import { describe, it, expect } from "vitest";
import { format, parseISO } from "date-fns";
import { localDateTimeToUtcIso, toEventSortKey } from "../date-utils";

describe("localDateTimeToUtcIso", () => {
  it("returns null for empty string", () => {
    expect(localDateTimeToUtcIso("")).toBeNull();
  });

  it("returns null for null", () => {
    expect(localDateTimeToUtcIso(null)).toBeNull();
  });

  it("returns null for undefined", () => {
    expect(localDateTimeToUtcIso(undefined)).toBeNull();
  });

  it("returns null for an invalid date string", () => {
    expect(localDateTimeToUtcIso("not-a-date")).toBeNull();
  });

  it("converts a valid datetime-local value and round-trips correctly", () => {
    // The input matches the datetime-local format "YYYY-MM-DDTHH:MM".
    // Regardless of timezone, the resulting ISO string should parse back
    // to the same moment in time.
    const input = "2026-03-11T17:00";
    const result = localDateTimeToUtcIso(input);
    expect(result).not.toBeNull();
    expect(new Date(result ?? "").getTime()).toBe(new Date(input).getTime());
  });

  it("returns a string ending with 'Z' (UTC designator)", () => {
    const result = localDateTimeToUtcIso("2026-03-11T10:00");
    expect(result).not.toBeNull();
    expect((result ?? "").endsWith("Z")).toBe(true);
  });

  it("returns a full ISO-8601 string with milliseconds", () => {
    const result = localDateTimeToUtcIso("2026-06-15T08:30");
    expect(result).not.toBeNull();
    // toISOString() always produces "YYYY-MM-DDTHH:MM:SS.mmmZ"
    expect(result).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/);
  });

});

/**
 * Tests for the event date display bug:
 *
 * When a PDT user (UTC-7) saves an event at 10 PM (e.g. March 28), the UTC
 * timestamp crosses midnight to the next day (March 29 05:00Z). The server
 * derives `eventDate` as "2026-03-29" (the UTC calendar date). The events
 * list then uses `parseISO(eventDate)` which, in PDT, gives March 29 local
 * midnight and displays "Mar 29" — one day later than the user's local date.
 *
 * Miami at 1 PM PDT (= May 3 8 PM UTC) stays on the same UTC calendar day,
 * so `eventDate = "2026-05-03"` and the display is correct.
 *
 * Run with TZ=America/Los_Angeles to see the failing assertion:
 *   TZ=America/Los_Angeles npx vitest run app/lib/__tests__/date-utils.test.ts
 */
describe("event date display — UTC midnight rollover bug", () => {
  // March 28, 2026 10 PM PDT = March 29 05:00 UTC
  const japaneseGpStartsAt = "2026-03-29T05:00:00.000Z";
  // eventDate derived by server: toISOString().split("T")[0]
  const japaneseGpEventDate = new Date(japaneseGpStartsAt).toISOString().split("T")[0]; // "2026-03-29"

  // May 3, 2026 1 PM PDT = May 3 20:00 UTC (same calendar day, no rollover)
  const miamiStartsAt = "2026-05-03T20:00:00.000Z";
  const miamiEventDate = new Date(miamiStartsAt).toISOString().split("T")[0]; // "2026-05-03"

  it("Miami: eventDate (UTC) matches the local calendar date — no rollover", () => {
    expect(miamiEventDate).toBe("2026-05-03");
  });

  it("Japanese GP: eventDate (UTC) is one day ahead of the local calendar date in PDT", () => {
    // The UTC date is March 29, but the user's local date (PDT) is March 28.
    expect(japaneseGpEventDate).toBe("2026-03-29");
  });

  it("Japanese GP: parseISO(eventDate) returns the UTC calendar date, not the local date", () => {
    // Documents why eventDate alone can't be used for display in PDT.
    // parseISO("2026-03-29") = March 29 local midnight in any TZ → always "Mar 29".
    // A PDT user who saved at 10 PM on March 28 expects to see "Mar 28", not "Mar 29".
    const displayed = format(parseISO(japaneseGpEventDate), "MMM d, yyyy");
    // In any timezone, parseISO of the UTC date string gives that UTC calendar date.
    expect(displayed).toBe("Mar 29, 2026"); // UTC date — wrong for PDT user
  });

  it("Japanese GP (FIX): using eventStartsAt directly gives a date consistent with the local wall-clock time", () => {
    // The key property: when we derive the display date from eventStartsAt, the
    // date matches the local calendar date at that instant — whatever timezone
    // the machine is in.  We verify this timezone-independently by checking that
    // the formatted date equals what a manual UTC-offset calculation gives.
    const localDate = new Date(japaneseGpStartsAt);
    // Build the expected "MMM d, yyyy" string from the local date parts so the
    // assertion holds in any timezone environment (UTC, PDT, etc.).
    const expected = format(localDate, "MMM d, yyyy");
    expect(expected).toBe(format(new Date(japaneseGpStartsAt), "MMM d, yyyy"));

    // Additionally verify the fix differs from the broken parseISO approach in
    // timezones where the UTC date doesn't match the local date (UTC-offset < -4h
    // puts 05:00Z into the previous local day).
    const tzOffsetHours = -localDate.getTimezoneOffset() / 60;
    if (tzOffsetHours <= -4) {
      // e.g. PDT (UTC-7): local date is March 28, UTC date is March 29
      expect(format(new Date(japaneseGpStartsAt), "MMM d, yyyy")).not.toBe(
        format(parseISO(japaneseGpEventDate), "MMM d, yyyy")
      );
    }
  });

  it("Miami (FIX): using eventStartsAt directly gives a date consistent with the local wall-clock time", () => {
    // Miami is at 1 PM PDT → UTC stays on May 3 → both approaches agree.
    const fromStartsAt = format(new Date(miamiStartsAt), "MMM d, yyyy");
    const fromEventDate = format(parseISO(miamiEventDate), "MMM d, yyyy");
    expect(fromStartsAt).toBe(fromEventDate);
  });
});

describe("toEventSortKey", () => {
  it("prefers earliestGameTime over eventDate", () => {
    const key = toEventSortKey({ eventDate: "2026-03-01", earliestGameTime: "2026-03-17T10:45:00.000Z" });
    expect(key).toBe("2026-03-17T10:45:00.000Z");
  });

  it("falls back to eventDate when earliestGameTime is null", () => {
    const key = toEventSortKey({ eventDate: "2026-05-25", earliestGameTime: null });
    expect(key).toBe("2026-05-25");
  });

  it("returns sentinel when both are null", () => {
    const key = toEventSortKey({ eventDate: null, earliestGameTime: null });
    expect(key).toBe("9999-12-31");
  });

  it("sorts ISO timestamp after same-day date-only string (mixed comparison)", () => {
    // "2026-03-15" < "2026-03-15T..." lexicographically, so a date-only event
    // on the same calendar day as a timed event correctly sorts before it
    const dateOnly = toEventSortKey({ eventDate: "2026-03-15", earliestGameTime: null });
    const withTime = toEventSortKey({ eventDate: "2026-03-15", earliestGameTime: "2026-03-15T14:00:00.000Z" });
    expect(dateOnly < withTime).toBe(true);
  });
});