/**
 * From https://github.com/donmccurdy/zstddec by Don McCurdy
 */
interface DecoderExports {
    memory: Uint8Array;

    ZSTD_findDecompressedSize: (compressedPtr: number, compressedSize: number) => number;
    ZSTD_decompress: (uncompressedPtr: number, uncompressedSize: number, compressedPtr: number, compressedSize: number) => number;
    malloc: (ptr: number) => number;
    free: (ptr: number) => void;
}

let init: Promise<void>;
let instance: {exports: DecoderExports};
let heap: Uint8Array;

const IMPORT_OBJECT = {

    env: {

        emscripten_notify_memory_growth: function (index: number): void {

            heap = new Uint8Array(instance.exports.memory.buffer);

        }

    }

};

/**
 * ZSTD (Zstandard) decoder.
 */
export class ZSTDDecoder {

    public static WasmModuleURL = "https://preview.babylonjs.com/zstddec.wasm";

    init (): Promise<void> {

        if (init) { return init; }

        if (typeof fetch !== 'undefined') {

            // Web.

            init = fetch(ZSTDDecoder.WasmModuleURL)
                .then((response) => {
                    if (response.ok) {
                        return response.arrayBuffer();
                    }
                    throw new Error(`Could not fetch the wasm component for the Zstandard decompression lib: ${response.status} - ${response.statusText}`);
                })
                .then((arrayBuffer) => WebAssembly.instantiate(arrayBuffer, IMPORT_OBJECT))
                .then(this._init);

        } else {

            // Node.js.

            init = WebAssembly
                .instantiateStreaming(fetch(ZSTDDecoder.WasmModuleURL), IMPORT_OBJECT)
                .then(this._init);

        }

        return init;

    }

    _init (result: WebAssembly.WebAssemblyInstantiatedSource): void {

        instance = result.instance as unknown as { exports: DecoderExports };

        IMPORT_OBJECT.env.emscripten_notify_memory_growth(0); // initialize heap.

    }

    decode (array: Uint8Array, uncompressedSize = 0): Uint8Array {

        if (! instance) { throw new Error(`ZSTDDecoder: Await .init() before decoding.`); }

        // Write compressed data into WASM memory.
        const compressedSize = array.byteLength;
        const compressedPtr = instance.exports.malloc(compressedSize);
        heap.set(array, compressedPtr);

        // Decompress into WASM memory.
        uncompressedSize = uncompressedSize || Number(instance.exports.ZSTD_findDecompressedSize(compressedPtr, compressedSize));
        const uncompressedPtr = instance.exports.malloc(uncompressedSize);
        const actualSize = instance.exports.ZSTD_decompress(uncompressedPtr, uncompressedSize, compressedPtr, compressedSize);

        // Read decompressed data and free WASM memory.
        const dec = heap.slice(uncompressedPtr, uncompressedPtr + actualSize);
        instance.exports.free(compressedPtr);
        instance.exports.free(uncompressedPtr);

        return dec;

    }

}

/**
 * BSD License
 *
 * For Zstandard software
 *
 * Copyright (c) 2016-present, Yann Collet, Facebook, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name Facebook nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */