Final-Year-Project/Backend/realtime/gateway.ts

import { and, eq, lt } from 'drizzle-orm';
import { Server as HttpServer } from 'http';
import { Server as SocketIOServer } from 'socket.io';
import { z } from 'zod';

import { db } from '../db/client';
import { deviceCommands, devices } from '../db/schema';
import { verifyDeviceToken } from '../utils/device-token';

const HEARTBEAT_INTERVAL_MS = 15_000;
const RETRY_INTERVAL_MS = 5_000;
const RETRY_DISPATCH_DELAY_MS = 10_000;
const MAX_RETRIES = 3;

const commandAckSchema = z.object({
  commandId: z.string().uuid(),
  status: z.enum(['acknowledged', 'rejected']),
  error: z.string().optional(),
});

const roomForDevice = (deviceId: string): string => `device:${deviceId}`;

let io: SocketIOServer | null = null;
let retryTimer: ReturnType<typeof setInterval> | null = null;

const countSocketsForDevice = (deviceId: string): number => {
  if (!io) {
    return 0;
  }

  return io.sockets.adapter.rooms.get(roomForDevice(deviceId))?.size ?? 0;
};

export const isDeviceOnline = (deviceId: string): boolean => countSocketsForDevice(deviceId) > 0;

export const sendRealtimeToDevice = (
  deviceId: string,
  eventName: string,
  payload: Record<string, unknown>,
): boolean => {
  if (!io || !isDeviceOnline(deviceId)) {
    return false;
  }

  io.to(roomForDevice(deviceId)).emit(eventName, payload);
  return true;
};

const markDevicePresence = async (deviceId: string, status: 'online' | 'offline') => {
  const now = new Date();

  await db
    .update(devices)
    .set({
      status,
      lastSeenAt: now,
      updatedAt: now,
    })
    .where(eq(devices.id, deviceId));
};

const emitCommand = (command: {
  id: string;
  sourceDeviceId: string;
  targetDeviceId: string;
  commandType: string;
  payload: Record<string, unknown> | null;
  createdAt: Date;
}): boolean => {
  if (!io) {
    return false;
  }

  if (countSocketsForDevice(command.targetDeviceId) === 0) {
    return false;
  }

  io.to(roomForDevice(command.targetDeviceId)).emit('command:received', {
    commandId: command.id,
    sourceDeviceId: command.sourceDeviceId,
    commandType: command.commandType,
    payload: command.payload,
    createdAt: command.createdAt,
  });

  return true;
};

export const dispatchCommandById = async (commandId: string): Promise<void> => {
  const command = await db.query.deviceCommands.findFirst({
    where: eq(deviceCommands.id, commandId),
  });

  if (!command) {
    return;
  }

  const now = new Date();

  const delivered = emitCommand({
    id: command.id,
    sourceDeviceId: command.sourceDeviceId,
    targetDeviceId: command.targetDeviceId,
    commandType: command.commandType,
    payload: command.payload,
    createdAt: command.createdAt,
  });

  await db
    .update(deviceCommands)
    .set({
      status: delivered ? 'sent' : 'queued',
      lastDispatchedAt: now,
      retryCount: delivered ? command.retryCount : command.retryCount,
      updatedAt: now,
      error: delivered ? null : 'target device offline',
    })
    .where(eq(deviceCommands.id, command.id));
};

const retryPendingCommands = async () => {
  const threshold = new Date(Date.now() - RETRY_DISPATCH_DELAY_MS);

  const pending = await db.query.deviceCommands.findMany({
    where: and(eq(deviceCommands.status, 'sent'), lt(deviceCommands.lastDispatchedAt, threshold)),
    limit: 100,
    orderBy: (fields, operators) => [operators.asc(fields.createdAt)],
  });

  for (const command of pending) {
    const now = new Date();
    const nextRetryCount = command.retryCount + 1;

    if (nextRetryCount > MAX_RETRIES) {
      await db
        .update(deviceCommands)
        .set({
          status: 'failed',
          updatedAt: now,
          error: 'max retries exceeded',
        })
        .where(eq(deviceCommands.id, command.id));
      continue;
    }

    const delivered = emitCommand({
      id: command.id,
      sourceDeviceId: command.sourceDeviceId,
      targetDeviceId: command.targetDeviceId,
      commandType: command.commandType,
      payload: command.payload,
      createdAt: command.createdAt,
    });

    await db
      .update(deviceCommands)
      .set({
        status: delivered ? 'sent' : 'queued',
        lastDispatchedAt: now,
        retryCount: nextRetryCount,
        updatedAt: now,
        error: delivered ? null : 'target device offline',
      })
      .where(eq(deviceCommands.id, command.id));
  }
};

export const setupRealtimeGateway = (server: HttpServer): SocketIOServer => {
  if (io) {
    return io;
  }

  io = new SocketIOServer(server, {
    cors: {
      origin: process.env.BETTER_AUTH_TRUSTED_ORIGINS?.split(',').map((origin) => origin.trim()).filter(Boolean) ?? true,
      credentials: true,
    },
    pingInterval: HEARTBEAT_INTERVAL_MS,
  });

  io.use(async (socket, next) => {
    try {
      const tokenFromAuth = typeof socket.handshake.auth?.token === 'string' ? socket.handshake.auth.token : null;
      const authorization = socket.handshake.headers.authorization;
      const tokenFromHeader =
        typeof authorization === 'string' && authorization.startsWith('Bearer ')
          ? authorization.slice('Bearer '.length).trim()
          : null;

      const token = tokenFromAuth ?? tokenFromHeader;

      if (!token) {
        next(new Error('Missing device token'));
        return;
      }

      const payload = verifyDeviceToken(token);

      if (!payload) {
        next(new Error('Invalid device token'));
        return;
      }

      const device = await db.query.devices.findFirst({
        where: and(eq(devices.id, payload.deviceId), eq(devices.userId, payload.userId)),
      });

      if (!device) {
        next(new Error('Device not found'));
        return;
      }

      if (device.role !== payload.role) {
        next(new Error('Token role does not match device role'));
        return;
      }

      socket.data.deviceAuth = payload;
      next();
    } catch (error) {
      next(error instanceof Error ? error : new Error('Authentication failed'));
    }
  });

  io.on('connection', async (socket) => {
    const auth = socket.data.deviceAuth as { userId: string; deviceId: string; role: 'camera' | 'client' };
    const deviceRoom = roomForDevice(auth.deviceId);

    socket.join(deviceRoom);
    await markDevicePresence(auth.deviceId, 'online');

    socket.emit('connected', {
      deviceId: auth.deviceId,
      role: auth.role,
      serverTime: new Date().toISOString(),
    });

    socket.on('heartbeat', async () => {
      await markDevicePresence(auth.deviceId, 'online');
      socket.emit('heartbeat:ack', { at: new Date().toISOString() });
    });

    socket.on('command:ack', async (input) => {
      const parsed = commandAckSchema.safeParse(input);

      if (!parsed.success) {
        socket.emit('error:command_ack', {
          message: 'Invalid command ack payload',
          errors: parsed.error.flatten(),
        });
        return;
      }

      const command = await db.query.deviceCommands.findFirst({
        where: eq(deviceCommands.id, parsed.data.commandId),
      });

      if (!command) {
        socket.emit('error:command_ack', { message: 'Command not found' });
        return;
      }

      if (command.targetDeviceId !== auth.deviceId) {
        socket.emit('error:command_ack', { message: 'Not authorized to ack this command' });
        return;
      }

      const now = new Date();

      await db
        .update(deviceCommands)
        .set({
          status: parsed.data.status,
          acknowledgedAt: now,
          updatedAt: now,
          error: parsed.data.status === 'rejected' ? parsed.data.error ?? 'rejected' : null,
        })
        .where(eq(deviceCommands.id, command.id));

      io?.to(roomForDevice(command.sourceDeviceId)).emit('command:status', {
        commandId: command.id,
        status: parsed.data.status,
        acknowledgedAt: now.toISOString(),
        error: parsed.data.error,
      });
    });

    socket.on('disconnect', async () => {
      // Small delay allows fast reconnects to reuse presence without flapping.
      setTimeout(async () => {
        if (countSocketsForDevice(auth.deviceId) === 0) {
          await markDevicePresence(auth.deviceId, 'offline');
        }
      }, 500);
    });
  });

  if (!retryTimer) {
    retryTimer = setInterval(() => {
      retryPendingCommands().catch((error) => {
        console.error('Failed retrying pending commands', error);
      });
    }, RETRY_INTERVAL_MS);
  }

  return io;
};