import { describe, expect, it } from 'vitest';
import { MAX_SCALE, MIN_SCALE, TIME_SCALES, scaleToSlider, sliderToScale } from './timeScale';

const STEPS = TIME_SCALES.length - 1; // 9 intervals across the 10 ladder positions (v0.14.0)

describe('sliderToScale', () => {
  it('is exact at the endpoints (0 → 1×, 1 → 1000×)', () => {
    expect(sliderToScale(0)).toBe(MIN_SCALE);
    expect(sliderToScale(1)).toBe(MAX_SCALE);
  });

  it('maps each of the 10 positions to the ladder', () => {
    const expected = [1, 2, 5, 10, 25, 50, 100, 250, 500, 1000];
    for (let i = 0; i < TIME_SCALES.length; i++) {
      expect(sliderToScale(i / STEPS)).toBe(expected[i]);
    }
  });

  it('is monotonic non-decreasing across the whole range', () => {
    let prev = sliderToScale(0);
    for (let i = 1; i <= 2000; i++) {
      const s = sliderToScale(i / 2000);
      expect(s).toBeGreaterThanOrEqual(prev);
      prev = s;
    }
  });

  it('only ever returns a ladder value', () => {
    for (let i = 0; i <= 2000; i++) {
      expect(TIME_SCALES).toContain(sliderToScale(i / 2000));
    }
  });

  it('clamps out-of-range and non-finite input', () => {
    expect(sliderToScale(-0.5)).toBe(MIN_SCALE);
    expect(sliderToScale(1.5)).toBe(MAX_SCALE);
    expect(sliderToScale(NaN)).toBe(MIN_SCALE);
  });
});

describe('scaleToSlider', () => {
  it('is exact at the endpoints (1× → 0, 1000× → 1)', () => {
    expect(scaleToSlider(1)).toBe(0);
    expect(scaleToSlider(1000)).toBe(1);
  });

  it('places each ladder value on its own position', () => {
    for (let i = 0; i < TIME_SCALES.length; i++) {
      expect(scaleToSlider(TIME_SCALES[i])).toBeCloseTo(i / STEPS, 12);
    }
  });

  it('stays within [0, 1] for in-range scales', () => {
    for (let s = MIN_SCALE; s <= MAX_SCALE; s++) {
      const t = scaleToSlider(s);
      expect(t).toBeGreaterThanOrEqual(0);
      expect(t).toBeLessThanOrEqual(1);
    }
  });

  it('clamps out-of-range and non-finite input', () => {
    expect(scaleToSlider(0)).toBe(0);
    expect(scaleToSlider(-3)).toBe(0);
    expect(scaleToSlider(1001)).toBe(1); // above the ladder top → clamped to 1000× → t=1
    expect(scaleToSlider(NaN)).toBe(0);
  });
});

describe('round-trip', () => {
  it('sliderToScale(scaleToSlider(s)) === s for every ladder value', () => {
    for (const s of TIME_SCALES) {
      expect(sliderToScale(scaleToSlider(s))).toBe(s);
    }
  });

  it('maps off-ladder scales to the nearest ladder step by log distance', () => {
    expect(sliderToScale(scaleToSlider(3))).toBe(2); // ln 3 ≈ 1.10 → closer to 2 (ln ≈ 0.69) than 5 (ln ≈ 1.61)
    expect(sliderToScale(scaleToSlider(60))).toBe(50); // legacy max from the v0.9.x era sits between 50 and 100, nearer 50
    expect(sliderToScale(scaleToSlider(200))).toBe(250); // ln 200 ≈ 5.30 → closer to 250 (ln ≈ 5.52) than 100 (ln ≈ 4.61)
  });
});