'use strict'

module.exports = setProgram;


function setProgram (gl, vSrc, fSrc) {
	if (!gl) throw Error('WebGL context is not provided')

	// TODO: delete program by passing null
	// TODO: keep track of used programs to avoid this request below, think how

	// if just getProgram
	if (!vSrc && !fSrc) {
		return gl.getParameter(gl.CURRENT_PROGRAM)
	}

	// if WebGLProgram directly - enable program
	if (vSrc && typeof vSrc !== 'string') {
		gl.useProgram(vSrc)
		if (!vSrc.gl) vSrc.gl = gl
		return vSrc
	}

	// otherwise create and enable program
	// TODO: cache shaders
	// TODO: provide gl on a program
	if (!vSrc || !fSrc) throw Error('Vertex/fragment source is not provided')

	var fShader = gl.createShader(gl.FRAGMENT_SHADER)
	var vShader = gl.createShader(gl.VERTEX_SHADER)

	gl.shaderSource(fShader, fSrc)
	gl.shaderSource(vShader, vSrc)

	gl.compileShader(fShader)

	if (!gl.getShaderParameter(fShader, gl.COMPILE_STATUS)) {
		throw Error(gl.getShaderInfoLog(fShader))
	}

	gl.compileShader(vShader)

	if (!gl.getShaderParameter(vShader, gl.COMPILE_STATUS)) {
		throw Error(gl.getShaderInfoLog(vShader))
	}


	var program = gl.createProgram()
	gl.attachShader(program, vShader)
	gl.attachShader(program, fShader)
	gl.linkProgram(program)

	if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
		throw Error(gl.getProgramInfoLog(program))
	}

	gl.useProgram(program)

	// save gl reference
	program.gl = gl

	return program;
}