Implement POST /api/cycle/period endpoint (P1.2)

Add period logging endpoint that allows users to record their period start date.
This is a critical path item that unblocks GET /api/cycle/current and GET /api/today.

Features:
- Protected with withAuth middleware
- Validates startDate is present, valid format (YYYY-MM-DD), and not in future
- Updates user.lastPeriodDate in PocketBase
- Creates PeriodLog record for historical tracking
- Returns updated cycle information (cycleDay, phase)

Tests: 8 tests covering authentication, validation, database operations, and error handling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/api/cycle/period/route.test.ts

@@ -0,0 +1,208 @@
+// ABOUTME: Unit tests for period logging API route.
+// ABOUTME: Tests POST /api/cycle/period for period start date logging.
+import type { NextRequest } from "next/server";
+import { NextResponse } from "next/server";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import type { User } from "@/types";
+
+// Module-level variable to control mock user in tests
+let currentMockUser: User | null = null;
+
+// Mock PocketBase client for database operations
+const mockPbUpdate = vi.fn();
+const mockPbCreate = vi.fn();
+
+vi.mock("@/lib/pocketbase", () => ({
+  createPocketBaseClient: vi.fn(() => ({
+    collection: vi.fn((_name: string) => ({
+      update: mockPbUpdate,
+      create: mockPbCreate,
+    })),
+  })),
+  loadAuthFromCookies: vi.fn(),
+  isAuthenticated: vi.fn(() => currentMockUser !== null),
+  getCurrentUser: vi.fn(() => currentMockUser),
+}));
+
+// Mock the auth-middleware module
+vi.mock("@/lib/auth-middleware", () => ({
+  withAuth: vi.fn((handler) => {
+    return async (request: NextRequest) => {
+      if (!currentMockUser) {
+        return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+      }
+      return handler(request, currentMockUser);
+    };
+  }),
+}));
+
+import { POST } from "./route";
+
+describe("POST /api/cycle/period", () => {
+  const mockUser: User = {
+    id: "user123",
+    email: "test@example.com",
+    garminConnected: false,
+    garminOauth1Token: "",
+    garminOauth2Token: "",
+    garminTokenExpiresAt: new Date("2025-06-01"),
+    calendarToken: "cal-secret-token",
+    lastPeriodDate: new Date("2024-12-15"),
+    cycleLength: 28,
+    notificationTime: "07:00",
+    timezone: "America/New_York",
+    activeOverrides: [],
+    created: new Date("2024-01-01"),
+    updated: new Date("2025-01-10"),
+  };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    currentMockUser = null;
+    mockPbUpdate.mockResolvedValue({});
+    mockPbCreate.mockResolvedValue({ id: "periodlog123" });
+  });
+
+  it("returns 401 when not authenticated", async () => {
+    currentMockUser = null;
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: "2025-01-10" }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(401);
+    const body = await response.json();
+    expect(body.error).toBe("Unauthorized");
+  });
+
+  it("returns 400 when startDate is missing", async () => {
+    currentMockUser = mockUser;
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({}),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.error).toContain("startDate");
+  });
+
+  it("returns 400 when startDate is invalid format", async () => {
+    currentMockUser = mockUser;
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: "invalid-date" }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.error).toContain("Invalid");
+  });
+
+  it("returns 400 when startDate is in the future", async () => {
+    currentMockUser = mockUser;
+
+    // Set a date far in the future
+    const futureDate = new Date();
+    futureDate.setFullYear(futureDate.getFullYear() + 1);
+    const futureDateStr = futureDate.toISOString().split("T")[0];
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: futureDateStr }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.error).toContain("future");
+  });
+
+  it("updates user lastPeriodDate and creates PeriodLog", async () => {
+    currentMockUser = mockUser;
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: "2025-01-10" }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(200);
+
+    // Verify user record was updated
+    expect(mockPbUpdate).toHaveBeenCalledWith(
+      "user123",
+      expect.objectContaining({
+        lastPeriodDate: "2025-01-10",
+      }),
+    );
+
+    // Verify PeriodLog was created
+    expect(mockPbCreate).toHaveBeenCalledWith(
+      expect.objectContaining({
+        user: "user123",
+        startDate: "2025-01-10",
+      }),
+    );
+  });
+
+  it("returns updated cycle information", async () => {
+    currentMockUser = mockUser;
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: "2025-01-10" }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(200);
+    const body = await response.json();
+
+    // Should return cycle info
+    expect(body.lastPeriodDate).toBe("2025-01-10");
+    expect(body.cycleDay).toBeTypeOf("number");
+    expect(body.phase).toBeTypeOf("string");
+    expect(body.message).toBe("Period start date logged successfully");
+  });
+
+  it("calculates correct cycle day for new period", async () => {
+    currentMockUser = mockUser;
+
+    // If period started today, cycle day should be 1
+    const today = new Date().toISOString().split("T")[0];
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: today }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(200);
+    const body = await response.json();
+
+    expect(body.cycleDay).toBe(1);
+    expect(body.phase).toBe("MENSTRUAL");
+  });
+
+  it("handles database update errors gracefully", async () => {
+    currentMockUser = mockUser;
+    mockPbUpdate.mockRejectedValue(new Error("Database error"));
+
+    const mockRequest = {
+      json: vi.fn().mockResolvedValue({ startDate: "2025-01-10" }),
+    } as unknown as NextRequest;
+
+    const response = await POST(mockRequest);
+
+    expect(response.status).toBe(500);
+    const body = await response.json();
+    expect(body.error).toBe("Failed to update period date");
+  });
+});

src/app/api/cycle/period/route.ts

@@ -1,8 +1,96 @@
 // ABOUTME: API route for logging period start dates.
 // ABOUTME: Recalculates all phase dates when period is logged.
+import type { NextRequest } from "next/server";
 import { NextResponse } from "next/server";
 
-export async function POST() {
-  // TODO: Implement period logging
-  return NextResponse.json({ message: "Not implemented" }, { status: 501 });
+import { withAuth } from "@/lib/auth-middleware";
+import { getCycleDay, getPhase } from "@/lib/cycle";
+import { createPocketBaseClient } from "@/lib/pocketbase";
+
+interface PeriodLogRequest {
+  startDate?: string;
 }
+
+/**
+ * Validates a date string is in YYYY-MM-DD format and represents a valid date.
+ */
+function isValidDateFormat(dateStr: string): boolean {
+  const regex = /^\d{4}-\d{2}-\d{2}$/;
+  if (!regex.test(dateStr)) {
+    return false;
+  }
+  const date = new Date(dateStr);
+  return !Number.isNaN(date.getTime());
+}
+
+/**
+ * Checks if a date is in the future (after today).
+ */
+function isFutureDate(dateStr: string): boolean {
+  const inputDate = new Date(dateStr);
+  const today = new Date();
+  today.setHours(0, 0, 0, 0);
+  inputDate.setHours(0, 0, 0, 0);
+  return inputDate > today;
+}
+
+export const POST = withAuth(async (request: NextRequest, user) => {
+  try {
+    const body = (await request.json()) as PeriodLogRequest;
+
+    // Validate startDate is present
+    if (!body.startDate) {
+      return NextResponse.json(
+        { error: "startDate is required" },
+        { status: 400 },
+      );
+    }
+
+    // Validate date format
+    if (!isValidDateFormat(body.startDate)) {
+      return NextResponse.json(
+        { error: "Invalid date format. Use YYYY-MM-DD" },
+        { status: 400 },
+      );
+    }
+
+    // Validate date is not in the future
+    if (isFutureDate(body.startDate)) {
+      return NextResponse.json(
+        { error: "startDate cannot be in the future" },
+        { status: 400 },
+      );
+    }
+
+    const pb = createPocketBaseClient();
+
+    // Update user's lastPeriodDate
+    await pb.collection("users").update(user.id, {
+      lastPeriodDate: body.startDate,
+    });
+
+    // Create PeriodLog record
+    await pb.collection("period_logs").create({
+      user: user.id,
+      startDate: body.startDate,
+    });
+
+    // Calculate updated cycle information
+    const lastPeriodDate = new Date(body.startDate);
+    const cycleDay = getCycleDay(lastPeriodDate, user.cycleLength, new Date());
+    const phase = getPhase(cycleDay);
+
+    return NextResponse.json({
+      message: "Period start date logged successfully",
+      lastPeriodDate: body.startDate,
+      cycleDay,
+      phase,
+    });
+  } catch (error) {
+    console.error("Period logging error:", error);
+    return NextResponse.json(
+      { error: "Failed to update period date" },
+      { status: 500 },
+    );
+  }
+});