/*
 * Copyright 2020 - 2024 The Matrix.org Foundation C.I.C.
 *
 * 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 { EventEmitter } from "events";

import { ITransport } from "./ITransport";
import {
    invertedDirection,
    isErrorResponse,
    IWidgetApiRequest,
    IWidgetApiRequestData,
    IWidgetApiResponse,
    IWidgetApiResponseData,
    WidgetApiResponseError,
    WidgetApiAction,
    WidgetApiDirection,
    WidgetApiToWidgetAction,
} from "..";

interface IOutboundRequest {
    request: IWidgetApiRequest;
    resolve: (response: IWidgetApiResponse) => void;
    reject: (err: Error) => void;
}

/**
 * Transport for the Widget API over postMessage.
 */
export class PostmessageTransport extends EventEmitter implements ITransport {
    public strictOriginCheck = false;
    public targetOrigin = "*";
    public timeoutSeconds = 10;

    private _ready = false;
    private _widgetId: string | null;
    private readonly outboundRequests = new Map<string, IOutboundRequest | null>();
    private readonly stopController = new AbortController();

    public get ready(): boolean {
        return this._ready;
    }

    public get widgetId(): string | null {
        return this._widgetId || null;
    }

    public constructor(
        private readonly sendDirection: WidgetApiDirection,
        initialWidgetId: string | null,
        private readonly transportWindow: Window | typeof globalThis,
        private readonly inboundWindow: Window | typeof globalThis,
    ) {
        super();
        this._widgetId = initialWidgetId;
    }

    private get nextRequestId(): string {
        const idBase = `widgetapi-${Date.now()}`;
        let index = 0;
        let id = idBase;
        while (this.outboundRequests.has(id)) {
            id = `${idBase}-${index++}`;
        }

        // reserve the ID
        this.outboundRequests.set(id, null);

        return id;
    }

    private sendInternal(message: IWidgetApiRequest | IWidgetApiResponse): void {
        console.log(`[PostmessageTransport] Sending object to ${this.targetOrigin}: `, message);
        this.transportWindow.postMessage(message, this.targetOrigin);
    }

    public reply<T extends IWidgetApiResponseData>(request: IWidgetApiRequest, responseData: T): void {
        return this.sendInternal(<IWidgetApiResponse>{
            ...request,
            response: responseData,
        });
    }

    public send<T extends IWidgetApiRequestData, R extends IWidgetApiResponseData>(
        action: WidgetApiAction,
        data: T,
    ): Promise<R> {
        return this.sendComplete(action, data).then((r) => <R>r.response);
    }

    public sendComplete<T extends IWidgetApiRequestData, R extends IWidgetApiResponse>(
        action: WidgetApiAction,
        data: T,
    ): Promise<R> {
        if (!this.ready || !this.widgetId) {
            return Promise.reject(new Error("Not ready or unknown widget ID"));
        }
        const request: IWidgetApiRequest = {
            api: this.sendDirection,
            widgetId: this.widgetId,
            requestId: this.nextRequestId,
            action: action,
            data: data,
        };
        if (action === WidgetApiToWidgetAction.UpdateVisibility) {
            request["visible"] = data["visible"];
        }
        return new Promise<R>((prResolve, prReject) => {
            const resolve = (response: IWidgetApiResponse): void => {
                cleanUp();
                prResolve(<R>response);
            };
            const reject = (err: Error): void => {
                cleanUp();
                prReject(err);
            };

            const timerId = setTimeout(() => reject(new Error("Request timed out")), (this.timeoutSeconds || 1) * 1000);

            const onStop = (): void => reject(new Error("Transport stopped"));
            this.stopController.signal.addEventListener("abort", onStop);

            const cleanUp = (): void => {
                this.outboundRequests.delete(request.requestId);
                clearTimeout(timerId);
                this.stopController.signal.removeEventListener("abort", onStop);
            };

            this.outboundRequests.set(request.requestId, { request, resolve, reject });
            this.sendInternal(request);
        });
    }

    public start(): void {
        this.inboundWindow.addEventListener("message", this.handleMessage);
        this._ready = true;
    }

    public stop(): void {
        this._ready = false;
        this.stopController.abort();
        this.inboundWindow.removeEventListener("message", this.handleMessage);
    }

    private readonly handleMessage = (ev: MessageEvent): void => {
        if (this.stopController.signal.aborted) return;
        if (!ev.data) return; // invalid event

        if (this.strictOriginCheck && ev.origin !== globalThis.origin) return; // bad origin

        // treat the message as a response first, then downgrade to a request
        const response = <IWidgetApiResponse>ev.data;
        if (!response.action || !response.requestId || !response.widgetId) return; // invalid request/response

        if (response.response) {
            if (response.api !== this.sendDirection) return; // wrong direction
            this.handleResponse(response);
        } else {
            const request = <IWidgetApiRequest>response;
            if (request.api !== invertedDirection(this.sendDirection)) return; // wrong direction
            this.handleRequest(request);
        }
    };

    private handleRequest(request: IWidgetApiRequest): void {
        if (this.widgetId) {
            if (this.widgetId !== request.widgetId) return; // wrong widget
        } else {
            this._widgetId = request.widgetId;
        }

        this.emit("message", new CustomEvent("message", { detail: request }));
    }

    private handleResponse(response: IWidgetApiResponse): void {
        if (response.widgetId !== this.widgetId) return; // wrong widget

        const req = this.outboundRequests.get(response.requestId);
        if (!req) return; // response to an unknown request

        if (isErrorResponse(response.response)) {
            const { message, ...data } = response.response.error;
            req.reject(new WidgetApiResponseError(message, data));
        } else {
            req.resolve(response);
        }
    }
}