import { NextRequest, NextResponse } from 'next/server';
import { adminFirestore, adminMessaging } from '@/lib/firebase-admin';

export async function POST(req: NextRequest) {
    const { recipientUid, title, body, icon, chatId } = await req.json();

    if (!recipientUid || !title || !body || !chatId) {
        return NextResponse.json({ error: 'Missing required fields: recipientUid, title, body, chatId' }, { status: 400 });
    }

    try {
        const userDoc = await adminFirestore.collection('users').doc(recipientUid).get();
        if (!userDoc.exists) {
            return NextResponse.json({ error: 'Recipient user not found' }, { status: 404 });
        }
        
        const fcmToken = userDoc.data()?.fcmToken;

        if (!fcmToken) {
            console.log(`Notification not sent: User ${recipientUid} does not have an FCM token.`);
            return NextResponse.json({ success: true, message: 'User has no FCM token.' });
        }

        const message = {
            token: fcmToken,
            notification: {
                title: title,
                body: body,
            },
            webpush: {
                notification: {
                    icon: '/favicon.ico', // Always use a static, known-good icon
                },
                fcm_options: {
                    link: `/?chatId=${chatId}`
                }
            },
        };

        const response = await adminMessaging.send(message);
        console.log('Successfully sent message:', response);
        return NextResponse.json({ success: true, messageId: response });

    } catch (error: any) {
        console.error('Error sending FCM message:', error);
        
        let errorMessage = 'Internal Server Error';
        let statusCode = 500;

        if (error.code === 'messaging/invalid-argument') {
            errorMessage = 'Invalid argument provided for FCM message.';
            statusCode = 400;
        } else if (error.code === 'messaging/registration-token-not-registered') {
             errorMessage = `The FCM token for user ${recipientUid} is no longer valid. It might be expired.`;
             await adminFirestore.collection('users').doc(recipientUid).update({ fcmToken: '' });
             statusCode = 404;
        } else if (error.code === 'messaging/invalid-registration-token') {
             errorMessage = `Invalid FCM registration token for user ${recipientUid}.`;
             await adminFirestore.collection('users').doc(recipientUid).update({ fcmToken: '' });
             statusCode = 400;
        }
        
        return NextResponse.json({ error: 'Failed to send notification', details: errorMessage }, { status: statusCode });
    }
}