/*
* DAPjs
* Copyright Arm Limited 2020
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/

// https://github.com/anonyco/FastestSmallestTextEncoderDecoder

const PARTIAL_CHAR_TEST = /[\xc0-\xff][\x80-\xbf]*$/g;
const DOUBLE_BYTE_REPLACE = /[\xc0-\xff][\x80-\xbf]*/g;

export class TextDecoder {

    private partialChar: string | undefined;

    /**
     * Decode an ArrayBuffer to a string, handling double-byte characters
     * @param input The ArrayBuffer to decode
     */
    public decode(input: ArrayBuffer): string {

        const numberArray = Array.prototype.slice.call(new Uint8Array(input));
        let data = String.fromCodePoint.apply(undefined, numberArray);

        if (this.partialChar) {
            // Previous double-byte character was cut off
            data = `${this.partialChar}${data}`;
            this.partialChar = undefined;
        }

        const match = data.match(PARTIAL_CHAR_TEST);
        if (match) {
            // Partial double-byte character at end of string, save it and truncate data
            const length = match[0].length;
            this.partialChar = data.slice(-length);
            data = data.slice(0, -length);
        }

        return data.replace(DOUBLE_BYTE_REPLACE, this.decoderReplacer);
    }

    private decoderReplacer(encoded: string): string {
        let codePoint = encoded.codePointAt(0)! << 24;
        const leadingOnes = Math.clz32(~codePoint);
        let endPos = 0;
        const stringLen = encoded.length;
        let result = '';
        if (leadingOnes < 5 && stringLen >= leadingOnes) {
            codePoint = (codePoint << leadingOnes) >>> (24 + leadingOnes);
            for (endPos = 1; endPos < leadingOnes; endPos = endPos + 1) {
                codePoint = (codePoint << 6) | (encoded.codePointAt(endPos)! & 0x3f);
            }
            if (codePoint <= 0xFFFF) { // BMP code point
                result += String.fromCodePoint(codePoint);
            } else if (codePoint <= 0x10FFFF) {
                // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
                codePoint = codePoint - 0x10000;
                result += String.fromCodePoint(
                    (codePoint >> 10) + 0xD800,  // highSurrogate
                    (codePoint & 0x3ff) + 0xDC00 // lowSurrogate
                );
            } else endPos = 0; // to fill it in with INVALIDs
        }
        for (; endPos < stringLen; endPos = endPos + 1) {
            result += '\ufffd'; // replacement character
        }
        return result;
    }
}