/**

* Buffered Binary Ajax 0.2.1

* Copyright (c) 2010 António Afonso, antonio.afonso gmail, http://www.aadsm.net/

* MIT License [http://www.opensource.org/licenses/mit-license.php]

*

* Adapted from Binary Ajax 0.1.5

*/

/**

* This function prepares a BufferedBinaryFile object for reading the file pointed by the URL given.

*

* @param {String} strUrl The URL with the location of the file to be read.

* @param {function(BufferedBinaryFile)} fncCallback The function that will be invoked when the BufferedBinaryFile is ready to be used.

* @param {function()} fncError The function that will be invoked when an error occrus, for instance, the file pointed by the URL is doesn't exist.

*/

var BinaryFile = require('./binaryfile');

var BufferedBinaryAjax = function(strUrl, fncCallback, fncError) {

function sendRequest(strURL, fncCallback, fncError, aRange, bAcceptRanges, iFileSize, bAsync) {

var oHTTP = createRequest();

if (oHTTP) {

var iDataOffset = 0;

if (aRange && !bAcceptRanges) {

iDataOffset = aRange[0];

}

var iDataLen = 0;

if (aRange) {

iDataLen = aRange[1]-aRange[0]+1;

}

if( typeof bAsync === "undefined" ) bAsync = true;

if (fncCallback) {

if (typeof(oHTTP.onload) != "undefined") {

oHTTP.onload = function() {

if (oHTTP.status == "200" || oHTTP.status == "206") {

oHTTP.fileSize = iFileSize || oHTTP.getResponseHeader("Content-Length");

fncCallback(oHTTP);

} else {

if (fncError) {

fncError({error: "xhr", "xhr": oHTTP});

}

}

oHTTP = null;

};

if (fncError) {

oHTTP.onerror = function() {

fncError({error: "xhr", "xhr": oHTTP});

oHTTP = null;

};

}

} else {

oHTTP.onreadystatechange = function() {

if (oHTTP.readyState == 4) {

if (oHTTP.status == "200" || oHTTP.status == "206") {

oHTTP.fileSize = iFileSize || oHTTP.getResponseHeader("Content-Length");

fncCallback(oHTTP);

} else {

if (fncError) {

fncError({error: "xhr", "xhr": oHTTP});

}

}

oHTTP = null;

}

};

}

}

oHTTP.open("GET", strURL, bAsync);

if (oHTTP.overrideMimeType) oHTTP.overrideMimeType('text/plain; charset=x-user-defined');

if (aRange && bAcceptRanges) {

oHTTP.setRequestHeader("Range", "bytes=" + aRange[0] + "-" + aRange[1]);

}

oHTTP.setRequestHeader("If-Modified-Since", "Sat, 01 Jan 1970 00:00:00 GMT");

oHTTP.send(null);

} else {

if (fncError) {

fncError({error: "Unable to create XHR object"});

}

}

}

function createRequest() {

var oHTTP = null;

if (typeof window === 'undefined') {

oHTTP = new (require("xmlhttprequest").XMLHttpRequest)();

} else if (window.XMLHttpRequest) {

oHTTP = new window.XMLHttpRequest();

} else if (window.ActiveXObject) {

oHTTP = new window.ActiveXObject("Microsoft.XMLHTTP");

}

return oHTTP;

}

function getHead(strURL, fncCallback, fncError) {

var oHTTP = createRequest();

if (oHTTP) {

if (fncCallback) {

if (typeof(oHTTP.onload) != "undefined") {

oHTTP.onload = function() {

if (oHTTP.status == "200" || oHTTP.status == "206") {

fncCallback(this);

} else {

if (fncError) {

fncError({error: "xhr", "xhr": oHTTP});

}

}

oHTTP = null;

};

if (fncError) {

oHTTP.onerror = function() {

fncError({error: "xhr", "xhr": oHTTP});

oHTTP = null;

};

}

} else {

oHTTP.onreadystatechange = function() {

if (oHTTP.readyState == 4) {

if (oHTTP.status == "200" || oHTTP.status == "206") {

fncCallback(this);

} else {

if (fncError) {

fncError({error: "xhr", "xhr": oHTTP});

}

}

oHTTP = null;

}

};

}

}

oHTTP.open("HEAD", strURL, true);

oHTTP.send(null);

} else {

if (fncError) {

fncError({error: "Unable to create XHR object"});

}

}

}

/**

* @class Reads a remote file without having to download it all.

*

* Creates a new BufferedBinaryFile that will download chunks of the file pointed by the URL given only on a per need basis.

*

* @param {string} strUrl The URL with the location of the file to be read.

* @param {number} iLength The size of the file.

* @param {number} [blockSize=2048] The size of the chunk that will be downloaded when data is read.

* @param {number} [blockRadius=0] The number of chunks, immediately after and before the chunk needed, that will also be downloaded.

*

* @constructor

* @augments BinaryFile

*/

function BufferedBinaryFile(strUrl, iLength, blockSize, blockRadius) {

var undefined;

var downloadedBytesCount = 0;

var binaryFile = new BinaryFile("", 0, iLength);

var blocks = [];

blockSize = blockSize || 1024*2;

blockRadius = (typeof blockRadius === "undefined") ? 0 : blockRadius;

blockTotal = ~~((iLength-1)/blockSize) + 1;

function getBlockRangeForByteRange(range) {

var blockStart = ~~(range[0]/blockSize) - blockRadius;

var blockEnd = ~~(range[1]/blockSize)+1 + blockRadius;

if( blockStart < 0 ) blockStart = 0;

if( blockEnd >= blockTotal ) blockEnd = blockTotal-1;

return [blockStart, blockEnd];

}

// TODO: wondering if a "recently used block" could help things around

// here.

function getBlockAtOffset(offset) {

var blockRange = getBlockRangeForByteRange([offset, offset]);

waitForBlocks(blockRange);

return blocks[~~(offset/blockSize)];

}

/**

* @param {?function()} callback If a function is passed then this function will be asynchronous and the callback invoked when the blocks have been loaded, otherwise it blocks script execution until the request is completed.

*/

function waitForBlocks(blockRange, callback) {

// Filter out already downloaded blocks or return if found out that

// the entire block range has already been downloaded.

while( blocks[blockRange[0]] ) {

blockRange[0]++;

if( blockRange[0] > blockRange[1] ) return callback ? callback() : undefined;

}

while( blocks[blockRange[1]] ) {

blockRange[1]--;

if( blockRange[0] > blockRange[1] ) return callback ? callback() : undefined;

}

var range = [blockRange[0]*blockSize, (blockRange[1]+1)*blockSize-1];

//console.log("Getting: " + range[0] + " to " + range[1]);

sendRequest(

strUrl,

function(http) {

var size = parseInt(http.getResponseHeader("Content-Length"), 10);

// Range header not supported

if( size == iLength ) {

blockRange[0] = 0;

blockRange[1] = blockTotal-1;

range[0] = 0;

range[1] = iLength-1;

}

var block = {

data: http.responseBody || http.responseText,

offset: range[0]

};

for( var i = blockRange[0]; i <= blockRange[1]; i++ ) {

blocks[i] = block;

}

downloadedBytesCount += range[1] - range[0] + 1;

if (callback) callback();

},

fncError,

range,

"bytes",

undefined,

!!callback

);

}

// Mixin all BinaryFile's methods.

// Not using prototype linking since the constructor needs to know

// the length of the file.

for( var key in binaryFile ) {

if( binaryFile.hasOwnProperty(key) &&

typeof binaryFile[key] === "function") {

this[key] = binaryFile[key];

}

}

/**

* @override

*/

this.getByteAt = function(iOffset) {

var block = getBlockAtOffset(iOffset);

if( block && typeof block.data == "string" ) {

return block.data.charCodeAt(iOffset - block.offset) & 0xFF;

} else if( block && typeof block.data == "unknown" ) {

return IEBinary_getByteAt(block.data, iOffset - block.offset);

} else {

return ""

}

};

/**

* Gets the number of total bytes that have been downloaded.

*

* @returns The number of total bytes that have been downloaded.

*/

this.getDownloadedBytesCount = function() {

return downloadedBytesCount;

};

/**

* Downloads the byte range given. Useful for preloading.

*

* @param {Array} range Two element array that denotes the first byte to be read on the first position and the last byte to be read on the last position. A range of [2, 5] will download bytes 2,3,4 and 5.

* @param {?function()} callback The function to invoke when the blocks have been downloaded, this makes this call asynchronous.

*/

this.loadRange = function(range, callback) {

var blockRange = getBlockRangeForByteRange(range);

waitForBlocks(blockRange, callback);

};

}

function init() {

getHead(

strUrl,

function(oHTTP) {

var iLength = parseInt(oHTTP.getResponseHeader("Content-Length"),10) || -1;

fncCallback(new BufferedBinaryFile(strUrl, iLength));

},

fncError

);

}

init();

};

module.exports = BufferedBinaryAjax;