/*---------------------------------------------------------------------------------------------

* Copyright (c) Microsoft Corporation. All rights reserved.

* Licensed under the MIT License. See License.txt in the project root for license information.

*--------------------------------------------------------------------------------------------*/

'use strict';

import stream = require('vs/base/node/stream');

export var UTF8 = 'utf8';

export var UTF16be = 'utf16be';

export var UTF16le = 'utf16le';

export function detectEncodingByBOMFromBuffer(buffer: NodeBuffer, bytesRead: number): string {

if (!buffer || bytesRead < 2) {

return null;

}

var b0 = buffer.readUInt8(0);

var b1 = buffer.readUInt8(1);

// UTF-16 BE

if (b0 === 0xFE && b1 === 0xFF) {

return UTF16be;

}

// UTF-16 LE

if (b0 === 0xFF && b1 === 0xFE) {

return UTF16le;

}

if (bytesRead < 3) {

return null;

}

var b2 = buffer.readUInt8(2);

// UTF-8

if (b0 === 0xEF && b1 === 0xBB && b2 === 0xBF) {

return UTF8;

}

return null;

};

/**

* Detects the Byte Order Mark in a given file.

* If no BOM is detected, `encoding` will be null.

*/

export function detectEncodingByBOM(file: string, callback: (error: Error, encoding: string) => void): void {

stream.readExactlyByFile(file, 3, (err: Error, buffer: NodeBuffer, bytesRead: number) => {

if (err) {

return callback(err, null);

}

return callback(null, detectEncodingByBOMFromBuffer(buffer, bytesRead));

});

}