import { cyan, magenta } from 'colors';
import { Response } from 'express';
import * as fs from 'fs';
import { socketMap, timeMap, userOperations } from './SocketData';

/**
 * DashStats focuses on tracking user data for each session.
 *
 * This includes time connected, number of operations, and
 * the rate of their operations
 */

export namespace DashStats {
    export const SAMPLING_INTERVAL = 1000; // in milliseconds (ms) - Time interval to update the frontend.
    export const RATE_INTERVAL = 10; // in seconds (s) - Used to calculate rate

    const statsCSVDirectory = './src/server/stats/';
    const statsCSVFilename = statsCSVDirectory + 'userLoginStats.csv';

    /**
     * UserStats holds the stats associated with a particular user.
     */
    interface UserStats {
        socketId: string;
        username: string;
        time: string;
        operations: number;
        rate: number;
    }

    /**
     * UserLastOperations is the queue object for each user
     * storing their past operations.
     */
    interface UserLastOperations {
        sampleOperations: number; // stores how many operations total are in this rate section (10 sec, for example)
        lastSampleOperations: number; // stores how many total operations were recorded at the last sample
        previousOperationsQueue: number[]; // stores the operations to calculate rate.
    }

    /**
     * StatsDataBundle represents an object that will be sent to the frontend view
     * on each websocket update.
     */
    interface StatsDataBundle {
        connectedUsers: UserStats[];
    }

    /**
     * CSVStore represents how objects will be stored in the CSV
     */
    interface CSVStore {
        USERNAME: string;
        ACTION: string;
        TIME: string;
    }

    /**
     * ServerTraffic describes the current traffic going to the backend.
     */
    enum ServerTraffic {
        NOT_BUSY,
        BUSY,
        VERY_BUSY,
    }

    // These values can be changed after further testing how many
    // users correspond to each traffic level in Dash.
    const BUSY_SERVER_BOUND = 2;
    const VERY_BUSY_SERVER_BOUND = 3;

    const serverTrafficMessages = ['Not Busy', 'Busy', 'Very Busy'];

    // lastUserOperations maps each username to a UserLastOperations
    // structure
    export const lastUserOperations = new Map<string, UserLastOperations>();

    /**
     * convertToCSV() is a helper method that stringifies a CSVStore object
     * that can be written to the CSV file later.
     * @param dataObject the object to stringify
     * @returns the object as a string.
     */
    function convertToCSV(dataObject: CSVStore): string {
        return `${dataObject.USERNAME},${dataObject.ACTION},${dataObject.TIME}\n`;
    }
    /**
     * getLastOperationsOrDefault() is a helper method that will attempt
     * to query the lastUserOperations map for a specified username. If the
     * username is not in the map, an empty UserLastOperations object is returned.
     * @param username
     * @returns the user's UserLastOperations structure or an empty
     * UserLastOperations object (All values set to 0) if the username is not found.
     */
    function getLastOperationsOrDefault(username: string): UserLastOperations {
        if (lastUserOperations.get(username) === undefined) {
            const initializeOperationsQueue = [];
            for (let i = 0; i < RATE_INTERVAL; i++) {
                initializeOperationsQueue.push(0);
            }
            return {
                sampleOperations: 0,
                lastSampleOperations: 0,
                previousOperationsQueue: initializeOperationsQueue,
            };
        }
        return lastUserOperations.get(username)!;
    }

    /**
     * updateLastOperations updates a specific user's UserLastOperations information
     * for the current sampling cycle. The method removes old/outdated counts for
     * operations from the queue and adds new data for the current sampling
     * cycle to the queue, updating the total count as it goes.
     * @param lastOperationData the old UserLastOperations data that must be updated
     * @param currentOperations the total number of operations measured for this sampling cycle.
     * @returns the udpated UserLastOperations structure.
     */
    function updateLastOperations(lastOperationData: UserLastOperations, currentOperations: number): UserLastOperations {
        // create a copy of the UserLastOperations to modify
        const newLastOperationData: UserLastOperations = {
            sampleOperations: lastOperationData.sampleOperations,
            lastSampleOperations: lastOperationData.lastSampleOperations,
            previousOperationsQueue: lastOperationData.previousOperationsQueue.slice(),
        };

        let newSampleOperations = newLastOperationData.sampleOperations;
        newSampleOperations -= newLastOperationData.previousOperationsQueue.shift()!; // removes and returns the first element of the queue
        const operationsThisCycle = currentOperations - lastOperationData.lastSampleOperations;
        newSampleOperations += operationsThisCycle; // add the operations this cycle to find out what our count for the interval should be (e.g operations in the last 10 seconds)

        // update values for the copy object
        newLastOperationData.sampleOperations = newSampleOperations;

        newLastOperationData.previousOperationsQueue.push(operationsThisCycle);
        newLastOperationData.lastSampleOperations = currentOperations;

        return newLastOperationData;
    }

    /**
     * getUserOperationsOrDefault() is a helper method to get the user's total
     * operations for the CURRENT sampling interval. The method will return 0
     * if the username is not in the userOperations map.
     * @param username the username to search the map for
     * @returns the total number of operations recorded up to this sampling cycle.
     */
    function getUserOperationsOrDefault(username: string): number {
        return userOperations.get(username) === undefined ? 0 : userOperations.get(username)!;
    }

    /**
     * getCurrentStats() calculates the total stats for this cycle. In this case,
     * getCurrentStats() returns an Array of UserStats[] objects describing
     * the stats for each user
     * @returns an array of UserStats storing data for each user at the current moment.
     */
    function getCurrentStats(): UserStats[] {
        const socketPairs: UserStats[] = [];
        Array.from(socketMap.entries()).forEach(([key, value]) => {
            const username = value.split(' ')[0];
            const connectionTime = new Date(timeMap[username]);

            const connectionTimeString = connectionTime.toLocaleDateString() + ' ' + connectionTime.toLocaleTimeString();

            if (!key.disconnected) {
                const lastRecordedOperations = getLastOperationsOrDefault(username);
                const currentUserOperationCount = getUserOperationsOrDefault(username);

                socketPairs.push({
                    socketId: key.id,
                    username: username,
                    time: connectionTimeString.includes('Invalid Date') ? '' : connectionTimeString,
                    operations: userOperations.get(username) ? userOperations.get(username)! : 0,
                    rate: lastRecordedOperations.sampleOperations,
                });
                lastUserOperations.set(username, updateLastOperations(lastRecordedOperations, currentUserOperationCount));
            }
        });
        return socketPairs;
    }

    /**
     * handleStats is called when the /stats route is called, providing a JSON
     * object with relevant stats. In this case, we return the number of
     * current connections and
     * @param res Response object from Express
     */
    export function handleStats(res: Response) {
        const current = getCurrentStats();
        res.json({
            currentConnections: current.length,
            socketMap: current,
        });
    }

    /**
     * getUpdatedStatesBundle() sends an updated copy of the current stats to the
     * frontend /statsview route via websockets.
     *
     * @returns a StatsDataBundle that is sent to the frontend view on each websocket update
     */
    export function getUpdatedStatsBundle(): StatsDataBundle {
        const current = getCurrentStats();

        return {
            connectedUsers: current,
        };
    }

    /**
     * handleStatsView() is called when the /statsview route is called. This
     * will use pug to render a frontend view of the current stats
     *
     * @param res
     */
    export function handleStatsView(res: Response) {
        const current = getCurrentStats();
        const connectedUsers = current.map(({ time, username, operations }) => time + ' - ' + username + ' Operations: ' + operations);

        let serverTraffic = ServerTraffic.NOT_BUSY;
        if (current.length < BUSY_SERVER_BOUND) {
            serverTraffic = ServerTraffic.NOT_BUSY;
        } else if (current.length >= BUSY_SERVER_BOUND && current.length < VERY_BUSY_SERVER_BOUND) {
            serverTraffic = ServerTraffic.BUSY;
        } else {
            serverTraffic = ServerTraffic.VERY_BUSY;
        }

        res.render('stats.pug', {
            title: 'Dash Stats',
            numConnections: connectedUsers.length,
            serverTraffic: serverTraffic,
            serverTrafficMessage: serverTrafficMessages[serverTraffic],
            connectedUsers: connectedUsers,
        });
    }

    /**
     * logUserLogin() writes a login event to the CSV file.
     *
     * @param username the username in the format of "username@domain.com logged in"
     * @param socket the websocket associated with the current connection
     */
    export function logUserLogin(username: string | undefined) {
        if (!(username === undefined)) {
            const currentDate = new Date();
            console.log(magenta(`User ${username.split(' ')[0]} logged in at: ${currentDate.toISOString()}`));

            const toWrite: CSVStore = {
                USERNAME: username,
                ACTION: 'loggedIn',
                TIME: currentDate.toISOString(),
            };

            if (!fs.existsSync(statsCSVDirectory)) fs.mkdirSync(statsCSVDirectory);
            const statsFile = fs.createWriteStream(statsCSVFilename, { flags: 'a' });
            statsFile.write(convertToCSV(toWrite));
            statsFile.end();
            console.log(cyan(convertToCSV(toWrite)));
        }
    }

    /**
     * logUserLogout() writes a logout event to the CSV file.
     *
     * @param username the username in the format of "username@domain.com logged in"
     * @param socket the websocket associated with the current connection.
     */
    export function logUserLogout(username: string | undefined) {
        if (!(username === undefined)) {
            const currentDate = new Date();

            const statsFile = fs.createWriteStream(statsCSVFilename, { flags: 'a' });
            const toWrite: CSVStore = {
                USERNAME: username,
                ACTION: 'loggedOut',
                TIME: currentDate.toISOString(),
            };
            statsFile.write(convertToCSV(toWrite));
            statsFile.end();
        }
    }
}