extern crate termios;

use rand::seq::SliceRandom;
use nonblock::NonBlockingReader;

const FIELD_COLS: usize = 10;
const FIELD_ROWS_VISIBLE: usize = 20;
const FIELD_ROWS: usize = FIELD_ROWS_VISIBLE + 20;
const FIELD_SIZE: usize = FIELD_COLS * FIELD_ROWS;
const FIGURE_SIZE_COLS: usize = 4;
const FIGURE_SIZE_ROWS: usize = 4;
const FIGURE_SIZE: usize = FIGURE_SIZE_COLS*FIGURE_SIZE_ROWS;
const CELLS_I: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0];
const CELLS_L2:[u8; FIGURE_SIZE] = [0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0];
const CELLS_L: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0];
const CELLS_B: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0];
const CELLS_S: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0];
const CELLS_T: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0];
const CELLS_Z: [u8; FIGURE_SIZE] = [0, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0];
const NEXT_COUNT: usize = 4;
const DISPLAY_NEXT_OFFSET_DOWN: usize = 4;
const DISPLAY_HOLD_OFFSET_DOWN: usize = 4;
const GHOST_MASK: u8 = 8;

enum StepResult {
    StateChanged,
    Quit,
}

#[derive(Clone)]
#[derive(Debug)]
enum FigureKind {
    I,
    J,
    L,
    O,
    S,
    T,
    Z,
}

struct Timeout {
    beginning: nix::sys::time::TimeSpec,
    duration: std::time::Duration,
}

impl Default for Timeout {
    #[inline]
    fn default() -> Self {
        Self {
            beginning: nix::sys::time::TimeSpec::new(0, 0),
            duration: std::time::Duration::default(),
        }
    }
}

impl Timeout {
    fn from_duration(d: std::time::Duration) -> Self {
        Timeout{
            beginning: nix::time::clock_gettime(nix::time::ClockId::CLOCK_MONOTONIC).unwrap(),
            duration: d,
        }
    }
    fn is_elapsed(&self) -> bool {
        std::time::Duration::from(self.beginning) + self.duration <= std::time::Duration::from(nix::time::clock_gettime(nix::time::ClockId::CLOCK_MONOTONIC).unwrap())
    }
}

#[derive(Clone)]
struct Figure {
    kind: FigureKind,
    cells: [u8; FIGURE_SIZE],
}

impl Figure {
    fn from_kind(kind: FigureKind) -> Self {
        match kind {
            FigureKind::I => Self{ cells: CELLS_I, kind },
            FigureKind::J => Self{ cells: CELLS_L2, kind },
            FigureKind::L => Self{ cells: CELLS_L, kind },
            FigureKind::O => Self{ cells: CELLS_B, kind },
            FigureKind::S => Self{ cells: CELLS_S, kind },
            FigureKind::T => Self{ cells: CELLS_T, kind },
            FigureKind::Z => Self{ cells: CELLS_Z, kind },
        }
    }
    fn rotate_cw_4x4(&mut self) {
        let mut tmp: [u8; 4 * 4] = Default::default();
        for y in 0..4 {
            for x in 0..4 {
                tmp[y + (3 - x) * 4] = self.cells[x + y * 4];
            }
        }
        self.cells = tmp;
    }
    fn rotate_cw_3x3(&mut self) {
        let mut tmp: [u8; 3 * 3] = Default::default();
        for y in 0..3 {
            for x in 0..3 {
                tmp[y + (2 - x) * 3] = self.cells[x + y * 4];
            }
        }
        for y in 0..3 {
            for x in 0..3 {
                self.cells[x + y * 4] = tmp[x + y * 3];
            }
        }
    }
    fn rotate(&mut self) {
        match self.kind {
            FigureKind::I => self.rotate_cw_4x4(),
            FigureKind::J => self.rotate_cw_3x3(),
            FigureKind::L => self.rotate_cw_3x3(),
            FigureKind::O => {},
            FigureKind::S => self.rotate_cw_3x3(),
            FigureKind::T => self.rotate_cw_3x3(),
            FigureKind::Z => self.rotate_cw_3x3(),
        }
    }
}

#[derive(Clone)]
struct Field {
    cells: [u8; FIELD_SIZE],
}

impl Default for Field {
    #[inline]
    fn default() -> Self {
        Self { cells: [0; FIELD_SIZE] }
    }
}

impl Field {
    fn render(&mut self, figure: &Figure, x: isize, y: isize) {
        for i in 0..FIGURE_SIZE {
            let f_x = (i % FIGURE_SIZE_COLS) as isize + x;
            let f_y = (i / FIGURE_SIZE_ROWS) as isize + y;
            if f_x < 0 {
                continue;
            } else if f_x >= FIELD_COLS as isize {
                continue;
            } else if f_y < 0 {
                continue;
            } else if f_y >= FIELD_ROWS as isize {
                continue;
            }
            let color = figure.cells[i] & !GHOST_MASK;
            if color != 0 {
                self.cells[f_x as usize + f_y as usize * FIELD_COLS] = figure.cells[i];
            }
        }
    }
    fn has_collision(&self, figure: &Figure, x: isize, y: isize) -> bool {
        for i in 0..FIGURE_SIZE {
            let f_x = (i % FIGURE_SIZE_COLS) as isize + x;
            let f_y = (i / FIGURE_SIZE_ROWS) as isize + y;
            let color = figure.cells[i] & !GHOST_MASK;
            if color != 0 {
                if f_x < 0 {
                    return true;
                } else if f_x >= FIELD_COLS as isize {
                    return true;
                } else if f_y < 0 {
                    return true;
                } else if f_y >= FIELD_ROWS as isize {
                    return true;
                } else {
                    let fcolor = self.cells[f_x as usize + f_y as usize * FIELD_COLS] & !GHOST_MASK;
                    if fcolor != 0 {
                        return true;
                    }
                }
            }
        }
        false
    }
    fn is_line_complete(&self, line: usize) -> bool {
        assert!(line < FIELD_ROWS);
        self.cells[FIELD_COLS * line..][..FIELD_COLS].iter().fold(1, |a, e| a & e) != 0
    }
    fn kill_line(&mut self, line: usize) {
        for row in line..FIELD_ROWS - 1 {
            for col in 0..FIELD_COLS {
                self.cells[col + row * FIELD_COLS] = self.cells[col + (row + 1) * FIELD_COLS];
            }
        }
        for col in 0..FIELD_COLS {
            self.cells[col + (FIELD_ROWS - 1) * FIELD_COLS] = 0;
        }
    }
}

struct Bag {
    index: u8,
    pieces: [u8; 7],
}

impl Bag {
    fn next(&mut self) -> FigureKind {
        if self.index >= 7 {
            self.index = 0;
            self.pieces.shuffle(&mut rand::thread_rng());
        }
        let i = self.index;
        self.index += 1;
        match self.pieces[i as usize] {
            1 => FigureKind::I,
            2 => FigureKind::J,
            3 => FigureKind::L,
            5 => FigureKind::O,
            6 => FigureKind::S,
            4 => FigureKind::T,
            7 => FigureKind::Z,
            _ => unreachable!(),
        }
    }
}

impl Default for Bag {
    #[inline]
    fn default() -> Self {
        let mut pieces: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
        pieces.shuffle(&mut rand::thread_rng());
        Self{
            index: 0,
            pieces
        }
    }
}

struct Game {
    field: Field,
    figure: Figure,
    x: isize,
    y: isize,
    fall_timeout: Timeout,
    place_timeout: Option<Timeout>,
    bag: Bag,
    figure_next: [Figure; NEXT_COUNT],
    figure_on_hold: Figure,
}

impl Default for Game {
    #[inline]
    fn default() -> Self {
        let mut bag = Bag::default();
        let figure_on_hold = Figure::from_kind(bag.next());
        let figure = Figure::from_kind(bag.next());
        let figure_next = [
            Figure::from_kind(bag.next()),
            Figure::from_kind(bag.next()),
            Figure::from_kind(bag.next()),
            Figure::from_kind(bag.next()),
        ];
        Self{
            field: Field::default(),
            figure,
            x: 3,
            y: 17,
            fall_timeout: Timeout::from_duration(std::time::Duration::from_millis(500)),
            place_timeout: None,
            bag,
            figure_next,
            figure_on_hold,
        }
    }
}

impl Game {
    fn place_figure(&mut self) {
        self.field.render(&self.figure, self.x, self.y);
        self.figure = self.figure_next[0].clone();
        for i in 0..NEXT_COUNT - 1 {
            self.figure_next[i] = self.figure_next[i + 1].clone();
        }
        self.figure_next[NEXT_COUNT - 1] = Figure::from_kind(self.bag.next());
        (self.x, self.y) = (3, 17);
        for line in 0..FIELD_ROWS - 1 {
            while self.field.is_line_complete(line) {
                self.field.kill_line(line);
            }
        }
    }
    fn hold_figure(&mut self) {
        (self.figure_on_hold, self.figure) = (Figure::from_kind(self.figure.kind.clone()), self.figure_on_hold.clone());
        (self.x, self.y) = (3, 17);
    }
    fn reset_fall_timeout(&mut self) {
        self.fall_timeout = Timeout::from_duration(std::time::Duration::from_millis(500));
    }
    fn start_place_timeout(&mut self) {
        self.place_timeout = Some(Timeout::from_duration(std::time::Duration::from_millis(500)));
    }
    fn stop_place_timeout(&mut self) {
        self.place_timeout = None
    }
    fn reset_place_timeout(&mut self) {
        if let Some(_) = self.place_timeout {
            self.start_place_timeout();
        }
    }
    fn handle_input(&mut self, c: char) -> Option<StepResult> {
        match c {
            'q' => return Some(StepResult::Quit),
            ' ' => {
                while !self.field.has_collision(&self.figure, self.x, self.y - 1) {
                    self.y -= 1;
                }
                self.place_figure();
                self.stop_place_timeout();
            },
            'j' => {
                if !self.field.has_collision(&self.figure, self.x - 1, self.y) {
                    self.x -= 1;
                }
            }
            'k' => {
                if !self.field.has_collision(&self.figure, self.x, self.y - 1) {
                    self.y -= 1;
                    self.reset_fall_timeout();
                } else {
                    self.start_place_timeout();
                }
            }
            ';' | 'i' => {
                let mut figure = self.figure.clone();
                figure.rotate();
                if !self.field.has_collision(&figure, self.x, self.y) {
                    self.figure.rotate()
                }
            }
            'l' => {
                if !self.field.has_collision(&self.figure, self.x + 1, self.y) {
                    self.x += 1;
                }
            }
            'h' => {
                self.hold_figure();
                self.reset_fall_timeout();
                self.stop_place_timeout();
            }
            _ => {},
        }
        self.reset_place_timeout();
        Some(StepResult::StateChanged)
    }
    fn advance_figure(&mut self) {
        if self.field.has_collision(&self.figure, self.x, self.y - 1) {
            self.place_figure();
        } else {
            self.y -= 1;
        }
        if self.field.has_collision(&self.figure, self.x, self.y - 1) {
            self.start_place_timeout();
        }
        self.reset_fall_timeout();
    }
    fn step(&mut self, c_optional: Option<char>) -> Option<StepResult> {
        let handle_input_result = if let Some(c) = c_optional {
             self.handle_input(c)
        } else {
            None
        };
        let advance_figure_result = if let Some(t) = &self.place_timeout {
            if t.is_elapsed() {
                self.advance_figure();
                Some(StepResult::StateChanged)
            } else {
                None
            }
        } else if self.fall_timeout.is_elapsed() {
            self.advance_figure();
            Some(StepResult::StateChanged)
        } else {
            None
        };
        if let None = handle_input_result {
            advance_figure_result
        } else {
            handle_input_result
        }
    }
}

fn display_hold(figure: &Figure, y_global: usize) {
    let offset = DISPLAY_HOLD_OFFSET_DOWN;
    let at_figure = y_global >= (1 + offset) && y_global < FIGURE_SIZE_ROWS + (1 + offset);
    if y_global == offset {
        print!("   Hold:  ");
    } else if at_figure {
        print!(" ");
        let y = FIGURE_SIZE_ROWS - 1 - (y_global - 1 - offset);
        for x in 0..FIGURE_SIZE_COLS {
            let c = figure.cells[y * FIGURE_SIZE_COLS + x];
            if c == 0 {
                print!("  ");
            } else {
                print!("██");
            }
        }
        print!(" ");
    } else {
        print!("          ");
    }
}

fn display_next(figure: &[Figure; NEXT_COUNT], y_global: usize) {
    let offset = DISPLAY_NEXT_OFFSET_DOWN;
    if y_global == offset {
        print!("   Next:  ");
    } else {
        for i in 0..NEXT_COUNT {
            let at_figure = y_global >= (1 + offset + FIGURE_SIZE_ROWS * i) && y_global < (1 + offset + FIGURE_SIZE_ROWS * (i + 1));
            if at_figure {
                print!(" ");
                let y = FIGURE_SIZE_ROWS - 1 - (y_global - 1 - offset - FIGURE_SIZE_ROWS * i);
                for x in 0..FIGURE_SIZE_COLS {
                    let c = figure[i].cells[y * FIGURE_SIZE_COLS + x];
                    if c == 0 {
                        print!("  ");
                    } else {
                        print!("██");
                    }
                }
                break;
            }
        }
    }
}

fn display_field(field: &Field, y: usize) {
    print!("|");
    for x in 0..FIELD_COLS {
        let color = field.cells[(FIELD_ROWS_VISIBLE - 1 - y) * FIELD_COLS + x] & !GHOST_MASK;
        let ghost = field.cells[(FIELD_ROWS_VISIBLE - 1 - y) * FIELD_COLS + x] & GHOST_MASK != 0;
        if color == 0 {
            print!("  ");
        } else if ghost {
            print!("░░");
        } else {
            print!("██");
        }
    }
    print!("|");
}

fn display_game(game: &Game) {
    cursor_to_home();
    let mut field = game.field.clone();
    let mut ghost = game.figure.clone();
    for i in 0..FIGURE_SIZE {
        ghost.cells[i] |= GHOST_MASK;
    }
    let mut y_ghost = game.y;
    while !field.has_collision(&ghost, game.x, y_ghost) {
        y_ghost -= 1;
    }
    y_ghost += 1;
    field.render(&ghost, game.x, y_ghost);
    field.render(&game.figure, game.x, game.y);
    for y in 0..FIELD_ROWS_VISIBLE {
        display_hold(&game.figure_on_hold, y);
        display_field(&field, y);
        display_next(&game.figure_next, y);
        print!("\r\x1b[1B");
    }
    if game.field.has_collision(&game.figure, game.x, game.y) {
        println!("Collision!");
    } else {
        clear_line();
    }
}

fn clear_screen() {
    print!("\x1B[2J");
}

fn cursor_to_home() {
    print!("\x1B[H");
}

fn clear_line() {
    println!("\x1B[2K");
}

fn main() {
    let termios_state_initial = termios::Termios::from_fd(0).unwrap();
    let mut termios_state = termios_state_initial.clone();
    let c_lflag = termios_state.c_lflag;
    termios_state.c_lflag &= !(termios::ICANON | termios::ECHO);
    termios::tcsetattr(0, termios::TCSADRAIN, &termios_state).unwrap();
    termios_state.c_lflag = c_lflag;
    clear_screen();
    let mut game = Game::default();
    display_game(&game);
    let mut noblock_stdin = NonBlockingReader::from_fd(std::io::stdin()).unwrap();
    'outer: while !noblock_stdin.is_eof() {
        let mut buf = String::new();
        noblock_stdin.read_available_to_string(&mut buf).unwrap();
        let mut changed = false;
        if buf.len() > 0 {
            for c in buf.bytes() {
                if let Some(result) = game.step(Some(c as char)) {
                    match result {
                        StepResult::StateChanged => changed = true,
                        StepResult::Quit => break 'outer,
                    }
                }
            }
        } else {
            if let Some(result) = game.step(None) {
                match result {
                    StepResult::StateChanged => changed = true,
                    StepResult::Quit => break 'outer,
                }
            }
        }
        if changed {
            display_game(&game);
        }
        std::thread::sleep(std::time::Duration::from_millis(1));
    }
    termios::tcsetattr(0, termios::TCSADRAIN, &termios_state_initial).unwrap();
}