const vertex_shader_source = `
	attribute vec4 aPos;
	attribute vec4 aColor;

	uniform mat4 uModView;
	uniform mat4 uProj;

	varying lowp vec4 vColor;

	void main()
	{
		gl_Position = uProj * uModView * aPos;
		vColor = aColor;
	}
`;

const fragment_shader_source = `
	varying lowp vec4 vColor;

	void main()
	{
		gl_FragColor = vColor;
	}
`;

function initShaderProgram(gl)
{
	const vertexShader = loadShader(gl, gl.VERTEX_SHADER, vertex_shader_source);
	const fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fragment_shader_source);

	const shaderProgram = gl.createProgram();
	gl.attachShader(shaderProgram, vertexShader);
	gl.attachShader(shaderProgram, fragmentShader);
	gl.linkProgram(shaderProgram);

	if(!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS))
	{
		alert(`Unable to initialize the shader program: ${gl.getProgramInfoLog(shaderProgram)}`);
		return null;
	}
	return shaderProgram;
}

function loadShader(gl, type, source)
{
	const shader = gl.createShader(type);

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

	if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS))
	{
		alert(`An error occurred compiling the shaders: ${gl.getShaderInfoLog(shader)}`);
		gl.deleteShader(shader);
		return null;
	}

	return shader;
}

export { initShaderProgram };