const express = require('express');
const router = express.Router();
const db = require('../db');

// POST /api/dms/open — Find-or-create a DM channel between two users
router.post('/open', async (req, res) => {
    const { userId, targetUserId } = req.body;

    if (!userId || !targetUserId) {
        return res.status(400).json({ error: 'userId and targetUserId required' });
    }

    if (userId === targetUserId) {
        return res.status(400).json({ error: 'Cannot DM yourself' });
    }

    // Deterministic channel name so the same pair always maps to one channel
    const sorted = [userId, targetUserId].sort();
    const dmName = `dm-${sorted[0]}-${sorted[1]}`;

    try {
        // Check if DM channel already exists
        const existing = await db.query(
            'SELECT id FROM channels WHERE name = $1 AND type = $2',
            [dmName, 'dm']
        );

        if (existing.rows.length > 0) {
            return res.json({ channelId: existing.rows[0].id, created: false });
        }

        // Create the DM channel + participants in a transaction
        await db.query('BEGIN');

        const channelResult = await db.query(
            'INSERT INTO channels (name, type) VALUES ($1, $2) RETURNING id',
            [dmName, 'dm']
        );
        const channelId = channelResult.rows[0].id;

        await db.query(
            'INSERT INTO dm_participants (channel_id, user_id) VALUES ($1, $2), ($1, $3)',
            [channelId, userId, targetUserId]
        );

        await db.query('COMMIT');

        res.json({ channelId, created: true });
    } catch (err) {
        await db.query('ROLLBACK');
        console.error('Error opening DM:', err);
        res.status(500).json({ error: 'Server error' });
    }
});

// GET /api/dms/user/:userId — List all DM channels for a user with the other user's info
router.get('/user/:userId', async (req, res) => {
    const { userId } = req.params;

    try {
        const result = await db.query(`
            SELECT c.id AS channel_id, c.name AS channel_name, c.created_at,
                   other_user.id AS other_user_id, other_user.username AS other_username
            FROM dm_participants my
            JOIN channels c ON c.id = my.channel_id AND c.type = 'dm'
            JOIN dm_participants other ON other.channel_id = my.channel_id AND other.user_id != $1
            JOIN users other_user ON other_user.id = other.user_id
            WHERE my.user_id = $1
            ORDER BY c.created_at DESC
        `, [userId]);

        res.json(result.rows);
    } catch (err) {
        console.error('Error fetching DM channels:', err);
        res.status(500).json({ error: 'Server error' });
    }
});

module.exports = router;