import { describe, expect, it } from "vitest";
import {
  addDays,
  habitDoneInPeriod,
  habitStreak,
  localDateIn,
  weekdayOf,
  weekStartOf,
} from "./coach.js";

const dates = (...values: string[]) => new Set(values);

describe("calendar dates", () => {
  it("reads the date in the user's time zone, not the server's", () => {
    const instant = new Date("2026-10-03T23:30:00Z");
    expect(localDateIn("UTC", instant)).toBe("2026-10-03");
    expect(localDateIn("Europe/Vienna", instant)).toBe("2026-10-04");
    expect(localDateIn("America/Los_Angeles", instant)).toBe("2026-10-03");
    expect(localDateIn("Pacific/Kiritimati", new Date("2026-10-03T10:30:00Z"))).toBe("2026-10-04");
  });

  it("moves across months, years and daylight saving changes by whole days", () => {
    expect(addDays("2026-10-31", 1)).toBe("2026-11-01");
    expect(addDays("2027-01-01", -1)).toBe("2026-12-31");
    expect(addDays("2026-03-28", 2)).toBe("2026-03-30");
    expect(weekdayOf("2026-10-03")).toBe(6);
    expect(weekStartOf("2026-10-03")).toBe("2026-09-28");
    expect(weekStartOf("2026-10-04")).toBe("2026-09-28");
    expect(weekStartOf("2026-10-05")).toBe("2026-10-05");
  });
});

describe("habit streaks", () => {
  const saturday = "2026-10-03";

  it("counts consecutive days and keeps today open until it is done", () => {
    const done = dates("2026-09-30", "2026-10-01", "2026-10-02");
    expect(habitStreak("daily", done, saturday)).toBe(3);
    expect(habitStreak("daily", new Set([...done, saturday]), saturday)).toBe(4);
    expect(habitStreak("daily", dates("2026-09-30", "2026-10-01"), saturday)).toBe(0);
    expect(habitStreak("daily", dates(), saturday)).toBe(0);
  });

  it("skips weekends for weekday habits", () => {
    const monday = "2026-10-05";
    const done = dates("2026-10-01", "2026-10-02");
    expect(habitStreak("weekdays", done, saturday)).toBe(2);
    expect(habitStreak("weekdays", done, monday)).toBe(2);
    expect(habitStreak("weekdays", new Set([...done, monday]), monday)).toBe(3);
    expect(habitStreak("weekdays", dates("2026-10-01"), monday)).toBe(0);
  });

  it("counts weeks with at least one done day for weekly habits", () => {
    const done = dates("2026-09-15", "2026-09-26", "2026-09-29");
    expect(habitStreak("weekly", done, saturday)).toBe(3);
    expect(habitStreak("weekly", dates("2026-09-15", "2026-09-26"), saturday)).toBe(2);
    expect(habitStreak("weekly", dates("2026-09-15"), saturday)).toBe(0);
  });

  it("reads a weekly habit as done for the rest of the week", () => {
    expect(habitDoneInPeriod("weekly", dates("2026-09-29"), saturday)).toBe(true);
    expect(habitDoneInPeriod("weekly", dates("2026-09-27"), saturday)).toBe(false);
    expect(habitDoneInPeriod("daily", dates("2026-10-02"), saturday)).toBe(false);
    expect(habitDoneInPeriod("daily", dates(saturday), saturday)).toBe(true);
  });
});