const jsnes = require('jsnes');
const { createCanvas } = require('canvas');
const { writeFileSync } = require('fs');

var SCREEN_WIDTH = 256;
var SCREEN_HEIGHT = 240;
var FRAMEBUFFER_SIZE = SCREEN_WIDTH*SCREEN_HEIGHT;

var canvas_ctx, image;
var framebuffer_u8, framebuffer_u32;

function requestAnimationFrame(f) {
        setImmediate(() => f(Date.now()));
}

var nes = new jsnes.NES({
    onFrame: function(framebuffer_24){
        for(var i = 0; i < FRAMEBUFFER_SIZE; i++) framebuffer_u32[i] = 0xFF000000 | framebuffer_24[i];
    },
});

function onAnimationFrame(){
    requestAnimationFrame(onAnimationFrame);

    image.data.set(framebuffer_u8);
    canvas_ctx.putImageData(image, 0, 0);
    nes.frame();

    saveImage(); // Save screenshot.
}

function saveImage() {
     const buffer = canvas_ctx.canvas.toBuffer('image/png');
     writeFileSync('./test.png', buffer);
}

function nes_init(){
    var canvas = createCanvas(SCREEN_WIDTH, SCREEN_HEIGHT);
    canvas_ctx = canvas.getContext("2d");
    image = canvas_ctx.getImageData(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);

    canvas_ctx.fillStyle = "black";
    canvas_ctx.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);

    // Allocate framebuffer array.
    var buffer = new ArrayBuffer(image.data.length);
    framebuffer_u8 = new Uint8ClampedArray(buffer);
    framebuffer_u32 = new Uint32Array(buffer);
}

function nes_boot(rom_data){
    nes.loadROM(rom_data);
    requestAnimationFrame(onAnimationFrame);
}

// This is init function.
function nes_load_data(rom_data){
    nes_init();
    nes_boot(rom_data);
}

// Start functionality.
nes_load_data('binary rom data');