// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

import { DefaultHttpClient, HttpClient } from "./HttpClient";
import { IConnection } from "./IConnection";
import { IHttpConnectionOptions } from "./IHttpConnectionOptions";
import { ILogger, LogLevel } from "./ILogger";
import { HttpTransportType, ITransport, TransferFormat } from "./ITransport";
import { LongPollingTransport } from "./LongPollingTransport";
import { ServerSentEventsTransport } from "./ServerSentEventsTransport";
import { Arg, createLogger } from "./Utils";
import { WebSocketTransport } from "./WebSocketTransport";

/** @private */
const enum ConnectionState {
    Connecting,
    Connected,
    Disconnected,
}

/** @private */
export interface INegotiateResponse {
    connectionId?: string;
    availableTransports?: IAvailableTransport[];
    url?: string;
    accessToken?: string;
}

/** @private */
export interface IAvailableTransport {
    transport: keyof typeof HttpTransportType;
    transferFormats: Array<keyof typeof TransferFormat>;
}

const MAX_REDIRECTS = 100;

/** @private */
export class HttpConnection implements IConnection {
    private connectionState: ConnectionState;
    private baseUrl: string;
    private readonly httpClient: HttpClient;
    private readonly logger: ILogger;
    private readonly options: IHttpConnectionOptions;
    private transport: ITransport;
    private startPromise: Promise<void>;
    private stopError?: Error;
    private accessTokenFactory?: () => string | Promise<string>;

    public readonly features: any = {};
    public onreceive: (data: string | ArrayBuffer) => void;
    public onclose: (e?: Error) => void;

    constructor(url: string, options: IHttpConnectionOptions = {}) {
        Arg.isRequired(url, "url");

        this.logger = createLogger(options.logger);
        this.baseUrl = this.resolveUrl(url);

        options = options || {};
        options.accessTokenFactory = options.accessTokenFactory || (() => null);
        options.logMessageContent = options.logMessageContent || false;

        this.httpClient = options.httpClient || new DefaultHttpClient(this.logger);
        this.connectionState = ConnectionState.Disconnected;
        this.options = options;
    }

    public start(): Promise<void>;
    public start(transferFormat: TransferFormat): Promise<void>;
    public start(transferFormat?: TransferFormat): Promise<void> {
        transferFormat = transferFormat || TransferFormat.Binary;

        Arg.isIn(transferFormat, TransferFormat, "transferFormat");

        this.logger.log(LogLevel.Debug, `Starting connection with transfer format '${TransferFormat[transferFormat]}'.`);

        if (this.connectionState !== ConnectionState.Disconnected) {
            return Promise.reject(new Error("Cannot start a connection that is not in the 'Disconnected' state."));
        }

        this.connectionState = ConnectionState.Connecting;

        this.startPromise = this.startInternal(transferFormat);
        return this.startPromise;
    }

    public send(data: string | ArrayBuffer): Promise<void> {
        if (this.connectionState !== ConnectionState.Connected) {
            throw new Error("Cannot send data if the connection is not in the 'Connected' State.");
        }

        return this.transport.send(data);
    }

    public async stop(error?: Error): Promise<void> {
        this.connectionState = ConnectionState.Disconnected;

        try {
            await this.startPromise;
        } catch (e) {
            // this exception is returned to the user as a rejected Promise from the start method
        }

        // The transport's onclose will trigger stopConnection which will run our onclose event.
        if (this.transport) {
            this.stopError = error;
            await this.transport.stop();
            this.transport = null;
        }
    }

    private async startInternal(transferFormat: TransferFormat): Promise<void> {
        // Store the original base url and the access token factory since they may change
        // as part of negotiating
        let url = this.baseUrl;
        this.accessTokenFactory = this.options.accessTokenFactory;

        try {
            if (this.options.skipNegotiation) {
                if (this.options.transport === HttpTransportType.WebSockets) {
                    // No need to add a connection ID in this case
                    this.transport = this.constructTransport(HttpTransportType.WebSockets);
                    // We should just call connect directly in this case.
                    // No fallback or negotiate in this case.
                    await this.transport.connect(url, transferFormat);
                } else {
                    throw Error("Negotiation can only be skipped when using the WebSocket transport directly.");
                }
            } else {
                let negotiateResponse: INegotiateResponse = null;
                let redirects = 0;

                do {
                    negotiateResponse = await this.getNegotiationResponse(url);
                    // the user tries to stop the connection when it is being started
                    if (this.connectionState === ConnectionState.Disconnected) {
                        return;
                    }

                    if (negotiateResponse.url) {
                        url = negotiateResponse.url;
                    }

                    if (negotiateResponse.accessToken) {
                        // Replace the current access token factory with one that uses
                        // the returned access token
                        const accessToken = negotiateResponse.accessToken;
                        this.accessTokenFactory = () => accessToken;
                    }

                    redirects++;
                }
                while (negotiateResponse.url && redirects < MAX_REDIRECTS);

                if (redirects === MAX_REDIRECTS && negotiateResponse.url) {
                    throw Error("Negotiate redirection limit exceeded.");
                }

                await this.createTransport(url, this.options.transport, negotiateResponse, transferFormat);
            }

            if (this.transport instanceof LongPollingTransport) {
                this.features.inherentKeepAlive = true;
            }

            this.transport.onreceive = this.onreceive;
            this.transport.onclose = (e) => this.stopConnection(e);

            // only change the state if we were connecting to not overwrite
            // the state if the connection is already marked as Disconnected
            this.changeState(ConnectionState.Connecting, ConnectionState.Connected);
        } catch (e) {
            this.logger.log(LogLevel.Error, "Failed to start the connection: " + e);
            this.connectionState = ConnectionState.Disconnected;
            this.transport = null;
            throw e;
        }
    }

    private async getNegotiationResponse(url: string): Promise<INegotiateResponse> {
        const token = await this.accessTokenFactory();
        let headers;
        if (token) {
            headers = {
                ["Authorization"]: `Bearer ${token}`,
            };
        }

        const negotiateUrl = this.resolveNegotiateUrl(url);
        this.logger.log(LogLevel.Debug, `Sending negotiation request: ${negotiateUrl}`);
        try {
            const response = await this.httpClient.post(negotiateUrl, {
                content: "",
                headers,
            });

            if (response.statusCode !== 200) {
                throw Error(`Unexpected status code returned from negotiate ${response.statusCode}`);
            }

            return JSON.parse(response.content as string) as INegotiateResponse;
        } catch (e) {
            this.logger.log(LogLevel.Error, "Failed to complete negotiation with the server: " + e);
            throw e;
        }
    }

    private createConnectUrl(url: string, connectionId: string) {
        return url + (url.indexOf("?") === -1 ? "?" : "&") + `id=${connectionId}`;
    }

    private async createTransport(url: string, requestedTransport: HttpTransportType | ITransport, negotiateResponse: INegotiateResponse, requestedTransferFormat: TransferFormat): Promise<void> {
        let connectUrl = this.createConnectUrl(url, negotiateResponse.connectionId);
        if (this.isITransport(requestedTransport)) {
            this.logger.log(LogLevel.Debug, "Connection was provided an instance of ITransport, using that directly.");
            this.transport = requestedTransport;
            await this.transport.connect(connectUrl, requestedTransferFormat);

            // only change the state if we were connecting to not overwrite
            // the state if the connection is already marked as Disconnected
            this.changeState(ConnectionState.Connecting, ConnectionState.Connected);
            return;
        }

        const transports = negotiateResponse.availableTransports;
        for (const endpoint of transports) {
            this.connectionState = ConnectionState.Connecting;
            const transport = this.resolveTransport(endpoint, requestedTransport, requestedTransferFormat);
            if (typeof transport === "number") {
                this.transport = this.constructTransport(transport);
                if (negotiateResponse.connectionId === null) {
                    negotiateResponse = await this.getNegotiationResponse(url);
                    connectUrl = this.createConnectUrl(url, negotiateResponse.connectionId);
                }
                try {
                    await this.transport.connect(connectUrl, requestedTransferFormat);
                    this.changeState(ConnectionState.Connecting, ConnectionState.Connected);
                    return;
                } catch (ex) {
                    this.logger.log(LogLevel.Error, `Failed to start the transport '${HttpTransportType[transport]}': ${ex}`);
                    this.connectionState = ConnectionState.Disconnected;
                    negotiateResponse.connectionId = null;
                }
            }
        }

        throw new Error("Unable to initialize any of the available transports.");
    }

    private constructTransport(transport: HttpTransportType) {
        switch (transport) {
            case HttpTransportType.WebSockets:
                return new WebSocketTransport(this.accessTokenFactory, this.logger, this.options.logMessageContent);
            case HttpTransportType.ServerSentEvents:
                return new ServerSentEventsTransport(this.httpClient, this.accessTokenFactory, this.logger, this.options.logMessageContent);
            case HttpTransportType.LongPolling:
                return new LongPollingTransport(this.httpClient, this.accessTokenFactory, this.logger, this.options.logMessageContent);
            default:
                throw new Error(`Unknown transport: ${transport}.`);
        }
    }

    private resolveTransport(endpoint: IAvailableTransport, requestedTransport: HttpTransportType, requestedTransferFormat: TransferFormat): HttpTransportType | null {
        const transport = HttpTransportType[endpoint.transport];
        if (transport === null || transport === undefined) {
            this.logger.log(LogLevel.Debug, `Skipping transport '${endpoint.transport}' because it is not supported by this client.`);
        } else {
            const transferFormats = endpoint.transferFormats.map((s) => TransferFormat[s]);
            if (transportMatches(requestedTransport, transport)) {
                if (transferFormats.indexOf(requestedTransferFormat) >= 0) {
                    if ((transport === HttpTransportType.WebSockets && typeof WebSocket === "undefined") ||
                        (transport === HttpTransportType.ServerSentEvents && typeof EventSource === "undefined")) {
                        this.logger.log(LogLevel.Debug, `Skipping transport '${HttpTransportType[transport]}' because it is not supported in your environment.'`);
                    } else {
                        this.logger.log(LogLevel.Debug, `Selecting transport '${HttpTransportType[transport]}'`);
                        return transport;
                    }
                } else {
                    this.logger.log(LogLevel.Debug, `Skipping transport '${HttpTransportType[transport]}' because it does not support the requested transfer format '${TransferFormat[requestedTransferFormat]}'.`);
                }
            } else {
                this.logger.log(LogLevel.Debug, `Skipping transport '${HttpTransportType[transport]}' because it was disabled by the client.`);
            }
        }
        return null;
    }

    private isITransport(transport: any): transport is ITransport {
        return transport && typeof (transport) === "object" && "connect" in transport;
    }

    private changeState(from: ConnectionState, to: ConnectionState): boolean {
        if (this.connectionState === from) {
            this.connectionState = to;
            return true;
        }
        return false;
    }

    private async stopConnection(error?: Error): Promise<void> {
        this.transport = null;

        // If we have a stopError, it takes precedence over the error from the transport
        error = this.stopError || error;

        if (error) {
            this.logger.log(LogLevel.Error, `Connection disconnected with error '${error}'.`);
        } else {
            this.logger.log(LogLevel.Information, "Connection disconnected.");
        }

        this.connectionState = ConnectionState.Disconnected;

        if (this.onclose) {
            this.onclose(error);
        }
    }

    private resolveUrl(url: string): string {
        // startsWith is not supported in IE
        if (url.lastIndexOf("https://", 0) === 0 || url.lastIndexOf("http://", 0) === 0) {
            return url;
        }

        if (typeof window === "undefined" || !window || !window.document) {
            throw new Error(`Cannot resolve '${url}'.`);
        }

        // Setting the url to the href propery of an anchor tag handles normalization
        // for us. There are 3 main cases.
        // 1. Relative  path normalization e.g "b" -> "http://localhost:5000/a/b"
        // 2. Absolute path normalization e.g "/a/b" -> "http://localhost:5000/a/b"
        // 3. Networkpath reference normalization e.g "//localhost:5000/a/b" -> "http://localhost:5000/a/b"
        const aTag = window.document.createElement("a");
        aTag.href = url;

        this.logger.log(LogLevel.Information, `Normalizing '${url}' to '${aTag.href}'.`);
        return aTag.href;
    }

    private resolveNegotiateUrl(url: string): string {
        const index = url.indexOf("?");
        let negotiateUrl = url.substring(0, index === -1 ? url.length : index);
        if (negotiateUrl[negotiateUrl.length - 1] !== "/") {
            negotiateUrl += "/";
        }
        negotiateUrl += "negotiate";
        negotiateUrl += index === -1 ? "" : url.substring(index);
        return negotiateUrl;
    }
}

function transportMatches(requestedTransport: HttpTransportType, actualTransport: HttpTransportType) {
    return !requestedTransport || ((actualTransport & requestedTransport) !== 0);
}