tui_file_explorer/

inline_editor.rs

//! Inline text editor for the TUI file explorer.
//!
//! Provides a minimal, modal-free text editor that can open, display, edit, and
//! save plain-text files directly inside the terminal UI.  Only files up to
//! `MAX_EDIT_FILE_SIZE` bytes are accepted — anything larger is rejected to
//! avoid freezing the terminal.
//!
//! ## Key bindings
//!
//! | Key           | Action                                       |
//! |---------------|----------------------------------------------|
//! | Arrow keys    | Move cursor                                  |
//! | Home / End    | Jump to beginning / end of line               |
//! | PgUp / PgDn   | Scroll one page (20 lines)                   |
//! | Printable     | Insert character at cursor                   |
//! | Enter         | Split line at cursor                         |
//! | Backspace     | Delete char before cursor / join lines        |
//! | Delete        | Delete char at cursor / join lines            |
//! | Tab           | Insert 4 spaces                              |
//! | Ctrl+S        | Save to disk                                 |
//! | Esc           | Exit the editor                              |

use std::fs;
use std::io;
use std::path::{Path, PathBuf};

use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
use ratatui::Frame;
use ratatui::layout::Rect;
use ratatui::style::{Color, Style};
use ratatui::text::{Line, Span};
use ratatui::widgets::Paragraph;

use crate::palette::Theme;

// ── Constants ─────────────────────────────────────────────────────────────────

/// Maximum file size the editor will open (10 MiB).
const MAX_EDIT_FILE_SIZE: u64 = 10 * 1024 * 1024;

/// Number of spaces inserted for a Tab key press.
const TAB_WIDTH: usize = 4;

/// Number of lines scrolled per PgUp / PgDn key press.
const PAGE_SIZE: usize = 20;

// ── EditorAction ──────────────────────────────────────────────────────────────

/// Result of handling a key event in the inline editor.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum EditorAction {
    /// Key was consumed, continue editing.
    Continue,
    /// File was saved successfully.
    Saved,
    /// User wants to exit the editor.
    Exit,
}

// ── InlineEditor ──────────────────────────────────────────────────────────────

/// A simple, single-file text editor that lives inside the TUI.
#[derive(Debug)]
pub struct InlineEditor {
    /// Lines of the file being edited.
    lines: Vec<String>,
    /// Current cursor row (0-based line index).
    cursor_row: usize,
    /// Current cursor column (0-based character index).
    cursor_col: usize,
    /// Vertical scroll offset (first visible line).
    scroll_row: usize,
    /// Horizontal scroll offset.
    scroll_col: usize,
    /// Path to the file being edited.
    path: PathBuf,
    /// Whether the buffer has been modified since last save.
    modified: bool,
    /// Status message shown at the bottom.
    status: String,
}

impl InlineEditor {
    /// Open a file for editing.
    ///
    /// Returns `Err` if the file does not exist, cannot be read, or exceeds
    /// `MAX_EDIT_FILE_SIZE`.
    pub fn open(path: &Path) -> io::Result<Self> {
        let meta = fs::metadata(path)?;
        if meta.len() > MAX_EDIT_FILE_SIZE {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "file is too large ({} bytes, max {})",
                    meta.len(),
                    MAX_EDIT_FILE_SIZE
                ),
            ));
        }

        let content = fs::read_to_string(path)?;
        let mut lines: Vec<String> = content.lines().map(String::from).collect();
        if lines.is_empty() {
            lines.push(String::new());
        }

        Ok(Self {
            lines,
            cursor_row: 0,
            cursor_col: 0,
            scroll_row: 0,
            scroll_col: 0,
            path: path.to_path_buf(),
            modified: false,
            status: String::new(),
        })
    }

    // ── Key handling ──────────────────────────────────────────────────────

    /// Handle a key event. Returns the [`EditorAction`] to take.
    pub fn handle_key(&mut self, key: KeyEvent) -> EditorAction {
        press_only!(key, EditorAction::Continue);

        match (key.modifiers, key.code) {
            // ── Save ──────────────────────────────────────────────────
            (KeyModifiers::CONTROL, KeyCode::Char('s')) => match self.save() {
                Ok(()) => {
                    self.status = "saved".into();
                    EditorAction::Saved
                }
                Err(e) => {
                    self.status = format!("save failed: {e}");
                    EditorAction::Continue
                }
            },

            // ── Exit ──────────────────────────────────────────────────
            (_, KeyCode::Esc) => EditorAction::Exit,

            // ── Navigation ────────────────────────────────────────────
            (_, KeyCode::Up) => {
                self.move_up();
                EditorAction::Continue
            }
            (_, KeyCode::Down) => {
                self.move_down();
                EditorAction::Continue
            }
            (_, KeyCode::Left) => {
                self.move_left();
                EditorAction::Continue
            }
            (_, KeyCode::Right) => {
                self.move_right();
                EditorAction::Continue
            }
            (_, KeyCode::Home) => {
                self.cursor_col = 0;
                self.adjust_scroll_col();
                EditorAction::Continue
            }
            (_, KeyCode::End) => {
                self.cursor_col = self.current_line_len();
                self.adjust_scroll_col();
                EditorAction::Continue
            }
            (_, KeyCode::PageUp) => {
                self.page_up();
                EditorAction::Continue
            }
            (_, KeyCode::PageDown) => {
                self.page_down();
                EditorAction::Continue
            }

            // ── Editing ───────────────────────────────────────────────
            (_, KeyCode::Char(c))
                if key.modifiers.is_empty() || key.modifiers == KeyModifiers::SHIFT =>
            {
                self.insert_char(c);
                EditorAction::Continue
            }
            (_, KeyCode::Enter) => {
                self.insert_newline();
                EditorAction::Continue
            }
            (_, KeyCode::Backspace) => {
                self.backspace();
                EditorAction::Continue
            }
            (_, KeyCode::Delete) => {
                self.delete();
                EditorAction::Continue
            }
            (_, KeyCode::Tab) => {
                self.insert_tab();
                EditorAction::Continue
            }

            // ── Everything else ───────────────────────────────────────
            _ => EditorAction::Continue,
        }
    }

    // ── Persistence ───────────────────────────────────────────────────────

    /// Save the current buffer to disk.
    pub fn save(&mut self) -> io::Result<()> {
        let content = self.lines.join("\n");
        fs::write(&self.path, &content)?;
        self.modified = false;
        Ok(())
    }

    // ── Getters ───────────────────────────────────────────────────────────

    /// Number of lines in the buffer.
    #[must_use]
    pub fn line_count(&self) -> usize {
        self.lines.len()
    }

    /// Whether the buffer has been modified since the last save.
    #[must_use]
    pub fn is_modified(&self) -> bool {
        self.modified
    }

    /// Path to the file being edited.
    #[must_use]
    pub fn path(&self) -> &Path {
        &self.path
    }

    /// Current status message.
    #[must_use]
    pub fn status(&self) -> &str {
        &self.status
    }

    /// Current cursor row (0-based).
    #[must_use]
    pub fn cursor_row(&self) -> usize {
        self.cursor_row
    }

    /// Current cursor column (0-based).
    #[must_use]
    pub fn cursor_col(&self) -> usize {
        self.cursor_col
    }

    /// Slice of all lines in the buffer.
    #[must_use]
    pub fn lines(&self) -> &[String] {
        &self.lines
    }

    /// Vertical scroll offset (first visible line).
    #[must_use]
    pub fn scroll_row(&self) -> usize {
        self.scroll_row
    }

    /// Horizontal scroll offset.
    #[must_use]
    pub fn scroll_col(&self) -> usize {
        self.scroll_col
    }

    // ── Movement helpers (private) ────────────────────────────────────────

    fn move_up(&mut self) {
        if self.cursor_row > 0 {
            self.cursor_row -= 1;
            self.clamp_cursor_col();
            self.adjust_scroll_row();
        }
    }

    fn move_down(&mut self) {
        if self.cursor_row + 1 < self.lines.len() {
            self.cursor_row += 1;
            self.clamp_cursor_col();
            self.adjust_scroll_row();
        }
    }

    fn move_left(&mut self) {
        if self.cursor_col > 0 {
            self.cursor_col -= 1;
        } else if self.cursor_row > 0 {
            self.cursor_row -= 1;
            self.cursor_col = self.current_line_len();
        }
        self.adjust_scroll_row();
        self.adjust_scroll_col();
    }

    fn move_right(&mut self) {
        let len = self.current_line_len();
        if self.cursor_col < len {
            self.cursor_col += 1;
        } else if self.cursor_row + 1 < self.lines.len() {
            self.cursor_row += 1;
            self.cursor_col = 0;
        }
        self.adjust_scroll_row();
        self.adjust_scroll_col();
    }

    fn page_up(&mut self) {
        self.cursor_row = self.cursor_row.saturating_sub(PAGE_SIZE);
        self.scroll_row = self.scroll_row.saturating_sub(PAGE_SIZE);
        self.clamp_cursor_col();
        self.adjust_scroll_row();
    }

    fn page_down(&mut self) {
        let max_row = self.lines.len().saturating_sub(1);
        self.cursor_row = (self.cursor_row + PAGE_SIZE).min(max_row);
        self.scroll_row = (self.scroll_row + PAGE_SIZE).min(max_row);
        self.clamp_cursor_col();
        self.adjust_scroll_row();
    }

    // ── Editing helpers (private) ─────────────────────────────────────────

    fn insert_char(&mut self, c: char) {
        let byte_idx = self.cursor_byte_offset();
        self.lines[self.cursor_row].insert(byte_idx, c);
        self.cursor_col += 1;
        self.modified = true;
        self.adjust_scroll_col();
    }

    fn insert_newline(&mut self) {
        let byte_idx = self.cursor_byte_offset();
        let tail = self.lines[self.cursor_row][byte_idx..].to_string();
        self.lines[self.cursor_row].truncate(byte_idx);
        self.cursor_row += 1;
        self.cursor_col = 0;
        self.lines.insert(self.cursor_row, tail);
        self.modified = true;
        self.adjust_scroll_row();
        self.adjust_scroll_col();
    }

    fn backspace(&mut self) {
        if self.cursor_col > 0 {
            let byte_start = self.byte_offset_of_char(self.cursor_row, self.cursor_col - 1);
            let byte_end = self.byte_offset_of_char(self.cursor_row, self.cursor_col);
            self.lines[self.cursor_row].replace_range(byte_start..byte_end, "");
            self.cursor_col -= 1;
            self.modified = true;
        } else if self.cursor_row > 0 {
            let removed = self.lines.remove(self.cursor_row);
            self.cursor_row -= 1;
            self.cursor_col = self.current_line_len();
            self.lines[self.cursor_row].push_str(&removed);
            self.modified = true;
        }
        self.adjust_scroll_row();
        self.adjust_scroll_col();
    }

    fn delete(&mut self) {
        let len = self.current_line_len();
        if self.cursor_col < len {
            let byte_start = self.cursor_byte_offset();
            let byte_end = self.byte_offset_of_char(self.cursor_row, self.cursor_col + 1);
            self.lines[self.cursor_row].replace_range(byte_start..byte_end, "");
            self.modified = true;
        } else if self.cursor_row + 1 < self.lines.len() {
            let next = self.lines.remove(self.cursor_row + 1);
            self.lines[self.cursor_row].push_str(&next);
            self.modified = true;
        }
    }

    fn insert_tab(&mut self) {
        for _ in 0..TAB_WIDTH {
            self.insert_char(' ');
        }
    }

    // ── Internal utilities ────────────────────────────────────────────────

    /// Character-length of the current line.
    fn current_line_len(&self) -> usize {
        self.lines[self.cursor_row].chars().count()
    }

    /// Byte offset corresponding to `self.cursor_col` in the current line.
    fn cursor_byte_offset(&self) -> usize {
        self.byte_offset_of_char(self.cursor_row, self.cursor_col)
    }

    /// Byte offset of the `col`-th character in `line_idx`.
    fn byte_offset_of_char(&self, line_idx: usize, col: usize) -> usize {
        self.lines[line_idx]
            .char_indices()
            .nth(col)
            .map_or(self.lines[line_idx].len(), |(i, _)| i)
    }

    /// Clamp `cursor_col` to the length of the current line.
    fn clamp_cursor_col(&mut self) {
        let len = self.current_line_len();
        if self.cursor_col > len {
            self.cursor_col = len;
        }
    }

    /// Ensure `scroll_row` keeps the cursor visible within `PAGE_SIZE` lines.
    fn adjust_scroll_row(&mut self) {
        if self.cursor_row < self.scroll_row {
            self.scroll_row = self.cursor_row;
        } else if self.cursor_row >= self.scroll_row + PAGE_SIZE {
            self.scroll_row = self.cursor_row.saturating_sub(PAGE_SIZE - 1);
        }
    }

    /// Ensure `scroll_col` keeps the cursor visible.
    fn adjust_scroll_col(&mut self) {
        if self.cursor_col < self.scroll_col {
            self.scroll_col = self.cursor_col;
        }
        // We use a generous window — the render function uses the actual
        // available width, but here we clamp to a sane default.
        let visible_cols = 80usize;
        if self.cursor_col >= self.scroll_col + visible_cols {
            self.scroll_col = self.cursor_col.saturating_sub(visible_cols - 1);
        }
    }
}

// ── Rendering ─────────────────────────────────────────────────────────────────

/// Render the inline editor into the given area.
///
/// Layout (top to bottom):
///
/// 1. **Header** — 1 line: `✏️  Editing: <filename> [modified]`
/// 2. **Content** — remaining lines minus footer: line numbers + text
/// 3. **Footer** — 1 line: status message + cursor position + key hints
pub fn render_inline_editor(frame: &mut Frame, area: Rect, editor: &InlineEditor, theme: &Theme) {
    if area.height < 3 {
        return; // not enough room for header + 1 content line + footer
    }

    let header_area = Rect {
        x: area.x,
        y: area.y,
        width: area.width,
        height: 1,
    };
    let footer_area = Rect {
        x: area.x,
        y: area.y + area.height - 1,
        width: area.width,
        height: 1,
    };
    let content_area = Rect {
        x: area.x,
        y: area.y + 1,
        width: area.width,
        height: area.height.saturating_sub(2),
    };

    // ── Header ────────────────────────────────────────────────────────────
    let file_name = editor.path.file_name().map_or_else(
        || editor.path.display().to_string(),
        |n| n.to_string_lossy().to_string(),
    );

    let mod_indicator = if editor.modified { " [modified]" } else { "" };
    let header_text = format!("✏️  Editing: {file_name}{mod_indicator}");
    let header = Paragraph::new(Line::from(vec![Span::styled(
        header_text,
        Style::default().fg(theme.brand).bold(),
    )]));
    frame.render_widget(header, header_area);

    // ── Content ───────────────────────────────────────────────────────────
    let visible_rows = content_area.height as usize;
    let gutter_width: u16 = 5; // "NNNNN"
    let sep_width: u16 = 3; // " │ "
    let text_start_col = content_area.x + gutter_width + sep_width;
    let text_width = content_area.width.saturating_sub(gutter_width + sep_width) as usize;

    for row_offset in 0..visible_rows {
        let line_idx = editor.scroll_row + row_offset;
        let y = content_area.y + crate::to_u16(row_offset);

        if line_idx >= editor.lines.len() {
            // Past end of file — render a tilde like vi
            let tilde = Paragraph::new(Line::from(Span::styled(
                "    ~",
                Style::default().fg(theme.dim),
            )));
            frame.render_widget(
                tilde,
                Rect {
                    x: content_area.x,
                    y,
                    width: content_area.width,
                    height: 1,
                },
            );
            continue;
        }

        let is_cursor_line = line_idx == editor.cursor_row;
        let line_bg = if is_cursor_line {
            theme.sel_bg
        } else {
            Color::Reset
        };

        // ── Line number ───────────────────────────────────────────────
        let line_num = format!("{:>5}", line_idx + 1);
        let gutter = Paragraph::new(Line::from(Span::styled(
            line_num,
            Style::default().fg(theme.accent).bg(line_bg),
        )));
        frame.render_widget(
            gutter,
            Rect {
                x: content_area.x,
                y,
                width: gutter_width,
                height: 1,
            },
        );

        // ── Separator ─────────────────────────────────────────────────
        let sep = Paragraph::new(Line::from(Span::styled(
            " │ ",
            Style::default().fg(theme.dim).bg(line_bg),
        )));
        frame.render_widget(
            sep,
            Rect {
                x: content_area.x + gutter_width,
                y,
                width: sep_width,
                height: 1,
            },
        );

        // ── Line text with cursor ─────────────────────────────────────
        let line = &editor.lines[line_idx];
        let chars: Vec<char> = line.chars().collect();
        let visible_start = editor.scroll_col;

        let mut spans: Vec<Span> = Vec::new();

        if is_cursor_line {
            // Build char-by-char so we can highlight the cursor position.
            for vi in 0..text_width {
                let ci = visible_start + vi; // character index in line
                if ci == editor.cursor_col {
                    // Cursor: render a block character in accent colour.
                    if ci < chars.len() {
                        spans.push(Span::styled(
                            chars[ci].to_string(),
                            Style::default().fg(theme.brand).bg(theme.accent),
                        ));
                    } else {
                        spans.push(Span::styled(
                            "█",
                            Style::default().fg(theme.accent).bg(line_bg),
                        ));
                        // pad the rest if needed
                        if vi + 1 < text_width {
                            let pad = " ".repeat(text_width - vi - 1);
                            spans
                                .push(Span::styled(pad, Style::default().fg(theme.fg).bg(line_bg)));
                        }
                        break;
                    }
                } else if ci < chars.len() {
                    spans.push(Span::styled(
                        chars[ci].to_string(),
                        Style::default().fg(theme.fg).bg(line_bg),
                    ));
                } else {
                    // Past end of line — fill remaining with bg.
                    let remaining = text_width - vi;
                    spans.push(Span::styled(
                        " ".repeat(remaining),
                        Style::default().fg(theme.fg).bg(line_bg),
                    ));
                    break;
                }
            }
            // Edge case: cursor is exactly at visible_start + 0 and text_width
            // is 0 — nothing to render.
        } else {
            // Non-cursor line: render the visible portion in one go.
            let visible: String = chars.iter().skip(visible_start).take(text_width).collect();
            spans.push(Span::styled(
                visible,
                Style::default().fg(theme.fg).bg(line_bg),
            ));
        }

        let text_line = Paragraph::new(Line::from(spans));
        frame.render_widget(
            text_line,
            Rect {
                x: text_start_col,
                y,
                width: crate::to_u16(text_width),
                height: 1,
            },
        );
    }

    // ── Scroll thumb ─────────────────────────────────────────────────────────────
    crate::render::paint_scrollbar(
        frame,
        content_area,
        editor.lines.len(),
        editor.scroll_row,
        theme.accent,
    );

    // ── Footer ───────────────────────────────────────────────────────────────────
    let status_style = if editor.status.starts_with("save failed") {
        Style::default().fg(theme.brand)
    } else {
        Style::default().fg(theme.success)
    };

    let right_info = format!(
        "Ln {}, Col {} │ Ctrl+S save │ Esc exit",
        editor.cursor_row + 1,
        editor.cursor_col + 1,
    );

    let right_width = right_info.chars().count();
    let left_width = area.width as usize - right_width.min(area.width as usize);

    let status_display: String = if editor.status.len() > left_width {
        editor.status.chars().take(left_width).collect()
    } else {
        let pad = left_width.saturating_sub(editor.status.chars().count());
        format!("{}{}", editor.status, " ".repeat(pad))
    };

    let footer = Paragraph::new(Line::from(vec![
        Span::styled(status_display, status_style),
        Span::styled(right_info, Style::default().fg(theme.dim)),
    ]));
    frame.render_widget(footer, footer_area);
}

// ── Tests ─────────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests;