Shopper's cart

/**
 * The shopper's cart, read one way for every band that sells — a cart page,
 * a drawer, a checkout, the count on the store's header — so the lines, the
 * quantities and the totals agree wherever they are shown.
 *
 * The store keeps no carts, so the sample shopper's is a rule over the shelf:
 * the shop's three bestsellers under `CART_CEILING_CENTS`, each from a
 * different department, one of each. A small first order that sits under the
 * free-delivery line, so a band can show the line being crossed. Replace
 * `shopperCart` with your cart store and every band follows.
 *
 * Server-only, because it reads the shelf: a section hands the lines to its
 * island as props, and the island totals them with `checkout.ts`.
 */
import type { YearMonth } from "@/lib/dashboards/ecommerce/checkout"
import { storeShelf, type StockState } from "@/lib/dashboards/ecommerce/storefront"
import { REFERENCE_DATE, db } from "@/lib/sample-data"

/** The most a product in the sample cart costs, in cents. */
export const CART_CEILING_CENTS = 3_000

/** A line of the cart: the product as the cart shows it, its price, how many, and the most it can hold. */
export type CartLine = {
  productId: string
  name: string
  category: string
  href: string
  /** What one costs, in cents: the catalogue's list price. */
  unitCents: number
  qty: number
  /** Units on hand: a line never holds more. */
  stock: number
  stockState: StockState
}

/**
 * The sample shopper's cart: the bestselling products in stock at or under
 * `CART_CEILING_CENTS`, one per department until there are three, one of each,
 * in the shelf's order.
 */
export function shopperCart(): CartLine[] {
  const departments = new Set<string>()
  const lines: CartLine[] = []
  for (const product of storeShelf()) {
    if (lines.length === 3) break
    if (product.priceCents > CART_CEILING_CENTS || product.stock === 0 || departments.has(product.category)) continue
    departments.add(product.category)
    lines.push({
      productId: product.id,
      name: product.name,
      category: product.category,
      href: product.href,
      unitCents: product.priceCents,
      qty: 1,
      stock: product.stock,
      stockState: product.stockState,
    })
  }
  return lines
}

/** Every country the shop has a customer in, A to Z: the places it delivers to. */
export function shipsTo(): string[] {
  return [...new Set(db.customers.all().map((customer) => customer.country))].sort((a, b) => a.localeCompare(b))
}

/**
 * "Now", as a checkout needs it: the instant an order placed now would be
 * placed at — `REFERENCE_DATE`, as an ISO string an island can take — and the
 * month a card must not have run out before.
 */
export function checkoutNow(): { placedAt: string; month: YearMonth } {
  return {
    placedAt: REFERENCE_DATE.toISOString(),
    month: { year: REFERENCE_DATE.getUTCFullYear(), month: REFERENCE_DATE.getUTCMonth() + 1 },
  }
}

/** The number the next order would be given: one past the book's last, in its own series. */
export function nextOrderNumber(): string {
  return `ORD-${100_000 + db.orders.all().length + 1}`
}