/*
 * ImageInfo 0.1.2 - A JavaScript library for reading image metadata.
 * Copyright (c) 2008 Jacob Seidelin, jseidelin@nihilogic.dk, http://blog.nihilogic.dk/
 * MIT License [http://www.nihilogic.dk/licenses/mit-license.txt]
 */


var ImageInfo = {};

ImageInfo.useRange = false;
ImageInfo.range = 10240;

(function() {

	var files = [];

	function readFileData(url, callback, errorCallback ) {
		BinaryAjax(
			url,
			function(http) {
				var tags = readInfoFromData(http.binaryResponse);
				var mime = http.getResponseHeader("Content-Type");

				tags["mimeType"] = mime;
				tags["byteSize"] = http.fileSize;

				files[url] = tags;
				if (callback) callback();
			},
			function(http) {
                            if (errorCallback) errorCallback();
                        },
			ImageInfo.useRange ? [0, ImageInfo.range] : null
		);
	}

	function readInfoFromData(data) {

		if (data.getByteAt(0) === 0xFF && data.getByteAt(1) === 0xD8) {
			return readJPEGInfo(data);
		}
		if (data.getByteAt(0) === 0x89 && data.getStringAt(1, 3) === "PNG") {
			return readPNGInfo(data);
		}
		if (data.getStringAt(0,3) === "GIF") {
			return readGIFInfo(data);
		}
		if (data.getByteAt(0) === 0x42 && data.getByteAt(1) === 0x4D) {
			return readBMPInfo(data);
		}

		return {
			format : "UNKNOWN"
		};
	}

        function getPNGITXTBlocks( data ) {
            var result= {};
            var offset= 8;
            while ( offset<data.getLength() ) {
                var len= data.getLongAt( offset,true );
                var chunkType= data.getStringAt( offset+4,4 );
                if ( chunkType==='tEXt' ) {
                    str= data.getStringAt( offset+8, len );
                    
                    i= str.indexOf('\x00');
                    result[str.substr(0,i)]= str.substr(i+1);
                }
                offset= offset + len + 12; // 12 bytes for lenth, chunk type, and CRC
            }
            return result;
        }

	function readPNGInfo(data) {
		var w = data.getLongAt(16,true);
		var h = data.getLongAt(20,true);

		var bpc = data.getByteAt(24);
		var ct = data.getByteAt(25);

		var bpp = bpc;
		if (ct === 4) bpp *= 2;
		if (ct === 2) bpp *= 3;
		if (ct === 6) bpp *= 4;

		var alpha = data.getByteAt(25) >= 4;

                var data1 = getPNGITXTBlocks(data);
                
		return {
			format : "PNG",
			version : "",
			width : w,
			height : h,
			bpp : bpp,
			alpha : alpha,
                        data: data1,
			exif : {}
		};
	}

	function readGIFInfo(data) {
		var version = data.getStringAt(3,3);
		var w = data.getShortAt(6);
		var h = data.getShortAt(8);

		var bpp = ((data.getByteAt(10) >> 4) & 7) + 1;

		return {
			format : "GIF",
			version : version,
			width : w,
			height : h,
			bpp : bpp,
			alpha : false,
			exif : {}
		};
	}

	function readJPEGInfo(data) {

		var w = 0;
		var h = 0;
		var comps = 0;
		var len = data.getLength();
		var offset = 2;
		while (offset < len) {
			var marker = data.getShortAt(offset, true);
			offset += 2;
			if (marker === 0xFFC0) {
				h = data.getShortAt(offset + 3, true);
				w = data.getShortAt(offset + 5, true);
				comps = data.getByteAt(offset + 7, true);
				break;
			} else {
				offset += data.getShortAt(offset, true);
			}
		}

		var exif = {};

		if (typeof EXIF !== "undefined" && EXIF.readFromBinaryFile) {
			exif = EXIF.readFromBinaryFile(data);
		}

		return {
			format : "JPEG",
			version : "",
			width : w,
			height : h,
			bpp : comps * 8,
			alpha : false,
			exif : exif
		};
	}

	function readBMPInfo(data) {
		var w = data.getLongAt(18);
		var h = data.getLongAt(22);
		var bpp = data.getShortAt(28);
		return {
			format : "BMP",
			version : "",
			width : w,
			height : h,
			bpp : bpp,
			alpha : false,
			exif : {}
		};
	}

	ImageInfo.loadInfo = function(url, cb, errorCallback ) {
		if (!files[url]) {
			readFileData(url, cb, errorCallback );
		} else {
			if (cb) cb();
		}
	};

	ImageInfo.getAllFields = function(url) {
		if (!files[url]) return null;

		var tags = {};
		for (var a in files[url]) {
			if (files[url].hasOwnProperty(a))
				tags[a] = files[url][a];
		}
		return tags;
	};

	ImageInfo.getField = function(url, field) {
		if (!files[url]) return null;
		return files[url][field];
	};


})();