Fis-Retransmission/test/socket/socket-client.ts

import { Observable, Subject, takeWhile } from "rxjs";
import { prepareResponseMessages } from "../../services/utility/prepareFISmessage";
import { BaseMessage } from "../../dependencies/logging/interface/export";
import { io, Socket } from "socket.io-client";
import { WrappedMessage } from "../../interfaces/general.interface";
import * as fs from 'fs'
import { ClientInfo } from "./socket.service";

let onHoldMessagesSubject: Subject<WrappedMessage> = new Subject()
let toBePassedOverToApp: Subject<BaseMessage> = new Subject()
// Serve static files (optional)
let sender: Subject<BaseMessage> = prepareResponseMessages(1, 2000)
let serverSocketUrl: string = 'http://192.168.100.96:3000'
let socket: Socket


establishSocketConnection(serverSocketUrl).then(() => {
    sender.subscribe({
        next: message => {
            makeRequest(message).subscribe({
                complete: () => console.log(`Request ${message.header.messageID} has acquired all responses.`)
            })
        }
    })
})

// the interface the client Program will make without having to decide transport protocol
function makeRequest(request: BaseMessage): Observable<any> {
    return new Observable((response) => {
        sendMessage(request)
        toBePassedOverToApp.subscribe({
            next: (message: BaseMessage) => {
                // console.log(message.header.messageName)
                // The identification of responses mapping to the request be adjusted accordingly
                // For now it's a simple demulti-plexing
                if (message.header.messageID == request.header.messageID && message.header.messageName != 'Complete') {
                    response.next(message)
                }
                if (message.header.messageID == request.header.messageID && message.header.messageName == 'Complete') {
                    response.complete()
                }
            },
            error: err => console.error(err),
            complete: () => { }
        })
    })
}

// socket util: Assuming that the client program would already have something like this in place
async function establishSocketConnection(serverUrl: string): Promise<any> {
    return new Promise((resolve, reject) => {
        try {
            socket = io(serverUrl, {
                reconnection: true,              // Enable automatic reconnections
                reconnectionAttempts: 100,        // Retry up to 10 times
                reconnectionDelay: 500,          // Start with a 500ms delay
                reconnectionDelayMax: 10000,     // Delay can grow to a max of 10 seconds
                randomizationFactor: 0.3,
            })

            // Check if it's a previuos client.
            let data: ClientInfo | null = checkOwnClientInfo('info.json')
            if (data) {
                socket.emit('notification', { agenda: 'existingClient', data: data })
            } else {
                socket.emit('notification', { agenda: 'newClient' })
            }

            // Listen for a connection event
            socket.on('connect', () => {
                // socket.emit('Hello from the client!')
                console.log('Connected to the server:', socket.id)
            });

            // Listen for messages from the server
            socket.on('response', (msg: WrappedMessage) => {
                console.log('Message from server:', msg.payload.header.messageName, ' for ', msg.payload.header.messageID);

                // Check the sequence by ensuring the message value before the current message exists, then pass them over to "App"
                // onHoldMessagesSubject.next(msg)
                // checkMessage(msg).then(() => [
                //     toBePassedOverToApp.next(msg.payload as BaseMessage)
                // ]).catch((err) => console.error(err))
                toBePassedOverToApp.next(msg.payload as BaseMessage)
            })

            socket.on('notification', (msg: any) => {
                if (msg.notification == 'Your credentials') {
                    console.log(`Assigned client Name: ${msg.socketInfo.clientName}`)
                    writeFile(msg.socketInfo as ClientInfo)
                }
                if (msg.notification == 'Your updated credentials') {
                    console.log(`Updated socket ID: `, msg)
                    // writeFile(msg.socketInfo as ClientInfo)
                }
                if (msg.notification == 'Failed Request') {
                    console.log(`Resending request...`, msg.data.header.messageID)
                    setTimeout(() => {
                        sender.next(msg.data)
                    }, 1000)
                }
            })

            resolve('')
            // Handle disconnection
            socket.on('disconnect', () => {
                console.log('Disconnected from the server');
                // receiverConnectionState.next('OFFLINE')
            });
        }
        catch (error) {
            reject(error)
        }
    })
}


function checkOwnClientInfo(filename: string): ClientInfo | null {
    // Check if the file exists
    if (fs.existsSync(filename)) {
        try {
            // Read the file contents
            const fileData = fs.readFileSync(filename, 'utf8');

            // If the file is empty, return an error
            if (fileData.trim() === "") {
                throw new Error("File is empty");
            }

            // Parse and return the data if present
            const jsonData = JSON.parse(fileData);
            return jsonData;

        } catch (err) {
            // Handle parsing errors or other file-related errors
            console.error("Error reading or parsing file:", err.message);
            return null;
        }
    } else {
        console.error("File does not exist");
        return null;
    }
}

function writeFile(data: ClientInfo) {
    // Write JSON data to a file
    fs.writeFile('info.json', JSON.stringify(data, null, 2), (err) => {
        if (err) {
            console.error('Error writing file', err);
        } else {
            console.log('File has been written');
        }
    });
}

async function sendMessage(message: BaseMessage): Promise<any> {
    return new Promise((resolve, reject) => {
        try {
            // extra precaution: According to chatgpt, if disconnected, then the payload will be loaded back in event queue whilst the socket will try to reestablish connection
            // https://socket.io/docs/v4/client-offline-behavior/
            socket.emit('request', message); // inherently an aysnc
            console.log(`SocketEmit() for message to event queue ${message.header.messageID}`)
            resolve('')
        } catch (error) {
            console.error('Error emitting message:', error);
            sender.next(message)
            reject(error)
        }
    })
}


// SO concept will be that if the message behind it is received, then 
async function checkMessage(message: WrappedMessage): Promise<any> {
    return new Promise((resolve, reject) => {
        if (message.previousMessageID) {
            onHoldMessagesSubject.pipe(
                takeWhile(item => message.previousMessageID === item.thisMessageID)
            ).subscribe({
                complete: () => {
                    resolve('previousMessageID matched')
                    // console.log(`${message.payload.header.messageID} : Previous messageID(${message.previousMessageID}) matched`)
                    // console.log(`matched`)
                }
            })
        } else {
            console.log('No previous messageID. This should be the first message')
            resolve('No previous message ID. Please Proceed.')
        }
    })
}