and rows
        let buf_total_width: usize = self.buf.iter()
            .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
            .sum();
        let content_width = prompt_width + buf_total_width + suggestion_width;
        let total_rows = if tw > 0 && content_width > 0 {
            (content_width.saturating_sub(1)) / tw
        } else {
            0
        };
        self.prev_total_rows = total_rows;

        // Position cursor at self.pos
        let buf_pos_width: usize = self.buf[..self.pos].iter()
            .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
            .sum();
        let cursor_total = prompt_width + buf_pos_width;
        let cursor_row = if tw > 0 { cursor_total / tw } else { 0 };
        let cursor_col = if tw > 0 { cursor_total % tw } else { cursor_total };

        // Move from end-of-content row to cursor row
        let end_row = total_rows;
        if end_row > cursor_row {
            term.move_up((end_row - cursor_row) as u16)?;
        }
        term.move_to_column(col(cursor_col))?;
        term.flush()?;
        Ok(())
    }

    /// Map a single key event to a [`KeyAction`], mutating the buffer as needed.
    fn handle_key(&mut self, key: KeyEvent, history: &mut History) -> KeyAction {
        let state = BufferState {
            is_empty: self.is_empty(),
            at_end: self.pos == self.buf.len(),
            has_suggestion: self.suggestion.is_some(),
            last_action: self.last_action,
        };

        let (action, count) = self.keymap.resolve(key, &state);

        if !matches!(action, EditAction::TabComplete) {
            self.tab_count = 0;
        }

        // Undo snapshot management
        // - Insert group boundary: when transitioning from insert to non-insert, save once
        // - Destructive ops: always save pre-op state (once)
        // - Insert start: save when first insert after non-insert
        if self.last_was_insert && !matches!(action, EditAction::InsertChar(_)) {
            // Finalize the insert group — save current state as group boundary
            self.undo.save(&self.buf, self.pos);
        }
        match action {
            EditAction::InsertChar(_) => {
                if !self.last_was_insert {
                    self.undo.save(&self.buf, self.pos);
                }
            }
            EditAction::KillToEnd | EditAction::KillToStart
            | EditAction::KillBackwardWord | EditAction::KillForwardWord
            | EditAction::DeleteBackward | EditAction::DeleteForward
            | EditAction::Yank | EditAction::YankPop
            | EditAction::TransposeChars | EditAction::TransposeWords
            | EditAction::UpcaseWord | EditAction::DowncaseWord | EditAction::CapitalizeWord => {
                if !self.last_was_insert {
                    // Not transitioning from insert — save pre-op state directly
                    self.undo.save(&self.buf, self.pos);
                }
                // If last_was_insert, boundary save above already captured the state
            }
            _ => {}
        }

        // Determine if consecutive kill for append
        let is_consecutive_kill = action.is_kill() && self.last_action.is_kill();

        // Execute action
        let key_action = self.execute_action(action, count, history, is_consecutive_kill);

        // Update tracking state
        self.last_was_insert = matches!(action, EditAction::InsertChar(ch) if ch != ' ');
        if !matches!(action, EditAction::Yank | EditAction::YankPop) {
            self.yank_state = None;
        }
        self.last_action = action;

        key_action
    }

    fn execute_action(
        &mut self,
        action: EditAction,
        count: u32,
        history: &mut History,
        consecutive_kill: bool,
    ) -> KeyAction {
        match action {
            EditAction::InsertChar(ch) => {
                for _ in 0..count {
                    self.insert_char(ch);
                }
                KeyAction::Continue
            }
            EditAction::MoveBackward => {
                for _ in 0..count { self.move_cursor_left(); }
                KeyAction::Continue
            }
            EditAction::MoveForward => {
                for _ in 0..count { self.move_cursor_right(); }
                KeyAction::Continue
            }
            EditAction::MoveToStart => {
                self.move_to_start();
                KeyAction::Continue
            }
            EditAction::MoveToEnd => {
                self.move_to_end();
                KeyAction::Continue
            }
            EditAction::MoveBackwardWord => {
                for _ in 0..count { self.move_backward_word(); }
                KeyAction::Continue
            }
            EditAction::MoveForwardWord => {
                for _ in 0..count { self.move_forward_word(); }
                KeyAction::Continue
            }
            EditAction::DeleteBackward => {
                for _ in 0..count { self.backspace(); }
                KeyAction::Continue
            }
            EditAction::DeleteForward => {
                for _ in 0..count { self.delete(); }
                KeyAction::Continue
            }
            EditAction::KillToEnd => {
                let killed = self.kill_to_end();
                self.kill_ring.kill(&killed, consecutive_kill);
                KeyAction::Continue
            }
            EditAction::KillToStart => {
                let killed = self.kill_to_start();
                self.kill_ring.prepend(&killed, consecutive_kill);
                KeyAction::Continue
            }
            EditAction::KillBackwardWord => {
                for _ in 0..count {
                    let killed = self.kill_backward_word();
                    self.kill_ring.prepend(&killed, consecutive_kill);
                }
                KeyAction::Continue
            }
            EditAction::KillForwardWord => {
                for _ in 0..count {
                    let killed = self.kill_forward_word();
                    self.kill_ring.kill(&killed, consecutive_kill);
                }
                KeyAction::Continue
            }
            EditAction::Yank => {
                if let Some(text) = self.kill_ring.yank().map(|s| s.to_string()) {
                    let (start, len) = self.insert_str(&text);
                    self.yank_state = Some(YankState { start, len });
                }
                KeyAction::Continue
            }
            EditAction::YankPop => {
                if let Some(ys) = self.yank_state.clone() {
                    self.remove_range(ys.start, ys.len);
                    if let Some(text) = self.kill_ring.yank_pop().map(|s| s.to_string()) {
                        let (start, len) = self.insert_str(&text);
                        self.yank_state = Some(YankState { start, len });
                    }
                }
                KeyAction::Continue
            }
            EditAction::TransposeChars => {
                for _ in 0..count { self.transpose_chars(); }
                KeyAction::Continue
            }
            EditAction::TransposeWords => {
                for _ in 0..count { self.transpose_words(); }
                KeyAction::Continue
            }
            EditAction::UpcaseWord => {
                for _ in 0..count { self.upcase_word(); }
                KeyAction::Continue
            }
            EditAction::DowncaseWord => {
                for _ in 0..count { self.downcase_word(); }
                KeyAction::Continue
            }
            EditAction::CapitalizeWord => {
                for _ in 0..count { self.capitalize_word(); }
                KeyAction::Continue
            }
            EditAction::Undo => {
                for _ in 0..count {
                    if let Some((buf, pos)) = self.undo.undo() {
                        self.buf = buf;
                        self.pos = pos;
                    }
                }
                KeyAction::Continue
            }
            EditAction::ClearScreen => {
                KeyAction::ClearScreen
            }
            EditAction::Cancel => {
                KeyAction::Continue
            }
            EditAction::AcceptSuggestion => {
                self.accept_full_suggestion();
                KeyAction::Continue
            }
            EditAction::AcceptWordSuggestion => {
                self.accept_word_suggestion();
                KeyAction::Continue
            }
            EditAction::SetNumericArg(_) => {
                KeyAction::Continue
            }
            EditAction::Submit => KeyAction::Submit,
            EditAction::Eof => KeyAction::Eof,
            EditAction::Interrupt => KeyAction::Interrupt,
            EditAction::FuzzySearch => KeyAction::FuzzySearch,
            EditAction::TabComplete => {
                self.tab_count += 1;
                KeyAction::TabComplete
            }
            EditAction::HistoryPrev => {
                for _ in 0..count {
                    if let Some(line) = history.navigate_up(&self.buffer()) {
                        self.buf = line.chars().collect();
                        self.pos = self.buf.len();
                    }
                }
                self.suggestion = None;
                KeyAction::Continue
            }
            EditAction::HistoryNext => {
                for _ in 0..count {
                    if let Some(line) = history.navigate_down() {
                        self.buf = line.chars().collect();
                        self.pos = self.buf.len();
                    }
                }
                self.suggestion = None;
                KeyAction::Continue
            }
            EditAction::Noop => KeyAction::Continue,
        }
    }

    // ── Tab completion support ─────────────────────────────────────────

    /// Read a line of input with Tab completion support.
    ///
    /// Behaves identically to [`read_line`] but also handles Tab key events
    /// by invoking the completion engine.
    #[allow(clippy::too_many_arguments)]
    pub fn read_line_with_completion<T: Terminal>(
        &mut self,
        prompt: &str,
        upper_lines: &[String],
        history: &mut History,
        term: &mut T,
        ctx: &CompletionContext,
        cmd_ctx: &mut CommandCompletionContext<'_>,
        scanner: &mut HighlightScanner,
        checker_env: &CheckerEnv<'_>,
        accumulated: &str,
    ) -> io::Result<Option<String>> {
        self.clear();
        term.enable_raw_mode()?;
        let result = self.read_line_loop_with_completion(prompt, upper_lines, history, term, ctx, cmd_ctx, scanner, checker_env, accumulated);
        let _ = term.disable_raw_mode();
        result
    }

    #[allow(clippy::too_many_arguments)]
    fn read_line_loop_with_completion<T: Terminal>(
        &mut self,
        prompt: &str,
        upper_lines: &[String],
        history: &mut History,
        term: &mut T,
        ctx: &CompletionContext,
        cmd_ctx: &mut CommandCompletionContext<'_>,
        scanner: &mut HighlightScanner,
        checker_env: &CheckerEnv<'_>,
        accumulated: &str,
    ) -> io::Result<Option<String>> {
        let prompt_width = display_width(prompt);
        loop {
            term.flush()?;
            match term.read_event()? {
                Event::Key(key_event) => {
                    match self.handle_key(key_event, history) {
                        KeyAction::Submit => {
                            history.reset_cursor();
                            term.reset_style()?;
                            if self.prev_total_rows > 0 {
                                let buf_pos_width: usize = self.buf[..self.pos].iter()
                                    .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
                                    .sum();
                                let (tw, _) = term.size().unwrap_or((80, 24));
                                let tw = tw as usize;
                                let cursor_row = if tw > 0 { (prompt_width + buf_pos_width) / tw } else { 0 };
                                if self.prev_total_rows > cursor_row {
                                    term.move_down((self.prev_total_rows - cursor_row) as u16)?;
                                }
                            }
                            term.move_to_column(0)?;
                            term.write_str("\r\n")?;
                            term.flush()?;
                            return Ok(Some(self.buffer()));
                        }
                        KeyAction::Eof => {
                            return Ok(None);
                        }
                        KeyAction::Interrupt => {
                            history.reset_cursor();
                            term.reset_style()?;
                            if self.prev_total_rows > 0 {
                                let buf_pos_width: usize = self.buf[..self.pos].iter()
                                    .map(|c| UnicodeWidthChar::width(*c).unwrap_or(0))
                                    .sum();
                                let (tw, _) = term.size().unwrap_or((80, 24));
                                let tw = tw as usize;
                                let cursor_row = if tw > 0 { (prompt_width + buf_pos_width) / tw } else { 0 };
                                if self.prev_total_rows > cursor_row {
                                    term.move_down((self.prev_total_rows - cursor_row) as u16)?;
                                }
                            }
                            term.move_to_column(0)?;
                            term.write_str("\r\n")?;
                            term.flush()?;
                            self.clear();
                            return Ok(Some(String::new()));
                        }
                        KeyAction::FuzzySearch => {
                            self.suggestion = None;
                            term.reset_style()?;
                            term.disable_raw_mode()?;
                            if let Ok(Some(line)) = FuzzySearchUI::run(history, term) {
                                self.buf = line.chars().collect();
                                self.pos = self.buf.len();
                            }
                            term.enable_raw_mode()?;
                            term.move_to_column(0)?;
                            term.clear_current_line()?;
                            for line in upper_lines {
                                term.write_str(line)?;
                                term.write_str("\r\n")?;
                            }
                            term.write_str(prompt)?;
                        }
                        KeyAction::TabComplete => {
                            term.reset_style()?;
                            self.handle_tab_complete(term, prompt, upper_lines, ctx, cmd_ctx)?;
                        }
                        KeyAction::ClearScreen => {
                            term.clear_all()?;
                            for line in upper_lines {
                                term.write_str(line)?;
                                term.write_str("\r\n")?;
                            }
                            term.write_str(prompt)?;
                        }
                        KeyAction::Continue => {}
                    }
                    self.update_suggestion(history);
                    let spans = scanner.scan(accumulated, &self.buf, checker_env);
                    let (tw, _) = term.size().unwrap_or((80, 24));
                    self.redraw(term, prompt, prompt_width, &spans, tw)?;
                }
                Event::Resize(_cols, _rows) => {
                    let (tw, _) = term.size().unwrap_or((80, 24));
                    self.update_suggestion(history);
                    let spans = scanner.scan(accumulated, &self.buf, checker_env);
                    self.redraw(term, prompt, prompt_width, &spans, tw)?;
                }
                _ => {}
            }
        }
    }

    fn handle_tab_complete<T: Terminal>(
        &mut self,
        term: &mut T,
        prompt: &str,
        upper_lines: &[String],
        ctx: &CompletionContext,
        cmd_ctx: &mut CommandCompletionContext<'_>,
    ) -> io::Result<()> {
        let (word_start, word) = {
            let buf = self.buffer();
            let (ws, w) = extract_completion_word(&buf, self.pos);
            (ws, w.to_owned())
        };
        let is_cmd_pos = {
            let buf = self.buffer();
            is_command_position(&buf, word_start)
        };

        let (candidates, common_prefix, dir_prefix) =
            if is_cmd_pos && !word.contains('/') {
                // Command name completion
                let (cands, common) = cmd_ctx.completer.complete_common_prefix(
                    &word,
                    cmd_ctx.path,
                    cmd_ctx.builtins,
                    cmd_ctx.aliases,
                );
                (cands, common, String::new())
            } else {
                // Path completion (existing)
                let result = completion::complete(&self.buffer(), self.pos, ctx);
                (result.candidates, result.common_prefix, result.dir_prefix)
            };

        if candidates.is_empty() {
            return Ok(());
        }

        if self.tab_count == 1 {
            if candidates.len() == 1 {
                // Single candidate: replace word
                let candidate = &candidates[0];
                let is_dir = candidate.ends_with('/');
                let mut replacement = format!("{}{}", dir_prefix, candidate);
                if !is_dir {
                    replacement.push(' ');
                }
                self.replace_word(word_start, &replacement);
            } else {
                // Multiple candidates: replace with common prefix if longer
                let current_word_len = self.buffer()[word_start..self.pos].len();
                let new_word = format!("{}{}", dir_prefix, common_prefix);
                if new_word.len() > current_word_len {
                    self.replace_word(word_start, &new_word);
                }
            }
        } else if self.tab_count >= 2 && candidates.len() >= 2 {
            // Show interactive completion UI
            self.suggestion = None;
            term.disable_raw_mode()?;
            let selected = CompletionUI::run(&candidates, term)?;
            if let Some(sel) = selected {
                let is_dir = sel.ends_with('/');
                let mut replacement = format!("{}{}", dir_prefix, sel);
                if !is_dir {
                    replacement.push(' ');
                }
                self.replace_word(word_start, &replacement);
            }
            term.enable_raw_mode()?;
            term.move_to_column(0)?;
            term.clear_current_line()?;
            for line in upper_lines {
                term.write_str(line)?;
                term.write_str("\r\n")?;
            }
            term.write_str(prompt)?;
        }

        Ok(())
    }

    /// Replace the word starting at byte offset `word_start` with `replacement`.
    fn replace_word(&mut self, word_start: usize, replacement: &str) {
        // Convert byte offset to char index
        let char_start = self.buffer()[..word_start].chars().count();
        // Drain chars from char_start to current pos
        let drain_end = self.pos;
        self.buf.drain(char_start..drain_end);
        // Insert replacement chars at char_start
        let rep_chars: Vec<char> = replacement.chars().collect();
        let rep_len = rep_chars.len();
        for (i, ch) in rep_chars.into_iter().enumerate() {
            self.buf.insert(char_start + i, ch);
        }
        self.pos = char_start + rep_len;
    }
}