const prisma = require('../config/db');
const { v4: uuidv4 } = require('uuid');

/**
 * Generate tickets for a registration when payment status is "paid".
 *
 * Rules:
 *  - Exactly ONE ticket per registrationOption (keyed by eventOptionId).
 *  - If duplicate registrationOptions exist for the same eventOptionId (old data),
 *    consolidate them: merge quantities, keep the one with scan history, delete the rest.
 *  - If duplicate ticket records exist for the same registrationOption (old data),
 *    keep the primary (scanned one, or oldest), update its quantity, delete the rest.
 *
 * @param {string} registrationId
 * @returns {Promise<Array>} newly-created ticket records (empty when all already existed)
 */
const generateTicketsForRegistration = async (registrationId) => {
  try {
    const registration = await prisma.registration.findUnique({
      where: { id: registrationId },
      include: {
        registrationOptions: {
          include: {
            eventOption: true,
            tickets: { include: { usages: true }, orderBy: { createdAt: 'asc' } }
          }
        },
        event: true,
        user: true
      }
    });

    if (!registration) throw new Error('Registration not found');
    if (registration.status !== 'paid') return [];

    // If event has a required form, ensure sufficient responses exist
    try {
      const form = await prisma.eventForm.findUnique({ where: { eventId: registration.eventId } });
      if (form && form.isRequired) {
        const requiredCount = (registration.registrationOptions || [])
          .filter(ro => ro.eventOption?.isMainTicket)
          .reduce((s, ro) => s + (ro.quantity || 0), 0);
        const responsesCount = await prisma.formResponse.count({ where: { registrationId } });
        if (responsesCount < requiredCount) return [];
      }
    } catch (_) { /* form models unavailable — don't block */ }

    // ── Step 1: Consolidate duplicate registrationOptions for the same (eventOptionId, variantId) ──
    // Key on both fields so that different variants of the same option are never merged
    const byOption = new Map();
    for (const ro of registration.registrationOptions) {
      const key = `${ro.eventOptionId}::${ro.variantId || ''}`;
      if (!byOption.has(key)) byOption.set(key, []);
      byOption.get(key).push(ro);
    }

    // For each group with duplicates, merge into the one that has tickets (or the first).
    // Different (eventOptionId, variantId) groups touch disjoint rows, so process groups
    // concurrently instead of one at a time.
    await Promise.all(Array.from(byOption.values()).map(async (group) => {
      if (group.length <= 1) return;

      // Prefer the option that already has tickets
      const withTickets = group.filter(ro => (ro.tickets || []).length > 0);
      const primary = withTickets.length > 0 ? withTickets[0] : group[0];
      const duplicates = group.filter(ro => ro.id !== primary.id);

      // Move all tickets from duplicates to primary (independent rows — safe to parallelize)
      await Promise.all(duplicates.map(dup => Promise.all(
        (dup.tickets || []).map(t =>
          prisma.ticket.update({ where: { id: t.id }, data: { registrationOptionId: primary.id, updatedAt: new Date() } })
        )
      )));

      // Single write of the merged quantity, then delete the now-empty duplicate options
      const totalMergedQty = duplicates.reduce((s, d) => s + (d.quantity || 0), 0);
      await prisma.registrationOption.update({
        where: { id: primary.id },
        data: { quantity: (primary.quantity || 0) + totalMergedQty }
      });
      await Promise.all(duplicates.map(dup => prisma.registrationOption.delete({ where: { id: dup.id } })));

      // Re-load the primary's current quantity + tickets after merge
      const updated = await prisma.registrationOption.findUnique({ where: { id: primary.id } });
      primary.quantity = updated?.quantity ?? primary.quantity;
      primary.tickets = await prisma.ticket.findMany({
        where: { registrationOptionId: primary.id },
        include: { usages: true },
        orderBy: { createdAt: 'asc' }
      });
    }));

    // ── Step 2: For each unique option, ensure exactly one ticket with correct qty ──
    // Re-read fresh list (some options may have been deleted above)
    const freshOptions = await prisma.registrationOption.findMany({
      where: { registrationId },
      include: {
        tickets: { include: { usages: true }, orderBy: { createdAt: 'asc' } }
      }
    });

    // Each option owns disjoint tickets, so resolve them concurrently instead of one at a time.
    const perOptionResults = await Promise.all(freshOptions.map(async (option) => {
      const targetQty = option.quantity || 1;
      const existingTickets = option.tickets || [];

      if (existingTickets.length === 0) {
        // Create one ticket
        return prisma.ticket.create({
          data: {
            id: uuidv4(),
            qrCode: uuidv4(),
            registrationOptionId: option.id,
            userId: registration.userId,
            eventId: registration.eventId,
            quantity: targetQty,
            updatedAt: new Date()
          }
        });
      }

      // Pick primary: prefer scanned, otherwise oldest
      const withUsages = existingTickets.filter(t => (t.usages || []).length > 0);
      const primary = withUsages.length > 0 ? withUsages[0] : existingTickets[0];

      const updates = [];
      // Update quantity on primary if needed
      if (primary.quantity !== targetQty) {
        updates.push(prisma.ticket.update({ where: { id: primary.id }, data: { quantity: targetQty, updatedAt: new Date() } }));
      }

      // Delete unscanned duplicates
      const dups = existingTickets.filter(t => t.id !== primary.id && (t.usages || []).length === 0);
      if (dups.length > 0) {
        updates.push(prisma.ticket.deleteMany({ where: { id: { in: dups.map(t => t.id) } } }));
      }
      if (updates.length > 0) await Promise.all(updates);
      return null;
    }));

    return perOptionResults.filter(Boolean);
  } catch (error) {
    console.error('Error generating tickets:', error);
    throw error;
  }
};

module.exports = { generateTicketsForRegistration };