import type { ItemId, StoreItem } from "@/app/types";
import { CATALOG } from "./catalog";

// ---------------------------------------------------------------------------
// PriceProvider: the single seam between "where prices come from" and the
// rest of the app. The cost math only ever calls `getItem`.
//
// To use live retailer prices later:
//   1. Fetch prices on the SERVER (a Server Action or route handler) so the
//      API key never reaches the browser.
//   2. Build a snapshot `StoreItem[]` from the response.
//   3. Pass `new SnapshotPriceProvider("Live grocery prices", snapshot)` into
//      the grocery/planner functions instead of `averageGroceryProvider`.
// The math stays synchronous and testable because it works on a snapshot.
// ---------------------------------------------------------------------------

export interface PriceProvider {
  /** Shown in the UI so users know where prices came from. */
  readonly label: string;
  getItem(id: ItemId): StoreItem | undefined;
}

export class SnapshotPriceProvider implements PriceProvider {
  private readonly byId: Map<ItemId, StoreItem>;

  constructor(
    readonly label: string,
    items: StoreItem[],
  ) {
    this.byId = new Map(items.map((item) => [item.id, item]));
  }

  getItem(id: ItemId): StoreItem | undefined {
    return this.byId.get(id);
  }
}

export const averageGroceryProvider: PriceProvider = new SnapshotPriceProvider(
  "Based on average grocery prices as of October 2026",
  CATALOG,
);