/*
 * Copyright (c) 2023 Marceline Cramer
 * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see https://www.gnu.org/licenses/.
 */

use std::{
    env::args,
    fs::File,
    io::{stdout, Read, Stdout, Write},
    os::fd::FromRawFd,
};

use crossterm::{
    cursor,
    event::{read, Event, KeyCode, KeyEvent},
    terminal, ExecutableCommand, Result,
};
use yacexits::{exit, EX_DATAERR, EX_UNAVAILABLE};

mod buffer;
mod theme;

use buffer::Buffer;
use theme::StyleStore;

#[derive(Copy, Clone, Debug, Default)]
pub struct Cursor {
    pub column: usize,
    pub line: usize,
}

#[derive(Clone, Debug, Default)]
struct NormalState {
    pub error: Option<String>,
}

#[derive(Clone, Debug, Default)]
struct CommandState {
    pub buf: String,
    pub cursor: usize,
}

#[derive(Copy, Clone, Debug)]
struct InsertState {
    append: bool,
}

#[derive(Clone, Debug)]
enum Mode {
    Normal(NormalState),
    Command(CommandState),
    Visual,
    Insert(InsertState),
}

impl Default for Mode {
    fn default() -> Self {
        Mode::Normal(Default::default())
    }
}

impl Mode {
    pub fn cursor_style(&self) -> cursor::SetCursorStyle {
        use cursor::SetCursorStyle as Style;
        match self {
            Mode::Normal(_) => Style::SteadyBlock,
            Mode::Visual => Style::BlinkingBlock,
            Mode::Insert(_) => Style::BlinkingBar,
            Mode::Command(_) => Style::SteadyUnderScore,
        }
    }
}

#[derive(Copy, Clone, Debug)]
pub enum Direction {
    Left,
    Down,
    Up,
    Right,
}

struct State {
    pub style_store: StyleStore,
    pub buffer: Buffer,
    pub cursor: Cursor,
    pub scroll: Cursor,
    pub size: (usize, usize),
    pub mode: Mode,
    pub quit: bool,
}

impl State {
    pub fn from_str(text: &str) -> Result<Self> {
        let (cols, rows) = terminal::size()?;

        Ok(Self {
            style_store: StyleStore::default(),
            buffer: Buffer::from_str(text),
            cursor: Cursor::default(),
            scroll: Cursor::default(),
            size: (cols as usize, rows as usize),
            mode: Mode::default(),
            quit: false,
        })
    }

    pub fn draw(&mut self, out: &mut impl Write) -> Result<()> {
        // begin update
        let (cols, rows) = terminal::size()?;
        out.execute(terminal::BeginSynchronizedUpdate)?;
        out.execute(terminal::Clear(terminal::ClearType::All))?;

        // draw status line
        let mut set_cursor_pos = None;
        let mut show_status_bar = false;

        match &self.mode {
            Mode::Command(CommandState { buf, cursor }) => {
                let col = *cursor as u16 + 1;
                let row = rows - 1;
                out.execute(cursor::MoveTo(0, row))?;
                write!(out, ":{}", buf)?;
                set_cursor_pos = Some((col, row));
                show_status_bar = true;
            }
            Mode::Normal(NormalState { error: Some(error) }) => {
                let error_style = self.style_store.get_scope("error");
                out.execute(cursor::MoveTo(0, rows - 1))?;
                error_style.print_styled(out, error)?;
                show_status_bar = true;
            }
            _ => {}
        }

        // draw buffer
        let buffer_rows = if show_status_bar { rows - 1 } else { rows };
        let lr_width =
            self.buffer
                .draw(&mut self.style_store, cols, buffer_rows, self.scroll, out)?;

        // draw cursor
        let cursor_pos = set_cursor_pos.unwrap_or_else(|| {
            // calculate cursor position on buffer
            let cursor = self.buffer.clamped_cursor(self.cursor);
            let col = cursor.column.saturating_sub(self.scroll.column) as u16;
            let row = cursor.line.saturating_sub(self.scroll.line) as u16;
            let col = col + lr_width as u16;
            (col, row)
        });

        out.execute(cursor::MoveTo(cursor_pos.0, cursor_pos.1))?;
        out.execute(self.mode.cursor_style())?;

        // finish update
        out.execute(terminal::EndSynchronizedUpdate)?;
        Ok(())
    }

    pub fn on_event(&mut self, event: Event) {
        match &self.mode {
            Mode::Normal(state) => self.on_normal_event(event, state.clone()),
            Mode::Command(state) => self.on_command_event(event, state.clone()),
            Mode::Visual => self.on_visual_event(event),
            Mode::Insert(state) => self.on_insert_event(event, state.clone()),
        }
    }

    fn on_normal_event(&mut self, event: Event, mut state: NormalState) {
        // reset the error from the last event
        state.error = None;

        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Char('i') => {
                    let state = InsertState { append: false };
                    self.mode = Mode::Insert(state);
                }
                KeyCode::Char('a') => {
                    let state = InsertState { append: true };
                    self.move_cursor(Direction::Right);
                    self.mode = Mode::Insert(state);
                }
                KeyCode::Char('o') => {
                    let state = InsertState { append: false };
                    self.cursor.line += 1;
                    self.cursor.column = 0;
                    self.buffer.insert_char(self.cursor, '\n');
                    self.mode = Mode::Insert(state);
                }
                KeyCode::Char(':') => {
                    self.mode = Mode::Command(Default::default());
                }
                KeyCode::Char('v') => {
                    self.mode = Mode::Visual;
                }
                code => self.on_any_key(code),
            },
            event => self.on_any_event(event),
        }

        match self.mode {
            Mode::Normal(_) => self.mode = Mode::Normal(state),
            _ => {}
        }
    }

    fn on_command_event(&mut self, event: Event, mut state: CommandState) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Char(c) => {
                    state.buf.insert(state.cursor, c);
                    state.cursor += 1;
                }
                KeyCode::Backspace => {
                    if state.cursor > 0 {
                        state.cursor -= 1;
                        state.buf.remove(state.cursor);
                    }
                }
                KeyCode::Delete if state.cursor < state.buf.len() => {
                    state.buf.remove(state.cursor);
                }
                KeyCode::Left if state.cursor > 0 => {
                    state.cursor -= 1;
                }
                KeyCode::Right if state.cursor < state.buf.len() => {
                    state.cursor += 1;
                }
                KeyCode::Enter => {
                    // TODO add to command history
                    let result = self.execute_command(&state.buf);
                    let error = result.err();
                    self.mode = Mode::Normal(NormalState { error });
                    return;
                }
                code => return self.on_any_key(code),
            },
            event => return self.on_any_event(event),
        }

        self.mode = Mode::Command(state);
    }

    fn on_visual_event(&mut self, event: Event) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Esc => {
                    self.mode = Mode::default();
                }
                code => self.on_any_key(code),
            },
            event => self.on_any_event(event),
        }
    }

    fn on_insert_event(&mut self, event: Event, state: InsertState) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Char(c) => {
                    self.buffer.insert_char(self.cursor, c);
                    self.move_cursor(Direction::Right)
                }
                KeyCode::Backspace => {
                    self.move_cursor(Direction::Left);
                    self.buffer.remove(self.cursor);
                }
                KeyCode::Delete => {
                    self.buffer.remove(self.cursor);
                }
                KeyCode::Enter => {
                    self.buffer.insert_char(self.cursor, '\n');
                    self.cursor.line += 1;
                    self.cursor.column = 0;
                }
                KeyCode::Esc => {
                    if state.append {
                        self.move_cursor(Direction::Left);
                    }

                    self.mode = Mode::default();
                }
                code => self.on_any_key(code),
            },
            event => self.on_any_event(event),
        }
    }

    fn on_any_event(&mut self, event: Event) {
        match event {
            Event::Resize(cols, rows) => {
                self.size = (cols as usize, rows as usize);
            }
            Event::Key(KeyEvent { code, .. }) => self.on_any_key(code),
            _ => {}
        }
    }

    fn on_any_key(&mut self, code: KeyCode) {
        match code {
            KeyCode::Esc => self.mode = Mode::default(),
            KeyCode::Char('h') | KeyCode::Left => self.move_cursor(Direction::Left),
            KeyCode::Char('j') | KeyCode::Down => self.move_cursor(Direction::Down),
            KeyCode::Char('k') | KeyCode::Up => self.move_cursor(Direction::Up),
            KeyCode::Char('l') | KeyCode::Right => self.move_cursor(Direction::Right),
            _ => {}
        }
    }

    fn execute_command(&mut self, command: &str) -> std::result::Result<(), String> {
        match command {
            "q" => self.quit = true,
            command => return Err(format!("unrecognized command {:?}", command)),
        }

        Ok(())
    }

    fn move_cursor(&mut self, direction: Direction) {
        self.buffer.move_cursor(&mut self.cursor, direction, true);

        if self.cursor.column < self.scroll.column + 3 {
            self.scroll.column = self.cursor.column.saturating_sub(3);
        } else if self.cursor.column + 6 >= self.scroll.column + self.size.0 {
            self.scroll.column = self.cursor.column.saturating_sub(self.size.0 - 6);
        }

        if self.cursor.line < self.scroll.line {
            self.scroll.line = self.cursor.line;
        } else if self.cursor.line + 3 >= self.scroll.line + self.size.1 {
            self.scroll.line = self.cursor.line + 3 - self.size.1;
        }
    }
}

fn screen_main(stdout: &mut Stdout, mut state: State) -> Result<()> {
    while !state.quit {
        state.draw(stdout)?;
        let event = read()?;
        state.on_event(event);
    }

    Ok(())
}

fn main() -> Result<()> {
    let argv = args().collect::<Vec<String>>();
    let mut buf = Vec::new();

    match argv.get(1).map(|s| s.as_str()) {
        Some("-") | None => {
            let stdin = 0; // get stdin as a file descriptor
            if unsafe { libc::isatty(stdin) } == 0 {
                unsafe { File::from_raw_fd(stdin) }
            } else {
                File::open("/dev/null").unwrap()
            }
        }
        Some(path) => std::fs::File::open(path).unwrap_or_else(|_| {
            eprintln!("{}: {}: No such file or directory.", argv[0], argv[1]);
            exit(EX_UNAVAILABLE);
        }),
    }
    .read_to_end(&mut buf)
    .unwrap();

    let text = String::from_utf8(buf).unwrap_or_else(|_| {
        eprintln!(
            "{}: {}: File contents are not valid UTF-8.",
            argv[0], argv[1]
        );
        exit(EX_DATAERR);
    });

    let state = State::from_str(&text)?;
    let mut stdout = stdout();
    terminal::enable_raw_mode()?;
    stdout.execute(terminal::EnterAlternateScreen)?;
    let result = screen_main(&mut stdout, state);
    stdout.execute(terminal::LeaveAlternateScreen)?;
    terminal::disable_raw_mode()?;
    result
}