rsview 0.2.0

//! rsview — proof-of-concept lazy JSON viewer in Rust.
//!
//! Demonstrates the core of react-obj-view's CLI in native Rust: a file is
//! memory-mapped, parsed on expand (subtrees are byte ranges, not materialized
//! values), and a level is flattened only as far as the viewport scrolls
//! (windowing). Opening a multi-GB file stays near-constant memory.

mod scanner;
mod search;
use scanner::{container_empty, decode_str, skip_ws, value_kind, Cursor, Kind, RawChild};
use search::Search;

use memmap2::Mmap;
use ratatui::{
    crossterm::event::{self, Event, KeyCode, KeyEventKind},
    layout::{Constraint, Layout},
    style::{Color, Modifier, Style},
    text::{Line, Span},
    widgets::Paragraph,
    Frame,
};
use std::{collections::HashSet, fs::File, sync::Arc, time::Duration};

/// How many children to show in a collapsed container's inline preview.
const PREVIEW_ITEMS: usize = 5;
/// Max display width of a collapsed preview before it's truncated with `…`.
const PREVIEW_WIDTH: usize = 64;

// Syntax-highlight palette (ANSI named colors so it adapts to the terminal theme).
const C_KEY: Color = Color::Cyan; // object keys
const C_INDEX: Color = Color::DarkGray; // array indices
const C_STR: Color = Color::Green; // string values
const C_NUM: Color = Color::Yellow; // numbers
const C_BOOL: Color = Color::Magenta; // true / false
const C_PUNCT: Color = Color::DarkGray; // braces, colon, markers, previews

/// The foreground color for a value of the given kind.
fn value_color(kind: Kind) -> Color {
    match kind {
        Kind::Str => C_STR,
        Kind::Number => C_NUM,
        Kind::Bool => C_BOOL,
        Kind::Null | Kind::Object | Kind::Array => C_PUNCT,
    }
}

/// A lazily-expanding tree node. Children are scanned on demand from `cursor`
/// (resumable), so a collapsed node costs O(1) and a huge level only enumerates
/// as far as it's scrolled.
struct Node {
    label: String,
    start: usize,
    end: usize,
    kind: Kind,
    is_index: bool,
    has_children: bool,
    expanded: bool,
    done: bool,
    children: Vec<Node>,
    cursor: Option<Cursor>,
}

impl Node {
    fn is_container(&self) -> bool {
        matches!(self.kind, Kind::Object | Kind::Array)
    }

    fn from_raw(rc: RawChild, b: &[u8]) -> Node {
        let is_cont = matches!(rc.kind, Kind::Object | Kind::Array);
        let has = is_cont && !container_empty(b, rc.start, rc.end);
        Node {
            label: rc.label,
            start: rc.start,
            end: rc.end,
            kind: rc.kind,
            is_index: rc.is_index,
            has_children: has,
            expanded: false,
            done: false,
            children: Vec::new(),
            cursor: None,
        }
    }

    fn toggle(&mut self) {
        if !self.is_container() || !self.has_children {
            return;
        }
        self.expanded = !self.expanded;
        // Init the child cursor on first expand only; collapse keeps the cursor +
        // already-scanned children so re-expand resumes instead of rescanning.
        if self.expanded && self.cursor.is_none() && self.children.is_empty() && !self.done {
            self.cursor = Some(Cursor::new(self.start, self.end, matches!(self.kind, Kind::Array)));
        }
    }

    /// Ensure `children[i]` exists, scanning more from the cursor if needed.
    fn ensure_child(&mut self, b: &[u8], i: usize) {
        while self.children.len() <= i {
            let nx = match self.cursor.as_mut() {
                Some(c) => c.next(b),
                None => None,
            };
            match nx {
                Some(rc) => self.children.push(Node::from_raw(rc, b)),
                None => {
                    self.done = true;
                    break;
                }
            }
        }
    }

    /// The value text shown after the label. Collapsed containers get a real
    /// one-line preview of their first few children; expanded ones get the
    /// opening brace; scalars get their (truncated) literal.
    fn preview(&self, b: &[u8]) -> String {
        match self.kind {
            Kind::Object | Kind::Array => {
                let arr = matches!(self.kind, Kind::Array);
                if !self.has_children {
                    if arr { "[]".into() } else { "{}".into() }
                } else if self.expanded {
                    if arr { "[".into() } else { "{".into() }
                } else {
                    self.collapsed_preview(b)
                }
            }
            Kind::Str => format!("\"{}\"", truncate(&decode_str(b, self.start, self.end), 70)),
            _ => truncate(&String::from_utf8_lossy(&b[self.start..self.end]), 70),
        }
    }

    /// Scan the first few children of a collapsed container and render them
    /// inline, e.g. `{ version: "0.3.2", deps: {…}, … }`. Uses a fresh resumable
    /// `Cursor`, capped at `PREVIEW_ITEMS`, so it's O(few) regardless of size.
    fn collapsed_preview(&self, b: &[u8]) -> String {
        let arr = matches!(self.kind, Kind::Array);
        let (open, close) = if arr { ("[", "]") } else { ("{", "}") };
        let mut cur = Cursor::new(self.start, self.end, arr);
        let mut parts: Vec<String> = Vec::new();
        let mut more = false;
        loop {
            if parts.len() == PREVIEW_ITEMS {
                more = cur.next(b).is_some(); // is there at least one more?
                break;
            }
            match cur.next(b) {
                Some(rc) => {
                    let v = brief(b, &rc);
                    parts.push(if arr { v } else { format!("{}: {}", rc.label, v) });
                }
                None => break,
            }
        }
        if parts.is_empty() {
            return format!("{open}{close}");
        }
        let mut body = parts.join(", ");
        if more {
            body.push_str(", …");
        }
        truncate(&format!("{open} {body} {close}"), PREVIEW_WIDTH)
    }
}

/// A brief one-level rendering of a value for use inside a parent's preview:
/// nested containers collapse to `{…}`/`[…]`, scalars show their literal.
fn brief(b: &[u8], rc: &RawChild) -> String {
    match rc.kind {
        Kind::Object => {
            if container_empty(b, rc.start, rc.end) { "{}".into() } else { "{…}".into() }
        }
        Kind::Array => {
            if container_empty(b, rc.start, rc.end) { "[]".into() } else { "[…]".into() }
        }
        Kind::Str => format!("\"{}\"", truncate(&decode_str(b, rc.start, rc.end), 24)),
        _ => truncate(&String::from_utf8_lossy(&b[rc.start..rc.end]), 24),
    }
}

fn truncate(s: &str, n: usize) -> String {
    if s.chars().count() <= n {
        s.to_string()
    } else {
        let t: String = s.chars().take(n).collect();
        format!("{t}…")
    }
}

/// A flattened, on-screen row plus the index path back to its node. Carries the
/// label/value/kind separately so the renderer can syntax-color each segment.
struct Row {
    depth: usize,
    label: String,
    value: String,
    kind: Kind,
    is_index: bool,
    has_children: bool,
    expanded: bool,
    path: Vec<usize>,
}

/// Windowed flatten: walk the expanded tree DFS, scanning children on demand,
/// and stop once `budget` rows exist. A pathologically flat level (millions of
/// keys) therefore only flattens ~a screenful, not the whole thing.
fn flatten(node: &mut Node, b: &[u8], depth: usize, budget: usize, out: &mut Vec<Row>, path: &mut Vec<usize>) {
    if out.len() >= budget {
        return;
    }
    out.push(Row {
        depth,
        label: node.label.clone(),
        value: node.preview(b),
        kind: node.kind,
        is_index: node.is_index,
        has_children: node.has_children,
        expanded: node.expanded,
        path: path.clone(),
    });
    if node.expanded && node.is_container() {
        let mut i = 0;
        while out.len() < budget {
            node.ensure_child(b, i);
            if i >= node.children.len() {
                break; // level fully enumerated
            }
            path.push(i);
            flatten(&mut node.children[i], b, depth + 1, budget, out, path);
            path.pop();
            i += 1;
        }
    }
}

fn get<'a>(mut n: &'a Node, path: &[usize]) -> &'a Node {
    for &i in path {
        n = &n.children[i];
    }
    n
}

fn get_mut<'a>(mut n: &'a mut Node, path: &[usize]) -> &'a mut Node {
    for &i in path {
        n = &mut n.children[i];
    }
    n
}

/// Expand every ancestor of `path` (scanning children up to each step) so the
/// target node becomes reachable in the flattened rows. The target itself is
/// left as-is — only the chain above it is opened.
fn expand_to(n: &mut Node, b: &[u8], path: &[usize]) {
    if path.is_empty() {
        return;
    }
    if n.is_container() && n.has_children && !n.expanded {
        n.toggle();
    }
    n.ensure_child(b, path[0]);
    if path[0] < n.children.len() {
        expand_to(&mut n.children[path[0]], b, &path[1..]);
    }
}

#[derive(PartialEq)]
enum Mode {
    Normal,
    Search,
}

struct App {
    root: Node,
    name: String,
    focus: usize,
    scroll: usize,
    rows: Vec<Row>,
    mode: Mode,
    /// Live search-input buffer (typed while in `Mode::Search`).
    query: String,
    /// The running search, if any. `None` once cleared/cancelled.
    search: Option<Search>,
    /// Which match `n`/`N` is currently on.
    match_idx: usize,
    /// Set of match paths, for O(1) row highlighting. Grown incrementally.
    match_set: HashSet<Vec<usize>>,
    /// How many of `search.matches` are already in `match_set`.
    indexed: usize,
    /// A pending jump target: the next frame flattens far enough to land on it.
    want_path: Option<Vec<usize>>,
}

impl App {
    fn new(b: &[u8], path: &str) -> App {
        let rstart = skip_ws(b, 0, b.len());
        let kind = value_kind(b, rstart);
        let is_cont = matches!(kind, Kind::Object | Kind::Array);
        let has = is_cont && !container_empty(b, rstart, b.len());
        let name = std::path::Path::new(path)
            .file_name()
            .map(|s| s.to_string_lossy().into_owned())
            .unwrap_or_else(|| "ROOT".into());
        let mut root = Node {
            label: name.clone(),
            start: rstart,
            end: b.len(), // root spans to EOF; the scanner stops at the real closer
            kind,
            is_index: false,
            has_children: has,
            expanded: false,
            done: false,
            children: Vec::new(),
            cursor: None,
        };
        if has {
            root.toggle(); // auto-expand the root (like --depth 1)
        }
        App {
            root,
            name,
            focus: 0,
            scroll: 0,
            rows: Vec::new(),
            mode: Mode::Normal,
            query: String::new(),
            search: None,
            match_idx: 0,
            match_set: HashSet::new(),
            indexed: 0,
            want_path: None,
        }
    }

    fn toggle_focus(&mut self) {
        if self.rows.is_empty() {
            return;
        }
        let path = self.rows[self.focus].path.clone();
        get_mut(&mut self.root, &path).toggle();
    }

    /// (Re)launch the live search for the current `query`. Dropping the previous
    /// `Search` cancels its worker thread; an empty query just clears results.
    fn relaunch(&mut self, mmap: &Arc<Mmap>) {
        if let Some(old) = self.search.take() {
            old.cancel(); // belt-and-suspenders; Drop also flips the flag
        }
        self.match_set.clear();
        self.indexed = 0;
        self.match_idx = 0;
        self.want_path = None;
        if self.query.is_empty() {
            return;
        }
        self.search = Some(Search::spawn(Arc::clone(mmap), self.query.clone()));
    }

    /// Pull newly-found matches into `match_set` so rows can be highlighted.
    fn pump_search(&mut self) {
        if let Some(s) = self.search.as_mut() {
            s.drain();
        }
        let n = self.search.as_ref().map_or(0, |s| s.matches.len());
        while self.indexed < n {
            let p = self.search.as_ref().unwrap().matches[self.indexed].clone();
            self.match_set.insert(p);
            self.indexed += 1;
        }
    }

    /// Move to the next/previous match (`dir` = +1 / -1) and queue a jump to it.
    fn step_match(&mut self, dir: i32, b: &[u8]) {
        let n = self.search.as_ref().map_or(0, |s| s.matches.len());
        if n == 0 {
            return;
        }
        self.match_idx = if dir >= 0 {
            (self.match_idx + 1) % n
        } else {
            (self.match_idx + n - 1) % n
        };
        let path = self.search.as_ref().unwrap().matches[self.match_idx].clone();
        self.jump_to(&path, b);
    }

    /// Expand the ancestors of `path` and queue the row for focus next frame.
    fn jump_to(&mut self, path: &[usize], b: &[u8]) {
        expand_to(&mut self.root, b, path);
        self.want_path = Some(path.to_vec());
    }

    fn clear_search(&mut self) {
        if let Some(s) = self.search.take() {
            s.cancel();
        }
        self.query.clear();
        self.match_set.clear();
        self.indexed = 0;
        self.match_idx = 0;
        self.want_path = None;
    }

    fn collapse_or_parent(&mut self) {
        if self.rows.is_empty() {
            return;
        }
        let path = self.rows[self.focus].path.clone();
        let (expanded, cont) = {
            let n = get(&self.root, &path);
            (n.expanded, n.is_container())
        };
        if expanded && cont {
            get_mut(&mut self.root, &path).toggle();
        } else if !path.is_empty() {
            let pp = &path[..path.len() - 1];
            if let Some(idx) = self.rows.iter().position(|r| r.path.as_slice() == pp) {
                self.focus = idx;
            }
        }
    }
}

fn ui(f: &mut Frame, app: &App, h: usize) {
    let chunks = Layout::vertical([
        Constraint::Length(1),
        Constraint::Min(0),
        Constraint::Length(1),
    ])
    .split(f.area());

    let title = format!(" {}   {}/{}+", app.name, app.focus + 1, app.rows.len());
    f.render_widget(
        Paragraph::new(title).style(Style::default().fg(Color::Cyan).add_modifier(Modifier::BOLD)),
        chunks[0],
    );

    let cur_match = app
        .search
        .as_ref()
        .and_then(|s| s.matches.get(app.match_idx));

    let mut lines = Vec::new();
    let end = (app.scroll + h).min(app.rows.len());
    for i in app.scroll..end {
        let r = &app.rows[i];
        let marker = if r.has_children {
            if r.expanded {
                "▼"
            } else {
                "▶"
            }
        } else {
            " "
        };
        let indent = "  ".repeat(r.depth);

        let line = if i == app.focus {
            // Selection bar: plain reversed, colors dropped for maximum contrast.
            let text = format!("{indent}{marker} {}: {}", r.label, r.value);
            Line::from(Span::styled(text, Style::default().add_modifier(Modifier::REVERSED)))
        } else if cur_match == Some(&r.path) || app.match_set.contains(&r.path) {
            // A search hit: whole row yellow (current match also bold).
            let text = format!("{indent}{marker} {}: {}", r.label, r.value);
            let mut st = Style::default().fg(Color::Yellow);
            if cur_match == Some(&r.path) {
                st = st.add_modifier(Modifier::BOLD);
            }
            Line::from(Span::styled(text, st))
        } else {
            // Normal row: syntax-colored segments.
            let key_color = if r.is_index { C_INDEX } else { C_KEY };
            Line::from(vec![
                Span::raw(indent),
                Span::styled(marker, Style::default().fg(C_PUNCT)),
                Span::raw(" "),
                Span::styled(r.label.clone(), Style::default().fg(key_color)),
                Span::styled(": ", Style::default().fg(C_PUNCT)),
                Span::styled(r.value.clone(), Style::default().fg(value_color(r.kind))),
            ])
        };
        lines.push(line);
    }
    f.render_widget(Paragraph::new(lines), chunks[1]);

    let footer = if app.mode == Mode::Search {
        let count = app.search.as_ref().map_or(0, |s| s.matches.len());
        let more = match &app.search {
            Some(s) if !s.finished => "+",
            _ => "",
        };
        Span::styled(
            format!(" /{}    {}{} matches · enter go · esc cancel", app.query, count, more),
            Style::default().fg(Color::Yellow),
        )
    } else if app.search.is_some() {
        let count = app.search.as_ref().map_or(0, |s| s.matches.len());
        Span::styled(
            format!(
                " /{}  {}/{}  · n/N next/prev · / search · q quit",
                app.query,
                app.match_idx + 1,
                count
            ),
            Style::default().fg(Color::DarkGray),
        )
    } else {
        Span::styled(
            " ↑/↓ move · enter/→ expand · ← collapse · / search · g top · q quit",
            Style::default().fg(Color::DarkGray),
        )
    };
    f.render_widget(Paragraph::new(Line::from(footer)), chunks[2]);
}

fn run(
    term: &mut ratatui::DefaultTerminal,
    app: &mut App,
    b: &[u8],
    mmap: &Arc<Mmap>,
) -> std::io::Result<()> {
    loop {
        // Fold in any matches the worker thread has produced since last frame.
        app.pump_search();

        let (_, th) = ratatui::crossterm::terminal::size()?;
        let h = (th.saturating_sub(2) as usize).max(1);
        // Normally flatten only as far as the viewport needs. When a jump is
        // pending, flatten just far enough to include the target's row.
        let budget = match &app.want_path {
            Some(p) => p.iter().sum::<usize>() + p.len() + h + 64,
            None => (app.scroll + h + 64).max(app.focus + 64),
        };
        app.rows.clear();
        let mut path = Vec::new();
        flatten(&mut app.root, b, 0, budget, &mut app.rows, &mut path);

        // Land a queued jump: find the target's row and focus it.
        if let Some(p) = app.want_path.take() {
            if let Some(idx) = app.rows.iter().position(|r| r.path == p) {
                app.focus = idx;
            }
        }

        if app.focus >= app.rows.len() {
            app.focus = app.rows.len().saturating_sub(1);
        }
        if app.focus < app.scroll {
            app.scroll = app.focus;
        }
        if app.focus >= app.scroll + h {
            app.scroll = app.focus + 1 - h;
        }

        term.draw(|f| ui(f, app, h))?;

        // Short poll so streaming match counts keep ticking even without input.
        if !event::poll(Duration::from_millis(100))? {
            continue;
        }
        let Event::Key(k) = event::read()? else {
            continue;
        };
        if k.kind != KeyEventKind::Press {
            continue;
        }

        if app.mode == Mode::Search {
            // Live search input: each edit drops the old worker and starts fresh.
            match k.code {
                KeyCode::Esc => {
                    app.mode = Mode::Normal;
                    app.clear_search();
                }
                KeyCode::Enter => {
                    app.mode = Mode::Normal;
                    if app.search.as_ref().is_some_and(|s| !s.matches.is_empty()) {
                        let first = app.search.as_ref().unwrap().matches[0].clone();
                        app.match_idx = 0;
                        app.jump_to(&first, b);
                    }
                }
                KeyCode::Backspace => {
                    app.query.pop();
                    app.relaunch(mmap);
                }
                KeyCode::Char(c) => {
                    app.query.push(c);
                    app.relaunch(mmap);
                }
                _ => {}
            }
            continue;
        }

        // Normal mode.
        match k.code {
            KeyCode::Char('q') | KeyCode::Esc => return Ok(()),
            KeyCode::Char('/') => {
                app.mode = Mode::Search;
                app.query.clear();
                app.relaunch(mmap);
            }
            KeyCode::Char('n') => app.step_match(1, b),
            KeyCode::Char('N') => app.step_match(-1, b),
            KeyCode::Down | KeyCode::Char('j') => app.focus += 1,
            KeyCode::Up | KeyCode::Char('k') => app.focus = app.focus.saturating_sub(1),
            KeyCode::PageDown => app.focus += h,
            KeyCode::PageUp => app.focus = app.focus.saturating_sub(h),
            KeyCode::Home | KeyCode::Char('g') => {
                app.focus = 0;
                app.scroll = 0;
            }
            KeyCode::Enter | KeyCode::Char(' ') | KeyCode::Right => app.toggle_focus(),
            KeyCode::Left => app.collapse_or_parent(),
            _ => {}
        }
    }
}

fn main() -> std::io::Result<()> {
    let path = match std::env::args().nth(1) {
        Some(p) => p,
        None => {
            eprintln!("usage: rsview <file.json>");
            std::process::exit(2);
        }
    };
    let file = File::open(&path)?;
    // SAFETY: the file isn't mutated while mapped for the lifetime of the viewer.
    // Wrapped in an Arc so the search worker thread can share the same mapping
    // (zero-copy) without lifetime gymnastics.
    let mmap = Arc::new(unsafe { Mmap::map(&file)? });
    let b: &[u8] = &mmap;

    let mut app = App::new(b, &path);
    let mut term = ratatui::init();
    let res = run(&mut term, &mut app, b, &mmap);
    ratatui::restore();
    res
}