import { describe, expect, it } from "vitest";
import { addDaysIso, daysBetweenIso, fmtAge, fmtDate, initials, tenure, toIsoDate, yearsBetweenIso } from "@/lib/format";

describe("fmtDate", () => {
  it("formats an ISO date string in de-AT order", () => {
    expect(fmtDate("2026-03-05")).toBe("05.03.2026");
  });

  // A date-only column has no time and no zone. Routing it through a Date
  // would anchor it to UTC midnight and render the previous day wherever the
  // renderer sits west of UTC — including a server/browser hydration split.
  it("never shifts a date-only string across a day boundary", () => {
    expect(fmtDate("2026-01-01")).toBe("01.01.2026");
    expect(fmtDate("2026-12-31")).toBe("31.12.2026");
  });

  it("renders a timestamp in Vienna time regardless of the runtime zone", () => {
    // 23:30 UTC on 5 March is already 6 March in Vienna (UTC+1 before the
    // DST switch); the same instant is still 5 March in UTC.
    expect(fmtDate("2026-03-05T23:30:00Z")).toBe("06.03.2026");
  });

  it("returns an em dash for null/undefined/empty input", () => {
    expect(fmtDate(null)).toBe("–");
    expect(fmtDate(undefined)).toBe("–");
    expect(fmtDate("")).toBe("–");
  });

  it("returns an em dash for an invalid date string", () => {
    expect(fmtDate("not-a-date")).toBe("–");
  });
});

describe("initials", () => {
  it("uppercases the first letter of each name", () => {
    expect(initials("maria", "gruber")).toBe("MG");
  });

  it("trims surrounding whitespace before taking the first letter", () => {
    expect(initials("  Anna", "Huber  ")).toBe("AH");
  });
});

describe("fmtAge", () => {
  it("computes age correctly when the birthday has already passed this year", () => {
    const today = new Date();
    const birthDate = new Date(today.getFullYear() - 30, 0, 1); // Jan 1, definitely passed
    expect(fmtAge(birthDate)).toBe(30);
  });

  it("subtracts one year when the birthday has not yet occurred this year", () => {
    const today = new Date();
    const future = new Date(today.getFullYear() - 30, 11, 31); // Dec 31, likely not yet passed
    if (today.getMonth() === 11 && today.getDate() === 31) return; // skip on the one day this'd be flaky
    expect(fmtAge(future)).toBe(29);
  });
});

describe("tenure", () => {
  it("formats whole years and months since entry", () => {
    const start = new Date(2020, 0, 15);
    const end = new Date(2023, 2, 15); // exactly 3 years, 2 months later
    expect(tenure(start, end)).toBe("3 Jahre, 2 Monate");
  });

  it("uses singular Jahr/Monat for exactly 1", () => {
    const start = new Date(2020, 0, 1);
    const end = new Date(2021, 1, 1); // 1 year, 1 month
    expect(tenure(start, end)).toBe("1 Jahr, 1 Monat");
  });

  it("falls back to 'unter 1 Monat' for less than a month", () => {
    const start = new Date(2024, 0, 1);
    const end = new Date(2024, 0, 15);
    expect(tenure(start, end)).toBe("unter 1 Monat");
  });

  it("defaults the end date to today when no end date is given", () => {
    const start = new Date();
    expect(tenure(start)).toBe("unter 1 Monat");
  });
});

describe("daysBetweenIso", () => {
  it("computes whole days between two dates", () => {
    expect(daysBetweenIso("2026-01-01", "2026-01-11")).toBe(10);
  });

  it("returns a negative number when the second date precedes the first", () => {
    expect(daysBetweenIso("2026-01-11", "2026-01-01")).toBe(-10);
  });

  // Both ends are anchored at UTC midnight, so the DST switch in between
  // cannot turn 30 calendar days into 29.96 and round down.
  it("is exact across a DST transition", () => {
    expect(daysBetweenIso("2026-03-15", "2026-04-15")).toBe(31);
    expect(daysBetweenIso("2026-10-15", "2026-11-15")).toBe(31);
  });
});

describe("addDaysIso", () => {
  it("rolls over month and year boundaries", () => {
    expect(addDaysIso("2026-12-31", 1)).toBe("2027-01-01");
    expect(addDaysIso("2026-01-31", 1)).toBe("2026-02-01");
  });

  it("handles a leap day", () => {
    expect(addDaysIso("2028-02-28", 1)).toBe("2028-02-29");
  });
});

describe("yearsBetweenIso", () => {
  it("counts only completed years", () => {
    expect(yearsBetweenIso("1990-05-15", "2026-05-15")).toBe(36);
    expect(yearsBetweenIso("1990-05-15", "2026-05-14")).toBe(35);
  });
});

describe("toIsoDate", () => {
  it("passes a date-only string through untouched", () => {
    expect(toIsoDate("2026-01-01")).toBe("2026-01-01");
  });

  it("resolves a timestamp to the Vienna calendar day", () => {
    expect(toIsoDate("2026-03-05T23:30:00Z")).toBe("2026-03-06");
  });
});