-- Snake game
-- 2021 by Roman "shinkarom" Shynkarenko
-- Controls: move snake with 2, 4, 6, 8 (internal controls, not keyboard keys)
-- After game ends, restart it by pressing 5 again, the internal control)

speed = 12
frames = 0
segments = {}
food = {}
direction = {dx = 1, dy = 0}
should_stop = false
score = 0
scene = 0

function occupied(xx, yy)
    for i = 1, #segments do
        if (xx == segments[i].x) and (yy == segments[i].y) then return true end
    end
    return false
end

function generate_food()
    local x = rnd(64)
    local y = rnd(32)
    while occupied(x, y) do
        x = rnd(64)
        y = rnd(32)
    end
    food.x = x
    food.y = y
end

generate_food()

function init_game()
    segments = {}
    food = {}
    direction = {dx = 1, dy = 0}
    should_stop = false
    score = 0
    scene = 0

    for i = 1,3 do
        segments[i] = { x = 10 - i + 1, y = 10}
    end

    generate_food()
end

init_game()

function move_snake()
    for i = #segments - 1, 1, -1 do
        segments[i+1].x = segments[i].x
        segments[i+1].y = segments[i].y
    end
    segments[1].x = target.x
    segments[1].y = target.y
end

function process_input()
    if key_released(8) and direction.dy == 0 then
        direction.dy = 1
        direction.dx = 0
    end
    if key_released(2) and direction.dy == 0 then
        direction.dy = -1
        direction.dx = 0
    end
    if key_released(4) and direction.dx == 0 then
        direction.dx = -1
        direction.dy = 0
    end
    if key_released(6) and direction.dx == 0 then
        direction.dx = 1
        direction.dy = 0
    end 
end

function draw_it()
    draw(food_sprite, food.x, food.y)
    for i = 1, #segments do
        draw(segment, segments[i].x, segments[i].y)
    end 
end

function eat_food()
    local new_segment = {x = food.x, y = food.y}
    table.insert(segments, 1, new_segment)
    generate_food()
    score = score + 1
    sound_timer = 15
end

function stop()
    should_stop = true
    sound_timer = 45
    scene = 1
end

function collision_with_snake()
    for i=2,#segments do
        if target.x == segments[i].x and target.y == segments[i].y then
            stop()
        end
    end
end

function collision_with_wall()
    if (target.x <= 0) or 
    (target.x >= 63) or 
    (target.y <= 0) or 
    (target.y >= 31) then
        stop()
    end
end

function vblank()
	cls()
    if scene == 0 then
        if not should_stop then
            frames = frames + 1
            if frames % speed == 0 then
                target = {x = segments[1].x + direction.dx,
                        y = segments[1].y + direction.dy}
                if target.x == food.x and target.y == food.y then
                    eat_food()
                else
                    move_snake()
                    collision_with_snake()
                    collision_with_wall()
                end      
            end
            process_input()
        end
        draw_it()
    elseif scene == 1 then
        local digits = bcd(score)
        draw(get_sprite(digits[1]), 20, 15)
        draw(get_sprite(digits[2]), 25, 15)
        draw(get_sprite(digits[3]), 30, 15)
        if key_released(5) then
            init_game()
            scene = 0
        end
    end
end

segment = {0x80}
food_sprite = {0x80}