extern crate termios;

use rand::Rng;
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];

enum StepResult {
    StateChanged,
    Quit,
}

#[derive(Clone)]
#[derive(Debug)]
enum FigureKind {
    I,
    L2,
    L,
    T,
    B,
    S,
    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 kind_random() -> Self {
        return match rand::thread_rng().gen_range(0..7) {
            0 => Self::kind_i(),
            1 => Self::kind_l2(),
            2 => Self::kind_l(),
            3 => Self::kind_b(),
            4 => Self::kind_s(),
            5 => Self::kind_t(),
            6 => Self::kind_z(),
            _ => unreachable!(),
        };
    }
    const fn kind_i() -> Self { Self{ cells: CELLS_I, kind: FigureKind::I } }
    const fn kind_l2() -> Self { Self{ cells: CELLS_L2, kind: FigureKind::L2 } }
    const fn kind_l() -> Self { Self{ cells: CELLS_L, kind: FigureKind::L } }
    const fn kind_b() -> Self { Self{ cells: CELLS_B, kind: FigureKind::B } }
    const fn kind_s() -> Self { Self{ cells: CELLS_S, kind: FigureKind::S } }
    const fn kind_t() -> Self { Self{ cells: CELLS_T, kind: FigureKind::T } }
    const fn kind_z() -> Self { Self{ cells: CELLS_Z, kind: FigureKind::Z } }
    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::L2 => self.rotate_cw_3x3(),
            FigureKind::L => self.rotate_cw_3x3(),
            FigureKind::B => {},
            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;
            }
            if figure.cells[i] != 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;
            if figure.cells[i] != 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 if self.cells[f_x as usize + f_y as usize * FIELD_COLS] != 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 Game {
    field: Field,
    figure: Figure,
    x: isize,
    y: isize,
    fall_timeout: Timeout,
    place_timeout: Option<Timeout>,
}

impl Default for Game {
    #[inline]
    fn default() -> Self {
        Self{
            field: Field::default(),
            figure: Figure::kind_random(),
            x: 3,
            y: 17,
            fall_timeout: Timeout::from_duration(std::time::Duration::from_millis(500)),
            place_timeout: None,
        }
    }
}

impl Game {
    fn place_figure(&mut self) {
        self.field.render(&self.figure, self.x, self.y);
        self.figure = Figure::kind_random();
        (self.x, self.y) = (3, 17);
        self.stop_place_timeout();
        for line in 0..FIELD_ROWS - 1 {
            while self.field.is_line_complete(line) {
                self.field.kill_line(line);
            }
        }
    }
    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()
            },
            'h' => {
                if self.field.has_collision(&self.figure, self.x, self.y) {
                    self.x -= 1
                } else if !self.field.has_collision(&self.figure, self.x - 1, self.y) {
                    self.x -= 1
                }
            }
            'j' => {
                if self.field.has_collision(&self.figure, self.x, self.y) {
                    self.y -= 1
                } else if !self.field.has_collision(&self.figure, self.x, self.y - 1) {
                    self.y -= 1
                }
            }
            ';' | 'k' => {
                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, self.y) {
                    self.x += 1
                } else if !self.field.has_collision(&self.figure, self.x + 1, self.y) {
                    self.x += 1
                }
            }
            _ => {},
        }
        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 print_field(field: &Field) {
    cursor_to_home();
    for y in 0..FIELD_ROWS_VISIBLE {
        print!("|");
        for x in 0..FIELD_COLS {
            let c = field.cells[(FIELD_ROWS_VISIBLE - 1 - y) * FIELD_COLS + x];
            if c == 0 {
                print!("  ");
            } else {
                print!("██");
            }
        }
        print!("|\r\x1b[1B");
    }
}

fn display_game(game: &Game) {
    cursor_to_home();
    let mut field = game.field.clone();
    field.render(&game.figure, game.x, game.y);
    print_field(&field);
    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();
}