const prisma = require('../config/db');
const { safeErrorMessage } = require('../utils/errorUtils');
const { logAdminAction } = require('../utils/adminAudit');
const { getClientIp } = require('../utils/requestUtils');
const { normalizeCode, previewCoupon, buildCouponLines, describeCoupon, countCouponUses } = require('../utils/coupons');
const { resolveOptionPrice, resolveVariantTierPrice } = require('../utils/pricing');
const { describeBundle } = require('../utils/bundles');

const TYPES = ['percent', 'fixed', 'comp'];
const ROLES = ['user', 'staff', 'supervisor', 'admin'];
const STAFF_ROLES = ['staff', 'supervisor', 'admin'];

const COUPON_DETAIL_INCLUDE = {
  events: { include: { event: { select: { id: true, title: true, startDate: true } } } },
  options: { include: { eventOption: { select: { id: true, name: true, eventId: true } }, variant: { select: { id: true, name: true } } } },
  allowedUsers: { include: { user: { select: { id: true, name: true, email: true } } } },
  createdBy: { select: { id: true, name: true } },
};

const optionalDate = (v, label) => {
  if (v === undefined) return undefined;
  if (v === null || v === '') return null;
  const d = new Date(v);
  if (isNaN(d.getTime())) throw new Error(`${label} is not a valid date`);
  return d;
};

const optionalInt = (v, label, min = 0) => {
  if (v === undefined) return undefined;
  if (v === null || v === '') return null;
  const n = Number(v);
  if (!Number.isInteger(n) || n < min) throw new Error(`${label} must be a whole number of at least ${min}`);
  return n;
};

/**
 * Turns a create/update body into Prisma data plus the relation lists. On update,
 * fields left out of the body are left alone.
 */
async function parseCouponBody(body, { isCreate }) {
  const data = {};
  if (isCreate || body.code !== undefined) {
    const code = normalizeCode(body.code);
    if (!/^[A-Z0-9_-]{3,32}$/.test(code)) {
      throw new Error('Codes are 3–32 letters, numbers, hyphens or underscores');
    }
    data.code = code;
  }
  if (isCreate || body.type !== undefined) {
    if (!TYPES.includes(body.type)) throw new Error("Discount type must be 'percent', 'fixed' or 'comp'");
    data.type = body.type;
  }
  if (isCreate || body.value !== undefined) {
    const type = data.type || body.type;
    const value = type === 'comp' ? 0 : Number(body.value);
    if (type !== 'comp' && !(value > 0)) throw new Error('Enter a discount value greater than zero');
    if (type === 'percent' && value > 100) throw new Error('A percentage discount can\'t be more than 100');
    data.value = value;
  }
  if (body.description !== undefined) data.description = body.description ? String(body.description).trim() : null;
  if (body.stackEarlyBird !== undefined) data.stackEarlyBird = !!body.stackEarlyBird;
  if (body.active !== undefined) data.active = !!body.active;
  const validFrom = optionalDate(body.validFrom, 'Valid from');
  const validUntil = optionalDate(body.validUntil, 'Valid until');
  if (validFrom !== undefined) data.validFrom = validFrom;
  if (validUntil !== undefined) data.validUntil = validUntil;
  if (validFrom && validUntil && validFrom > validUntil) throw new Error('"Valid from" must be before "Valid until"');
  const maxUses = optionalInt(body.maxUses, 'Max total uses', 1);
  const maxUsesPerUser = optionalInt(body.maxUsesPerUser, 'Max uses per person', 1);
  const minQuantity = optionalInt(body.minQuantity, 'Minimum quantity', 1);
  if (maxUses !== undefined) data.maxUses = maxUses;
  if (maxUsesPerUser !== undefined) data.maxUsesPerUser = maxUsesPerUser;
  if (minQuantity !== undefined) data.minQuantity = minQuantity;
  if (body.restrictRoles !== undefined) {
    const roles = Array.isArray(body.restrictRoles) ? body.restrictRoles : [];
    if (roles.some(r => !ROLES.includes(r))) throw new Error('Unknown role in restrictions');
    data.restrictRoles = roles;
  }
  if (body.restrictDomain !== undefined) {
    const domain = String(body.restrictDomain || '').trim().toLowerCase().replace(/^@/, '');
    if (domain && !/^[a-z0-9.-]+\.[a-z]{2,}$/.test(domain)) throw new Error('Enter an email domain like church.org');
    data.restrictDomain = domain || null;
  }

  const eventIds = body.eventIds !== undefined ? [...new Set((body.eventIds || []).filter(Boolean))] : undefined;
  const scopes = body.options !== undefined
    ? (body.options || []).filter(o => o && o.eventOptionId).map(o => ({ eventOptionId: o.eventOptionId, variantId: o.variantId || null }))
    : undefined;
  const userIds = body.userIds !== undefined ? [...new Set((body.userIds || []).filter(Boolean))] : undefined;

  if (scopes && scopes.length > 0) {
    const optionRows = await prisma.eventOption.findMany({
      where: { id: { in: scopes.map(s => s.eventOptionId) } },
      select: { id: true, eventId: true, variants: { select: { id: true } } },
    });
    for (const s of scopes) {
      const row = optionRows.find(o => o.id === s.eventOptionId);
      if (!row) throw new Error('One of the selected ticket options no longer exists');
      if (s.variantId && !row.variants.some(v => v.id === s.variantId)) throw new Error('One of the selected variants no longer exists');
      // A scoped option implies its event, so the code can't be used elsewhere by mistake.
      if (eventIds && eventIds.length > 0 && !eventIds.includes(row.eventId)) {
        throw new Error('Selected ticket options must belong to the selected events');
      }
    }
  }
  return { data, eventIds, scopes, userIds };
}

function relationWrites({ eventIds, scopes, userIds }, isCreate) {
  const out = {};
  if (eventIds !== undefined) out.events = { ...(isCreate ? {} : { deleteMany: {} }), create: eventIds.map(eventId => ({ eventId })) };
  if (scopes !== undefined) out.options = { ...(isCreate ? {} : { deleteMany: {} }), create: scopes };
  if (userIds !== undefined) out.allowedUsers = { ...(isCreate ? {} : { deleteMany: {} }), create: userIds.map(userId => ({ userId })) };
  return out;
}

// @desc    List coupons with their use counts
// @route   GET /api/coupons
// @access  Private/Supervisor
const listCoupons = async (req, res) => {
  try {
    const coupons = await prisma.coupon.findMany({ include: COUPON_DETAIL_INCLUDE, orderBy: { createdAt: 'desc' } });
    const totals = await prisma.couponRedemption.groupBy({
      by: ['couponId'],
      where: { releasedAt: null, registration: { status: { not: 'cancelled' } } },
      _count: { _all: true },
      _sum: { discountAmount: true },
    });
    const byId = Object.fromEntries(totals.map(t => [t.couponId, t]));
    res.json(coupons.map(c => ({
      ...c,
      summary: describeCoupon(c),
      uses: byId[c.id]?._count?._all || 0,
      totalDiscount: byId[c.id]?._sum?.discountAmount || 0,
    })));
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

// @desc    Get one coupon with its redemptions
// @route   GET /api/coupons/:id
// @access  Private/Supervisor
const getCoupon = async (req, res) => {
  try {
    const coupon = await prisma.coupon.findUnique({
      where: { id: req.params.id },
      include: {
        ...COUPON_DETAIL_INCLUDE,
        redemptions: {
          orderBy: { createdAt: 'desc' },
          include: {
            user: { select: { id: true, name: true, email: true } },
            appliedBy: { select: { id: true, name: true } },
            registration: { select: { id: true, status: true, event: { select: { id: true, title: true } } } },
          },
        },
      },
    });
    if (!coupon) { res.status(404); throw new Error('Coupon not found'); }
    res.json({ ...coupon, summary: describeCoupon(coupon) });
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

// @desc    Create a coupon
// @route   POST /api/coupons
// @access  Private/Supervisor
const createCoupon = async (req, res) => {
  try {
    let parsed;
    try {
      parsed = await parseCouponBody(req.body || {}, { isCreate: true });
    } catch (e) { res.status(400); throw e; }
    if (await prisma.coupon.findUnique({ where: { code: parsed.data.code } })) {
      res.status(409); throw new Error(`The code ${parsed.data.code} already exists`);
    }
    const coupon = await prisma.coupon.create({
      data: { ...parsed.data, createdById: req.user.id, ...relationWrites(parsed, true) },
      include: COUPON_DETAIL_INCLUDE,
    });
    logAdminAction({
      actorId: req.user.id, actorRole: req.user.role, action: 'coupon_created',
      targetType: 'Coupon', targetId: coupon.id,
      metadata: { code: coupon.code, type: coupon.type, value: coupon.value },
      ip: getClientIp(req),
    });
    res.status(201).json({ ...coupon, summary: describeCoupon(coupon), uses: 0, totalDiscount: 0 });
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

// @desc    Update a coupon (including turning it off). Discounts already applied keep
//          their locked amount.
// @route   PUT /api/coupons/:id
// @access  Private/Supervisor
const updateCoupon = async (req, res) => {
  try {
    const existing = await prisma.coupon.findUnique({ where: { id: req.params.id } });
    if (!existing) { res.status(404); throw new Error('Coupon not found'); }
    let parsed;
    try {
      parsed = await parseCouponBody({ type: existing.type, ...req.body }, { isCreate: false });
    } catch (e) { res.status(400); throw e; }
    if (parsed.data.code && parsed.data.code !== existing.code) {
      const used = await prisma.couponRedemption.count({ where: { couponId: existing.id } });
      if (used > 0) { res.status(400); throw new Error('This code has been used, so it can\'t be renamed. Turn it off and create a new one instead.'); }
      if (await prisma.coupon.findUnique({ where: { code: parsed.data.code } })) {
        res.status(409); throw new Error(`The code ${parsed.data.code} already exists`);
      }
    }
    const coupon = await prisma.coupon.update({
      where: { id: existing.id },
      data: { ...parsed.data, ...relationWrites(parsed, false) },
      include: COUPON_DETAIL_INCLUDE,
    });
    const disabled = existing.active && coupon.active === false;
    const changedKeys = Object.keys(req.body || {});
    logAdminAction({
      actorId: req.user.id, actorRole: req.user.role,
      action: disabled && changedKeys.length === 1 ? 'coupon_disabled' : 'coupon_updated',
      targetType: 'Coupon', targetId: coupon.id,
      metadata: { code: coupon.code, changedKeys },
      ip: getClientIp(req),
    });
    const { usesTotal } = await countCouponUses(coupon.id, null);
    res.json({ ...coupon, summary: describeCoupon(coupon), uses: usesTotal });
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

/**
 * Who a basket is being priced for: the logged-in buyer, or, for staff, the attendee
 * (`forUserId`) or a walk-in with no account yet (`forUserId: null`).
 */
async function basketBuyer(req, forUserId) {
  const isStaff = !!(req.user && STAFF_ROLES.includes(req.user.role));
  let buyer = req.user ? { id: req.user.id, role: req.user.role, email: req.user.email } : null;
  if (isStaff && forUserId) {
    buyer = await prisma.user.findUnique({ where: { id: forUserId }, select: { id: true, role: true, email: true } });
  } else if (isStaff && forUserId === null) {
    buyer = null; // a walk-in without an account yet
  }
  return { buyer, isStaff };
}

/** Prices a basket the same way registration will, as coupon/bundle lines. */
async function priceBasket(event, options, buyer) {
  const registrationOptions = [];
  // A "pick sessions" line counts once per chosen session.
  const expanded = (options || []).flatMap(o => (Array.isArray(o.sessionIds) && o.sessionIds.length ? o.sessionIds.map(sessionId => ({ ...o, sessionId })) : [o]));
  for (const o of expanded) {
    const eo = event.eventOptions.find(x => x.id === o.eventOptionId);
    const qty = Number(o.quantity || 0);
    if (!eo || qty < 1) continue;
    const resolved = o.variantId
      ? await resolveVariantTierPrice(eo, o.variantId, qty, buyer)
      : await resolveOptionPrice(eo, qty, buyer);
    registrationOptions.push({
      eventOptionId: eo.id, variantId: o.variantId || null, quantity: qty, eventOption: eo,
      tranches: [{ quantity: qty, priceSnapshot: resolved.price, appliedTierId: resolved.tierId }],
    });
  }
  return buildCouponLines({ registrationOptions });
}

// @desc    Check a code against the items someone is about to register for
// @route   POST /api/coupons/validate
// @access  Public (login needed for restricted codes)
// Body: { code, eventId, options: [{ eventOptionId, variantId?, quantity }], forUserId? }
// Staff can pass forUserId to check on an attendee's behalf, or leave it out for a new
// attendee — restricted codes are then checked when the registration is saved.
const validateCode = async (req, res) => {
  try {
    const { code, eventId, options, forUserId } = req.body || {};
    if (!code || !eventId || !Array.isArray(options) || options.length === 0) {
      res.status(400); throw new Error('code, eventId and options are required');
    }
    const event = await prisma.event.findUnique({
      where: { id: eventId },
      include: { eventOptions: { include: { earlyBirdTiers: true, variants: true } } },
    });
    if (!event) { res.status(404); throw new Error('Event not found'); }

    const { buyer, isStaff } = await basketBuyer(req, forUserId);
    const lines = await priceBasket(event, options, buyer);
    const subtotal = lines.reduce((s, l) => s + l.unitPrice * l.quantity, 0);

    try {
      const { coupon, discount, bundles } = await previewCoupon({
        code, eventId, user: buyer, lines,
        deferRestrictions: isStaff && !buyer,
      });
      res.json({
        valid: true,
        code: coupon.code,
        type: coupon.type,
        value: coupon.value,
        summary: describeCoupon(coupon),
        description: coupon.description,
        discount,
        bundleDiscount: bundles.discount,
        bundles: bundles.applications,
        subtotal,
        total: Math.max(0, subtotal - bundles.discount - discount),
      });
    } catch (e) {
      if (!e.isCouponError) throw e;
      res.status(400).json({ valid: false, message: e.message });
    }
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

// @desc    Coupon and bundle-deal uses for the Discounts report
// @route   GET /api/coupons/redemptions?eventIds=a,b&from=&to=
// @access  Private/Supervisor
const listRedemptions = async (req, res) => {
  try {
    const eventIds = String(req.query.eventIds || '').split(',').map(s => s.trim()).filter(Boolean);
    const from = req.query.from ? new Date(req.query.from) : null;
    const to = req.query.to ? new Date(req.query.to) : null;
    const where = {
      releasedAt: null,
      registration: { status: { not: 'cancelled' }, ...(eventIds.length ? { eventId: { in: eventIds } } : {}) },
      ...(from || to ? { createdAt: { ...(from && !isNaN(from) ? { gte: from } : {}), ...(to && !isNaN(to) ? { lte: to } : {}) } } : {}),
    };
    const rows = await prisma.couponRedemption.findMany({
      where,
      orderBy: { createdAt: 'desc' },
      include: {
        coupon: { select: { id: true, code: true, type: true, value: true } },
        user: { select: { id: true, name: true, email: true } },
        appliedBy: { select: { id: true, name: true } },
        registration: { select: { id: true, status: true, event: { select: { id: true, title: true } } } },
      },
    });
    // Bundle deals, in the same shape. Their rows are rebuilt whenever a registration's
    // discounts are recalculated, so dates go by when the registration was made.
    const regDate = from || to ? { createdAt: { ...(from && !isNaN(from) ? { gte: from } : {}), ...(to && !isNaN(to) ? { lte: to } : {}) } } : {};
    const bundleRows = await prisma.registrationBundle.findMany({
      where: { registration: { status: { not: 'cancelled' }, ...(eventIds.length ? { eventId: { in: eventIds } } : {}), ...regDate } },
      include: {
        bundle: { include: { items: { include: { eventOption: { select: { name: true } }, variant: { select: { name: true } } } } } },
        registration: { select: { id: true, status: true, createdAt: true, user: { select: { id: true, name: true, email: true } }, event: { select: { id: true, title: true } } } },
      },
    });
    res.json([
      ...rows.map(r => ({ ...r, kind: 'coupon', uses: 1, summary: describeCoupon(r.coupon) })),
      ...bundleRows.map(b => ({
        id: b.id,
        kind: 'bundle',
        uses: b.count,
        discountAmount: b.discount,
        createdAt: b.registration.createdAt,
        summary: describeBundle(b.bundle),
        coupon: { id: b.bundleId, code: b.bundle.name },
        user: b.registration.user,
        appliedBy: null,
        registration: { id: b.registration.id, status: b.registration.status, event: b.registration.event },
      })),
    ]);
  } catch (error) {
    res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(error) });
  }
};

module.exports = { listCoupons, getCoupon, createCoupon, updateCoupon, validateCode, listRedemptions, basketBuyer, priceBasket };