/**
 * Copyright 2015 CANAL+ Group
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import hasWebassembly from "../../../../../compat/has_webassembly";
import log from "../../../../../log";
import { assertUnreachable } from "../../../../../utils/assert";
import globalScope from "../../../../../utils/global_scope";
import noop from "../../../../../utils/noop";
import type { IIrParserResponse, ILoadedXlinkData } from "../../common";
import parseMpdIr from "../../common";
import type {
  IMPDIntermediateRepresentation,
  IPeriodIntermediateRepresentation,
} from "../../node_parser_types";
import type {
  IDashParserResponse,
  ILoadedResource,
  IMPDParserArguments,
} from "../../parsers_types";
import { generateRootChildrenParser } from "./generators";
import { generateXLinkChildrenParser } from "./generators/XLink";
import ParsersStack from "./parsers_stack";
import type { AttributeName, TagName } from "./types";
import { CustomEventType } from "./types";

const MAX_READ_SIZE = 15e3;

export default class DashWasmParser {
  /**
   * Current "status" of the DASH-WASM parser.
   *
   * Can be either:
   *   - "uninitialized": Its `initialize` method hasn't been called yet.
   *   - "initializing": The `DashWasmParser` is in the process of fetching
   *     and instantiating the WebAssembly code.
   *   - "initialized": The `DashWasmParser` is ready to parse.
   *   - "failure": The `DashWasmParser` initialization failed.
   */
  public status: "uninitialized" | "initializing" | "initialized" | "failure";

  /**
   * Promise used to notify of the initialization status.
   * `null` when no initialization has happened yet.
   */
  private _initProm: Promise<void> | null;
  /** Abstraction simplifying the exploitation of the DASH-WASM parser's events. */
  private _parsersStack: ParsersStack;
  /**
   * Created WebAssembly instance.
   * `null` when no WebAssembly instance is created.
   */
  private _instance: WebAssembly.WebAssemblyInstantiatedSource | null;
  /**
   * Information about the data read by the DASH-WASM parser.
   * `null` if we're not parsing anything for the moment.
   */
  private _mpdData: {
    /**
     * First not-yet read position in `mpd`, in bytes.
     * When the parser asks for new data, we start giving data from that point
     * on.
     */
    cursor: number;
    /**
     * Complete data that needs to be parsed.
     * This is either the full MPD or xlinks.
     */
    mpd: ArrayBuffer;
  } | null;
  /**
   * Warnings event currently encountered during parsing.
   * Emptied when no parsing is taking place.
   */
  private _warnings: Error[];
  /**
   * Memory used by the WebAssembly instance.
   * `null` when no WebAssembly instance is created.
   */
  private _linearMemory: WebAssembly.Memory | null;

  /**
   * `true` if we're currently parsing a MPD.
   * Used to explicitely forbid parsing a MPD when a parsing operation is
   * already pending, as the current logic cannot handle that.
   *
   * Note that this is not needed for now because parsing should happen
   * synchronously.
   * Still, this property was added to make it much more explicit, in case of
   * future improvements.
   */
  private _isParsing: boolean;

  /**
   * Create a new `DashWasmParser`.
   */
  constructor() {
    this._parsersStack = new ParsersStack();
    this._instance = null;
    this._mpdData = null;
    this._linearMemory = null;
    this.status = "uninitialized";
    this._initProm = null;
    this._warnings = [];
    this._isParsing = false;
  }

  /**
   * Returns Promise that will resolve when the initialization has ended (either
   * with success, in which cases the Promise resolves, either with failure, in
   * which case it rejects the corresponding error).
   *
   * This is actually the exact same Promise than the one returned by the first
   * `initialize` call.
   *
   * If that method was never called, returns a rejecting Promise.
   * @returns {Promise}
   */
  public waitForInitialization(): Promise<void> {
    return this._initProm ?? Promise.reject("No initialization performed yet.");
  }

  public async initialize(opts: IDashWasmParserOptions): Promise<void> {
    if (this.status !== "uninitialized") {
      return Promise.reject(new Error("DashWasmParser already initialized."));
    } else if (!this.isCompatible()) {
      this.status = "failure";
      return Promise.reject(new Error("Target not compatible with WebAssembly."));
    }
    this.status = "initializing";

    const parsersStack = this._parsersStack;

    /** Re-used TextDecoder instance. */
    const textDecoder = new TextDecoder();

    // eslint-disable-next-line @typescript-eslint/no-this-alias
    const self = this;

    const imports = {
      env: {
        memoryBase: 0,
        tableBase: 0,
        memory: new WebAssembly.Memory({ initial: 10 }),
        table: new WebAssembly.Table({ initial: 1, element: "anyfunc" }),
        onTagOpen,
        onCustomEvent,
        onAttribute,
        readNext,
        onTagClose,
      },
    };

    let objectUrl: string | null = null;
    let fetchedWasm: Promise<Response>;
    if (typeof opts.wasmUrl === "string") {
      fetchedWasm = fetch(opts.wasmUrl);
    } else {
      objectUrl = URL.createObjectURL(
        new Blob([opts.wasmUrl], { type: "application/wasm" }),
      );
      fetchedWasm = fetch(objectUrl);
    }

    const streamingProm =
      typeof WebAssembly.instantiateStreaming === "function"
        ? WebAssembly.instantiateStreaming(fetchedWasm, imports)
        : Promise.reject("`WebAssembly.instantiateStreaming` API not available");

    this._initProm = streamingProm
      .catch(async (e) => {
        if (objectUrl !== null) {
          URL.revokeObjectURL(objectUrl);
          objectUrl = null;
        }
        log.warn(
          "Unable to call `instantiateStreaming` on WASM",
          e instanceof Error ? e : "",
        );
        const res = await fetchedWasm;
        if (res.status < 200 || res.status >= 300) {
          throw new Error("WebAssembly request failed. status: " + String(res.status));
        }
        const resAb = await res.arrayBuffer();
        return WebAssembly.instantiate(resAb, imports);
      })
      .then((instanceWasm) => {
        if (objectUrl !== null) {
          URL.revokeObjectURL(objectUrl);
          objectUrl = null;
        }
        this._instance = instanceWasm;

        // TODO better types?
        this._linearMemory = this._instance.instance.exports.memory as WebAssembly.Memory;

        this.status = "initialized";
      })
      .catch((err: Error) => {
        const message = err instanceof Error ? err.toString() : "Unknown error";
        log.warn("DW: Could not create DASH-WASM parser:", message);
        this.status = "failure";
        throw err;
      });

    return this._initProm;

    /**
     * Callback called when a new Element has been encountered by the WASM parser.
     * @param {number} tag - Identify the tag encountered (@see TagName)
     */
    function onTagOpen(tag: TagName): void {
      // Call the active "childrenParser"
      return parsersStack.childrenParser(tag);
    }

    /**
     * Callback called when an open Element's ending tag has been encountered by
     * the WASM parser.
     * @param {number} tag - Identify the tag in question (@see TagName)
     */
    function onTagClose(tag: TagName): void {
      // Only pop current parsers from the `parsersStack` if that tag was the
      // active one.
      return parsersStack.popIfCurrent(tag);
    }

    /**
     * Callback called each time a new Element's attribute is encountered by
     * the WASM parser.
     *
     * TODO Merge all attributes into the same callback with `onTagOpen`? I
     * tried but there's some difficulties if doing that.
     *
     * @param {number} attr - Identify the Attribute in question (@see TagName)
     * @param {number} ptr - Pointer to the first byte containing the
     * attribute's data in the WebAssembly's linear memory.
     * @param {number} len - Length of the attribute's value, in bytes.
     */
    function onAttribute(attr: AttributeName, ptr: number, len: number): void {
      // Call the active "attributeParser"
      return parsersStack.attributeParser(attr, ptr, len);
    }

    /**
     * Callback called on the various "custom events" triggered by the WASM.
     *
     * @see CustomEventType
     * @param {number} evt - The type of the event
     * @param {number} ptr - Pointer to the first byte of the event's payload in
     * the WebAssembly's linear memory.
     * @param {number} len - Length of the payload, in bytes.
     */
    function onCustomEvent(evt: CustomEventType, ptr: number, len: number): void {
      const linearMemory = self._linearMemory as WebAssembly.Memory;
      const arr = new Uint8Array(linearMemory.buffer, ptr, len);
      if (evt === CustomEventType.Error) {
        const decoded = textDecoder.decode(arr);
        log.warn("WASM Error Event:", decoded);
        self._warnings.push(new Error(decoded));
      } else if (evt === CustomEventType.Log) {
        const decoded = textDecoder.decode(arr);
        log.warn("WASM Log Event:", decoded);
      }
    }

    /**
     * Callback called by the WebAssembly when it needs to read new data from
     * the MPD.
     *
     * @param {number} ptr - First byte offset, in the WebAssembly's linear
     * memory, where the MPD should be set (under an array of bytes form).
     * @param {number} wantedSize - Size of the data, in bytes, asked by the
     * WebAssembly parser. It might receive less depending on if there's less
     * data in the MPD or if it goes over the set maximum size it could read
     * at a time.
     * @returns {number} - Return the number of bytes effectively read and set
     * in WebAssembly's linear memory (at the `ptr` offset).
     */
    function readNext(ptr: number, wantedSize: number): number {
      if (self._mpdData === null) {
        throw new Error("DashWasmParser Error: No MPD to read.");
      }
      const linearMemory = self._linearMemory as WebAssembly.Memory;
      const { mpd, cursor } = self._mpdData;
      const sizeToRead = Math.min(wantedSize, MAX_READ_SIZE, mpd.byteLength - cursor);
      const arr = new Uint8Array(linearMemory.buffer, ptr, sizeToRead);
      arr.set(new Uint8Array(mpd, cursor, sizeToRead));
      self._mpdData.cursor += sizeToRead;
      return sizeToRead;
    }
  }

  /**
   * @param {Document} manifest - Original manifest as returned by the server
   * @param {Object} args
   * @returns {Object}
   */
  public runWasmParser(
    mpd: ArrayBuffer,
    args: IMPDParserArguments,
  ): IDashParserResponse<string> | IDashParserResponse<ArrayBuffer> {
    const [mpdIR, warnings] = this._parseMpd(mpd);
    if (mpdIR === null) {
      throw new Error("DASH Parser: Unknown error while parsing the MPD");
    }
    const ret = parseMpdIr(mpdIR, args, warnings);
    return this._processParserReturnValue(ret);
  }

  /**
   * Return `true` if the current plaform is compatible with WebAssembly and the
   * TextDecoder interface (for faster UTF-8 parsing), which are needed features
   * for the `DashWasmParser`.
   * @returns {boolean}
   */
  public isCompatible(): boolean {
    return hasWebassembly && typeof globalScope.TextDecoder === "function";
  }

  private _parseMpd(mpd: ArrayBuffer): [IMPDIntermediateRepresentation | null, Error[]] {
    if (this._instance === null) {
      throw new Error("DashWasmParser not initialized");
    }
    if (this._isParsing) {
      throw new Error("Parsing operation already pending.");
    }
    this._isParsing = true;
    this._mpdData = { mpd, cursor: 0 };

    const rootObj: { mpd?: IMPDIntermediateRepresentation } = {};

    const linearMemory = this._linearMemory as WebAssembly.Memory;
    const rootChildrenParser = generateRootChildrenParser(
      rootObj,
      linearMemory,
      this._parsersStack,
      mpd,
    );
    this._parsersStack.pushParsers(null, rootChildrenParser, noop);
    this._warnings = [];

    try {
      // TODO better type this
      (this._instance.instance.exports.parse as () => void)();
    } catch (err) {
      this._parsersStack.reset();
      this._warnings = [];
      this._isParsing = false;
      throw err;
    }

    const parsed = rootObj.mpd ?? null;
    const warnings = this._warnings;

    this._parsersStack.reset();
    this._warnings = [];
    this._isParsing = false;

    return [parsed, warnings];
  }

  private _parseXlink(
    xlinkData: ArrayBuffer,
  ): [IPeriodIntermediateRepresentation[], Error[]] {
    if (this._instance === null) {
      throw new Error("DashWasmParser not initialized");
    }
    if (this._isParsing) {
      throw new Error("Parsing operation already pending.");
    }
    this._isParsing = true;
    this._mpdData = { mpd: xlinkData, cursor: 0 };

    const rootObj: { periods: IPeriodIntermediateRepresentation[] } = {
      periods: [],
    };

    const linearMemory = this._linearMemory as WebAssembly.Memory;
    const xlinkParser = generateXLinkChildrenParser(
      rootObj,
      linearMemory,
      this._parsersStack,
      xlinkData,
    );
    this._parsersStack.pushParsers(null, xlinkParser, noop);
    this._warnings = [];

    try {
      // TODO better type this
      (this._instance.instance.exports.parse as () => void)();
    } catch (err) {
      this._parsersStack.reset();
      this._warnings = [];
      this._isParsing = false;
      throw err;
    }

    const { periods } = rootObj;
    const warnings = this._warnings;
    this._parsersStack.reset();
    this._warnings = [];
    this._isParsing = false;
    return [periods, warnings];
  }

  /**
   * Handle `parseMpdIr` return values, asking for resources if they are needed
   * and pre-processing them before continuing parsing.
   *
   * @param {Object} initialRes
   * @returns {Object}
   */
  private _processParserReturnValue(
    initialRes: IIrParserResponse,
  ): IDashParserResponse<string> | IDashParserResponse<ArrayBuffer> {
    if (initialRes.type === "done") {
      return initialRes;
    } else if (initialRes.type === "needs-clock") {
      const continueParsingMPD = (
        loadedClock: Array<ILoadedResource<string>>,
      ): IDashParserResponse<string> | IDashParserResponse<ArrayBuffer> => {
        if (loadedClock.length !== 1) {
          throw new Error("DASH parser: wrong number of loaded ressources.");
        }
        const newRet = initialRes.value.continue(loadedClock[0].responseData);
        return this._processParserReturnValue(newRet);
      };
      return {
        type: "needs-resources",
        value: {
          urls: [initialRes.value.url],
          format: "string",
          continue: continueParsingMPD,
        },
      };
    } else if (initialRes.type === "needs-xlinks") {
      const continueParsingMPD = (
        loadedXlinks: Array<ILoadedResource<ArrayBuffer>>,
      ): IDashParserResponse<string> | IDashParserResponse<ArrayBuffer> => {
        const resourceInfos: ILoadedXlinkData[] = [];
        for (let i = 0; i < loadedXlinks.length; i++) {
          const {
            responseData: xlinkResp,
            receivedTime,
            sendingTime,
            url,
          } = loadedXlinks[i];
          if (!xlinkResp.success) {
            throw xlinkResp.error;
          }
          const [periodsIr, periodsIRWarnings] = this._parseXlink(xlinkResp.data);
          resourceInfos.push({
            url,
            receivedTime,
            sendingTime,
            parsed: periodsIr,
            warnings: periodsIRWarnings,
          });
        }
        const newRet = initialRes.value.continue(resourceInfos);
        return this._processParserReturnValue(newRet);
      };

      return {
        type: "needs-resources",
        value: {
          urls: initialRes.value.xlinksUrls,
          format: "arraybuffer",
          continue: continueParsingMPD,
        },
      };
    } else {
      assertUnreachable(initialRes);
    }
  }
}

/** Options needed when constructing the DASH-WASM parser. */
export interface IDashWasmParserOptions {
  wasmUrl: string | ArrayBuffer;
}