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

export async function POST(req: NextRequest) {
    console.log("[/api/notify] Received a POST request.");
    
    let recipientUidForError: string | null = null;

    try {
        const { recipientUid, senderUid, title, body, icon, chatId } = await req.json();
        recipientUidForError = recipientUid;
        console.log("[/api/notify] Request body parsed:", { recipientUid, senderUid, title, body, icon, chatId });

        // The crucial check to prevent self-notifications
        if (senderUid && recipientUid === senderUid) {
            console.log(`[FCM Notify] Skipped: Sender and recipient are the same user (${senderUid}).`);
            return NextResponse.json({ success: true, message: 'Sender is recipient, notification skipped.' });
        }

        if (!recipientUid || !title || !body || !chatId) {
            console.log("[/api/notify] Missing required fields.");
            return NextResponse.json({ error: 'Missing required fields: recipientUid, title, body, chatId' }, { status: 400 });
        }

        console.log(`[/api/notify] Fetching user document for UID: ${recipientUid}`);
        const userDoc = await adminFirestore.collection('users').doc(recipientUid).get();
        
        if (!userDoc.exists) {
            console.log(`[/api/notify] Recipient user not found: ${recipientUid}`);
            return NextResponse.json({ error: 'Recipient user not found' }, { status: 404 });
        }
        
        const fcmToken = userDoc.data()?.fcmToken;
        console.log(`[/api/notify] Found FCM token: ${fcmToken ? 'Yes' : 'No'}`);

        if (!fcmToken) {
            console.log(`[/api/notify] 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}`
                }
            },
        };
        console.log("[/api/notify] Prepared message payload:", message);

        console.log("[/api/notify] Sending message via FCM...");
        const response = await adminMessaging.send(message);
        console.log('[/api/notify] Successfully sent message:', response);
        return NextResponse.json({ success: true, messageId: response });

    } catch (error: any) {
        console.error('[/api/notify] CRITICAL ERROR:', 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 ${recipientUidForError} is no longer valid. It might be expired.`;
             if (recipientUidForError) {
                await adminFirestore.collection('users').doc(recipientUidForError).update({ fcmToken: '' });
             }
             statusCode = 404;
        } else if (error.code === 'messaging/invalid-registration-token') {
             errorMessage = `Invalid FCM registration token for user ${recipientUidForError}.`;
             if (recipientUidForError) {
                await adminFirestore.collection('users').doc(recipientUidForError).update({ fcmToken: '' });
             }
             statusCode = 400;
        }
        
        return NextResponse.json({ error: 'Failed to send notification', details: errorMessage, rawError: error.message }, { status: statusCode });
    }
}