import url = require("url");
import http = require("http");
import https = require("https");
import ifm = require('./interfaces');
import pm = require('./proxy');

let tunnel: any;

export enum HttpCodes {
    OK = 200,
    MultipleChoices = 300,
    MovedPermanently = 301,
    ResourceMoved = 302,
    SeeOther = 303,
    NotModified = 304,
    UseProxy = 305,
    SwitchProxy = 306,
    TemporaryRedirect = 307,
    PermanentRedirect = 308,
    BadRequest = 400,
    Unauthorized = 401,
    PaymentRequired = 402,
    Forbidden = 403,
    NotFound = 404,
    MethodNotAllowed = 405,
    NotAcceptable = 406,
    ProxyAuthenticationRequired = 407,
    RequestTimeout = 408,
    Conflict = 409,
    Gone = 410,
    InternalServerError = 500,
    NotImplemented = 501,
    BadGateway = 502,
    ServiceUnavailable = 503,
    GatewayTimeout = 504,
}

/**
 * Returns the proxy URL, depending upon the supplied url and proxy environment variables.
 * @param serverUrl  The server URL where the request will be sent. For example, https://api.github.com
 */
export function getProxyUrl(serverUrl: string): string {
    let proxyUrl = pm.getProxyUrl(url.parse(serverUrl))
    return proxyUrl ? proxyUrl.href : ''
}

const HttpRedirectCodes: number[] = [HttpCodes.MovedPermanently, HttpCodes.ResourceMoved, HttpCodes.SeeOther, HttpCodes.TemporaryRedirect, HttpCodes.PermanentRedirect];
const HttpResponseRetryCodes: number[] = [HttpCodes.BadGateway, HttpCodes.ServiceUnavailable, HttpCodes.GatewayTimeout];
const RetryableHttpVerbs: string[] = ['OPTIONS', 'GET', 'DELETE', 'HEAD'];
const ExponentialBackoffCeiling = 10;
const ExponentialBackoffTimeSlice = 5;

export class HttpClientResponse implements ifm.IHttpClientResponse {
    constructor(message: http.IncomingMessage) {
        this.message = message;
    }

    public message: http.IncomingMessage;
    readBody(): Promise<string> {
        return new Promise<string>(async (resolve, reject) => {
            let output = Buffer.alloc(0);

            this.message.on('data', (chunk: Buffer) => {
                output = Buffer.concat([output, chunk]);
            });

            this.message.on('end', () => {
                resolve(output.toString());
            });
        });
    }
}

export function isHttps(requestUrl: string) {
    let parsedUrl: url.Url = url.parse(requestUrl);
    return parsedUrl.protocol === 'https:';
}

export class HttpClient {
    userAgent: string | undefined;
    handlers: ifm.IRequestHandler[];
    requestOptions: ifm.IRequestOptions;

    private _ignoreSslError: boolean = false;
    private _socketTimeout: number;
    private _allowRedirects: boolean = true;
    private _allowRedirectDowngrade: boolean = false;
    private _maxRedirects: number = 50;
    private _allowRetries: boolean = false;
    private _maxRetries: number = 1;
    private _agent;
    private _proxyAgent;
    private _keepAlive: boolean = false;
    private _disposed: boolean = false;

    constructor(userAgent?: string, handlers?: ifm.IRequestHandler[], requestOptions?: ifm.IRequestOptions) {
        this.userAgent = userAgent;
        this.handlers = handlers || [];
        this.requestOptions = requestOptions;
        if (requestOptions) {
            if (requestOptions.ignoreSslError != null) {
                this._ignoreSslError = requestOptions.ignoreSslError;
            }

            this._socketTimeout = requestOptions.socketTimeout;

            if (requestOptions.allowRedirects != null) {
                this._allowRedirects = requestOptions.allowRedirects;
            }

            if (requestOptions.allowRedirectDowngrade != null) {
                this._allowRedirectDowngrade = requestOptions.allowRedirectDowngrade;
            }

            if (requestOptions.maxRedirects != null) {
                this._maxRedirects = Math.max(requestOptions.maxRedirects, 0);
            }

            if (requestOptions.keepAlive != null) {
                this._keepAlive = requestOptions.keepAlive;
            }

            if (requestOptions.allowRetries != null) {
                this._allowRetries = requestOptions.allowRetries;
            }

            if (requestOptions.maxRetries != null) {
                this._maxRetries = requestOptions.maxRetries;
            }
        }
    }

    public options(requestUrl: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('OPTIONS', requestUrl, null, additionalHeaders || {});
    }

    public get(requestUrl: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('GET', requestUrl, null, additionalHeaders || {});
    }

    public del(requestUrl: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('DELETE', requestUrl, null, additionalHeaders || {});
    }

    public post(requestUrl: string, data: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('POST', requestUrl, data, additionalHeaders || {});
    }

    public patch(requestUrl: string, data: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('PATCH', requestUrl, data, additionalHeaders || {});
    }

    public put(requestUrl: string, data: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('PUT', requestUrl, data, additionalHeaders || {});
    }

    public head(requestUrl: string, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request('HEAD', requestUrl, null, additionalHeaders || {});
    }

    public sendStream(verb: string, requestUrl: string, stream: NodeJS.ReadableStream, additionalHeaders?: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        return this.request(verb, requestUrl, stream, additionalHeaders);
    }

    /**
     * Makes a raw http request.
     * All other methods such as get, post, patch, and request ultimately call this.
     * Prefer get, del, post and patch
     */
    public async request(verb: string, requestUrl: string, data: string | NodeJS.ReadableStream, headers: ifm.IHeaders): Promise<ifm.IHttpClientResponse> {
        if (this._disposed) {
            throw new Error("Client has already been disposed.");
        }

        let parsedUrl = url.parse(requestUrl);
        let info: ifm.IRequestInfo = this._prepareRequest(verb, parsedUrl, headers);

        // Only perform retries on reads since writes may not be idempotent.
        let maxTries: number = (this._allowRetries && RetryableHttpVerbs.indexOf(verb) != -1) ? this._maxRetries + 1 : 1;
        let numTries: number = 0;

        let response: HttpClientResponse;
        while (numTries < maxTries) {
            response = await this.requestRaw(info, data);

            // Check if it's an authentication challenge
            if (response && response.message && response.message.statusCode === HttpCodes.Unauthorized) {
                let authenticationHandler: ifm.IRequestHandler;

                for (let i = 0; i < this.handlers.length; i++) {
                    if (this.handlers[i].canHandleAuthentication(response)) {
                        authenticationHandler = this.handlers[i];
                        break;
                    }
                }

                if (authenticationHandler) {
                    return authenticationHandler.handleAuthentication(this, info, data);
                }  
                else {
                    // We have received an unauthorized response but have no handlers to handle it.
                    // Let the response return to the caller.
                    return response;
                }
            }

            let redirectsRemaining: number = this._maxRedirects;
            while (HttpRedirectCodes.indexOf(response.message.statusCode) != -1
                && this._allowRedirects
                && redirectsRemaining > 0) {

                const redirectUrl: string | null = response.message.headers["location"];
                if (!redirectUrl) {
                    // if there's no location to redirect to, we won't
                    break;
                }
                let parsedRedirectUrl = url.parse(redirectUrl);
                if (parsedUrl.protocol == 'https:' && parsedUrl.protocol != parsedRedirectUrl.protocol && !this._allowRedirectDowngrade) {
                    throw new Error("Redirect from HTTPS to HTTP protocol. This downgrade is not allowed for security reasons. If you want to allow this behavior, set the allowRedirectDowngrade option to true.");
                }

                // we need to finish reading the response before reassigning response
                // which will leak the open socket.
                await response.readBody();

                // let's make the request with the new redirectUrl
                info = this._prepareRequest(verb, parsedRedirectUrl, headers);
                response = await this.requestRaw(info, data);
                redirectsRemaining--;
            }

            if (HttpResponseRetryCodes.indexOf(response.message.statusCode) == -1) {
                // If not a retry code, return immediately instead of retrying
                return response;
            }

            numTries += 1;

            if (numTries < maxTries) {
                await response.readBody();
                await this._performExponentialBackoff(numTries);
            }
        }

        return response;
    }

    /**
     * Needs to be called if keepAlive is set to true in request options.
     */
    public dispose() {
        if (this._agent) {
            this._agent.destroy();
        }
        
        this._disposed = true;
    }

    /**
     * Raw request.
     * @param info 
     * @param data 
     */
    public requestRaw(info: ifm.IRequestInfo, data: string | NodeJS.ReadableStream): Promise<ifm.IHttpClientResponse> {
        return new Promise<ifm.IHttpClientResponse>((resolve, reject) => {
            let callbackForResult = function (err: any, res: ifm.IHttpClientResponse) {
                if (err) {
                    reject(err);
                }

                resolve(res);
            };

            this.requestRawWithCallback(info, data, callbackForResult);
        });
    }

    /**
     * Raw request with callback.
     * @param info 
     * @param data 
     * @param onResult 
     */
    public requestRawWithCallback(info: ifm.IRequestInfo, data: string | NodeJS.ReadableStream, onResult: (err: any, res: ifm.IHttpClientResponse) => void): void {
        let socket;

        if (typeof (data) === 'string') {
            info.options.headers["Content-Length"] = Buffer.byteLength(data, 'utf8');
        }

        let callbackCalled: boolean = false;
        let handleResult = (err: any, res: HttpClientResponse) => {
            if (!callbackCalled) {
                callbackCalled = true;
                onResult(err, res);
            }
        };

        let req: http.ClientRequest = info.httpModule.request(info.options, (msg: http.IncomingMessage) => {
            let res: HttpClientResponse = new HttpClientResponse(msg);
            handleResult(null, res);
        });

        req.on('socket', (sock) => {
            socket = sock;
        });

        // If we ever get disconnected, we want the socket to timeout eventually
        req.setTimeout(this._socketTimeout || 3 * 60000, () => {
            if (socket) {
                socket.end();
            }
            handleResult(new Error('Request timeout: ' + info.options.path), null);
        });

        req.on('error', function (err) {
            // err has statusCode property
            // res should have headers
            handleResult(err, null);
        });

        if (data && typeof (data) === 'string') {
            req.write(data, 'utf8');
        }

        if (data && typeof (data) !== 'string') {
            data.on('close', function () {
                req.end();
            });

            data.pipe(req);
        }
        else {
            req.end();
        }
    }

    /**
     * Gets an http agent. This function is useful when you need an http agent that handles
     * routing through a proxy server - depending upon the url and proxy environment variables.
     * @param serverUrl  The server URL where the request will be sent. For example, https://api.github.com
     */
    public getAgent(serverUrl: string): http.Agent {
        let parsedUrl = url.parse(serverUrl)
        return this._getAgent(parsedUrl)
    }

    private _prepareRequest(method: string, requestUrl: url.Url, headers: ifm.IHeaders): ifm.IRequestInfo {
        const info: ifm.IRequestInfo = <ifm.IRequestInfo>{};

        info.parsedUrl = requestUrl;
        const usingSsl: boolean = info.parsedUrl.protocol === 'https:';
        info.httpModule = usingSsl ? https : http;
        const defaultPort: number = usingSsl ? 443 : 80;
        
        info.options = <http.RequestOptions>{};
        info.options.host = info.parsedUrl.hostname;
        info.options.port = info.parsedUrl.port ? parseInt(info.parsedUrl.port) : defaultPort;
        info.options.path = (info.parsedUrl.pathname || '') + (info.parsedUrl.search || '');
        info.options.method = method;

        info.options.headers = this._mergeHeaders(headers);
        if (this.userAgent != null) {
            info.options.headers["user-agent"] = this.userAgent;
        }
        
        info.options.agent = this._getAgent(info.parsedUrl);

        // gives handlers an opportunity to participate
        if (this.handlers) {
            this.handlers.forEach((handler) => {
                handler.prepareRequest(info.options);
            });
        }

        return info;
    }

    private _mergeHeaders(headers: ifm.IHeaders) : ifm.IHeaders {
        const lowercaseKeys = obj => Object.keys(obj).reduce((c, k) => (c[k.toLowerCase()] = obj[k], c), {});

        if (this.requestOptions && this.requestOptions.headers) {
            return Object.assign(
                {},
                lowercaseKeys(this.requestOptions.headers),
                lowercaseKeys(headers)
            );
        }

        return lowercaseKeys(headers || {});
    }

    private _getAgent(parsedUrl: url.Url): http.Agent {
        let agent;
        let proxyUrl: url.Url = pm.getProxyUrl(parsedUrl);
        let useProxy = proxyUrl && proxyUrl.hostname;

        if (this._keepAlive && useProxy) {
            agent = this._proxyAgent;
        }

        if (this._keepAlive && !useProxy) {
            agent = this._agent;
        }

        // if agent is already assigned use that agent.
        if (!!agent) {
            return agent;
        }

        const usingSsl = parsedUrl.protocol === 'https:';
        let maxSockets = 100;
        if (!!this.requestOptions) {
            maxSockets = this.requestOptions.maxSockets || http.globalAgent.maxSockets
        }

        if (useProxy) {
            // If using proxy, need tunnel
            if (!tunnel) {
                tunnel = require('tunnel');
            }

            const agentOptions = {
                maxSockets: maxSockets,
                keepAlive: this._keepAlive,
                proxy: {
                    proxyAuth: proxyUrl.auth,
                    host: proxyUrl.hostname,
                    port: proxyUrl.port
                },
            };

            let tunnelAgent: Function;
            const overHttps = proxyUrl.protocol === 'https:';
            if (usingSsl) {
                tunnelAgent = overHttps ? tunnel.httpsOverHttps : tunnel.httpsOverHttp;
            } else {
                tunnelAgent = overHttps ? tunnel.httpOverHttps : tunnel.httpOverHttp;
            }

            agent = tunnelAgent(agentOptions);
            this._proxyAgent = agent;
        }

        // if reusing agent across request and tunneling agent isn't assigned create a new agent
        if (this._keepAlive && !agent) {
            const options = { keepAlive: this._keepAlive, maxSockets: maxSockets };
            agent = usingSsl ? new https.Agent(options) : new http.Agent(options);
            this._agent = agent;
        }

        // if not using private agent and tunnel agent isn't setup then use global agent
        if (!agent) {
            agent = usingSsl ? https.globalAgent : http.globalAgent;
        }

        if (usingSsl && this._ignoreSslError) {
            // we don't want to set NODE_TLS_REJECT_UNAUTHORIZED=0 since that will affect request for entire process
            // http.RequestOptions doesn't expose a way to modify RequestOptions.agent.options
            // we have to cast it to any and change it directly
            agent.options = Object.assign(agent.options || {}, { rejectUnauthorized: false });
        }

        return agent;
    }

    private _performExponentialBackoff(retryNumber: number): Promise<void> {
        retryNumber = Math.min(ExponentialBackoffCeiling, retryNumber);
        const ms: number = ExponentialBackoffTimeSlice*Math.pow(2, retryNumber);
        return new Promise(resolve => setTimeout(()=>resolve(), ms));
    } 
}