//
// initWebGL
//
// Initialize the Canvas element with the passed name as a WebGL object and return the
// WebGLRenderingContext. 
//
// Load shaders with the passed names and create a program with them. Return this program 
// in the 'program' property of the returned context.
//
// For each string in the passed attribs array, bind an attrib with that name at that index.
// Once the attribs are bound, link the program and then use it.
//
// Set the clear color to the passed array (4 values) and set the clear depth to the passed value.
// Enable depth testing and blending with a blend func of (SRC_ALPHA, ONE_MINUS_SRC_ALPHA)
//
function initWebGL(canvasName, vshader, fshader, attribs, clearColor, clearDepth)
{
    var canvas = document.getElementById(canvasName);
    var gl = canvas.getContext("webkit-3d");

    // create our shaders
    var vertexShader = loadShader(gl, vshader);
    var fragmentShader = loadShader(gl, fshader);

    if (!vertexShader || !fragmentShader)
        return null;

    // Create the program object
    gl.program = gl.createProgram();

    if (!gl.program)
        return null;

    // Attach our two shaders to the program
    gl.attachShader (gl.program, vertexShader);
    gl.attachShader (gl.program, fragmentShader);

    // Bind attributes
    for (var i in attribs)
        gl.bindAttribLocation (gl.program, i, attribs[i]);

    // Link the program
    gl.linkProgram(gl.program);

    // Check the link status
    var linked = gl.getProgramParameter(gl.program, gl.LINK_STATUS);
    if (!linked) {
        // something went wrong with the link
        var error = gl.getProgramInfoLog (gl.program);
        console.log("Error in program linking:"+error);

        gl.deleteProgram(gl.program);
        gl.deleteProgram(fragmentShader);
        gl.deleteProgram(vertexShader);

        return null;
    }

    gl.useProgram(gl.program);

    gl.clearColor (clearColor[0], clearColor[1], clearColor[2], clearColor[3]);
    gl.clearDepth (clearDepth);

    gl.enable(gl.DEPTH_TEST);
    gl.enable(gl.BLEND);
    gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);

    return gl;
}

//
// loadShader
//
// 'shaderId' is the id of a <script> element containing the shader source string.
// Load this shader and return the WebGLShader object corresponding to it.
//
function loadShader(ctx, shaderId)
{
    var shaderScript = document.getElementById(shaderId);
    if (!shaderScript) {
        console.log("*** Error: shader script '"+shaderId+"' not found");
        return null;
    }
        
    if (shaderScript.type == "x-shader/x-vertex")
        var shaderType = ctx.VERTEX_SHADER;
    else if (shaderScript.type == "x-shader/x-fragment")
        var shaderType = ctx.FRAGMENT_SHADER;
    else {
        console.log("*** Error: shader script '"+shaderId+"' of undefined type '"+shaderScript.type+"'");       
        return null;
    }

    // Create the shader object
    var shader = ctx.createShader(shaderType);
    if (shader == null) {
        console.log("*** Error: unable to create shader '"+shaderId+"'");       
        return null;
    }

    // Load the shader source
    ctx.shaderSource(shader, shaderScript.text);

    // Compile the shader
    ctx.compileShader(shader);

    // Check the compile status
    var compiled = ctx.getShaderParameter(shader, ctx.COMPILE_STATUS);
    if (!compiled) {
        // Something went wrong during compilation; get the error
        var error = ctx.getShaderInfoLog(shader);
        console.log("*** Error compiling shader '"+shaderId+"':"+error);
        ctx.deleteShader(shader);
        return null;
    }

    return shader;
}

// 
// makeBox
//
// Create a box with vertices, normals and texCoords. Create VBOs for each as well as the index array.
// Return an object with the following properties:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
// 
function makeBox(ctx)
{
    // box
    //    v6----- v5
    //   /|      /|
    //  v1------v0|
    //  | |     | |
    //  | |v7---|-|v4
    //  |/      |/
    //  v2------v3
    //
    // vertex coords array
    var vertices = new WebGLFloatArray(
        [  1, 1, 1,  -1, 1, 1,  -1,-1, 1,   1,-1, 1,    // v0-v1-v2-v3 front
           1, 1, 1,   1,-1, 1,   1,-1,-1,   1, 1,-1,    // v0-v3-v4-v5 right
           1, 1, 1,   1, 1,-1,  -1, 1,-1,  -1, 1, 1,    // v0-v5-v6-v1 top
          -1, 1, 1,  -1, 1,-1,  -1,-1,-1,  -1,-1, 1,    // v1-v6-v7-v2 left
          -1,-1,-1,   1,-1,-1,   1,-1, 1,  -1,-1, 1,    // v7-v4-v3-v2 bottom
           1,-1,-1,  -1,-1,-1,  -1, 1,-1,   1, 1,-1 ]   // v4-v7-v6-v5 back
    );

    // normal array
    var normals = new WebGLFloatArray(
        [  0, 0, 1,   0, 0, 1,   0, 0, 1,   0, 0, 1,     // v0-v1-v2-v3 front
           1, 0, 0,   1, 0, 0,   1, 0, 0,   1, 0, 0,     // v0-v3-v4-v5 right
           0, 1, 0,   0, 1, 0,   0, 1, 0,   0, 1, 0,     // v0-v5-v6-v1 top
          -1, 0, 0,  -1, 0, 0,  -1, 0, 0,  -1, 0, 0,     // v1-v6-v7-v2 left
           0,-1, 0,   0,-1, 0,   0,-1, 0,   0,-1, 0,     // v7-v4-v3-v2 bottom
           0, 0,-1,   0, 0,-1,   0, 0,-1,   0, 0,-1 ]    // v4-v7-v6-v5 back
       );


    // texCoord array
    var texCoords = new WebGLFloatArray(
        [  1, 1,   0, 1,   0, 0,   1, 0,    // v0-v1-v2-v3 front
           0, 1,   0, 0,   1, 0,   1, 1,    // v0-v3-v4-v5 right
           1, 0,   1, 1,   0, 1,   0, 0,    // v0-v5-v6-v1 top
           1, 1,   0, 1,   0, 0,   1, 0,    // v1-v6-v7-v2 left
           0, 0,   1, 0,   1, 1,   0, 1,    // v7-v4-v3-v2 bottom
           0, 0,   1, 0,   1, 1,   0, 1 ]   // v4-v7-v6-v5 back
       );

    // index array
    var indices = new WebGLUnsignedByteArray(
        [  0, 1, 2,   0, 2, 3,    // front
           4, 5, 6,   4, 6, 7,    // right
           8, 9,10,   8,10,11,    // top
          12,13,14,  12,14,15,    // left
          16,17,18,  16,18,19,    // bottom
          20,21,22,  20,22,23 ]   // back
      );

    var retval = { };
    
    retval.normalObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.normalObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, normals, ctx.STATIC_DRAW);
    
    retval.texCoordObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.texCoordObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, texCoords, ctx.STATIC_DRAW);

    retval.vertexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.vertexObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, vertices, ctx.STATIC_DRAW);
    
    ctx.bindBuffer(ctx.ARRAY_BUFFER, 0);

    retval.indexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, retval.indexObject);
    ctx.bufferData(ctx.ELEMENT_ARRAY_BUFFER, indices, ctx.STATIC_DRAW);
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, 0);
    
    retval.numIndices = indices.length;

    return retval;
}

// 
// makeSphere
//
// Create a sphere with the passed number of latitude and longitude bands and the passed radius. 
// Sphere has vertices, normals and texCoords. Create VBOs for each as well as the index array.
// Return an object with the following properties:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
// 
function makeSphere(ctx, radius, lats, longs)
{
    var geometryData = [ ];
    var normalData = [ ];
    var texCoordData = [ ];
    var indexData = [ ];
    
    for (var latNumber = 0; latNumber <= lats; ++latNumber) {
        for (var longNumber = 0; longNumber <= longs; ++longNumber) {
            var theta = latNumber * Math.PI / lats;
            var phi = longNumber * 2 * Math.PI / longs;
            var sinTheta = Math.sin(theta);
            var sinPhi = Math.sin(phi);
            var cosTheta = Math.cos(theta);
            var cosPhi = Math.cos(phi);
            
            var x = cosPhi * sinTheta;
            var y = cosTheta;
            var z = sinPhi * sinTheta;
            var u = 1-(longNumber/longs);
            var v = latNumber/lats;
            
            normalData.push(x);
            normalData.push(y);
            normalData.push(z);
            texCoordData.push(u);
            texCoordData.push(v);
            geometryData.push(radius * x);
            geometryData.push(radius * y);
            geometryData.push(radius * z);
        }
    }
    
    longs += 1;
    for (var latNumber = 0; latNumber < lats; ++latNumber) {
        for (var longNumber = 0; longNumber < longs; ++longNumber) {
            var first = (latNumber * longs) + (longNumber % longs);
            var second = first + longs;
            indexData.push(first);
            indexData.push(second);
            indexData.push(first+1);

            indexData.push(second);
            indexData.push(second+1);
            indexData.push(first+1);
        }
    }
    
    var retval = { };
    
    retval.normalObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.normalObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new WebGLFloatArray(normalData), ctx.STATIC_DRAW);

    retval.texCoordObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.texCoordObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new WebGLFloatArray(texCoordData), ctx.STATIC_DRAW);

    retval.vertexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ARRAY_BUFFER, retval.vertexObject);
    ctx.bufferData(ctx.ARRAY_BUFFER, new WebGLFloatArray(geometryData), ctx.STATIC_DRAW);
    
    retval.numIndices = indexData.length;
    retval.indexObject = ctx.createBuffer();
    ctx.bindBuffer(ctx.ELEMENT_ARRAY_BUFFER, retval.indexObject);
    ctx.bufferData(ctx.ELEMENT_ARRAY_BUFFER, new WebGLUnsignedShortArray(indexData), ctx.STREAM_DRAW);
    
    return retval;
}

//
// loadObj
//
// Load a .obj file from the passed URL. Return an object with a 'loaded' property set to false.
// When the object load is complete, the 'loaded' property becomes true and the following 
// properties are set:
//
//  normalObject        WebGLBuffer object for normals
//  texCoordObject      WebGLBuffer object for texCoords
//  vertexObject        WebGLBuffer object for vertices
//  indexObject         WebGLBuffer object for indices
//  numIndices          The number of indices in the indexObject
//  
function loadObj(ctx, url)
{
    var obj = { loaded : false };
    obj.ctx = ctx;
    var req = new XMLHttpRequest();
    req.obj = obj;
    req.onreadystatechange = function () { processLoadObj(req) };
    req.open("GET", url, true);
    req.send(null);
    return obj;
}

function processLoadObj(req) 
{
    console.log("req="+req)
    // only if req shows "complete"
    if (req.readyState == 4) {
        doLoadObj(req.obj, req.responseText);
    }
}

function doLoadObj(obj, text)
{
    vertexArray = [ ];
    normalArray = [ ];
    textureArray = [ ];
    indexArray = [ ];
    
    var vertex = [ ];
    var normal = [ ];
    var texture = [ ];
    var facemap = { };
    var index = 0;
        
    var lines = text.split("\n");
    for (var lineIndex in lines) {
        var line = lines[lineIndex].replace(/[ \t]+/g, " ").replace(/\s\s*$/, "");
        
        // ignore comments
        if (line[0] == "#")
            continue;
            
        var array = line.split(" ");
        if (array[0] == "v") {
            // vertex
            vertex.push(parseFloat(array[1]));
            vertex.push(parseFloat(array[2]));
            vertex.push(parseFloat(array[3]));
        }
        else if (array[0] == "vt") {
            // normal
            texture.push(parseFloat(array[1]));
            texture.push(parseFloat(array[2]));
        }
        else if (array[0] == "vn") {
            // normal
            normal.push(parseFloat(array[1]));
            normal.push(parseFloat(array[2]));
            normal.push(parseFloat(array[3]));
        }
        else if (array[0] == "f") {
            // face
            if (array.length != 4) {
                console.log("*** Error: face '"+line+"' not handled");
                continue;
            }
            
            for (var i = 1; i < 4; ++i) {
                if (!(array[i] in facemap)) {
                    // add a new entry to the map and arrays
                    var f = array[i].split("/");
                    var vtx, nor, tex;
                    
                    if (f.length == 1) {
                        vtx = parseInt(f[0]) - 1;
                        nor = vtx;
                        tex = vtx;
                    }
                    else if (f.length = 3) {
                        vtx = parseInt(f[0]) - 1;
                        tex = parseInt(f[1]) - 1;
                        nor = parseInt(f[2]) - 1;
                    }
                    else {
                        console.log("*** Error: did not understand face '"+array[i]+"'");
                        return null;
                    }
                    
                    // do the vertices
                    var x = 0;
                    var y = 0;
                    var z = 0;
                    if (vtx * 3 + 2 < vertex.length) {
                        x = vertex[vtx*3];
                        y = vertex[vtx*3+1];
                        z = vertex[vtx*3+2];
                    }
                    vertexArray.push(x);
                    vertexArray.push(y);
                    vertexArray.push(z);
                    
                    // do the textures
                    x = 0;
                    y = 0;
                    if (tex * 2 + 1 < texture.length) {
                        x = texture[tex*2];
                        y = texture[tex*2+1];
                    }
                    textureArray.push(x);
                    textureArray.push(y);
                    
                    // do the normals
                    x = 0;
                    y = 0;
                    z = 1;
                    if (nor * 3 + 2 < normal.length) {
                        x = normal[nor*3];
                        y = normal[nor*3+1];
                        z = normal[nor*3+2];
                    }
                    normalArray.push(x);
                    normalArray.push(y);
                    normalArray.push(z);
                    
                    facemap[array[i]] = index++;
                }
                
                indexArray.push(facemap[array[i]]);
            }
        }
    }

    // set the VBOs
    obj.normalObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.normalObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new WebGLFloatArray(normalArray), obj.ctx.STATIC_DRAW);

    obj.texCoordObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.texCoordObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new WebGLFloatArray(textureArray), obj.ctx.STATIC_DRAW);

    obj.vertexObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ARRAY_BUFFER, obj.vertexObject);
    obj.ctx.bufferData(obj.ctx.ARRAY_BUFFER, new WebGLFloatArray(vertexArray), obj.ctx.STATIC_DRAW);
    
    obj.numIndices = indexArray.length;
    obj.indexObject = obj.ctx.createBuffer();
    obj.ctx.bindBuffer(obj.ctx.ELEMENT_ARRAY_BUFFER, obj.indexObject);
    obj.ctx.bufferData(obj.ctx.ELEMENT_ARRAY_BUFFER, new WebGLUnsignedShortArray(indexArray), obj.ctx.STREAM_DRAW);
    
    obj.loaded = true;
}

//
// loadImageTexture
//
// Load the image at the passed url, place it in a new WebGLTexture object and return the WebGLTexture.
//
function loadImageTexture(ctx, url)
{
    var texture = ctx.createTexture();
    texture.image = new Image();
    texture.image.onload = function() { doLoadImageTexture(ctx, texture.image, texture) }
    texture.image.src = url;
    return texture;
}

function doLoadImageTexture(ctx, image, texture)
{
    ctx.enable(ctx.TEXTURE_2D);
    ctx.bindTexture(ctx.TEXTURE_2D, texture);
    ctx.texImage2D(ctx.TEXTURE_2D, 0, image);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_MAG_FILTER, ctx.LINEAR);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_MIN_FILTER, ctx.LINEAR_MIPMAP_LINEAR);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_WRAP_S, ctx.CLAMP_TO_EDGE);
    ctx.texParameteri(ctx.TEXTURE_2D, ctx.TEXTURE_WRAP_T, ctx.CLAMP_TO_EDGE);
    ctx.generateMipmap(ctx.TEXTURE_2D)
    ctx.bindTexture(ctx.TEXTURE_2D, 0);
}

//
// Framerate object
//
// This object keeps track of framerate and displays it as the innerHTML text of the 
// HTML element with the passed id. Once created you call snapshot at the end
// of every rendering cycle. Every 500ms the framerate is updated in the HTML element.
//
Framerate = function(id)
{
    this.numFramerates = 10;
    this.framerateUpdateInterval = 500;
    this.id = id;

    this.renderTime = -1;
    this.framerates = [ ];
    self = this;
    var fr = function() { self.updateFramerate() }
    setInterval(fr, this.framerateUpdateInterval);
}

Framerate.prototype.updateFramerate = function()
{
    var tot = 0;
    for (var i = 0; i < this.framerates.length; ++i)
        tot += this.framerates[i];
        
    var framerate = tot / this.framerates.length;
    framerate = Math.round(framerate);
    document.getElementById(this.id).innerHTML = "Framerate:"+framerate+"fps";
}

Framerate.prototype.snapshot = function()
{
    if (this.renderTime < 0)
        this.renderTime = new Date().getTime();
    else {
        var newTime = new Date().getTime();
        var t = newTime - this.renderTime;
        var framerate = 1000/t;
        this.framerates.push(framerate);
        while (this.framerates.length > this.numFramerates)
            this.framerates.shift();
        this.renderTime = newTime;
    }
}