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//! The terminal itself: raw mode, the alternate screen, and the diff that
//! turns a grid of cells into the fewest escape sequences that will do.
//!
//! Everything above this file paints into a [`Screen`] and never writes a byte,
//! which is what makes the widget layer testable. This is the one place that
//! knows a TTY exists, and it is behind the `terminal` feature so a build for a
//! machine with no terminal crate at all still has the tree and the layout.

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

use crossterm::event::{
    DisableMouseCapture, EnableMouseCapture, Event, KeyEventKind, MouseButton, MouseEventKind,
};
use crossterm::event::{
    KeyboardEnhancementFlags, PopKeyboardEnhancementFlags, PushKeyboardEnhancementFlags,
};
use crossterm::terminal::supports_keyboard_enhancement;
use crossterm::terminal::{
    disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen,
};
use crossterm::{cursor, execute, queue, style};

use crate::graphics::{self, Graphics, Placement};
use crate::keys;
use crate::screen::{attr, Color, Screen, Style};

/// How far one notch of the wheel moves a list, in rows.
const WHEEL_ROWS: i32 = 3;

/// One thing that happened, in the vocabulary [`crate::ui::Ui`] takes.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Input {
    Key(String),
    Click(u16, u16),
    Wheel(u16, u16, i32),
    Resize(u16, u16),
}

pub struct Term {
    out: Stdout,
    /// What is on the screen now, so a frame only sends what changed.
    last: Screen,
    mouse: bool,
    /// The pictures the terminal has been given, and where they are.
    graphics: Graphics,
    /// Whether the keyboard protocol was pushed, and so has to be popped.
    enhanced: bool,
}

impl Term {
    /// Take the terminal: raw mode, the alternate screen, mouse reporting, and
    /// no cursor until a focused entry asks for one.
    pub fn open(mouse: bool) -> io::Result<Self> {
        let (w, h) = crossterm::terminal::size().unwrap_or((80, 24));
        let mut out = io::stdout();
        enable_raw_mode()?;
        execute!(out, EnterAlternateScreen, cursor::Hide)?;
        if mouse {
            execute!(out, EnableMouseCapture)?;
        }
        // Shift+Enter is a newline in the compose bar and Enter sends the
        // line, which a terminal can only tell apart when it is asked to: the
        // legacy encoding gives both of them the same byte. This is the kitty
        // keyboard protocol's first flag and nothing more — the terminals that
        // have it answer the query, and the ones that do not are left as they
        // were, with Alt+Enter and Ctrl+J as the way to break a line there.
        let enhanced = matches!(supports_keyboard_enhancement(), Ok(true));
        if enhanced {
            let _ = execute!(
                out,
                PushKeyboardEnhancementFlags(KeyboardEnhancementFlags::DISAMBIGUATE_ESCAPE_CODES)
            );
        }
        graphics::set_cell(measure_cell());
        Ok(Self {
            out,
            last: Screen::new(w, h),
            mouse,
            enhanced,
            graphics: Graphics::default(),
        })
    }

    pub fn size(&self) -> (u16, u16) {
        crossterm::terminal::size().unwrap_or((80, 24))
    }

    /// Give the terminal back. Called from `tui_close`, and again from a panic
    /// hook — leaving a shell in raw mode with no cursor is the one failure a
    /// TUI must not have.
    pub fn close(&mut self) {
        // The pictures first: a placement is the terminal's, not the screen
        // buffer's, and one left behind outlives the alternate screen it was
        // made on.
        let _ = self.graphics.clear(&mut self.out);
        if self.mouse {
            let _ = execute!(self.out, DisableMouseCapture);
        }
        if self.enhanced {
            let _ = execute!(self.out, PopKeyboardEnhancementFlags);
        }
        let _ = execute!(self.out, cursor::Show, LeaveAlternateScreen);
        let _ = disable_raw_mode();
    }

    /// Wait up to `timeout_ms` for input and answer everything that had
    /// arrived. A zero timeout is a poll.
    pub fn poll(&mut self, timeout_ms: u64) -> Vec<Input> {
        let mut out = Vec::new();
        let deadline = std::time::Duration::from_millis(timeout_ms);
        if !crossterm::event::poll(deadline).unwrap_or(false) {
            return out;
        }
        // Drain what is queued rather than one event a call: a held arrow key
        // or a paste arrives as a burst, and handling one per frame would make
        // the UI lag behind the keyboard.
        loop {
            match crossterm::event::read() {
                Ok(Event::Key(key)) => {
                    // Windows reports both press and release; a release would
                    // type every character twice.
                    if key.kind != KeyEventKind::Release {
                        if let Some(name) = keys::name(key) {
                            out.push(Input::Key(name));
                        }
                    }
                }
                Ok(Event::Resize(w, h)) => out.push(Input::Resize(w, h)),
                Ok(Event::Mouse(mouse)) => match mouse.kind {
                    MouseEventKind::Down(MouseButton::Left) => {
                        out.push(Input::Click(mouse.column, mouse.row))
                    }
                    // Three rows a notch. A terminal reports one event per
                    // detent and a row is the whole of a line here, so a row a
                    // notch is a backlog that takes forty of them to cross a
                    // screen — which reads as a list that will not move rather
                    // than one moving slowly.
                    MouseEventKind::ScrollDown => {
                        out.push(Input::Wheel(mouse.column, mouse.row, WHEEL_ROWS))
                    }
                    MouseEventKind::ScrollUp => {
                        out.push(Input::Wheel(mouse.column, mouse.row, -WHEEL_ROWS))
                    }
                    _ => {}
                },
                Ok(_) => {}
                Err(_) => break,
            }
            if !crossterm::event::poll(std::time::Duration::ZERO).unwrap_or(false) {
                break;
            }
        }
        out
    }

    /// Send whatever differs between `screen` and what is already up there.
    pub fn flush(
        &mut self,
        screen: &Screen,
        cursor: Option<(u16, u16)>,
        images: &[Placement],
    ) -> io::Result<()> {
        if (self.last.width(), self.last.height()) != (screen.width(), screen.height()) {
            self.last = Screen::new(screen.width(), screen.height());
            // A resize is a new cell size as often as not — a font change, a
            // window dragged to another screen — and every picture's size is
            // measured in cells.
            graphics::set_cell(measure_cell());
            queue!(
                self.out,
                crossterm::terminal::Clear(crossterm::terminal::ClearType::All)
            )?;
        }
        let mut style = None;
        let mut at: Option<(u16, u16)> = None;
        let width = screen.width();
        let cells = screen.cells();
        for (i, cell) in cells.iter().enumerate() {
            let (x, y) = ((i as u16) % width, (i as u16) / width);
            let wide = !cell.trail && x + 1 < width && cells.get(i + 1).is_some_and(|c| c.trail);
            // A wide glyph is its two cells together: when only the right
            // half changed, a terminal has lost the whole glyph, so the left
            // half is written again as well.
            let changed = self.last.cell(x, y) != Some(cell)
                || (wide && self.last.cell(x + 1, y) != cells.get(i + 1));
            if !changed {
                continue;
            }
            // The right half of a double-width glyph is not written: the
            // character to its left was drawn across both cells and left the
            // cursor past them. Writing here would put a second copy of
            // whatever follows one column over, and every column after it on
            // that row would be a column out — which is what a mouse click is
            // then aimed at.
            if cell.trail {
                continue;
            }
            if wide {
                // Blank the right half first. Terminals do not agree on how
                // wide `✏️` or `↩️` is — a symbol carrying the emoji selector
                // is two columns in some and one in others — and one that
                // draws it narrow would otherwise leave whatever stood in that
                // column standing beside it.
                if style != Some(cell.style) {
                    write_style(&mut self.out, cell.style)?;
                    style = Some(cell.style);
                }
                queue!(self.out, cursor::MoveTo(x + 1, y), style::Print(' '))?;
                at = None;
            }
            // Only move when the run breaks: a full-width change is one seek
            // and a line of text, not a seek a cell.
            if at != Some((x, y)) {
                queue!(self.out, cursor::MoveTo(x, y))?;
            }
            if style != Some(cell.style) {
                write_style(&mut self.out, cell.style)?;
                style = Some(cell.style);
            }
            // The whole glyph, first character and rest: a terminal handed an
            // arrow without the selector that follows it draws the small mono
            // arrow rather than the emoji.
            let mut glyph = cell.ch.to_string();
            if let Some(tail) = &cell.tail {
                glyph.push_str(tail);
            }
            queue!(self.out, style::Print(&glyph))?;
            // After a wide glyph, where the cursor went is the terminal's
            // opinion rather than ours, so the next cell seeks instead of
            // trusting it.
            at = if wide { None } else { Some((x + 1, y)) };
        }
        queue!(self.out, style::ResetColor)?;
        // The pictures after the text, and before the cursor is put back: a
        // placement is drawn where the cursor is, so it moves the cursor, and
        // whatever the frame decided about the caret has to be the last word.
        let cell = graphics::cell();
        self.graphics.sync(&mut self.out, images, cell)?;
        match cursor {
            Some((x, y)) => queue!(self.out, cursor::MoveTo(x, y), cursor::Show)?,
            None => queue!(self.out, cursor::Hide)?,
        }
        self.out.flush()?;
        self.last = screen.clone();
        Ok(())
    }
}

impl Drop for Term {
    fn drop(&mut self) {
        self.close();
    }
}

fn convert(color: Color) -> style::Color {
    match color {
        Color::Default => style::Color::Reset,
        // The terminal downgrades the 256-colour palette itself, which is the
        // only place that knows how many colours it really has.
        Color::Indexed(i) => style::Color::AnsiValue(i),
        Color::Rgb(r, g, b) => style::Color::Rgb { r, g, b },
    }
}

fn write_style(out: &mut Stdout, style: Style) -> io::Result<()> {
    use style::Attribute;
    queue!(out, style::SetAttribute(Attribute::Reset))?;
    for (bit, on) in [
        (attr::BOLD, Attribute::Bold),
        (attr::DIM, Attribute::Dim),
        (attr::UNDERLINE, Attribute::Underlined),
        (attr::REVERSE, Attribute::Reverse),
        (attr::BLINK, Attribute::SlowBlink),
        (attr::ITALIC, Attribute::Italic),
    ] {
        if style.has(bit) {
            queue!(out, style::SetAttribute(on))?;
        }
    }
    queue!(
        out,
        style::SetForegroundColor(convert(style.fg)),
        style::SetBackgroundColor(convert(style.bg))
    )
}

/// What one cell measures, asked of the terminal.
fn measure_cell() -> (u16, u16) {
    match crossterm::terminal::window_size() {
        Ok(size) => graphics::cell_pixels(size.columns, size.rows, size.width, size.height),
        Err(_) => graphics::cell_pixels(0, 0, 0, 0),
    }
}