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tests/payment-plan.test.ts

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+import { describe, expect, test } from "vitest";
+import { buildSchedule, splitIntoInstallments } from "@/lib/payment-plan";
+import { calculatePrice } from "@/lib/pricing";
+
+describe("Exakte Zahlungsplaene laut Vorgabe", () => {
+  test.each([
+    ["Early Bird", "EARLY_BIRD", false, [[220_000], [110_000, 110_000], [80_000, 70_000, 70_000]]],
+    ["Early Bird Stammmodel", "EARLY_BIRD", true, [[198_000], [99_000, 99_000], [66_000, 66_000, 66_000]]],
+    ["Regulaer", "REGULAR", false, [[275_000], [137_500, 137_500], [95_000, 90_000, 90_000]]],
+    ["Regulaer Stammmodel", "REGULAR", true, [[247_500], [123_750, 123_750], [82_500, 82_500, 82_500]]],
+  ] as const)("%s", (_label, phase, code, expected) => {
+    const total = calculatePrice(phase, code).totalCents;
+    for (const [index, plan] of expected.entries()) {
+      const split = splitIntoInstallments(total, index + 1);
+      expect(split).toEqual(plan);
+      expect(split.reduce((a, b) => a + b, 0)).toBe(total);
+    }
+  });
+
+  test("1.237,50 € je Rate bleibt centgenau", () => {
+    expect(splitIntoInstallments(247_500, 2)).toEqual([123_750, 123_750]);
+  });
+
+  test("mehr als drei Raten sind ausgeschlossen", () => {
+    expect(() => splitIntoInstallments(220_000, 4)).toThrow();
+  });
+});
+
+describe("Faelligkeiten", () => {
+  const base = {
+    totalCents: 220_000,
+    campStartDate: "2027-06-05",
+    finalInstallmentLeadDays: 30,
+    minInstallmentGapDays: 14,
+  };
+
+  test("letzte Rate 30 Tage vor Anreise, zweite in der Mitte, Einzug 09:00 Berlin", () => {
+    const result = buildSchedule({ ...base, planType: "THREE_INSTALLMENTS", now: new Date("2026-11-15T10:00:00Z") });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+    // 172 Tage bis zur Frist -> zweite Rate nach 86 Tagen.
+    expect(result.installments.map((i) => i.dueDate)).toEqual([null, "2027-02-09", "2027-05-06"]);
+    // 06.05.2027 09:00 Sommerzeit = 07:00 UTC
+    expect(result.installments[2]!.dueAt!.toISOString()).toBe("2027-05-06T07:00:00.000Z");
+    expect(result.installments[0]!.amountCents).toBe(80_000);
+  });
+
+  test("ohne Camp-Termin keine Ratenzahlung, Einmalzahlung bleibt moeglich", () => {
+    const now = new Date("2026-11-15T10:00:00Z");
+    expect(buildSchedule({ ...base, campStartDate: null, planType: "TWO_INSTALLMENTS", now })).toEqual({
+      ok: false,
+      reason: "CAMP_DATE_MISSING",
+    });
+    expect(buildSchedule({ ...base, campStartDate: null, planType: "FULL", now }).ok).toBe(true);
+  });
+
+  test("zu knapp vor der Frist wird die Variante serverseitig deaktiviert", () => {
+    // Frist 06.05.2027; 20 Tage vorher reichen fuer zwei, nicht fuer drei Raten.
+    const now = new Date("2027-04-16T10:00:00Z");
+    expect(buildSchedule({ ...base, planType: "TWO_INSTALLMENTS", now }).ok).toBe(true);
+    expect(buildSchedule({ ...base, planType: "THREE_INSTALLMENTS", now })).toEqual({ ok: false, reason: "TOO_LATE" });
+    const later = new Date("2027-04-30T10:00:00Z");
+    expect(buildSchedule({ ...base, planType: "TWO_INSTALLMENTS", now: later })).toEqual({ ok: false, reason: "TOO_LATE" });
+  });
+});