// ❌ Pure but NOT domain — formats for human display
export const formatEventDate = (date: string | null) =>
  date ? format(parseISO(date), "MMMM d, yyyy") : undefined;
// → Belongs in lib/format.ts

// ✅ Pure AND domain — business rule that affects behavior
export const isPastEvent = (eventDate: string | null, now: Date) =>
  eventDate ? parseISO(eventDate) < now : false;
// → Belongs in domain/event/

// ✅ Pure AND domain — business calculation
export const calculateCommittedTotal = (items: readonly GiftItem[]) =>
  items.filter(i => i.status !== "idea").reduce((sum, i) => sum + i.pricePence, 0);
// → Belongs in domain/budget/

undefined

undefined

// ✅ Uses domain language
type GiftIdea = {
  readonly id: GiftIdeaId;
  readonly description: string;
  readonly occasion: OccasionId;
  readonly estimatedCost: Money;
};

// ❌ Technical jargon
type Item = { readonly id: string; readonly text: string; readonly parentId: string; };

type Currency = 'GBP' | 'USD' | 'EUR';
type Money = { readonly amount: number; readonly currency: Currency };

const createMoney = (amount: number, currency: Currency): Money => {
  if (amount < 0) throw new Error('Money cannot be negative');
  return { amount, currency };
};
// Factory throws = invariant violation (a bug in calling code).
// Schemas catch invalid user input at trust boundaries BEFORE
// the factory is called. If the factory throws, something
// bypassed the schema.

// Schema at trust boundary — parses raw strings into branded types
const PledgeInputSchema = z.object({
  occasionId: z.string().min(1).transform(createOccasionId),
  contributorId: z.string().min(1).transform(createContributorId),
  amount: z.object({ amount: z.number().positive(), currency: CurrencySchema }),
});

// Reconstitution from persistence — same pattern, used in driven adapters
const toOccasion = (row: OccasionRow): Occasion => ({
  id: createOccasionId(row.id),
  name: row.name,
  budget: createMoney(row.budgetAmount, parseCurrency(row.budgetCurrency)),
  totalPledged: createMoney(row.pledgedAmount, parseCurrency(row.budgetCurrency)),
  isFundingClosed: row.isFundingClosed,
});

type OccasionId = string & { readonly __brand: 'OccasionId' };
type GiftIdeaId = string & { readonly __brand: 'GiftIdeaId' };
type EmailAddress = string & { readonly __brand: 'EmailAddress' };

// Factory functions — the only way to create branded values
const createOccasionId = (raw: string): OccasionId => {
  if (!raw.trim()) throw new Error('OccasionId cannot be empty');
  return raw as OccasionId; // justified: factory validates, then brands
};

const createEmailAddress = (raw: string): EmailAddress => {
  if (!raw.includes('@')) throw new Error('Invalid email');
  return raw as EmailAddress; // justified: factory validates, then brands
};

type Occasion = {
  readonly id: OccasionId;
  readonly name: string;
  readonly date: Date;
  readonly giftIdeas: ReadonlyArray<GiftIdea>;
  readonly budget: Money;
};

// Immutable update — returns new valid state
const renameOccasion = (occasion: Occasion, newName: string): Occasion => ({
  ...occasion,
  name: newName,
});

// WRONG — boolean + optional allows { isVerified: true, verifiedAt: undefined }
type User = { readonly isVerified: boolean; readonly verifiedAt?: Date };

// RIGHT — impossible to be verified without a date
type User =
  | { readonly status: 'unverified' }
  | { readonly status: 'verified'; readonly verifiedAt: Date };

type Order =
  | { readonly status: 'draft'; readonly items: ReadonlyArray<OrderItem> }
  | { readonly status: 'placed'; readonly items: ReadonlyArray<OrderItem>; readonly placedAt: Date }
  | { readonly status: 'shipped'; readonly items: ReadonlyArray<OrderItem>; readonly placedAt: Date; readonly shippedAt: Date; readonly trackingNumber: string };

const describeOrder = (order: Order): string => {
  switch (order.status) {
    case 'draft': return `Draft with ${order.items.length} items`;
    case 'placed': return `Placed at ${order.placedAt.toISOString()}`;
    case 'shipped': return `Shipped: ${order.trackingNumber}`;
    default: { const _exhaustive: never = order; return _exhaustive; }
  }
};

// Specification: "can this contributor pledge to this occasion?"
const canPledge = (occasion: Occasion, contributor: Contributor, amount: Money): boolean =>
  !occasion.isFundingClosed &&
  amount.amount <= contributor.walletBalance.amount &&
  amount.currency === occasion.budget.currency;

// Compose specifications for complex eligibility
const isGiftReady = (occasion: Occasion): boolean =>
  occasion.totalPledged.amount >= occasion.budget.amount &&
  occasion.giftIdeas.some(idea => idea.status === 'selected');

// ❌ WRONG — cramming cross-entity logic into one entity
const addContribution = (occasion: Occasion, contribution: Contribution): Occasion => {
  // This needs to check the contributor's wallet balance — wrong aggregate!
};

// ✅ CORRECT — domain service operates across aggregates
const pledgeContribution = (
  occasion: Occasion,
  contributor: Contributor,
  amount: Money,
): PledgeResult => {
  if (amount.amount > contributor.walletBalance.amount) {
    return { success: false, reason: 'insufficient-balance' };
  }
  return {
    success: true,
    occasion: addContribution(occasion, { contributorId: contributor.id, amount }),
    contributor: deductBalance(contributor, amount),
  };
};

type PledgeResult =
  | { readonly success: true; readonly occasion: Occasion; readonly contributor: Contributor }
  | { readonly success: false; readonly reason: 'insufficient-balance' | 'funding-closed' | 'not-found' };

// Port (domain layer) — interface because it's a behavior contract
interface OccasionRepository {
  readonly findById: (id: OccasionId) => Promise<Occasion | undefined>;
  readonly save: (occasion: Occasion) => Promise<void>;
}

// Adapter (infrastructure layer) — see hexagonal-architecture skill

tests/
  occasions/
    create-occasion.test.ts       # Behavior: creating occasions
    add-gift-idea.test.ts         # Behavior: managing gift ideas
    occasion-budget.test.ts       # Behavior: budget constraints

const getTestOccasion = (overrides?: Partial<Occasion>): Occasion =>
  OccasionSchema.parse({
    id: createOccasionId('occasion-1'),
    name: "Mum's Birthday",
    giftIdeas: [],
    budget: createMoney(100, 'GBP'),
    ...overrides,
  });