feat(income): add account income analytics API

src/tbank/decimal.ts

@@ -3,6 +3,17 @@ const NANO = 1_000_000_000n;
 export type ProtoDecimal = { units?: string | number; nano?: string | number };
 export type Decimal = { value: bigint; scale: number };
 
+export function decimalFromString(value: string): Decimal {
+  if (!/^-?(?:0|[1-9]\d*)(?:\.\d+)?$/.test(value))
+    throw new Error('Invalid decimal string');
+  const negative = value.startsWith('-');
+  const [whole, fraction = ''] = (negative ? value.slice(1) : value).split('.');
+  return {
+    value: (negative ? -1n : 1n) * BigInt(`${whole}${fraction}`),
+    scale: fraction.length,
+  };
+}
+
 export function decimal(value: ProtoDecimal): Decimal {
   return {
     value: BigInt(value.units ?? 0) * NANO + BigInt(value.nano ?? 0),
@@ -32,9 +43,15 @@ export function isZero(value: Decimal): boolean {
   return value.value === 0n;
 }
 
+export function compare(left: Decimal, right: Decimal): number {
+  const difference = subtract(left, right).value;
+  return difference === 0n ? 0 : difference > 0n ? 1 : -1;
+}
+
 export function formatDecimal({ value, scale }: Decimal): string {
   if (value === 0n) return '0';
   const sign = value < 0n ? '-' : '';
+  if (scale === 0) return `${sign}${value < 0n ? -value : value}`;
   const digits = (value < 0n ? -value : value)
     .toString()
     .padStart(scale + 1, '0');