let gl;
let program;
let posLoc,
	colorLoc;
let objects = [];
let lastTimestamp;
let viewMatrix;
const {mat4, mat3, vec3} = glMatrix;

function main() {

	// Get canvas and setup WebGL context
    const canvas = document.getElementById("gl-canvas");
	gl = canvas.getContext('webgl2');

	// Configure viewport
	gl.viewport(0,0,canvas.width,canvas.height);
	gl.clearColor(1.0,1.0,1.0,1.0);

	gl.enable(gl.DEPTH_TEST);

	// Init shader program via additional function and bind it
	program = initShaders(gl, "vertex-shader", "fragment-shader");
	gl.useProgram(program);

	// Get locations of shader variables
	posLoc = gl.getAttribLocation(program, "vPosition");
	colorLoc = gl.getAttribLocation(program, "vColor");

	// get location for the vewMatrix
	const viewLoc = gl.getUniformLocation(program, "viewMatrix");

	//get location for the modelMatrix
	const modelLoc = gl.getUniformLocation(program, "modelMatrix");

	// define view matrix
	/*
	viewMatrix = [
		0.1767766922712326, -0.0589255653321743, -0.013334667310118675, 0, 
		0, 0.2357022613286972, -0.006667333655059338, 0, 
		-0.1767766922712326, -0.0589255653321743, -0.013334667310118675, 0, 
		0, 0, -0.8801880478858948, 1
	];
	*/
	
	eye = vec3.fromValues(0, 0.5, 10);
	target = vec3.fromValues(0, 0, 0);
	up = vec3.fromValues(0, 1, 0);

	viewMatrix = mat4.create();
	mat4.lookAt(viewMatrix, eye, target, up);


	//activate uniform for the viewmatrix
	gl.uniformMatrix4fv(viewLoc, false, viewMatrix);

	// Only clear once
	gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

	let island = new Insel();
	objects.push(island);

	let river = new River();
	objects.push(river);

	let tree = new Tree();
	tree.SetModelMatrix([1, 0, 0], [0, 0, 0], [1, 1, 1]);
	objects.push(tree);

	let cloud = new Cloud();
	cloud.SetModelMatrix([-1, 2, 1], [0, 0, 0], [1, 1, 1]);
	objects.push(cloud);

	document.body.addEventListener("keydown", move);
	
	window.requestAnimationFrame(render);
};

function move(e) 
{
	if (e.keyCode == '87') //w
	{
		eye[2] = eye[2] - 0.5;
		target[2] = target[2] - 0.5;
	} else if (e.keyCode == '83') //s
	{
		eye[2] = eye[2] + 0.5;
		target[2] = target[2] + 0.5;
	} else if (e.keyCode == '65') //a
	{
		eye[0] = eye[0] - 0.5;
		target[0] = target[0] - 0.5;
	} else if (e.keyCode == '68') //d
	{
		eye[0] = eye[0] + 0.5;
		target[0] = target[0] + 0.5;
	}
	
	//set the viewMatrix
	const viewLoc = gl.getUniformLocation(program, "viewMatrix");
	mat4.lookAt(viewMatrix, eye, target, up);
	gl.uniformMatrix4fv(viewLoc, false, viewMatrix);
}

function changeView(e) 
{
	//TODO: in Übungen
}

function render(timestamp)
{
	if(lastTimestamp == undefined) 
	{
		lastTimestamp = timestamp;
	}
		
	const elapsed = timestamp - lastTimestamp;

	for (var i = 0; i < objects.length; i++)
	{
		objects[i].render();
	} 

	window.requestAnimationFrame(render);
}

main();