import gg
// import sokol.sapp
import time
import rand

// constants
const top_height = 100
const canvas_size = 700
const game_size = 17
const tile_size = canvas_size / game_size
const tick_rate_ms = 100

// types
struct Pos {
    x int
    y int
}

fn (a Pos) + (b Pos) Pos {
    return Pos{a.x + b.x, a.y + b.y}
}

fn (a Pos) - (b Pos) Pos {
    return Pos{a.x - b.x, a.y - b.y}
}

enum Direction {
    up
    down
    left
    right
}

struct App {
mut:
    gg         &gg.Context = unsafe { nil }
    score      int
    snake      []Pos
    dir        Direction
    last_dir   Direction
    food       Pos
    start_time i64
    last_tick  i64
}

// utility
fn (mut app App) reset_game() {
    app.score = 0
    app.snake = [
        Pos{3, 8},
        Pos{2, 8},
        Pos{1, 8},
        Pos{0, 8},
    ]
    app.dir = .right
    app.last_dir = app.dir
    app.food = Pos{10, 8}
    app.start_time = time.ticks()
    app.last_tick = time.ticks()
}

fn (mut app App) move_food() {
    for {
        x := rand.intn(game_size) or { 0 }
        y := rand.intn(game_size) or { 0 }
        app.food = Pos{x, y}

        if app.food !in app.snake {
            return
        }
    }
}

// events
fn on_keydown(key gg.KeyCode, _ gg.Modifier, mut app App) {
    match key {
        .w, .up {
            if app.last_dir != .down {
                app.dir = .up
            }
        }
        .s, .down {
            if app.last_dir != .up {
                app.dir = .down
            }
        }
        .a, .left {
            if app.last_dir != .right {
                app.dir = .left
            }
        }
        .d, .right {
            if app.last_dir != .left {
                app.dir = .right
            }
        }
        else {}
    }
}

fn on_frame(mut app App) {
    app.gg.begin()

    now := time.ticks()

    if now - app.last_tick >= tick_rate_ms {
        app.last_tick = now

        // finding delta direction
        delta_dir := match app.dir {
            .up { Pos{0, -1} }
            .down { Pos{0, 1} }
            .left { Pos{-1, 0} }
            .right { Pos{1, 0} }
        }

        // "snaking" along
        mut prev := app.snake[0]
        app.snake[0] = app.snake[0] + delta_dir

        for i in 1 .. app.snake.len {
            tmp := app.snake[i]
            app.snake[i] = prev
            prev = tmp
        }

        // adding last segment
        if app.snake[0] == app.food {
            app.move_food()
            app.score++
            /*
            if app.score > app.best {
                app.best = app.score
                app.best.save()
            }*/
            app.snake << app.snake.last() + app.snake.last() - app.snake[app.snake.len - 2]
        }

        app.last_dir = app.dir
    }
    // drawing snake
    for pos in app.snake {
        app.gg.draw_rect(tile_size * pos.x, tile_size * pos.y + top_height, tile_size, tile_size,
            gg.blue)
    }

    // drawing food
    app.gg.draw_rect(tile_size * app.food.x, tile_size * app.food.y + top_height, tile_size,
        tile_size, gg.red)

    // drawing top
    app.gg.draw_rect(0, 0, canvas_size, top_height, gg.black)
    app.gg.draw_text(350, top_height / 2, 'Score: ${app.score}', gg.TextCfg{
        color:          gg.white
        align:          .center
        vertical_align: .middle
        size:           80
    })

    // checking if snake bit itself
    if app.snake[0] in app.snake[1..] {
        app.reset_game()
    }
    // checking if snake hit a wall
    if app.snake[0].x < 0 || app.snake[0].x >= game_size || app.snake[0].y < 0
        || app.snake[0].y >= game_size {
        app.reset_game()
    }

    app.gg.end()
}

// setup
fn main() {
    mut app := App{
        gg: &gg.Context{}
    }
    app.reset_game()

    app.gg = gg.new_context(
        bg_color:          gg.white
        frame_fn:          on_frame
        keydown_fn:        on_keydown
        user_data:         &app
        width:             canvas_size
        height:            top_height + canvas_size
        create_window:     true
        resizable:         false
        window_title:      'snek'
        html5_canvas_name: 'canvas'
    )

    app.gg.run()
}