feat: add portfolio

src/tbank/decimal.ts

@@ -0,0 +1,44 @@
+const NANO = 1_000_000_000n;
+
+export type ProtoDecimal = { units?: string | number; nano?: string | number };
+export type Decimal = { value: bigint; scale: number };
+
+export function decimal(value: ProtoDecimal): Decimal {
+  return {
+    value: BigInt(value.units ?? 0) * NANO + BigInt(value.nano ?? 0),
+    scale: 9,
+  };
+}
+
+export function add(left: Decimal, right: Decimal): Decimal {
+  const scale = Math.max(left.scale, right.scale);
+  return {
+    value:
+      left.value * 10n ** BigInt(scale - left.scale) +
+      right.value * 10n ** BigInt(scale - right.scale),
+    scale,
+  };
+}
+
+export function subtract(left: Decimal, right: Decimal): Decimal {
+  return add(left, { value: -right.value, scale: right.scale });
+}
+
+export function multiply(left: Decimal, right: Decimal): Decimal {
+  return { value: left.value * right.value, scale: left.scale + right.scale };
+}
+
+export function isZero(value: Decimal): boolean {
+  return value.value === 0n;
+}
+
+export function formatDecimal({ value, scale }: Decimal): string {
+  if (value === 0n) return '0';
+  const sign = value < 0n ? '-' : '';
+  const digits = (value < 0n ? -value : value)
+    .toString()
+    .padStart(scale + 1, '0');
+  const whole = digits.slice(0, -scale) || '0';
+  const fraction = digits.slice(-scale).replace(/0+$/, '');
+  return `${sign}${whole}${fraction ? `.${fraction}` : ''}`;
+}