/**  Get shader source by HTML-Element<id> */
export function getShader(gl: WebGL2RenderingContext, id: string): WebGLShader | null {
    const script: any = document.getElementById(id);
    if (!script) {
        console.error(`Couldn't get shader source from HTML for id: ${id}`);
        return null;
    }

    let shader: WebGLShader | null;
    if (script.type == "x-shader/x-fragment") {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (script.type == "x-shader/x-vertex") {
        shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
        console.error(`Script type is wrong for id: ${id}`);
        return null;
    }

    if (shader == null) {
        console.error("Cannot create Shaders!");
        return null;
    }

    gl.shaderSource(shader, script.text);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        console.error(`Shader compilation failed for ${id}:`, gl.getShaderInfoLog(shader));
        return null;
    }

    return shader;
}

export function createProgram(
    gl: WebGL2RenderingContext,
    vertexShaderId: string,
    fragmentShaderId: string,
    programName: string
): WebGLProgram | null {
    const vertexShader = getShader(gl, vertexShaderId);
    const fragmentShader = getShader(gl, fragmentShaderId);

    if (vertexShader == null || fragmentShader == null) {
        console.error(`Didn't find ${programName} shader sources!`);
        return null;
    }

    const program = gl.createProgram();
    if (program == null) {
        console.error(`${programName} program not created!`);
        return null;
    }

    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);
    gl.linkProgram(program);

    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
        console.error(`Could not initialize ${programName} shaders:`, gl.getProgramInfoLog(program));
        return null;
    }

    return program;
}