declare var DracoDecoderModule: any;
declare var WebAssembly: any;

module BABYLON {
    /**
     * Configuration for Draco compression
     */
    export interface IDracoCompressionConfiguration {
        /**
         * Configuration for the decoder.
         */
        decoder?: {
            /**
             * The url to the WebAssembly module.
             */
            wasmUrl?: string;

            /**
             * The url to the WebAssembly binary.
             */
            wasmBinaryUrl?: string;

            /**
             * The url to the fallback JavaScript module.
             */
            fallbackUrl?: string;
        };
    }

    /**
     * Draco compression (https://google.github.io/draco/)
     * 
     * This class wraps the Draco module.
     * 
     * **Encoder**
     * 
     * The encoder is not currently implemented.
     * 
     * **Decoder**
     * 
     * By default, the configuration points to a copy of the Draco decoder files for glTF from https://preview.babylonjs.com.
     * 
     * To update the configuration, use the following code:
     * ```javascript
     *     BABYLON.DracoCompression.Configuration = {
     *         decoder: {
     *             wasmUrl: "<url to the WebAssembly library>",
     *             wasmBinaryUrl: "<url to the WebAssembly binary>",
     *             fallbackUrl: "<url to the fallback JavaScript library>",
     *         }
     *     };
     * ```
     * 
     * Draco has two versions, one for WebAssembly and one for JavaScript. The decoder configuration can be set to only support Webssembly or only support the JavaScript version.
     * Decoding will automatically fallback to the JavaScript version if WebAssembly version is not configured or if WebAssembly is not supported by the browser.
     * Use `BABYLON.DracoCompression.DecoderAvailable` to determine if the decoder is available for the current session.
     * 
     * To decode Draco compressed data, create a DracoCompression object and call decodeMeshAsync:
     * ```javascript
     *     var dracoCompression = new BABYLON.DracoCompression();
     *     var vertexData = await dracoCompression.decodeMeshAsync(data, {
     *         [BABYLON.VertexBuffer.PositionKind]: 0
     *     });
     * ```
     * 
     * @see https://www.babylonjs-playground.com/#N3EK4B#0
     */
    export class DracoCompression implements IDisposable {
        private static _DecoderModulePromise: Promise<any>;

        /**
         * The configuration. Defaults to the following urls:
         * - wasmUrl: "https://preview.babylonjs.com/draco_wasm_wrapper_gltf.js"
         * - wasmBinaryUrl: "https://preview.babylonjs.com/draco_decoder_gltf.wasm"
         * - fallbackUrl: "https://preview.babylonjs.com/draco_decoder_gltf.js"
         */
        public static Configuration: IDracoCompressionConfiguration = {
            decoder: {
                wasmUrl: "https://preview.babylonjs.com/draco_wasm_wrapper_gltf.js",
                wasmBinaryUrl: "https://preview.babylonjs.com/draco_decoder_gltf.wasm",
                fallbackUrl: "https://preview.babylonjs.com/draco_decoder_gltf.js"
            }
        };

        /**
         * Returns true if the decoder is available.
         */
        public static get DecoderAvailable(): boolean {
            if (typeof DracoDecoderModule !== "undefined") {
                return true;
            }

            const decoder = DracoCompression.Configuration.decoder;
            if (decoder) {
                if (decoder.wasmUrl && decoder.wasmBinaryUrl && typeof WebAssembly === "object") {
                    return true;
                }

                if (decoder.fallbackUrl) {
                    return true;
                }
            }

            return false;
        }

        /**
         * Constructor
         */
        constructor() {
        }

        /**
         * Stop all async operations and release resources.
         */
        public dispose(): void {
        }

        /**
         * Decode Draco compressed mesh data to vertex data.
         * @param data The ArrayBuffer or ArrayBufferView for the Draco compression data
         * @param attributes A map of attributes from vertex buffer kinds to Draco unique ids
         * @returns A promise that resolves with the decoded vertex data
         */
        public decodeMeshAsync(data: ArrayBuffer | ArrayBufferView, attributes: { [kind: string]: number }): Promise<VertexData> {
            const dataView = data instanceof ArrayBuffer ? new Uint8Array(data) : data;

            return DracoCompression._GetDecoderModule().then(wrappedModule => {
                const module = wrappedModule.module;
                const vertexData = new VertexData();

                const buffer = new module.DecoderBuffer();
                buffer.Init(dataView, dataView.byteLength);

                const decoder = new module.Decoder();
                let geometry: any;
                let status: any;

                try {
                    const type = decoder.GetEncodedGeometryType(buffer);
                    switch (type) {
                        case module.TRIANGULAR_MESH:
                            geometry = new module.Mesh();
                            status = decoder.DecodeBufferToMesh(buffer, geometry);
                            break;
                        case module.POINT_CLOUD:
                            geometry = new module.PointCloud();
                            status = decoder.DecodeBufferToPointCloud(buffer, geometry);
                            break;
                        default:
                            throw new Error(`Invalid geometry type ${type}`);
                    }

                    if (!status.ok() || !geometry.ptr) {
                        throw new Error(status.error_msg());
                    }

                    const numPoints = geometry.num_points();

                    if (type === module.TRIANGULAR_MESH) {
                        const numFaces = geometry.num_faces();
                        const faceIndices = new module.DracoInt32Array();
                        try {
                            const indices = new Uint32Array(numFaces * 3);
                            for (let i = 0; i < numFaces; i++) {
                                decoder.GetFaceFromMesh(geometry, i, faceIndices);
                                const offset = i * 3;
                                indices[offset + 0] = faceIndices.GetValue(0);
                                indices[offset + 1] = faceIndices.GetValue(1);
                                indices[offset + 2] = faceIndices.GetValue(2);
                            }
                            vertexData.indices = indices;
                        }
                        finally {
                            module.destroy(faceIndices);
                        }
                    }

                    for (const kind in attributes) {
                        const uniqueId = attributes[kind];
                        const attribute = decoder.GetAttributeByUniqueId(geometry, uniqueId);
                        const dracoData = new module.DracoFloat32Array();
                        try {
                            decoder.GetAttributeFloatForAllPoints(geometry, attribute, dracoData);
                            const babylonData = new Float32Array(numPoints * attribute.num_components());
                            for (let i = 0; i < babylonData.length; i++) {
                                babylonData[i] = dracoData.GetValue(i);
                            }
                            vertexData.set(babylonData, kind);
                        }
                        finally {
                            module.destroy(dracoData);
                        }
                    }
                }
                finally {
                    if (geometry) {
                        module.destroy(geometry);
                    }

                    module.destroy(decoder);
                    module.destroy(buffer);
                }

                return vertexData;
            });
        }

        private static _GetDecoderModule(): Promise<any> {
            if (!DracoCompression._DecoderModulePromise) {
                let promise: Nullable<Promise<any>> = null;
                let config: any = {};

                if (typeof DracoDecoderModule !== "undefined") {
                    promise = Promise.resolve();
                }
                else {
                    const decoder = DracoCompression.Configuration.decoder;
                    if (decoder) {
                        if (decoder.wasmUrl && decoder.wasmBinaryUrl && typeof WebAssembly === "object") {
                            promise = Promise.all([
                                DracoCompression._LoadScriptAsync(decoder.wasmUrl),
                                DracoCompression._LoadFileAsync(decoder.wasmBinaryUrl).then(data => {
                                    config.wasmBinary = data;
                                })
                            ]);
                        }
                        else if (decoder.fallbackUrl) {
                            promise = DracoCompression._LoadScriptAsync(decoder.fallbackUrl);
                        }
                    }
                }

                if (!promise) {
                    throw new Error("Draco decoder module is not available");
                }

                DracoCompression._DecoderModulePromise = promise.then(() => {
                    return new Promise(resolve => {
                        config.onModuleLoaded = (decoderModule: any) => {
                            // decoderModule is Promise-like. Wrap before resolving to avoid loop.
                            resolve({ module: decoderModule });
                        };

                        DracoDecoderModule(config);
                    });
                });
            }

            return DracoCompression._DecoderModulePromise;
        }

        private static _LoadScriptAsync(url: string): Promise<void> {
            return new Promise((resolve, reject) => {
                Tools.LoadScript(url, () => {
                    resolve();
                }, message => {
                    reject(new Error(message));
                });
            });
        }

        private static _LoadFileAsync(url: string): Promise<ArrayBuffer> {
            return new Promise((resolve, reject) => {
                Tools.LoadFile(url, data => {
                    resolve(data as ArrayBuffer);
                }, undefined, undefined, true, (request, exception) => {
                    reject(exception);
                });
            });
        }
    }
}