// Game Constants and variables
let inputDir = {x: 0, y: 0};
const foodSound = new Audio('food.mp3');
const gameOverSound = new Audio('gameover.mp3');
const moveSound = new Audio('move.mp3');
const musicSound = new Audio('music.mp3');
let speed = 6;
let score = 0;
let lastPaintTime = 0;
let snakeArr = [        // array
    {x: 13, y: 15}
]
let food = {x: 6, y:7};   // object

// Game Functions
function main(ctime){
    window.requestAnimationFrame(main);
    // console.log(ctime);
    if((ctime - lastPaintTime)/1000 < 1/speed){
        return;
    }
    lastPaintTime = ctime;

    gameEngine();
}

function isCollide(sarr){
    // if snake bump into himself
    for (let i = 1; i < snakeArr.length; i++) {
        if(sarr[i].x === sarr[0].x && sarr[i].y === sarr[0].y){
            return true;
        }
    }
    // if snake bump into wall
    if(sarr[0].x >= 18 || sarr[0].x <= 0 || sarr[0].y >= 18 || sarr[0].y <= 0){
        return true;
    }
}

function gameEngine(){
    // Part 1: Updating the snake array and food
    if(isCollide(snakeArr)){
        gameOverSound.play();
        musicSound.pause();
        inputDir = {x:0, y:0};
        alert("Game Over!! Press any key to play again");
        snakeArr = [{x:13, y:15}];
        musicSound.play();
        score = 0;
        scoreBoard.innerHTML = "Score: " + score;
    }

    // If you have eaten the food , increment the score and regenrate the food
    if(snakeArr[0].y === food.y && snakeArr[0].x === food.x){
        foodSound.play();
        score += 1;
        if(score > hiscore){
            hiscoreval = score;
            localStorage.setItem('hiscore', JSON.stringify(hiscoreval));
            highScoreBoard.innerHTML = "HighScore: "+ hiscoreval;
        }
        scoreBoard.innerHTML = "Score: " + score;
        snakeArr.unshift({x: snakeArr[0].x + inputDir.x, y: snakeArr[0].y + inputDir.y});
        // generating random number between a and b
        // Math.round(a + (b - a)*Math.random())
        let a = 2;
        let b = 16;
        food = {x: Math.round(a + (b - a)*Math.random()), y: Math.round(a + (b - a)*Math.random())};
    }

    // Moving the snake
    for (let i = snakeArr.length - 2; i >= 0; i--) {
        snakeArr[i + 1] = {...snakeArr[i]};
    }
    
    snakeArr[0].x += inputDir.x;
    snakeArr[0].y += inputDir.y;

    // Part 2: Display the snake and food
    // Display Snake
    board.innerHTML = "";
    snakeArr.forEach((e,index)=>{
        snakeElement = document.createElement('div');
        snakeElement.style.gridRowStart = e.y;
        snakeElement.style.gridColumnStart = e.x;
        if(index === 0){
            snakeElement.classList.add('head');
        }
        else{
            snakeElement.classList.add('snake');
        }
        board.appendChild(snakeElement);
    })

    // Display Food
    foodElement = document.createElement('div');
    foodElement.style.gridRowStart = food.y;
    foodElement.style.gridColumnStart = food.x;
    foodElement.classList.add('food');
    board.appendChild(foodElement);
}


// Main logic starts here
let hiscore = localStorage.getItem('hiscore');
// localStorage.clear() -> to clear local storage / high score
if(hiscore == null){
    hiscoreval = 0;
    localStorage.setItem('hiscore', JSON.stringify(hiscoreval));
}
else{
    highscoreval = JSON.parse(localStorage.getItem(hiscore));
    highScoreBoard.innerHTML = "HighScore: "+ hiscore;
}
window.requestAnimationFrame(main);
window.addEventListener('keydown', e=>{
    inputDir = {x: 0, y: 1}; // start the game
    moveSound.play();
    switch (e.key) {
        case "ArrowUp":
            inputDir.x = 0;
            inputDir.y = -1;
            break;

        case "ArrowDown":
            inputDir.x = 0;
            inputDir.y = 1;
            break;

        case "ArrowRight":
            inputDir.x = 1;
            inputDir.y = 0;
            break;

        case "ArrowLeft":
            inputDir.x = -1;
            inputDir.y = 0;
            break;

        default:
            break;
    }
});