/* 
 * Copyright (c) 2023 Marceline Cramer
 * 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::io::{stdin, stdout, Read, Write};

use crossterm::{cursor, event, terminal, ExecutableCommand, Result};
use event::{Event, KeyCode, KeyEvent};
use ropey::Rope;

struct Buffer {
    pub text: Rope,
}

impl Buffer {
    pub fn from_str(text: &str) -> Self {
        Self {
            text: Rope::from_str(text),
        }
    }

    pub fn draw(&self, out: &mut (impl ExecutableCommand + Write)) -> Result<u32> {
        let (cols, rows) = terminal::size()?;
        let lr_width = self.text.len_lines().ilog10() + 1;

        out.execute(cursor::MoveTo(0, 0))?;

        for (row, line) in (0..rows).zip(self.text.lines()) {
            write!(out, "{:width$} ", row, width = lr_width as usize)?;
            write!(out, "{}", line.as_str().unwrap_or("").trim_end())?;
            out.execute(cursor::MoveToNextLine(1))?;
        }

        Ok(lr_width + 1)
    }

    pub fn clamped_cursor(&self, cursor: Cursor) -> Cursor {
        Cursor {
            line: cursor.line,
            column: cursor
                .column
                .min(self.text.line(cursor.line).len_chars() - 1),
        }
    }

    pub fn cursor_to_char(&self, cursor: Cursor) -> usize {
        let cursor = self.clamped_cursor(cursor);
        self.text.line_to_char(cursor.line) + cursor.column
    }

    pub fn move_cursor(&self, cursor: &mut Cursor, direction: Direction, enable_linewrap: bool) {
        *cursor = self.clamped_cursor(*cursor);
        match direction {
            Direction::Left => {
                if cursor.column > 0 {
                    cursor.column -= 1;
                } else if enable_linewrap && cursor.line > 0 {
                    cursor.line -= 1;
                    let line = self.text.line(cursor.line);
                    cursor.column = line.len_chars() - 1;
                }
            }
            Direction::Down => {
                if cursor.line < self.text.len_lines() {
                    cursor.line += 1;
                }
            }
            Direction::Up => {
                if cursor.line > 0 {
                    cursor.line -= 1;
                }
            }
            Direction::Right => {
                let line = self.text.line(cursor.line);
                if cursor.column + 2 > line.len_chars() {
                    if enable_linewrap && cursor.line < self.text.len_lines() {
                        cursor.line += 1;
                        cursor.column = 0;
                    }
                } else {
                    cursor.column += 1;
                }
            }
        }
    }
}

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

#[derive(Copy, Clone, Debug, Default)]
enum Mode {
    #[default]
    Normal,
    Command,
    Visual,
    Insert,
}

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)]
enum Direction {
    Left,
    Down,
    Up,
    Right,
}

struct State {
    pub buffer: Buffer,
    pub cursor: Cursor,
    pub mode: Mode,
    pub quit: bool,
}

impl State {
    pub fn from_str(text: &str) -> Self {
        Self {
            buffer: Buffer::from_str(text),
            cursor: Cursor::default(),
            mode: Mode::default(),
            quit: false,
        }
    }

    pub fn draw(&self, out: &mut impl Write) -> Result<()> {
        out.execute(terminal::BeginSynchronizedUpdate)?;
        out.execute(terminal::Clear(terminal::ClearType::All))?;
        let lr_width = self.buffer.draw(out)?;
        let cursor = self.buffer.clamped_cursor(self.cursor);
        let (col, row) = (cursor.column as u16, cursor.line as u16);
        let col = col + lr_width as u16;
        out.execute(cursor::MoveTo(col, row))?;
        out.execute(self.mode.cursor_style())?;
        out.execute(terminal::EndSynchronizedUpdate)?;
        Ok(())
    }

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

    fn on_normal_event(&mut self, event: Event) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Char('i') => {
                    self.mode = Mode::Insert;
                }
                KeyCode::Char(':') => {
                    self.mode = Mode::Command;
                }
                KeyCode::Char('v') => {
                    self.mode = Mode::Visual;
                }
                KeyCode::Esc => {
                    self.quit = true;
                }
                code => self.match_any_key(code),
            },
            _ => {}
        }
    }

    fn on_command_event(&mut self, event: Event) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Esc => {
                    self.mode = Mode::Normal;
                }
                code => self.match_any_key(code),
            },
            _ => {}
        }
    }

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

    fn on_insert_event(&mut self, event: Event) {
        match event {
            Event::Key(KeyEvent { code, .. }) => match code {
                KeyCode::Char(c) => {
                    let index = self.buffer.cursor_to_char(self.cursor);
                    self.buffer.text.insert_char(index, c);
                    self.move_cursor(Direction::Right)
                }
                KeyCode::Backspace => {
                    self.move_cursor(Direction::Left);
                    let index = self.buffer.cursor_to_char(self.cursor);
                    self.buffer.text.remove(index..=index);
                }
                KeyCode::Delete => {
                    let index = self.buffer.cursor_to_char(self.cursor);
                    self.buffer.text.remove(index..=index);
                }
                KeyCode::Enter => {
                    let index = self.buffer.cursor_to_char(self.cursor);
                    self.buffer.text.insert_char(index, '\n');
                    self.cursor.line += 1;
                    self.cursor.column = 0;
                }
                KeyCode::Esc => {
                    self.mode = Mode::Normal;
                }
                code => self.match_any_key(code),
            },
            _ => {}
        }
    }

    fn match_any_key(&mut self, code: KeyCode) {
        match code {
            KeyCode::Esc => self.mode = Mode::Normal,
            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 move_cursor(&mut self, direction: Direction) {
        self.buffer.move_cursor(&mut self.cursor, direction, true);
    }
}

fn main() -> Result<()> {
    let text = include_str!("main.rs");
    let mut state = State::from_str(text);
    let mut stdout = stdout();
    terminal::enable_raw_mode()?;
    stdout.execute(terminal::EnterAlternateScreen)?;

    while !state.quit {
        state.draw(&mut stdout)?;
        let event = event::read()?;
        state.on_event(event);
    }

    stdout.execute(terminal::LeaveAlternateScreen)?;
    Ok(())
}