/**
 * Early-bird pricing utility
 *
 * Rules:
 * - Base price is eventOption.price
 * - resolveOptionPrice: picks the cheapest applicable tier, checking both deadline AND stock limits.
 *   Used at registration-creation time and again at payment-initiation time.
 * - getEffectiveUnitPrice: deadline-only check; used for line-item display in Yoco checkout and
 *   as a fallback for legacy RegistrationOption rows that have no priceSnapshot.
 * - A RegistrationOption is an aggregate line (one per registration+option+variant); each
 *   purchase-at-a-price is its own RegistrationOptionTranche row underneath it (quantity +
 *   priceSnapshot + appliedTierId, never mutated after creation — mirrors the Payment model's
 *   append-only pattern). This is what lets someone buy more of the same ticket type after an
 *   early-bird tier expires without the new price bleeding onto tickets already bought.
 *   RegistrationOption.quantity/priceSnapshot/appliedTierId are kept as a maintained mirror
 *   (quantity = sum of tranche quantities; priceSnapshot/appliedTierId = most recent tranche)
 *   for code that only needs "how many" or a single display price.
 * - computeRegistrationTotalDue: sums quantity*priceSnapshot across each RegistrationOption's
 *   tranches (falling back to the legacy single-priceSnapshot/getEffectiveUnitPrice path for
 *   rows created before tranches existed).
 * - refreshPricingForRegistration: re-evaluates only the newest, not-yet-paid-for tranche of
 *   each RegistrationOption; if its tier has expired or lost stock, resolves the next
 *   applicable tier/price for just that tranche. Older tranches — already priced-in — are
 *   never touched.
 */

const prisma = require('../config/db');

/**
 * Compute effective unit price for an event option at a given time considering early-bird tiers.
 * Only checks deadline (not stock). Used for display and as a legacy fallback.
 *
 * @param {object} eventOption - includes price:number and earlyBirdTiers?:Array<{deadline:string|Date, price:number}>
 * @param {Date|string|null} referenceTime - usually the last payment time; if null, falls back to atTime
 * @param {Date} atTime - payment/evaluation time (e.g., now or payment.createdAt)
 * @returns {number}
 */
function getEffectiveUnitPrice(eventOption, referenceTime, atTime) {
  if (!eventOption) return 0;
  const base = Number(eventOption.price || 0);
  const tiers = Array.isArray(eventOption.earlyBirdTiers) ? eventOption.earlyBirdTiers.slice() : [];
  if (!tiers.length) return base;

  const t = atTime ? new Date(atTime) : new Date();
  // If no referenceTime (no payments yet), use atTime so early-bird applies based on "now"
  const ref = referenceTime ? new Date(referenceTime) : t;

  // Only tiers whose deadline is after BOTH reference and payment/evaluation times qualify
  const applicable = tiers
    .map(x => ({ ...x, deadline: new Date(x.deadline) }))
    .filter(x => (ref < x.deadline) && (t < x.deadline))
    .sort((a, b) => a.deadline.getTime() - b.deadline.getTime() || (a.order || 0) - (b.order || 0) || a.price - b.price);

  if (applicable.length === 0) return base;
  const chosen = applicable[0];
  const price = Number(chosen.price);
  if (!(price >= 0)) return base;
  return price;
}

/**
 * Resolve the best applicable early-bird tier price for an event option.
 * Checks BOTH deadline AND stock limits. Cancelled registrations are excluded from stock counts.
 * Tiers are sorted cheapest-first (best deal for the user); earliest deadline breaks ties.
 *
 * @param {object} option - EventOption with price, earlyBirdTiers[]
 * @param {number} requestedQty - quantity being purchased
 * @returns {Promise<{ price: number, tierId: string|null }>}
 */
async function resolveOptionPrice(option, requestedQty = 1) {
  const now = new Date();
  // Only option-level tiers (no variant association)
  const tiers = (Array.isArray(option.earlyBirdTiers) ? option.earlyBirdTiers : [])
    .filter(t => !t.variantId)
    .slice();

  // Sort cheapest-first; earliest deadline breaks ties
  tiers.sort((a, b) => {
    if (a.price !== b.price) return a.price - b.price;
    return new Date(a.deadline).getTime() - new Date(b.deadline).getTime();
  });

  for (const tier of tiers) {
    // Skip expired tiers
    if (now >= new Date(tier.deadline)) continue;

    // Check stock limit if one is set. Sold-so-far is summed across tranches (not
    // RegistrationOption rows directly) because one RegistrationOption can now span
    // multiple tiers across its tranches — the row's own appliedTierId/quantity only
    // reflects its most recent tranche.
    if (tier.stockLimit > 0) {
      const soldAgg = await prisma.registrationOptionTranche.aggregate({
        where: {
          appliedTierId: tier.id,
          registrationOption: { registration: { status: { not: 'cancelled' } } }
        },
        _sum: { quantity: true }
      });
      const tierSold = soldAgg._sum?.quantity || 0;
      if (tierSold + requestedQty > tier.stockLimit) continue; // tier exhausted — try next
    }

    return { price: tier.price, tierId: tier.id };
  }

  // No tier applicable — fall back to base option price
  return { price: option.price, tierId: null };
}

/**
 * Resolve the best applicable early-bird tier price for a specific variant.
 * Checks tiers that have variantId matching the given variant.
 * Falls back to variant.price (or option.price if variant has no override) when no tier applies.
 *
 * @param {object} option - EventOption with price, earlyBirdTiers[], variants[]
 * @param {string} variantId
 * @param {number} requestedQty
 * @returns {Promise<{ price: number, tierId: string|null }>}
 */
async function resolveVariantTierPrice(option, variantId, requestedQty = 1) {
  const now = new Date();
  const variant = (option.variants || []).find(v => v.id === variantId);
  const basePrice = (variant && variant.price !== null && variant.price !== undefined)
    ? Number(variant.price)
    : Number(option.price || 0);

  const tiers = (Array.isArray(option.earlyBirdTiers) ? option.earlyBirdTiers : [])
    .filter(t => t.variantId === variantId)
    .slice();

  if (!tiers.length) return { price: basePrice, tierId: null };

  tiers.sort((a, b) => {
    if (a.price !== b.price) return a.price - b.price;
    return new Date(a.deadline).getTime() - new Date(b.deadline).getTime();
  });

  for (const tier of tiers) {
    if (now >= new Date(tier.deadline)) continue;
    if (tier.stockLimit > 0) {
      const soldAgg = await prisma.registrationOptionTranche.aggregate({
        where: { appliedTierId: tier.id, registrationOption: { registration: { status: { not: 'cancelled' } } } },
        _sum: { quantity: true }
      });
      const tierSold = soldAgg._sum?.quantity || 0;
      if (tierSold + requestedQty > tier.stockLimit) continue;
    }
    return { price: tier.price, tierId: tier.id };
  }

  return { price: basePrice, tierId: null };
}

/**
 * Re-evaluate early-bird prices for all RegistrationOptions that have an appliedTierId.
 * If a tier is now expired or its stock is exhausted, the next applicable tier (or base price)
 * is resolved and priceSnapshot + appliedTierId are updated in the DB.
 *
 * Call this before processing any payment to ensure stock-based price forfeiture is enforced.
 *
 * @param {string} registrationId
 * @returns {Promise<{ changed: boolean }>}
 */
async function refreshPricingForRegistration(registrationId) {
  const registration = await prisma.registration.findUnique({
    where: { id: registrationId },
    include: {
      registrationOptions: {
        include: {
          eventOption: { include: { earlyBirdTiers: true, variants: true } },
          tranches: true,
        }
      },
      payments: true,
    }
  });
  if (!registration) return { changed: false };

  const totalPaid = (registration.payments || []).reduce((sum, p) => sum + (p.amount || 0), 0);

  // For each option, only its single newest tranche is ever a repricing candidate — older
  // tranches were already locked in at purchase time and must never be touched. A newest
  // tranche is only touched once payments-so-far are established to not yet cover it (i.e.
  // it's the still-unpaid remainder) — legacy rows with no tranches are left to the
  // getEffectiveUnitPrice fallback in computeRegistrationTotalDue instead.
  let registrationOlderTotal = 0;
  const candidates = [];
  for (const ro of registration.registrationOptions) {
    const tranches = ro.tranches || [];
    if (tranches.length === 0) continue;
    const sorted = [...tranches].sort((a, b) => new Date(a.createdAt) - new Date(b.createdAt));
    const newest = sorted[sorted.length - 1];
    const older = sorted.slice(0, -1);
    registrationOlderTotal += older.reduce((s, t) => s + Number(t.quantity || 0) * Number(t.priceSnapshot || 0), 0);
    candidates.push({ ro, newest });
  }

  // Payments don't even cover the already-locked-in older tranches yet — leave everything
  // alone rather than guessing which portion is "paid for".
  if (totalPaid < registrationOlderTotal - 0.001) return { changed: false };

  // Each candidate is independent, so resolve/update them concurrently instead of one at a
  // time — this loop sits directly in the payment-capture path.
  const results = await Promise.all(candidates.map(async ({ ro, newest }) => {
    // Only refresh tranches that were priced via a tier
    if (!newest.appliedTierId) return false;

    // Find the currently applied tier
    const currentTier = (ro.eventOption.earlyBirdTiers || []).find(t => t.id === newest.appliedTierId);

    if (currentTier && new Date() < new Date(currentTier.deadline)) {
      // The tier's deadline is still in the future — honor the locked price.
      return false;
    }

    // Deadline has passed (or tier record missing) — resolve the next applicable tier
    const resolved = ro.variantId
      ? await resolveVariantTierPrice(ro.eventOption, ro.variantId, newest.quantity)
      : await resolveOptionPrice(ro.eventOption, newest.quantity);

    const tierChanged = resolved.tierId !== newest.appliedTierId;
    const priceChanged = Math.abs(resolved.price - newest.priceSnapshot) > 0.001;

    if (tierChanged || priceChanged) {
      await prisma.registrationOptionTranche.update({
        where: { id: newest.id },
        data: { priceSnapshot: resolved.price, appliedTierId: resolved.tierId }
      });
      // Mirror onto the aggregate row — it's this option's most recent tranche.
      await prisma.registrationOption.update({
        where: { id: ro.id },
        data: { priceSnapshot: resolved.price, appliedTierId: resolved.tierId }
      });
      return true;
    }
    return false;
  }));

  return { changed: results.some(Boolean) };
}

/**
 * Compute the total for a single RegistrationOption line — sums quantity*priceSnapshot
 * across its tranches (each priced at whatever was in effect when it was purchased).
 * Falls back to the legacy single priceSnapshot/getEffectiveUnitPrice path for rows
 * created before tranches existed.
 *
 * @param {object} ro - RegistrationOption, optionally with .tranches[] included
 * @param {Date|null} lastPaymentAt - used only for the legacy getEffectiveUnitPrice fallback
 * @param {Date} atTime - evaluation time (used only for the legacy fallback)
 * @returns {number}
 */
function computeOptionLineTotal(ro, lastPaymentAt, atTime) {
  if (Array.isArray(ro.tranches) && ro.tranches.length > 0) {
    return ro.tranches.reduce((s, t) => s + Number(t.quantity || 0) * Number(t.priceSnapshot || 0), 0);
  }

  const qty = Number(ro.quantity || 0);
  let unit;
  if (ro.priceSnapshot !== null && ro.priceSnapshot !== undefined) {
    // priceSnapshot is authoritative — set at registration creation and kept current
    // by refreshPricingForRegistration at payment initiation time.
    unit = ro.priceSnapshot;
  } else {
    // Fallback: legacy row without a snapshot — re-evaluate from tier deadlines
    const eo = ro.eventOption || {};
    unit = getEffectiveUnitPrice(eo, lastPaymentAt, atTime);
  }
  return qty * unit;
}

/**
 * Compute total due for a registration at a given time.
 *
 * Sums computeOptionLineTotal() across each RegistrationOption (tranche-aware when
 * `.tranches` is included, legacy priceSnapshot/getEffectiveUnitPrice fallback otherwise).
 *
 * @param {object} registration - includes registrationOptions[].{priceSnapshot, quantity, eventOption, tranches?}
 *                                and optionally payments[]
 * @param {Date} atTime - evaluation time (used for legacy fallback only)
 * @returns {number}
 */
function computeRegistrationTotalDue(registration, atTime) {
  if (!registration || !Array.isArray(registration.registrationOptions)) return 0;

  // Determine the last payment time (used only for the legacy getEffectiveUnitPrice fallback)
  let lastPaymentAt = null;
  try {
    if (registration.payments && Array.isArray(registration.payments) && registration.payments.length > 0) {
      lastPaymentAt = new Date(Math.max(...registration.payments.map(p => new Date(p.createdAt).getTime())));
    }
  } catch {}

  return registration.registrationOptions.reduce((sum, ro) => sum + computeOptionLineTotal(ro, lastPaymentAt, atTime), 0);
}

/**
 * Attach computed, tranche-aware display totals to a registration in place: `lineTotal` on
 * each RegistrationOption and `totalDueComputed` on the registration itself. Lets API
 * responses hand the frontend an exact total instead of every page re-deriving
 * unitPrice*quantity client-side (which goes wrong once a line spans multiple tranches).
 *
 * @param {object} registration - requires registrationOptions[].tranches included
 * @returns {object} the same registration, mutated
 */
function attachComputedTotals(registration) {
  if (!registration) return registration;
  let lastPaymentAt = null;
  try {
    if (registration.payments && Array.isArray(registration.payments) && registration.payments.length > 0) {
      lastPaymentAt = new Date(Math.max(...registration.payments.map(p => new Date(p.createdAt).getTime())));
    }
  } catch {}
  const now = new Date();
  if (Array.isArray(registration.registrationOptions)) {
    for (const ro of registration.registrationOptions) {
      ro.lineTotal = computeOptionLineTotal(ro, lastPaymentAt, now);
    }
  }
  registration.totalDueComputed = computeRegistrationTotalDue(registration, now);
  return registration;
}

function attachComputedTotalsToList(registrations) {
  return (registrations || []).map(attachComputedTotals);
}

module.exports = {
  getEffectiveUnitPrice,
  resolveOptionPrice,
  resolveVariantTierPrice,
  refreshPricingForRegistration,
  computeOptionLineTotal,
  computeRegistrationTotalDue,
  attachComputedTotals,
  attachComputedTotalsToList,
};