import { describe, expect, it } from "vitest";
import { addBusinessDays, compareArithmetic } from "../../src/time/arithmetic";
import { inspectEpoch } from "../../src/time/epoch";
import { createUtcEvent, foldIcsLine } from "../../src/time/ics";
import { previewCron, previewRRule } from "../../src/time/recurrence";
import {
  compareTimeZones,
  nextTransitions,
  resolveLocalDateTime,
} from "../../src/time/zones";

describe("exact epoch conversion", () => {
  it("preserves negative nanoseconds", () => {
    const result = inspectEpoch("-0.000000001", "seconds");
    expect(result.epochNanoseconds).toBe(-1n);
    expect(result.iso).toBe("1969-12-31T23:59:59.999999999Z");
  });

  it("rejects sub-nanosecond precision", () => {
    expect(() => inspectEpoch("0.0000000001", "seconds")).toThrow(
      /smaller than one nanosecond/u,
    );
  });
});

describe("time-zone handling", () => {
  it("classifies a spring gap and autumn overlap", () => {
    expect(
      resolveLocalDateTime("2026-03-29T02:30", "Europe/Berlin").status,
    ).toBe("skipped");
    const overlap = resolveLocalDateTime("2026-10-25T02:30", "Europe/Berlin");
    expect(overlap.status).toBe("ambiguous");
    expect(overlap.choices.map((choice) => choice.offset)).toEqual([
      "+02:00",
      "+01:00",
    ]);
  });

  it("compares the same instant without changing its epoch", () => {
    const values = compareTimeZones("2026-01-01T00:00:00Z", [
      "UTC",
      "Asia/Tokyo",
    ]);
    expect(values[0]?.epochNanoseconds).toBe(values[1]?.epochNanoseconds);
    expect(values[1]?.local).toBe("2026-01-01T09:00:00");
  });

  it("rejects a non-integer transition count", () => {
    expect(() =>
      nextTransitions("2026-01-01T00:00:00Z", "Europe/Berlin", 1.5),
    ).toThrow(/between 1 and 32/u);
  });
});

describe("calendar arithmetic", () => {
  it("shows wall-clock and elapsed days diverging across DST", () => {
    const result = compareArithmetic(
      "2026-03-28T12:00:00Z",
      "Europe/Berlin",
      "P1D",
    );
    expect(result.differenceSeconds).toBe("-3600");
  });

  it("adds business days with explicit holidays", () => {
    expect(addBusinessDays("2026-12-24", 2, ["2026-12-25"]).result).toBe(
      "2026-12-29",
    );
  });

  it("bounds explicit holiday allocation", () => {
    expect(() =>
      addBusinessDays("2026-01-01", 1, Array(10_001).fill("2026-01-02")),
    ).toThrow(/10,000/u);
  });

  it("does not silently truncate a fractional business-day count", () => {
    expect(() => addBusinessDays("2026-01-01", 1.5)).toThrow(/±100,000/u);
  });
});

describe("bounded recurrence previews", () => {
  it("previews five-field cron in its named zone", () => {
    const result = previewCron(
      "0 9 * * MON-FRI",
      "2026-08-31T08:00:00Z",
      "Europe/Berlin",
      2,
      "5-part",
    );
    expect(result).toHaveLength(2);
    expect(result[0]?.zoned).toContain("T09:00:00");
  });

  it("previews a strict RRULE", () => {
    const result = previewRRule(
      "FREQ=DAILY;COUNT=3",
      "2026-09-01T09:00",
      "Europe/Berlin",
      10,
    );
    expect(result).toHaveLength(3);
    expect(result[0]?.zoned).toContain("2026-09-01T09:00:00");
  });
});

describe("iCalendar output", () => {
  it("creates CRLF UTC event lines", () => {
    const result = createUtcEvent({
      startLocal: "2026-09-01T10:00",
      timeZone: "Europe/Berlin",
      duration: "PT1H",
      summary: "Review, plan",
    });
    expect(result.ics).toContain("DTSTART:20260901T080000Z\r\n");
    expect(result.ics).toContain("SUMMARY:Review\\, plan");
    expect(result.ics.endsWith("\r\n")).toBe(true);
  });

  it("folds Unicode lines by UTF-8 octets", () => {
    const folded = foldIcsLine(`DESCRIPTION:${"ä".repeat(50)}`);
    expect(folded).toContain("\r\n ");
    expect(
      Math.max(
        ...folded
          .split("\r\n")
          .map((line) => new TextEncoder().encode(line).length),
      ),
    ).toBeLessThanOrEqual(75);
  });
});