/**
 * 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.
 * - computeRegistrationTotalDue: uses priceSnapshot when present (authoritative after
 *   refreshPricingForRegistration runs), otherwise falls back to getEffectiveUnitPrice.
 * - refreshPricingForRegistration: re-runs resolveOptionPrice for every RegistrationOption
 *   that has an appliedTierId; updates priceSnapshot + appliedTierId in the DB if the tier
 *   is now expired or its stock is exhausted.
 */

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
    if (tier.stockLimit > 0) {
      const soldAgg = await prisma.registrationOption.aggregate({
        where: {
          appliedTierId: tier.id,
          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.registrationOption.aggregate({
        where: { appliedTierId: tier.id, 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 } }
        }
      }
    }
  });
  if (!registration) return { changed: false };

  let anyChanged = false;

  for (const ro of registration.registrationOptions) {
    // Only refresh options that were priced via a tier
    if (!ro.appliedTierId) continue;

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

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

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

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

    if (tierChanged || priceChanged) {
      await prisma.registrationOption.update({
        where: { id: ro.id },
        data: {
          priceSnapshot: resolved.price,
          appliedTierId: resolved.tierId
        }
      });
      anyChanged = true;
    }
  }

  return { changed: anyChanged };
}

/**
 * Compute total due for a registration at a given time.
 *
 * Uses priceSnapshot when present (authoritative — set at registration time and refreshed
 * before payment via refreshPricingForRegistration). Falls back to getEffectiveUnitPrice
 * for legacy rows without a snapshot.
 *
 * @param {object} registration - includes registrationOptions[].{priceSnapshot, quantity, eventOption}
 *                                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) => {
    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 sum + qty * unit;
  }, 0);
}

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