const express = require('express');
const { collections, FieldValue, docToObject } = require('../db/firestore');
const authMiddleware = require('../middleware/auth');

const router = express.Router();
router.use(authMiddleware);

function enrollmentDocId(userId, programId) {
  return `${userId}_${programId}`;
}

async function annotateEnrollment(programDocs, userId) {
  if (programDocs.length === 0) return [];
  const enrollSnaps = await Promise.all(
    programDocs.map((d) =>
      collections.userPrograms.doc(enrollmentDocId(userId, d.id)).get()
    )
  );
  return programDocs.map((doc, i) => {
    const program = docToObject(doc);
    const e = enrollSnaps[i];
    program.is_enrolled = e.exists;
    if (e.exists) {
      const ed = e.data();
      program.current_week = ed.current_week ?? 1;
      program.is_active = ed.is_active ?? true;
      program.enrolled_at = ed.enrolled_at?.toDate?.().toISOString() ?? null;
    } else {
      program.current_week = null;
      program.is_active = null;
    }
    return program;
  });
}

// GET /api/programs/me/active — must come before /:id
router.get('/me/active', async (req, res) => {
  try {
    const enrollSnap = await collections.userPrograms
      .where('userId', '==', req.userId)
      .where('is_active', '==', true)
      .get();

    const programs = await Promise.all(
      enrollSnap.docs.map(async (e) => {
        const ed = e.data();
        const p = await collections.programs.doc(ed.programId).get();
        if (!p.exists) return null;
        const program = docToObject(p);
        program.current_week = ed.current_week ?? 1;
        program.enrolled_at = ed.enrolled_at?.toDate?.().toISOString() ?? null;
        return program;
      })
    );

    res.json({ programs: programs.filter(Boolean) });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Server error' });
  }
});

// GET /api/programs
router.get('/', async (req, res) => {
  const { difficulty, category } = req.query;
  try {
    let query = collections.programs;
    if (difficulty) query = query.where('difficulty', '==', difficulty);
    // Firestore can't do case-insensitive substring; for category we filter exact match.
    if (category) query = query.where('category', '==', category);

    const snap = await query.get();
    const sorted = snap.docs.slice().sort((a, b) => {
      const ad = a.data(), bd = b.data();
      if ((bd.is_featured ? 1 : 0) !== (ad.is_featured ? 1 : 0))
        return (bd.is_featured ? 1 : 0) - (ad.is_featured ? 1 : 0);
      const at = ad.created_at?.toMillis?.() ?? 0;
      const bt = bd.created_at?.toMillis?.() ?? 0;
      return bt - at;
    });

    const programs = await annotateEnrollment(sorted, req.userId);
    res.json({ programs });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Server error' });
  }
});

// GET /api/programs/:id
router.get('/:id', async (req, res) => {
  try {
    const snap = await collections.programs.doc(req.params.id).get();
    if (!snap.exists) return res.status(404).json({ message: 'Program not found' });
    const [program] = await annotateEnrollment([snap], req.userId);
    res.json({ program });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Server error' });
  }
});

// POST /api/programs/:id/enroll
router.post('/:id/enroll', async (req, res) => {
  try {
    const enrollRef = collections.userPrograms.doc(enrollmentDocId(req.userId, req.params.id));
    const programRef = collections.programs.doc(req.params.id);

    const enrollSnap = await enrollRef.get();
    const wasEnrolled = enrollSnap.exists;

    await enrollRef.set(
      {
        userId: req.userId,
        programId: req.params.id,
        enrolled_at: enrollSnap.exists ? enrollSnap.data().enrolled_at : FieldValue.serverTimestamp(),
        current_week: 1,
        is_active: true,
        completed_at: null,
      },
      { merge: true }
    );

    if (!wasEnrolled) {
      await programRef.update({ total_enrolled: FieldValue.increment(1) });
    }

    res.json({ message: 'Enrolled successfully' });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Server error' });
  }
});

// DELETE /api/programs/:id/enroll
router.delete('/:id/enroll', async (req, res) => {
  try {
    const enrollRef = collections.userPrograms.doc(enrollmentDocId(req.userId, req.params.id));
    await enrollRef.set({ is_active: false }, { merge: true });
    res.json({ message: 'Unenrolled' });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Server error' });
  }
});

module.exports = router;