/*
 * 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::{ffi::OsString, fs::OpenOptions, io::Write, path::PathBuf, sync::Arc};

use crossbeam_channel::Sender;
use crossterm::{
    cursor,
    event::{Event, KeyCode, KeyEvent},
    terminal, QueueableCommand, Result,
};
use parking_lot::Mutex;
use ropey::Rope;

use crate::{
    buffer::Buffer,
    config::{Config, ThemeWatcher},
    keybinds::{Key, Keybind},
    theme::{StyleStore, StyledString},
    Cursor, Direction,
};

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

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

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

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,
        }
    }
}

pub struct Rect {
    pub position: (usize, usize),
    pub size: (usize, usize),
}

pub struct Window {
    pub rect: Rect,
    pub contents: Vec<StyledString>,
}

impl Window {
    pub fn draw(
        &self,
        out: &mut impl QueueableCommand,
        styles: &mut StyleStore,
    ) -> crossterm::Result<()> {
        let x = self.rect.position.0 as u16;
        let base = *styles.get_scope("ui.window");
        let width = self.rect.size.0;
        let clip = 0..width;
        let padding: String = std::iter::repeat(' ').take(width).collect();
        for row in 0..self.rect.size.1 {
            let y = self.rect.position.1 as u16 + row as u16;
            out.queue(cursor::MoveTo(x, y))?;

            let remaining = if let Some(line) = self.contents.get(row) {
                line.print_sub(out, clip.clone(), base)?
            } else {
                width
            };

            let padding = &padding[0..remaining];
            base.print_styled(out, padding)?;
        }

        Ok(())
    }
}

pub struct State {
    pub styles: Arc<Mutex<StyleStore>>,
    pub config: Config,
    pub buffer: Buffer,
    pub undo_buffers: Vec<Buffer>,
    pub redo_buffers: Vec<Buffer>,
    pub cursor: Cursor,
    pub file: Option<OsString>,
    pub window: Option<Window>,
    pub mode: Mode,
    pub submode: Option<Key>,
    pub last_saved: Rope,
    pub scroll: Cursor,
    pub size: (usize, usize),
    pub quit: bool,
    pub error: Option<String>,
    pub theme_tx: Sender<PathBuf>,
}

impl State {
    pub fn from_str(file_name: Option<OsString>, text: &str) -> Result<Self> {
        let styles = Arc::new(Mutex::new(StyleStore::default()));
        let buffer = Buffer::from_str(styles.clone(), text);
        let last_saved = buffer.as_ref().clone();
        let (cols, rows) = terminal::size()?;
        let theme_tx = ThemeWatcher::spawn(styles.clone());

        Ok(Self {
            styles,
            config: Default::default(),
            buffer,
            undo_buffers: Vec::new(),
            redo_buffers: Vec::new(),
            cursor: Cursor::default(),
            file: file_name,
            mode: Mode::default(),
            submode: None,
            last_saved,
            scroll: Cursor::default(),
            size: (cols as usize, rows as usize),
            quit: false,
            error: None,
            theme_tx,
            window: None,
        })
    }

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

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

        if let Mode::Command(CommandState { buf, cursor }) = &self.mode {
            let col = *cursor as u16 + 1;
            let row = rows - 1;
            out.queue(cursor::MoveTo(0, row))?;
            write!(out, ":{}", buf)?;
            set_cursor_pos = Some((col, row));
            show_status_bar = true;
        } else if let Some(error) = self.error.as_ref() {
            let error_style = styles.get_scope("error");
            out.queue(cursor::MoveTo(0, rows - 1))?;
            error_style.print_styled(out, error)?;
            show_status_bar = true;
        }

        // done with styles
        drop(styles);

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

        // draw submode
        if let Some(submode) = self.submode {
            out.queue(cursor::MoveTo(cols - 10, rows - 1))?;
            write!(out, "{:?}", submode)?;
        }

        // draw open window
        if let Some(window) = self.window.as_ref() {
            let mut styles = self.styles.lock();
            window.draw(out, &mut styles)?;
        }

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

        // finish update
        out.queue(terminal::EndSynchronizedUpdate)?;
        out.flush()?;

        Ok(())
    }

    /// Sets the current error message.
    pub fn set_error(&mut self, error: impl ToString) {
        self.error = Some(error.to_string());
    }

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

        // close open window
        self.window.take();

        match event {
            Event::Resize(cols, rows) => {
                self.size = (cols as usize, rows as usize);
            }
            Event::Key(KeyEvent { code, .. }) => match &self.mode {
                Mode::Normal | Mode::Visual => {
                    self.on_key(code);
                }
                Mode::Command(state) => self.on_command_key(code, state.clone()),
                Mode::Insert(_) => {
                    if !self.on_key(code) {
                        if let KeyCode::Char(c) = code {
                            self.buffer.insert_char(self.cursor, c);
                            self.move_cursor(Direction::Right);
                        }
                    }
                }
            },
            _ => {}
        }
    }

    fn on_command_key(&mut self, code: KeyCode, mut state: CommandState) {
        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 _ = self
                    .execute_command(&state.buf)
                    .map_err(|err| self.set_error(err));
                self.mode = Mode::Normal;
                return;
            }
            KeyCode::Esc => {
                self.mode = Mode::default();
                return;
            }
            _ => {}
        }

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

    /// Processes a key press event.
    ///
    /// Returns `true` if the key was handled by a keybind, `false` otherwise.
    fn on_key(&mut self, key: Key) -> bool {
        let keybinds = match &self.mode {
            Mode::Normal => &self.config.keybinds.normal,
            Mode::Insert(_) => &self.config.keybinds.insert,
            Mode::Visual => &self.config.keybinds.visual,
            Mode::Command(_) => return false, // command mode is handled in [on_command_event]
        };

        if let Some(submode) = self.submode {
            // if we're currently in a submode, try to run this submode's keybind
            keybinds
                .submodes
                .get(&submode)
                .and_then(|submode| submode.get(&key))
                .cloned()
                .map(|keybind| self.execute_keybind(keybind));
            // whether or not there is a keybind we exit the submode
            self.submode = None;
        } else if keybinds.submodes.contains_key(&key) {
            // enter a submode if available
            self.submode = Some(key);
        } else if let Some(keybind) = keybinds.map.get(&key) {
            // run the keybind if available
            self.execute_keybind(keybind.clone());
        } else {
            // key is not bound; don't handle
            return false;
        }

        true
    }

    fn write_buffer(&mut self, file: OsString) -> Result<()> {
        self.last_saved = self.buffer.as_ref().clone();
        let out = self.buffer.as_ref().bytes().collect::<Vec<u8>>();
        let mut handle = OpenOptions::new()
            .create(true)
            .truncate(true)
            .write(true)
            .open(file)?;

        handle.write_all(out.as_slice())?;
        Ok(())
    }

    fn write_command(&mut self, command: &str, args: &[&str]) -> std::result::Result<(), String> {
        let handle = match self.file.clone() {
            Some(handle) => handle,
            None => match args.get(0) {
                Some(part) => {
                    let file = OsString::from(part);
                    self.file = Some(file.clone());
                    file
                }
                None => {
                    return Err(format!("{}: No file name.", command));
                }
            },
        };

        self.write_buffer(handle).map_err(|err| format!("{}", err))
    }

    fn execute_keybind(&mut self, keybind: Keybind) {
        match keybind {
            Keybind::Action(action) => action(self),
            Keybind::Command(command) => {
                let _ = self
                    .execute_command(&command)
                    .map_err(|err| self.set_error(err));
                self.mode = Mode::Normal;
                return;
            }
        }
    }

    fn execute_command(&mut self, command: &str) -> std::result::Result<(), String> {
        let command_parts = command.split(' ').collect::<Vec<&str>>();

        let command = match command_parts.get(0) {
            Some(command) => command,
            None => return Ok(()),
        };

        let args = &command_parts[1..];

        match *command {
            "q!" => self.quit = true,
            "q" => {
                if self.last_saved == *self.buffer.as_ref() {
                    self.quit = true;
                } else {
                    return Err("Buffer is unsaved (add ! to override)".into());
                }
            }
            "w" => return self.write_command(command, args),
            "wq" => {
                self.write_command(command, args)?;
                self.quit = true;
            }
            command => match command.parse::<usize>() {
                Err(_) => return Err(format!("{}: Unrecognized command.", command)),
                Ok(line) if line >= self.buffer.as_ref().len_lines() => {
                    return Err(format!("Line {} is out-of-bounds", line))
                }
                Ok(line) => {
                    self.cursor.line = line;
                    self.scroll_to_cursor();
                }
            },
        }

        Ok(())
    }

    pub fn move_cursor(&mut self, direction: Direction) {
        let wrap = self.config.move_linewrap;
        self.buffer.move_cursor(&mut self.cursor, direction, wrap);
        self.scroll_to_cursor();
    }

    pub fn scroll_to_cursor(&mut self) {
        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;
        }
    }

    /// If modified, saves the current buffer in undo history and clears the redo history.
    pub fn save_buffer(&mut self) {
        /*if let Some(last) = self.undo_buffers.last() {
            if *last.as_ref() == *self.buffer.as_ref() {
                return;
            }
        }*/

        let current = self.buffer.clone();
        self.undo_buffers.push(current);
        self.redo_buffers.clear();
    }

    /// Pops the last undo state from the history and pushes the current state to the redo buffers.
    pub fn undo(&mut self) {
        match self.undo_buffers.pop() {
            None => self.set_error("Already at oldest change"),
            Some(last) => {
                let current = std::mem::replace(&mut self.buffer, last);
                self.redo_buffers.push(current);
            }
        }
    }

    /// Pops the next redo state from the history and pushes the current state to the undo buffers.
    pub fn redo(&mut self) {
        match self.redo_buffers.pop() {
            None => self.set_error("Already at newest change"),
            Some(next) => {
                let current = std::mem::replace(&mut self.buffer, next);
                self.undo_buffers.push(current);
            }
        }
    }
}