feat : add monthly

lib/commission/income.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import { commissionIncomeDay, commissionIncomeMonth, commissionIncomeShares } from "./income";
+
+describe("commission income periods", () => {
+  it("uses Bangkok month boundaries and rolls across years", () => {
+    const december = commissionIncomeMonth("2026-12");
+    expect(december.from.toISOString()).toBe("2026-11-30T17:00:00.000Z");
+    expect(december.to.toISOString()).toBe("2026-12-31T17:00:00.000Z");
+    expect(december.next).toBe("2027-01");
+    expect(commissionIncomeMonth("2027-01").previous).toBe("2026-12");
+  });
+
+  it("defaults to the current Bangkok month for an invalid query", () => {
+    expect(commissionIncomeMonth("2026-13", new Date("2026-09-30T18:00:00Z")).month).toBe("2026-10");
+  });
+
+  it("assigns payments around midnight to the correct Bangkok day", () => {
+    expect(commissionIncomeDay(new Date("2026-10-01T16:59:59Z"))).toBe(1);
+    expect(commissionIncomeDay(new Date("2026-10-01T17:00:00Z"))).toBe(2);
+  });
+});
+
+it("calculates Buzz and Gunshin shares in satang", () => {
+  expect(commissionIncomeShares(101)).toEqual({ buzzSatang: 9090, gunshinSatang: 1010 });
+});

lib/commission/income.ts

@@ -0,0 +1,29 @@
+const BANGKOK_OFFSET = "+07:00";
+
+export function commissionIncomeMonth(value: string | string[] | undefined, now = new Date()) {
+  const currentParts = new Intl.DateTimeFormat("en-US", {
+    timeZone: "Asia/Bangkok", year: "numeric", month: "2-digit",
+  }).formatToParts(now);
+  const current = `${currentParts.find((part) => part.type === "year")!.value}-${currentParts.find((part) => part.type === "month")!.value}`;
+  const month = typeof value === "string" && /^(20\d{2}|[3-9]\d{3})-(0[1-9]|1[0-2])$/.test(value) ? value : current;
+  const [year, number] = month.split("-").map(Number);
+  const next = number === 12 ? `${year + 1}-01` : `${year}-${String(number + 1).padStart(2, "0")}`;
+  const previous = number === 1 ? `${year - 1}-12` : `${year}-${String(number - 1).padStart(2, "0")}`;
+  return {
+    month, year, number, previous, next,
+    from: new Date(`${month}-01T00:00:00${BANGKOK_OFFSET}`),
+    to: new Date(`${next}-01T00:00:00${BANGKOK_OFFSET}`),
+    days: new Date(Date.UTC(year, number, 0)).getUTCDate(),
+    leadingDays: (new Date(Date.UTC(year, number - 1, 1)).getUTCDay() + 6) % 7,
+  };
+}
+
+export function commissionIncomeDay(date: Date) {
+  return Number(new Intl.DateTimeFormat("en-US", {
+    timeZone: "Asia/Bangkok", day: "numeric",
+  }).format(date));
+}
+
+export function commissionIncomeShares(amountBaht: number) {
+  return { buzzSatang: amountBaht * 90, gunshinSatang: amountBaht * 10 };
+}