export function createDesk() {
  const stock = new Map([
    [701, 3],
    [702, 2],
  ]);
  const receipts = new Map();
  return {
    inventory() {
      return [...stock].map(([id, available]) => ({ id, available }));
    },
    checkout(input) {
      if (!input || typeof input !== 'object' || Array.isArray(input))
        throw Object.assign(new Error('Invalid request'), { status: 422 });
      const { key, kitId, quantity } = input;
      if (
        typeof key !== 'string' ||
        !/^[a-z0-9-]{1,40}$/.test(key) ||
        !Number.isSafeInteger(kitId) ||
        !Number.isSafeInteger(quantity) ||
        quantity < 1 ||
        quantity > 20
      )
        throw Object.assign(new Error('Invalid request'), { status: 422 });
      const signature = JSON.stringify({ kitId, quantity });
      if (receipts.has(key)) {
        const previous = receipts.get(key);
        if (previous.signature !== signature)
          throw Object.assign(new Error('Key conflict'), { status: 409 });
        return { ...previous.receipt, replayed: true };
      }
      if (!stock.has(kitId))
        throw Object.assign(new Error('Unknown kit'), { status: 404 });
      if (quantity > stock.get(kitId))
        throw Object.assign(new Error('Unavailable'), { status: 409 });
      if (receipts.size >= 1000)
        throw Object.assign(new Error('Demo receipt capacity reached'), {
          status: 503,
        });
      stock.set(kitId, stock.get(kitId) - quantity);
      const receipt = {
        kitId,
        quantity,
        available: stock.get(kitId),
        replayed: false,
        persistent: false,
      };
      receipts.set(key, { signature, receipt });
      return { ...receipt };
    },
  };
}