//! Editor functionality
use crate::helpers::*;

use std::cmp::PartialEq;
use std::fs::File;
use std::io;
use std::io::prelude::*;
use std::io::BufReader;
use std::string::ToString;

use self::EditorKey::*;

const KILO_TAB_STOP: usize = 4;

/// A representation of a line in the editor
#[derive(Debug, Default)]
pub struct EditorRow {
    chars: String,
    render: String,
}

impl EditorRow {
    pub fn new(chars: &str) -> Self {
        let mut instance = EditorRow::default();
        instance.chars = chars.to_owned();

        instance
    }
}

/// Main structure for the editor
/// `EditorConfig` struct in C version
#[derive(Debug, Default)]
pub struct Editor {
    cursor_x: usize,
    cursor_y: usize,
    render_x: usize,
    col_offset: usize,
    row_offset: usize,
    screen_cols: usize,
    screen_rows: usize,
    rows: Vec<EditorRow>,
    filename: String,
    output_buffer: String,
}

/// Keycode mapping enum
#[derive(Copy, Clone, Debug, PartialEq)]
pub enum EditorKey<T> {
    Escape,
    ArrowLeft,
    ArrowRight,
    ArrowUp,
    ArrowDown,
    DeleteKey,
    HomeKey,
    EndKey,
    PageUp,
    PageDown,
    /// Function keys (F1, etc.) T holds the index
    Function(T),
    /// Any other type of character
    OtherKey(T),
}

impl EditorKey<char> {
    pub fn unwrap(self) -> char {
        match self {
            self::OtherKey(val) => val,
            _ => panic!("called `EditorKey::unwrap()` on a `None` value"),
        }
    }
}

impl Editor {
    // ------------------------------------------------------------------------
    // Init
    // ------------------------------------------------------------------------

    pub fn new() -> Self {
        let mut instance = Self::default();
        let size = instance.get_window_size();
        instance.rows = vec![];
        instance.cursor_x = 0;
        instance.cursor_y = 0;
        instance.screen_cols = size.cols as usize;
        instance.screen_rows = (size.rows - 1) as usize;

        instance
    }

    // ------------------------------------------------------------------------
    // Terminal
    // ------------------------------------------------------------------------

    fn read_key(&mut self) -> Option<EditorKey<char>> {
        let stdin = io::stdin();
        let stdin = stdin.lock();
        let mut in_str = String::new();
        let mut buffer = BufReader::with_capacity(4, stdin);
        buffer.read_to_string(&mut in_str).unwrap();

        let mut input: Vec<EditorKey<char>> = vec![];

        for char in in_str.chars() {
            input.push(match char {
                '\x1b' => Escape,
                _ => OtherKey(char),
            });
        }

        if input.is_empty() {
            return None;
        }

        if input[0].eq(&Escape) {
            match input.len() {
                5 => {
                    // Escape code of the form `^[[NM~`
                    if input[4].eq(&OtherKey('~')) {
                        let action = match (input[2].unwrap(), input[3].unwrap()) {
                            ('1', '5') => Function('5'),
                            ('1', '7') => Function('6'),
                            ('1', '8') => Function('7'),
                            ('1', '9') => Function('8'),
                            ('2', '0') => Function('9'),
                            ('2', '1') => Function('X'), // F10
                            ('2', '4') => Function('T'), // F12
                            _ => Escape,
                        };

                        return Some(action);
                    }
                }
                4 => {
                    // Escape code of the form `^[[N~`
                    if input[3].eq(&OtherKey('~')) {
                        let action = match input[2].unwrap() {
                            '1' => HomeKey,
                            '3' => DeleteKey,
                            '4' => EndKey,
                            '5' => PageUp,
                            '6' => PageDown,
                            '7' => HomeKey,
                            '8' => EndKey,
                            _ => input[2], // Escape,
                        };

                        return Some(action);
                    }
                }
                3 => {
                    match input[1] {
                        // Escape code of the form `^[[X`
                        OtherKey('[') => {
                            let action = match input[2].unwrap() {
                                'A' => ArrowUp,
                                'B' => ArrowDown,
                                'C' => ArrowRight,
                                'D' => ArrowLeft,
                                'H' => HomeKey,
                                'F' => EndKey,

                                // Eh, just return escape otherwise
                                _ => input[2], //Escape,
                            };

                            return Some(action);
                        }
                        // Escape code of the form `^[OX`
                        OtherKey('O') => {
                            let action = match input[2].unwrap() {
                                'H' => HomeKey,
                                'F' => EndKey,
                                'P' => Function('1'),
                                'Q' => Function('2'),
                                'R' => Function('3'),
                                'S' => Function('4'),
                                _ => input[2], //Escape,
                            };

                            return Some(action);
                        }
                        _ => return Some(input[1]),
                    }
                }
                _ => return Some(input[0]),
            }
        }

        // If the character doesn't match any escape sequences, just
        // pass that character on
        return Some(input[0]);
    }

    fn get_window_size(&mut self) -> TermSize {
        match get_term_size() {
            Some(size) => size,
            None => unimplemented!("The easy way usually works"),
        }
    }

    // ------------------------------------------------------------------------
    // Input
    // ------------------------------------------------------------------------

    fn move_cursor(&mut self, key: &EditorKey<char>) {
        let row = self.rows.get(self.cursor_y);
        match key {
            ArrowLeft => {
                if self.cursor_x != 0 {
                    // Move cursor left
                    self.cursor_x -= 1;
                } else if self.cursor_y > 0 {
                    // Move to the end of the previous line
                    self.cursor_y -= 1;
                    self.cursor_x = self.rows[self.cursor_y].chars.len();
                }
            }
            ArrowRight => {
                if row.is_some() && self.cursor_x < row.unwrap().chars.len() {
                    // Move cursor right
                    self.cursor_x += 1;
                } else if row.is_some() && self.cursor_x == row.unwrap().chars.len() {
                    // Move to start of next line
                    self.cursor_y += 1;
                    self.cursor_x = 0;
                }
            }
            ArrowUp => {
                if self.cursor_y > 0 {
                    self.cursor_y -= 1;
                }
            }
            ArrowDown => {
                if self.cursor_y < self.rows.len() {
                    self.cursor_y += 1;
                }
            }
            _ => (),
        };

        let row = self.rows.get(self.cursor_y);
        let row_len = if row.is_some() {
            row.unwrap().chars.len()
        } else {
            0
        };

        // Snap to end of line when scrolling down
        if self.cursor_x > row_len {
            self.cursor_x = row_len;
        }
    }

    /// Route user input to the appropriate handler method
    pub fn process_keypress(&mut self) -> Option<EditorKey<char>> {
        let key = self.read_key();
        if key.is_some() {
            let char = key.unwrap();
            match char {
                OtherKey(c) => {
                    if c == ctrl_key('q') {
                        print!("\x1b[2J");
                        print!("\x1b[H");
                        // Break out of the input loop
                        return None;
                    }
                }
                DeleteKey => (),
                Escape => (),
                ArrowUp => self.move_cursor(&ArrowUp),
                ArrowDown => self.move_cursor(&ArrowDown),
                ArrowLeft => self.move_cursor(&ArrowLeft),
                ArrowRight => self.move_cursor(&ArrowRight),
                PageUp => self.page_up_or_down(PageUp),
                PageDown => self.page_up_or_down(PageDown),
                HomeKey => {
                    self.cursor_x = 0;
                }
                EndKey => {
                    if self.cursor_y < self.rows.len() {
                        self.cursor_x = self.rows[self.cursor_y].chars.len();
                    }
                }
                _ => (),
            };

            return key;
        }

        // Continue the main input loop
        Some(OtherKey('\0'))
    }

    fn page_up_or_down(&mut self, key: EditorKey<char>) {
        let mut times = self.screen_rows;

        // Update the cursor position
        match key {
            PageUp => {
                self.cursor_y = self.row_offset;
            }
            PageDown => {
                self.cursor_y = self.row_offset + self.screen_rows - 1;
                if self.cursor_y > self.rows.len() {
                    self.cursor_y = self.rows.len();
                }
            }
            _ => (),
        }

        // Scroll the file up or down
        while times > 1 {
            times -= 1;
            self.move_cursor(match key {
                PageUp => &ArrowUp,
                PageDown => &ArrowDown,
                _ => &OtherKey('\0'),
            })
        }
    }

    // ------------------------------------------------------------------------
    // Output
    // ------------------------------------------------------------------------

    /// Equivalent of the abAppend function
    /// in the original tutorial, just appends
    /// to the `output_buffer` String in the
    /// editor struct.
    fn append_out(&mut self, str: &str) {
        self.output_buffer.push_str(str);
    }

    fn scroll(&mut self) {
        self.render_x = 0;
        if self.cursor_y < self.rows.len() {
            self.render_x = self.row_cx_to_rx(self.cursor_y, self.cursor_x);
        }

        // Vertical scrolling
        if self.cursor_y < self.row_offset {
            self.row_offset = self.cursor_y;
        }
        if self.cursor_y >= self.row_offset + self.screen_rows {
            self.row_offset = self.cursor_y - self.screen_rows + 1;
        }

        // Horizontal scrolling
        if self.render_x < self.col_offset {
            self.col_offset = self.render_x;
        }
        if self.render_x >= self.col_offset + self.screen_cols {
            self.col_offset = self.render_x - self.screen_cols + 1;
        }
    }

    fn draw_rows(&mut self) {
        for y in 0..self.screen_rows {
            let file_row = y + self.row_offset;
            if file_row >= self.rows.len() {
                if self.rows.is_empty() && y == (self.screen_rows / 3) {
                    let mut welcome = format!(
                        "Oxidized Kilo editor -- version {}",
                        env!("CARGO_PKG_VERSION")
                    );
                    if welcome.len() > self.screen_cols {
                        welcome.truncate(self.screen_cols)
                    }

                    // Center welcome message
                    let mut padding = (self.screen_cols - welcome.len()) / 2;
                    if padding > 0 {
                        self.append_out("~");
                        padding -= 1;
                    }
                    for _ in 0..padding {
                        self.append_out(" ");
                    }

                    self.append_out(&welcome);
                } else {
                    self.append_out("~");
                }
            } else {
                let mut len = self.rows[file_row].render.len() - self.col_offset;
                if len > self.screen_cols {
                    len = self.screen_cols;
                }

                let output = self.rows[file_row].render.clone();
                // let mut output = self.rows[file_row].render.clone();
                // output.truncate(len);
                self.append_out(&output[self.col_offset..len]);
            }

            self.append_out("\x1b[K");
            self.append_out("\r\n");
        }
    }

    fn draw_status_bar(&mut self) {
        self.append_out("\x1b[7m");

        let filename = if self.filename.is_empty() {
            "[No Name]"
        } else {
            &self.filename
        };

        let mut message = format!("{:.20} - {} lines", filename, self.rows.len());
        let mut len = message.len();
        if len > self.screen_cols {
            len = self.screen_cols;
            message.truncate(len);
        }
        self.append_out(&message);

        for _ in len..self.screen_cols {
            self.append_out(" ");
        }
        self.append_out("\x1b[m");
    }

    pub fn refresh_screen(&mut self) -> io::Result<()> {
        self.scroll();
        self.output_buffer.clear();

        //  Hide cursor, reposition cursor
        self.append_out("\x1b[?25l");
        self.append_out("\x1b[H");

        self.draw_rows();
        self.draw_status_bar();

        // Move cursor to state position
        let y = (self.cursor_y - self.row_offset) + 1;
        let x = (self.render_x - self.col_offset) + 1;
        let cursor_code = format!("\x1b[{y};{x}H", y=y, x=x);
        self.append_out(&cursor_code);

        // Show cursor
        self.append_out("\x1b[?25h");

        let stdout = io::stdout();
        let mut handle = stdout.lock();
        handle.write_all(&self.output_buffer.as_bytes())
    }

    // ------------------------------------------------------------------------
    // Row Operations
    // ------------------------------------------------------------------------

    fn row_cx_to_rx(&mut self, index: usize, cx: usize) -> usize {
        let mut rx: usize = 0;
        let row = &mut self.rows[index];

        for char in row.chars.chars() {
            if char == '\t' {
                rx += (KILO_TAB_STOP - 1) - (rx % KILO_TAB_STOP);
            }
            rx += 1;
        }

        rx
    }

    fn update_row(&mut self, index: usize) {
        let row = &mut self.rows[index];
        let str = row.chars.clone();

        // Cheat at rendering tabs as spaces
        let str = str.replace('\t', "    ");
        row.render = str;
    }

    fn append_row(&mut self, row: &str) {
        self.rows.push(EditorRow::new(row));
        self.update_row(self.rows.len() - 1);
    }

    // ------------------------------------------------------------------------
    // File I/O
    // ------------------------------------------------------------------------

    /// Open a file for display
    pub fn open(&mut self, filename: &str) -> io::Result<()> {
        self.filename = filename.to_owned();
        let file = File::open(&self.filename)?;
        let buf_reader = BufReader::new(file);

        let lines = buf_reader.lines().map(|l| l.unwrap());

        for line in lines {
            self.append_row(&line);
        }

        Ok(())
    }
}