refactor: organize backend by business responsibility

src/modules/banking/bank-cards/domain/bank-card.calculations.ts

@@ -0,0 +1,91 @@
+export function moscowToday(now = new Date()): string {
+  return new Intl.DateTimeFormat('en-CA', {
+    timeZone: 'Europe/Moscow',
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+  }).format(now);
+}
+
+export function isCalendarDate(value: string): boolean {
+  if (value.length !== 10 || !/^\d{4}-\d{2}-\d{2}$/.test(value)) return false;
+  if (value.startsWith('0000')) return false;
+  const date = new Date(`${value}T00:00:00.000Z`);
+  return (
+    !Number.isNaN(date.getTime()) && date.toISOString().slice(0, 10) === value
+  );
+}
+
+export function bankBalance(
+  cardId: string,
+  opening: bigint,
+  operations: Array<{
+    kind: string;
+    cardId: string;
+    targetCardId: string | null;
+    amountKopecks: bigint;
+  }>,
+): bigint {
+  // ponytail: O(N) history fold; optimize only after measuring growing histories.
+  let balance = opening;
+  for (const operation of operations) {
+    if (operation.cardId === cardId) {
+      if (operation.kind === 'expense' || operation.kind === 'transfer')
+        balance -= operation.amountKopecks;
+      else if (operation.kind === 'topup' || operation.kind === 'refund')
+        balance += operation.amountKopecks;
+    }
+    if (operation.kind === 'transfer' && operation.targetCardId === cardId)
+      balance += operation.amountKopecks;
+  }
+  return balance;
+}
+
+export function bankSummary(
+  period: string | { from: string; to: string },
+  operations: Array<{
+    kind: string;
+    date: string;
+    amountKopecks: bigint;
+    categoryId: string | null;
+  }>,
+) {
+  let expenses = 0n;
+  let refunds = 0n;
+  const categories = new Map<
+    string,
+    { categoryId: string; expenses: bigint; refunds: bigint; net: bigint }
+  >();
+  // ponytail: O(N) history fold; optimize only after measuring growing histories.
+  for (const operation of operations) {
+    if (
+      typeof period === 'string'
+        ? operation.date.slice(0, 7) !== period
+        : operation.date < period.from || operation.date > period.to
+    )
+      continue;
+    if (operation.kind !== 'expense' && operation.kind !== 'refund') continue;
+    const expense = operation.kind === 'expense' ? operation.amountKopecks : 0n;
+    const refund = operation.kind === 'refund' ? operation.amountKopecks : 0n;
+    expenses += expense;
+    refunds += refund;
+    if (operation.categoryId !== null) {
+      const category = categories.get(operation.categoryId) ?? {
+        categoryId: operation.categoryId,
+        expenses: 0n,
+        refunds: 0n,
+        net: 0n,
+      };
+      category.expenses += expense;
+      category.refunds += refund;
+      category.net = category.expenses - category.refunds;
+      categories.set(category.categoryId, category);
+    }
+  }
+  return {
+    expenses,
+    refunds,
+    net: expenses - refunds,
+    categories: [...categories.values()],
+  };
+}