/*
* Canvas2Image v0.1
* Copyright (c) 2008 Jacob Seidelin, jseidelin@nihilogic.dk
* MIT License [http://www.opensource.org/licenses/mit-license.php]
*/

var Canvas2Image = (function () {

    // check if we have canvas support
    var bHasCanvas = false;
    var oCanvas = document.createElement("canvas");
    if (!!oCanvas.getContext && !!oCanvas.getContext("2d")) {
        bHasCanvas = true;
    }

    // no canvas, bail out.
    if (!bHasCanvas) {
        return {
            saveAsBMP: function () { },
            saveAsPNG: function () { },
            saveAsJPEG: function () { }
        }
    }

    var bHasImageData = !!oCanvas.getContext && !!oCanvas.getContext("2d").getImageData;
    var bHasDataURL = !!(oCanvas.toDataURL);
    var bHasBase64 = !!(window.btoa);

    var strDownloadMime = "image/octet-stream";

    // ok, we're good
    var readCanvasData = function (oCanvas) {
        var iWidth = parseInt(oCanvas.width);
        var iHeight = parseInt(oCanvas.height);
        return oCanvas.getContext("2d").getImageData(0, 0, iWidth, iHeight);
    }

    // base64 encodes either a string or an array of charcodes
    var encodeData = function (data) {
        var strData = "";
        if (typeof data == "string") {
            strData = data;
        } else {
            var aData = data;
            for (var i = 0; i < aData.length; i++) {
                strData += String.fromCharCode(aData[i]);
            }
        }
        return btoa(strData);
    }

    // creates a base64 encoded string containing BMP data
    // takes an imagedata object as argument
    var createBMP = function (oData) {
        var aHeader = [];

        var iWidth = oData.width;
        var iHeight = oData.height;

        aHeader.push(0x42); // magic 1
        aHeader.push(0x4D);

        var iFileSize = iWidth * iHeight * 3 + 54; // total header size = 54 bytes
        aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        aHeader.push(iFileSize % 256);

        aHeader.push(0); // reserved
        aHeader.push(0);
        aHeader.push(0); // reserved
        aHeader.push(0);

        aHeader.push(54); // dataoffset
        aHeader.push(0);
        aHeader.push(0);
        aHeader.push(0);

        var aInfoHeader = [];
        aInfoHeader.push(40); // info header size
        aInfoHeader.push(0);
        aInfoHeader.push(0);
        aInfoHeader.push(0);

        var iImageWidth = iWidth;
        aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        aInfoHeader.push(iImageWidth % 256);

        var iImageHeight = iHeight;
        aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        aInfoHeader.push(iImageHeight % 256);

        aInfoHeader.push(1); // num of planes
        aInfoHeader.push(0);

        aInfoHeader.push(24); // num of bits per pixel
        aInfoHeader.push(0);

        aInfoHeader.push(0); // compression = none
        aInfoHeader.push(0);
        aInfoHeader.push(0);
        aInfoHeader.push(0);

        var iDataSize = iWidth * iHeight * 3;
        aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        aInfoHeader.push(iDataSize % 256);

        for (var i = 0; i < 16; i++) {
            aInfoHeader.push(0); // these bytes not used
        }

        var iPadding = (4 - ((iWidth * 3) % 4)) % 4;

        var aImgData = oData.data;

        var strPixelData = "";
        var y = iHeight;
        do {
            var iOffsetY = iWidth * (y - 1) * 4;
            var strPixelRow = "";
            for (var x = 0; x < iWidth; x++) {
                var iOffsetX = 4 * x;

                strPixelRow += String.fromCharCode(aImgData[iOffsetY + iOffsetX + 2]);
                strPixelRow += String.fromCharCode(aImgData[iOffsetY + iOffsetX + 1]);
                strPixelRow += String.fromCharCode(aImgData[iOffsetY + iOffsetX]);
            }
            for (var c = 0; c < iPadding; c++) {
                strPixelRow += String.fromCharCode(0);
            }
            strPixelData += strPixelRow;
        } while (--y);

        var strEncoded = encodeData(aHeader.concat(aInfoHeader)) + encodeData(strPixelData);

        return strEncoded;
    }


    // sends the generated file to the client
    var saveFile = function (strData) {
        document.location.href = strData;
    }

    var makeDataURI = function (strData, strMime) {
        return "data:" + strMime + ";base64," + strData;
    }

    // generates a <img> object containing the imagedata
    var makeImageObject = function (strSource) {
        var oImgElement = document.createElement("img");
        oImgElement.src = strSource;
        return oImgElement;
    }

    var scaleCanvas = function (oCanvas, iWidth, iHeight) {
        if (iWidth && iHeight) {
            var oSaveCanvas = document.createElement("canvas");
            oSaveCanvas.width = iWidth;
            oSaveCanvas.height = iHeight;
            oSaveCanvas.style.width = iWidth + "px";
            oSaveCanvas.style.height = iHeight + "px";

            var oSaveCtx = oSaveCanvas.getContext("2d");

            oSaveCtx.drawImage(oCanvas, 0, 0, oCanvas.width, oCanvas.height, 0, 0, iWidth, iHeight);
            return oSaveCanvas;
        }
        return oCanvas;
    }

    return {

        saveAsPNG: function (oCanvas, bReturnImg, iWidth, iHeight) {
            if (!bHasDataURL) {
                return false;
            }
            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);
            var strData = oScaledCanvas.toDataURL("image/gif");
            if (bReturnImg) {
                return makeImageObject(strData);
            } else {
                saveFile(strData.replace("image/gif", strDownloadMime));
            }
            return true;
        },

        saveAsJPEG: function (oCanvas, bReturnImg, iWidth, iHeight) {
            if (!bHasDataURL) {
                return false;
            }

            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);
            var strMime = "image/gif";
            var strData = oScaledCanvas.toDataURL(strMime);

            // check if browser actually supports jpeg by looking for the mime type in the data uri.
            // if not, return false
            if (strData.indexOf(strMime) != 5) {
                return false;
            }

            if (bReturnImg) {
                return makeImageObject(strData);
            } else {
                saveFile(strData.replace(strMime, strDownloadMime));
            }
            return true;
        },

        saveAsBMP: function (oCanvas, bReturnImg, iWidth, iHeight) {
            if (!(bHasImageData && bHasBase64)) {
                return false;
            }

            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);

            var oData = readCanvasData(oScaledCanvas);
            var strImgData = createBMP(oData);
            if (bReturnImg) {
                return makeImageObject(makeDataURI(strImgData, "image/gif"));
            } else {
                saveFile(makeDataURI(strImgData, strDownloadMime));
            }
            return true;
        }
    };

})();