/**
 * SystemClock Component Tests
 *
 * Note: This file tests the time formatting logic used by the SystemClock component.
 * Full component rendering tests are challenging with Svelte 5 + @testing-library/svelte
 * due to SSR/CSR compatibility issues. The component itself is simple and visually
 * testable - it displays the current date and time, updating every second.
 *
 * What this component does:
 * - Displays date in British format: "7 February 2026"
 * - Displays time in 24-hour format: "14:35:42"
 * - Updates every second via setInterval
 * - Cleans up interval on unmount via $effect
 *
 * Manual testing checklist:
 * - [ ] Clock appears above the Send button
 * - [ ] Time updates every second
 * - [ ] Date format is "DD Month YYYY"
 * - [ ] Time format is "HH:MM:SS" (24-hour)
 * - [ ] Hover effect works (border turns accent colour)
 */

import { describe, it, expect } from "vitest";

// Helper function that mirrors the component's formatting logic
function formatDateTime(date: Date): string {
  const day = date.getDate();
  const month = date.toLocaleString("en-GB", { month: "long" });
  const year = date.getFullYear();

  const hours = String(date.getHours()).padStart(2, "0");
  const minutes = String(date.getMinutes()).padStart(2, "0");
  const seconds = String(date.getSeconds()).padStart(2, "0");

  return `${day} ${month} ${year}, ${hours}:${minutes}:${seconds}`;
}

describe("SystemClock date/time formatting", () => {
  it("formats date in British format (DD Month YYYY)", () => {
    // Use local timezone (not UTC) since the component uses local time
    const date = new Date(2026, 1, 7, 14, 35, 42); // Feb 7, 2026 14:35:42 local
    const formatted = formatDateTime(date);

    expect(formatted).toContain("7 February 2026");
  });

  it("formats time in 24-hour format (HH:MM:SS)", () => {
    const date = new Date(2026, 1, 7, 14, 35, 42);
    const formatted = formatDateTime(date);

    // Should have the pattern HH:MM:SS
    expect(formatted).toMatch(/\d{2}:\d{2}:\d{2}/);
    expect(formatted).toContain("14:35:42");
  });

  it("combines date and time with comma separator", () => {
    const date = new Date(2026, 1, 7, 14, 35, 42);
    const formatted = formatDateTime(date);

    expect(formatted).toBe("7 February 2026, 14:35:42");
  });

  it("pads single-digit hours, minutes, and seconds with zeros", () => {
    const date = new Date(2026, 1, 7, 3, 5, 8);
    const formatted = formatDateTime(date);

    // Should have leading zeros: 03:05:08, not 3:5:8
    expect(formatted).toContain("03:05:08");
  });

  it("handles different months correctly", () => {
    const date = new Date(2026, 11, 25, 12, 0, 0); // December is month 11
    const formatted = formatDateTime(date);

    expect(formatted).toContain("25 December 2026");
  });

  it("handles year changes correctly", () => {
    const date = new Date(2027, 0, 1, 0, 0, 0); // January is month 0
    const formatted = formatDateTime(date);

    expect(formatted).toContain("1 January 2027");
    expect(formatted).toContain("00:00:00");
  });

  it("handles midnight correctly", () => {
    const date = new Date(2026, 1, 7, 0, 0, 0);
    const formatted = formatDateTime(date);

    expect(formatted).toContain("00:00:00");
  });

  it("handles noon correctly", () => {
    const date = new Date(2026, 1, 7, 12, 0, 0);
    const formatted = formatDateTime(date);

    // 24-hour format, so noon is 12:00:00, not 00:00:00
    expect(formatted).toContain("12:00:00");
  });

  it("handles end of day correctly", () => {
    const date = new Date(2026, 1, 7, 23, 59, 59);
    const formatted = formatDateTime(date);

    expect(formatted).toContain("23:59:59");
  });

  it("handles month boundaries correctly", () => {
    // Last day of January
    const jan31 = new Date(2026, 0, 31, 23, 59, 59);
    expect(formatDateTime(jan31)).toContain("31 January 2026");

    // First day of February
    const feb1 = new Date(2026, 1, 1, 0, 0, 0);
    expect(formatDateTime(feb1)).toContain("1 February 2026");
  });

  it("handles leap year February correctly", () => {
    // 2024 is a leap year
    const feb29 = new Date(2024, 1, 29, 12, 0, 0);
    const formatted = formatDateTime(feb29);

    expect(formatted).toContain("29 February 2024");
  });

  it("handles all 12 months correctly", () => {
    const months = [
      "January",
      "February",
      "March",
      "April",
      "May",
      "June",
      "July",
      "August",
      "September",
      "October",
      "November",
      "December",
    ];

    months.forEach((month, index) => {
      const date = new Date(2026, index, 15, 12, 0, 0);
      const formatted = formatDateTime(date);

      expect(formatted).toContain(month);
    });
  });
});