// Convert ArrayBuffer to Base64 using non-native method for better perf
// https://gist.github.com/jonleighton/958841
// https://jsperf.com/encoding-xhr-image-data/6
export function arrayBufferToBase64(arrayBuffer: ArrayBuffer): string {
    let base64: string = '';
    let encodings: string = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

    let bytes: Uint8Array = new Uint8Array(arrayBuffer);
    let byteLength: number = bytes.byteLength;
    let byteRemainder: number = byteLength % 3;
    let mainLength: number = byteLength - byteRemainder;

    let a: number;
    let b: number;
    let c: number;
    let d: number;
    let chunk: any;

    // Main loop deals with bytes in chunks of 3
    for (let i: number = 0; i < mainLength; i = i + 3) {
        // Combine the three bytes into a single integer
        chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];

        // Use bitmasks to extract 6-bit segments from the triplet
        a = (chunk & 16515072) >> 18; // 16515072 = (2^6 - 1) << 18
        b = (chunk & 258048) >> 12; // 258048 = (2^6 - 1) << 12
        c = (chunk & 4032) >> 6; // 4032 = (2^6 - 1) << 6
        d = chunk & 63; // 63 = 2^6 - 1

        // Convert the raw binary segments to the appropriate ASCII encoding
        base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d];
    }

    // Deal with the remaining bytes and padding
    if (byteRemainder === 1) {
        chunk = bytes[mainLength];

        a = (chunk & 252) >> 2; // 252 = (2^6 - 1) << 2

        // Set the 4 least significant bits to zero
        b = (chunk & 3) << 4; // 3   = 2^2 - 1

        base64 += encodings[a] + encodings[b] + '==';
    } else if (byteRemainder === 2) {
        chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];

        a = (chunk & 64512) >> 10; // 64512 = (2^6 - 1) << 10
        b = (chunk & 1008) >> 4; // 1008  = (2^6 - 1) << 4

        // Set the 2 least significant bits to zero
        c = (chunk & 15) << 2; // 15    = 2^4 - 1

        base64 += encodings[a] + encodings[b] + encodings[c] + '=';
    }

    return base64;
}