// import modules for use in app
import term.ui as termui
import rand

// define some global constants
const (
    block_size = 1
    buffer     = 10
    green      = termui.Color{0, 255, 0}
    grey       = termui.Color{150, 150, 150}
    white      = termui.Color{255, 255, 255}
    blue       = termui.Color{0, 0, 255}
    red        = termui.Color{255, 0, 0}
    black      = termui.Color{0, 0, 0}
)

// what edge of the screen are you facing
enum Orientation {
    top
    right
    bottom
    left
}

// what's the current state of the game
enum GameState {
    pause
    gameover
    game
    oob // snake out-of-bounds
}

// simple 2d vector representation
struct Vec {
mut:
    x int
    y int
}

// determine orientation from vector (hacky way to set facing from velocity)
fn (v Vec) facing() Orientation {
    result := if v.x >= 0 {
        Orientation.right
    } else if v.x < 0 {
        Orientation.left
    } else if v.y >= 0 {
        Orientation.bottom
    } else {
        Orientation.top
    }
    return result
}

// generate a random vector with x in [min_x, max_x] and y in [min_y, max_y]
fn (mut v Vec) randomize(min_x int, min_y int, max_x int, max_y int) {
    v.x = rand.int_in_range(min_x, max_x) or { min_x }
    v.y = rand.int_in_range(min_y, max_y) or { min_y }
}

// part of snake's body representation
struct BodyPart {
mut:
    pos Vec = Vec{
        x: block_size
        y: block_size
    }
    color  termui.Color = green
    facing Orientation  = .top
}

// snake representation
struct Snake {
mut:
    app       &App = unsafe { nil }
    direction Orientation
    body      []BodyPart
    velocity  Vec = Vec{
        x: 0
        y: 0
    }
}

// length returns the snake's current length
fn (s Snake) length() int {
    return s.body.len
}

// impulse provides a impulse to change the snake's direction
fn (mut s Snake) impulse(direction Orientation) {
    mut vec := Vec{}
    match direction {
        .top {
            vec.x = 0
            vec.y = -1 * block_size
        }
        .right {
            vec.x = 2 * block_size
            vec.y = 0
        }
        .bottom {
            vec.x = 0
            vec.y = block_size
        }
        .left {
            vec.x = -2 * block_size
            vec.y = 0
        }
    }
    s.direction = direction
    s.velocity = vec
}

// move performs the calculations for the snake's movements
fn (mut s Snake) move() {
    mut i := s.body.len - 1
    width := s.app.width
    height := s.app.height
    // move the parts of the snake as appropriate
    for i = s.body.len - 1; i >= 0; i-- {
        mut piece := s.body[i]
        if i > 0 { // just move the body of the snake up one position
            piece.pos = s.body[i - 1].pos
            piece.facing = s.body[i - 1].facing
        } else { // verify that the move is valid and move the head if so
            piece.facing = s.direction
            new_x := piece.pos.x + s.velocity.x
            new_y := piece.pos.y + s.velocity.y
            piece.pos.x += if new_x > block_size && new_x < width - block_size {
                s.velocity.x
            } else {
                0
            }
            piece.pos.y += if new_y > block_size && new_y < height - block_size {
                s.velocity.y
            } else {
                0
            }
        }
        s.body[i] = piece
    }
}

// grow add another part to the snake when it catches the rat
fn (mut s Snake) grow() {
    head := s.get_tail()
    mut pos := Vec{}
    // add the segment on the opposite side of the previous tail
    match head.facing {
        .bottom {
            pos.x = head.pos.x
            pos.y = head.pos.y - block_size
        }
        .left {
            pos.x = head.pos.x + block_size
            pos.y = head.pos.y
        }
        .top {
            pos.x = head.pos.x
            pos.y = head.pos.y + block_size
        }
        .right {
            pos.x = head.pos.x - block_size
            pos.y = head.pos.y
        }
    }
    s.body << BodyPart{
        pos: pos
        facing: head.facing
    }
}

// get_body gets the parts of the snakes body
fn (s Snake) get_body() []BodyPart {
    return s.body
}

// get_head get snake's head
fn (s Snake) get_head() BodyPart {
    return s.body[0]
}

// get_tail get snake's tail
fn (s Snake) get_tail() BodyPart {
    return s.body[s.body.len - 1]
}

// randomize randomizes position and veolcity of snake
fn (mut s Snake) randomize() {
    speeds := [-2, 0, 2]
    mut pos := s.get_head().pos
    pos.randomize(buffer, buffer, s.app.width - buffer, s.app.height - buffer)
    for pos.x % 2 != 0 || (pos.x < buffer && pos.x > s.app.width - buffer) {
        pos.randomize(buffer, buffer, s.app.width - buffer, s.app.height - buffer)
    }
    s.velocity.y = rand.int_in_range(-1 * block_size, block_size) or { 0 }
    s.velocity.x = speeds[rand.intn(speeds.len) or { 0 }]
    s.direction = s.velocity.facing()
    s.body[0].pos = pos
}

// check_overlap determine if the snake's looped onto itself
fn (s Snake) check_overlap() bool {
    h := s.get_head()
    head_pos := h.pos
    for i in 2 .. s.length() {
        piece_pos := s.body[i].pos
        if head_pos.x == piece_pos.x && head_pos.y == piece_pos.y {
            return true
        }
    }
    return false
}

fn (s Snake) check_out_of_bounds() bool {
    h := s.get_head()
    return h.pos.x + s.velocity.x <= block_size
        || h.pos.x + s.velocity.x > s.app.width - s.velocity.x
        || h.pos.y + s.velocity.y <= block_size
        || h.pos.y + s.velocity.y > s.app.height - block_size - s.velocity.y
}

// draw draws the parts of the snake
fn (s Snake) draw() {
    mut a := s.app
    for part in s.get_body() {
        a.termui.set_bg_color(part.color)
        a.termui.draw_rect(part.pos.x, part.pos.y, part.pos.x + block_size, part.pos.y + block_size)
        $if verbose ? {
            text := match part.facing {
                .top { '^' }
                .bottom { 'v' }
                .right { '>' }
                .left { '<' }
            }
            a.termui.set_color(white)
            a.termui.draw_text(part.pos.x, part.pos.y, text)
        }
    }
}

// rat representation
struct Rat {
mut:
    pos Vec = Vec{
        x: block_size
        y: block_size
    }
    captured bool
    color    termui.Color = grey
    app      &App = unsafe { nil }
}

// randomize spawn the rat in a new spot within the playable field
fn (mut r Rat) randomize() {
    r.pos.randomize(2 * block_size + buffer, 2 * block_size + buffer, r.app.width - block_size - buffer,
        r.app.height - block_size - buffer)
}

[heap]
struct App {
mut:
    termui &termui.Context = unsafe { nil }
    snake  Snake
    rat    Rat
    width  int
    height int
    redraw bool      = true
    state  GameState = .game
}

// new_game setups the rat and snake for play
fn (mut a App) new_game() {
    mut snake := Snake{
        body: []BodyPart{len: 1, init: BodyPart{}}
        app: a
    }
    snake.randomize()
    mut rat := Rat{
        app: a
    }
    rat.randomize()
    a.snake = snake
    a.rat = rat
    a.state = .game
    a.redraw = true
}

// initialize the app and record the width and height of the window
fn init(mut app App) {
    w, h := app.termui.window_width, app.termui.window_height
    app.width = w
    app.height = h
    app.new_game()
}

// event handles different events for the app as they occur
fn event(e &termui.Event, mut app App) {
    match e.typ {
        .mouse_down {}
        .mouse_drag {}
        .mouse_up {}
        .key_down {
            match e.code {
                .up, .w { app.move_snake(.top) }
                .down, .s { app.move_snake(.bottom) }
                .left, .a { app.move_snake(.left) }
                .right, .d { app.move_snake(.right) }
                .r { app.new_game() }
                .c {}
                .p { app.state = if app.state == .game { GameState.pause } else { GameState.game } }
                .escape, .q { exit(0) }
                else { exit(0) }
            }
            if e.code == .c {
            } else if e.code == .escape {
                exit(0)
            }
        }
        else {}
    }
    app.redraw = true
}

// frame perform actions on every tick
fn frame(mut app App) {
    app.update()
    app.draw()
}

// update perform any calculations that are needed before drawing
fn (mut a App) update() {
    if a.state == .game {
        a.snake.move()
        if a.snake.check_out_of_bounds() {
            $if verbose ? {
                a.snake.body[0].color = red
            } $else {
                a.state = .oob
            }
        }
        if a.snake.check_overlap() {
            a.state = .gameover
            return
        }
        if a.check_capture() {
            a.rat.randomize()
            a.snake.grow()
        }
    }
}

// draw write to the screen
fn (mut a App) draw() {
    // reset screen
    a.termui.clear()
    a.termui.set_bg_color(white)
    a.termui.draw_empty_rect(1, 1, a.width, a.height)
    // determine if a special screen needs to be draw
    match a.state {
        .gameover {
            a.draw_gameover()
            a.redraw = false
        }
        .pause {
            a.draw_pause()
        }
        else {
            a.redraw = true
        }
    }
    a.termui.set_color(blue)
    a.termui.set_bg_color(white)
    a.termui.draw_text(3 * block_size, a.height - (2 * block_size), 'p - (un)pause r - reset q - quit')
    // draw the snake, rat, and score if appropriate
    if a.redraw {
        a.termui.set_bg_color(black)
        a.draw_gamescreen()
        if a.state == .oob {
            a.state = .gameover
        }
    }
    // write to the screen
    a.termui.reset_bg_color()
    a.termui.flush()
}

// move_snake move the snake in specified direction
fn (mut a App) move_snake(direction Orientation) {
    a.snake.impulse(direction)
}

// check_capture determine if the snake overlaps with the rat
fn (a App) check_capture() bool {
    snake_pos := a.snake.get_head().pos
    rat_pos := a.rat.pos
    return snake_pos.x <= rat_pos.x + block_size && snake_pos.x + block_size >= rat_pos.x
        && snake_pos.y <= rat_pos.y + block_size && snake_pos.y + block_size >= rat_pos.y
}

fn (mut a App) draw_snake() {
    a.snake.draw()
}

fn (mut a App) draw_rat() {
    a.termui.set_bg_color(a.rat.color)
    a.termui.draw_rect(a.rat.pos.x, a.rat.pos.y, a.rat.pos.x + block_size, a.rat.pos.y + block_size)
}

fn (mut a App) draw_gamescreen() {
    $if verbose ? {
        a.draw_debug()
    }
    a.draw_score()
    a.draw_rat()
    a.draw_snake()
}

fn (mut a App) draw_score() {
    a.termui.set_color(blue)
    a.termui.set_bg_color(white)
    score := a.snake.length() - 1
    a.termui.draw_text(a.width - (2 * block_size), block_size, '${score:03d}')
}

fn (mut a App) draw_pause() {
    a.termui.set_color(blue)
    a.termui.draw_text((a.width / 2) - block_size, 3 * block_size, 'Paused!')
}

fn (mut a App) draw_debug() {
    a.termui.set_color(blue)
    a.termui.set_bg_color(white)
    snake := a.snake
    a.termui.draw_text(block_size, 1 * block_size, 'Display_width: ${a.width:04d} Display_height: ${a.height:04d}')
    a.termui.draw_text(block_size, 2 * block_size, 'Vx: ${snake.velocity.x:+02d} Vy: ${snake.velocity.y:+02d}')
    a.termui.draw_text(block_size, 3 * block_size, 'F: ${snake.direction}')
    snake_head := snake.get_head()
    rat := a.rat
    a.termui.draw_text(block_size, 4 * block_size, 'Sx: ${snake_head.pos.x:+03d} Sy: ${snake_head.pos.y:+03d}')
    a.termui.draw_text(block_size, 5 * block_size, 'Rx: ${rat.pos.x:+03d} Ry: ${rat.pos.y:+03d}')
}

fn (mut a App) draw_gameover() {
    a.termui.set_bg_color(white)
    a.termui.set_color(red)
    a.rat.pos = Vec{
        x: -1
        y: -1
    }
    x_offset := '   #####                        '.len // take half of a line from the game over text and store the length
    start_x := (a.width / 2) - x_offset
    a.termui.draw_text(start_x, (a.height / 2) - 3 * block_size, '   #####                         #######                       ')
    a.termui.draw_text(start_x, (a.height / 2) - 2 * block_size, '  #     #   ##   #    # ######   #     # #    # ###### #####   ')
    a.termui.draw_text(start_x, (a.height / 2) - 1 * block_size, '  #        #  #  ##  ## #        #     # #    # #      #    #  ')
    a.termui.draw_text(start_x, (a.height / 2) - 0 * block_size, '  #  #### #    # # ## # #####    #     # #    # #####  #    #  ')
    a.termui.draw_text(start_x, (a.height / 2) + 1 * block_size, '  #     # ###### #    # #        #     # #    # #      #####   ')
    a.termui.draw_text(start_x, (a.height / 2) + 2 * block_size, '  #     # #    # #    # #        #     #  #  #  #      #   #   ')
    a.termui.draw_text(start_x, (a.height / 2) + 3 * block_size, '   #####  #    # #    # ######   #######   ##   ###### #    #  ')
}

fn main() {
    mut app := &App{}
    app.termui = termui.init(
        user_data: app
        event_fn: event
        frame_fn: frame
        init_fn: init
        hide_cursor: true
        frame_rate: 10
    )
    app.termui.run()!
}