/**
 * Adapted from https://github.com/beatgammit/base64-js
 * @author Jameson Little
 * @author Alex Goldring
 */

/**
 *
 * @type {string[]}
 */
const lookup = [];

/**
 *
 * @type {number[]}
 */
const revLookup = [];

const code = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

for (let i = 0, len = code.length; i < len; ++i) {
    lookup[i] = code[i];
    revLookup[code.charCodeAt(i)] = i;
}

// Support decoding URL-safe base64 strings, as Node.js does.
// See: https://en.wikipedia.org/wiki/Base64#URL_applications
revLookup['-'.charCodeAt(0)] = 62;
revLookup['_'.charCodeAt(0)] = 63;

/**
 *
 * @param {string} b64
 * @return {number[]}
 */
function getLens(b64) {
    const len = b64.length;

    if (len % 4 > 0) {
        throw new Error('Invalid string. Length must be a multiple of 4');
    }

    // Trim off extra bytes after placeholder bytes are found
    // See: https://github.com/beatgammit/base64-js/issues/42
    let validLen = b64.indexOf('=');

    if (validLen === -1) {
        validLen = len;
    }

    const placeHoldersLen = validLen === len
        ? 0
        : 4 - (validLen % 4);

    return [validLen, placeHoldersLen];
}

/**
 * base64 is 4/3 + up to two characters of the original data
 * @param {number} validLen
 * @param {number} placeHoldersLen
 */
function _byteLength(validLen, placeHoldersLen) {
    return ((validLen + placeHoldersLen) * 3 / 4) - placeHoldersLen;
}

/**
 *
 * @param {string} b64
 * @return {Uint8Array}
 */
function toByteArray(b64) {
    let tmp;
    const lens = getLens(b64);
    const validLen = lens[0];
    const placeHoldersLen = lens[1];

    const arr = new Uint8Array(_byteLength(validLen, placeHoldersLen));

    let curByte = 0;

    // if there are placeholders, only get up to the last complete 4 chars
    const len = placeHoldersLen > 0
        ? validLen - 4
        : validLen;

    let i = 0;

    for (; i < len; i += 4) {
        const char_0 = b64.charCodeAt(i);
        const char_1 = b64.charCodeAt(i + 1);
        const char_2 = b64.charCodeAt(i + 2);
        const char_3 = b64.charCodeAt(i + 3);

        tmp =
            (revLookup[char_0] << 18) |
            (revLookup[char_1] << 12) |
            (revLookup[char_2] << 6) |
            revLookup[char_3];

        arr[curByte++] = (tmp >> 16) & 0xFF;
        arr[curByte++] = (tmp >> 8) & 0xFF;
        arr[curByte++] = tmp & 0xFF;
    }

    if (placeHoldersLen === 2) {
        const char_0 = b64.charCodeAt(i);
        const char_1 = b64.charCodeAt(i + 1);

        tmp =
            (revLookup[char_0] << 2) |
            (revLookup[char_1] >> 4);

        arr[curByte++] = tmp & 0xFF;
    }

    if (placeHoldersLen === 1) {
        const char_0 = b64.charCodeAt(i);
        const char_1 = b64.charCodeAt(i + 1);
        const char_2 = b64.charCodeAt(i + 2);

        tmp =
            (revLookup[char_0] << 10) |
            (revLookup[char_1] << 4) |
            (revLookup[char_2] >> 2);

        arr[curByte++] = (tmp >> 8) & 0xFF;
        arr[curByte++] = tmp & 0xFF;
    }

    return arr;
}

/**
 *
 * @param {number} num
 * @return {string}
 */
function tripletToBase64(num) {
    return lookup[num >> 18 & 0x3F]
        + lookup[num >> 12 & 0x3F]
        + lookup[num >> 6 & 0x3F]
        + lookup[num & 0x3F]
        ;
}

/**
 *
 * @param {Uint8Array} uint8
 * @param {number} start
 * @param {number} end
 * @return {string}
 */
function encodeChunk(uint8, start, end) {
    const output = [];

    for (let i = start; i < end; i += 3) {

        const tmp = ((uint8[i] << 16) & 0xFF0000)
            + ((uint8[i + 1] << 8) & 0xFF00)
            + (uint8[i + 2] & 0xFF);

        output.push(tripletToBase64(tmp));
    }

    return output.join('');
}

/**
 * must be multiple of 3
 */
const MAX_CHUNK_LENGTH = 16383;

/**
 *
 * @param {Uint8Array} uint8
 * @return {string}
 */
function fromByteArray(uint8) {

    const len = uint8.length;

    const extraBytes = len % 3; // if we have 1 byte left, pad 2 bytes

    const parts = [];

    // go through the array every three bytes, we'll deal with trailing stuff later
    const len2 = len - extraBytes;

    for (let i = 0; i < len2; i += MAX_CHUNK_LENGTH) {
        const end = (i + MAX_CHUNK_LENGTH) > len2 ? len2 : (i + MAX_CHUNK_LENGTH);

        const chunk = encodeChunk(uint8, i, end);

        parts.push(chunk);
    }

    // pad the end with zeros, but make sure to not forget the extra bytes
    if (extraBytes === 1) {

        const tmp = uint8[len - 1];

        parts.push(
            lookup[tmp >> 2] +
            lookup[(tmp << 4) & 0x3F] +
            '=='
        );

    } else if (extraBytes === 2) {

        const tmp = (uint8[len - 2] << 8) + uint8[len - 1];

        parts.push(
            lookup[tmp >> 10] +
            lookup[(tmp >> 4) & 0x3F] +
            lookup[(tmp << 2) & 0x3F] +
            '='
        );

    }

    return parts.join('');
}

export class Base64 {
    /**
     *
     * @param {ArrayBuffer} value
     * @returns {string}
     */
    static encode(value) {

        const array = new Uint8Array(value);

        return fromByteArray(array);
    }

    /**
     *
     * @param {string} value
     * @returns {ArrayBuffer}
     */
    static decode(value) {
        /**
         *
         * @type {Uint8Array}
         */
        const array = toByteArray(value);

        return array.buffer;
    }
}
