const vs_src = `
  attribute vec4 aVertexPosition;

  uniform mat4 uModelViewMatrix;
  uniform mat4 uProjectionMatrix;

  void main() {
    gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;
  }
`;

// Fragment shader program

const fs_src = `
  void main() {
    gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
  }
`;

export class ShaderInfo {
	constructor(gl, program) {
		this.program = program;

		this.attribs = {
			position: gl.getAttribLocation(program, 'aVertexPosition')
		};

		this.uniforms = {
			projectionMatrix: gl.getUniformLocation(program, 'uProjectionMatrix'),
			modelViewMatrix: gl.getUniformLocation(program, 'uModelViewMatrix')
		};
	}
}

export function init(gl) {
	const vshader = loadShader(gl, gl.VERTEX_SHADER, vs_src);
	const fshader = loadShader(gl, gl.FRAGMENT_SHADER, fs_src);

	let program = gl.createProgram();
	gl.attachShader(program, vshader);
	gl.attachShader(program, fshader);

	gl.linkProgram(program);

	if(!gl.getProgramParameter(program, gl.LINK_STATUS)) {
		alert("Unable to initialize shader program: " + gl.getProgramInfoLog(program));
		return null;
	}

	return new ShaderInfo(gl, program);
}

export function loadShader(gl, type, src){
	const shader = gl.createShader(type)

	gl.shaderSource(shader, src);
	gl.compileShader(shader);

	if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
		alert('Failed to compile shader : ' + gl.getShaderInfoLog(shader));
		gl.deleteShader(shader);
		return null;
	}

	return shader;
}