function makeShader(gl, type, source) {
    const shader = gl.createShader(type);
    gl.shaderSource(shader, source);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        throw Error(`Shader compiler error: ${gl.getShaderInfoLog(shader)}`);
    }

    return shader;
}

export function makeProgram(gl, vertexShader, fragmentShader) {
    const vshader = makeShader(gl, gl.VERTEX_SHADER, vertexShader);
    const fshader = makeShader(gl, gl.FRAGMENT_SHADER, fragmentShader);

    const shaderProg = gl.createProgram();
    gl.attachShader(shaderProg, vshader);
    gl.attachShader(shaderProg, fshader);
    gl.linkProgram(shaderProg);

    if (!gl.getProgramParameter(shaderProg, gl.LINK_STATUS)) {
        throw Error(`Shader linker error: ${gl.getProgramInfoLog(shaderProg)}`);
    }

    return shaderProg;
}

function getImage(url) {
    return new Promise(resolve => {
        const image = new Image();
        image.onload = () => resolve(image);
        image.src = url;
    });
}

export async function loadTexture(gl, url) {
    const image = await getImage(url);
    const texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, 1);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);
    gl.generateMipmap(gl.TEXTURE_2D);

    return texture;
}