use std::io::{self, Stdout};

use crossterm::{
    cursor::Show,
    event::{
        self, DisableBracketedPaste, EnableBracketedPaste, Event, KeyCode, KeyEvent, KeyEventKind,
        KeyModifiers,
    },
    execute,
    terminal::{EnterAlternateScreen, LeaveAlternateScreen, disable_raw_mode, enable_raw_mode},
};
use ratatui::{
    Frame, Terminal,
    backend::CrosstermBackend,
    layout::Rect,
    style::{Color, Style},
    text::Line,
    widgets::Paragraph,
};
use unicode_segmentation::UnicodeSegmentation;
use unicode_width::UnicodeWidthStr;

use crate::{
    editor::{Editor, Effect, Input, Mode},
    session::EditorSession,
};

pub const CAPABILITIES: &[&str] = &["text", "styled_text"];
const TAB_WIDTH: usize = 4;

struct TerminalSession;

fn restore_terminal() {
    let _ = disable_raw_mode();
    let _ = execute!(
        io::stdout(),
        DisableBracketedPaste,
        LeaveAlternateScreen,
        Show
    );
}

impl TerminalSession {
    fn enter() -> io::Result<Self> {
        enable_raw_mode()?;
        let session = Self;
        execute!(io::stdout(), EnterAlternateScreen, EnableBracketedPaste)?;
        Ok(session)
    }
}

impl Drop for TerminalSession {
    fn drop(&mut self) {
        restore_terminal();
    }
}

/// Renders session state and translates terminal input; the session owns plugin
/// execution and retirement, so the adapter needs no lifecycle callback.
pub fn run(session: &mut EditorSession) -> io::Result<()> {
    let previous_hook = std::panic::take_hook();
    std::panic::set_hook(Box::new(move |info| {
        restore_terminal();
        previous_hook(info);
    }));
    let _session = TerminalSession::enter()?;
    let mut terminal: Terminal<CrosstermBackend<Stdout>> =
        Terminal::new(CrosstermBackend::new(io::stdout()))?;
    let (mut top, mut left) = (0, 0);
    while !session.editor().should_quit() {
        terminal.draw(|frame| draw(frame, session.editor(), &mut top, &mut left))?;
        match event::read()? {
            Event::Key(key) if key.kind != KeyEventKind::Release => {
                if let Some(input) = translate(key) {
                    session.handle(input);
                }
            }
            // Bracketed paste must never execute pasted Ex commands.
            Event::Paste(text) if session.editor().mode() == Mode::Insert => {
                session.apply(vec![Effect::Insert(text)]);
            }
            _ => {}
        }
    }
    Ok(())
}

fn translate(key: KeyEvent) -> Option<Input> {
    if key
        .modifiers
        .intersects(KeyModifiers::ALT | KeyModifiers::SUPER)
    {
        return None;
    }
    Some(match key.code {
        KeyCode::Char(c) if key.modifiers.contains(KeyModifiers::CONTROL) => Input::Ctrl(c),
        KeyCode::Char(c) => Input::Char(c),
        KeyCode::Esc => Input::Escape,
        KeyCode::Enter => Input::Enter,
        KeyCode::Backspace => Input::Backspace,
        KeyCode::Delete => Input::Delete,
        KeyCode::Left => Input::Left,
        KeyCode::Right => Input::Right,
        KeyCode::Up => Input::Up,
        KeyCode::Down => Input::Down,
        KeyCode::Home => Input::Home,
        KeyCode::End => Input::End,
        KeyCode::Tab => Input::Char('\t'),
        _ => return None,
    })
}

fn display_column(line: &str, grapheme_column: usize) -> usize {
    line.graphemes(true)
        .take(grapheme_column)
        .fold(0, |column, grapheme| {
            column
                + if grapheme == "\t" {
                    TAB_WIDTH - column % TAB_WIDTH
                } else {
                    UnicodeWidthStr::width(grapheme)
                }
        })
}

fn visible_line(line: &str, left: usize, width: usize) -> String {
    let mut visible = String::new();
    let mut column = 0;
    let right = left.saturating_add(width);
    for grapheme in line.graphemes(true) {
        let cells = if grapheme == "\t" {
            TAB_WIDTH - column % TAB_WIDTH
        } else {
            UnicodeWidthStr::width(grapheme)
        };
        let end = column + cells;
        if column >= right {
            break;
        }
        if end > left || (cells == 0 && column >= left) {
            if grapheme == "\t" || column < left || end > right {
                for _ in column.max(left)..end.min(right) {
                    visible.push(' ');
                }
            } else {
                visible.push_str(grapheme);
            }
        }
        column = end;
    }
    visible
}

fn draw(frame: &mut Frame, editor: &Editor, top: &mut usize, left: &mut usize) {
    let area = frame.area();
    if area.width == 0 || area.height < 3 {
        return;
    }
    let height = usize::from(area.height - 2);
    let width = usize::from(area.width);
    let cursor = editor.cursor();
    if cursor.row < *top {
        *top = cursor.row;
    } else if cursor.row >= top.saturating_add(height) {
        *top = cursor.row + 1 - height;
    }
    let column = display_column(&editor.lines()[cursor.row], cursor.column);
    if column < *left {
        *left = column;
    } else if column >= left.saturating_add(width) {
        *left = column + 1 - width;
    }
    let lines: Vec<Line> = editor
        .lines()
        .iter()
        .skip(*top)
        .take(height)
        .map(|line| Line::from(visible_line(line, *left, width)))
        .collect();
    frame.render_widget(
        Paragraph::new(lines),
        Rect::new(area.x, area.y, area.width, area.height - 2),
    );
    let path = editor
        .path()
        .map(|p| p.to_string_lossy().into_owned())
        .unwrap_or_else(|| "[No Name]".into());
    let path: String = path
        .chars()
        .map(|c| if c.is_control() { '�' } else { c })
        .collect();
    let status = format!(
        " {}  {}{}  {}:{}",
        editor.mode(),
        path,
        if editor.dirty() { " [+]" } else { "" },
        cursor.row + 1,
        cursor.column + 1
    );
    frame.render_widget(
        Paragraph::new(status).style(Style::default().fg(Color::Black).bg(Color::Cyan)),
        Rect::new(area.x, area.y + area.height - 2, area.width, 1),
    );
    let bottom = area.y + area.height - 1;
    if editor.mode() == Mode::Command {
        let command = format!(":{}", editor.command_line());
        let command_width = UnicodeWidthStr::width(command.as_str());
        let offset = command_width.saturating_sub(width - 1);
        frame.render_widget(
            Paragraph::new(visible_line(&command, offset, width)),
            Rect::new(area.x, bottom, area.width, 1),
        );
        frame.set_cursor_position((area.x + (command_width - offset) as u16, bottom));
    } else {
        frame.render_widget(
            Paragraph::new(editor.message()),
            Rect::new(area.x, bottom, area.width, 1),
        );
        frame.set_cursor_position((
            area.x + (column - *left) as u16,
            area.y + (cursor.row - *top) as u16,
        ));
    }
}

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

    #[test]
    fn tabs_and_wide_graphemes_scroll_in_terminal_cells() {
        let text = "a\t界e\u{301}z";
        assert_eq!(display_column(text, 4), 7);
        assert_eq!(visible_line(text, 2, 5), "  界e\u{301}");
        assert_eq!(visible_line(text, 5, 2), " e\u{301}");
    }
}