/**
 * Location eligibility + ranking for a cart and method.
 *
 * Policy: never silently assign a whole cart to one location when its items are
 * only stocked across several. Instead return SPLIT_REQUIRED with an explanation.
 */
import type { AvailabilityResult, Cart, LocationConfig, Method, PeakDay, ProductRule, Reason, ShopSettings, UsageSnapshot } from "./types";
import { computeAvailability, firstAvailable } from "./availability";
import { evaluateRules } from "./rules";
import { type CustomerAddress, type FeeQuote, type ZoneMatch, matchZone, quoteFee } from "./zones";

export type Inventory = Record<string, Record<string, number>>; // locationId → variantId → available

export interface RankedLocation {
  location: LocationConfig;
  eligible: boolean;
  reasons: Reason[];
  zone?: ZoneMatch;
  fee?: FeeQuote;
  distanceKm: number | null;
  first: { date: string; slot: string } | null;
  availability?: AvailabilityResult;
}

export interface RankInput {
  locations: LocationConfig[];
  method: Method;
  cart: Cart;
  rules: ProductRule[];
  peakDays: PeakDay[];
  usage: UsageSnapshot;
  settings: Pick<ShopSettings, "mixedPrepPolicy">;
  now: number;
  address?: CustomerAddress;
  inventory?: Inventory;
  ranking?: "priority" | "distance" | "earliest";
}

/**
 * A location with no inventory entry (not linked to a Shopify location) is "unknown" and
 * never blocks. For linked locations, a missing variant means none in stock there.
 */
export function stockedAt(inv: Inventory | undefined, locId: string, cart: Cart): boolean {
  if (!inv || !inv[locId]) return true;
  const at = inv[locId];
  return cart.items.every((i) => (at[i.variantId] ?? 0) >= i.quantity);
}

export function rankLocations(input: RankInput): { ranked: RankedLocation[]; splitRequired: Reason | null } {
  const constraints = evaluateRules(input.cart, input.rules, input.settings.mixedPrepPolicy);
  const subtotal = input.cart.subtotal ?? input.cart.items.reduce((s, i) => s + i.price * i.quantity, 0);
  const ranked: RankedLocation[] = [];

  for (const loc of input.locations) {
    const r: RankedLocation = { location: loc, eligible: true, reasons: [], distanceKm: null, first: null };
    ranked.push(r);
    if (input.method === "delivery") {
      const z = matchZone(loc, input.address ?? {});
      r.zone = z;
      r.distanceKm = z.distanceKm;
      if (!z.zone) {
        r.eligible = false;
        r.reasons.push(z.reason!);
      } else {
        r.fee = quoteFee(z.zone, subtotal);
        if (r.fee.belowMinimum) {
          r.eligible = false;
          r.reasons.push({
            code: "BELOW_MINIMUM_ORDER",
            message: `Delivery needs a minimum order of $${(r.fee.minOrder! / 100).toFixed(2)}`,
          });
        }
      }
    }
    if (input.method !== "shipping" && !stockedAt(input.inventory, loc.id, input.cart)) {
      r.eligible = false;
      r.reasons.push({ code: "OUT_OF_STOCK_AT_LOCATION", message: `Not all items are in stock at ${loc.name}` });
    }
    const av = computeAvailability({ ...input, location: loc, constraints });
    r.availability = av;
    if (av.blockers.length) {
      r.eligible = false;
      r.reasons.push(...av.blockers);
    }
    const f = firstAvailable(av);
    r.first = f ? { date: f.date, slot: f.slot.id } : null;
    if (r.eligible && !f) {
      r.eligible = false;
      r.reasons.push({ code: "DAY_FULL", message: "No available dates in the booking window" });
    }
  }

  const mode = input.ranking ?? "priority";
  ranked.sort((a, b) => {
    if (a.eligible !== b.eligible) return a.eligible ? -1 : 1;
    if (mode === "distance" && a.distanceKm != null && b.distanceKm != null && a.distanceKm !== b.distanceKm)
      return a.distanceKm - b.distanceKm;
    if (mode === "earliest" && a.first && b.first) {
      const ka = `${a.first.date} ${a.first.slot}`;
      const kb = `${b.first.date} ${b.first.slot}`;
      if (ka !== kb) return ka < kb ? -1 : 1;
    }
    return a.location.priority - b.location.priority;
  });

  // Split detection: nobody stocks everything, but the union does.
  let splitRequired: Reason | null = null;
  if (input.inventory && input.method !== "shipping" && !ranked.some((r) => r.eligible)) {
    const unionOk = input.cart.items.every(
      (i) => input.locations.reduce((s, l) => s + (input.inventory![l.id]?.[i.variantId] ?? 0), 0) >= i.quantity,
    );
    const anyStocked = input.locations.some((l) => stockedAt(input.inventory, l.id, input.cart));
    if (unionOk && !anyStocked)
      splitRequired = {
        code: "OUT_OF_STOCK_AT_LOCATION",
        message:
          "Your items are stocked at different locations. Choose shipping, or remove some items to schedule a single pickup or delivery.",
      };
  }
  return { ranked, splitRequired };
}