import { describe, it, expect } from 'vitest';
import { flattenArc } from './arc';

const onCircle = (p: [number, number], c: [number, number], r: number) =>
  Math.abs(Math.hypot(p[0] - c[0], p[1] - c[1]) - r) < 1e-6;

describe('flattenArc', () => {
  it('flattens a CCW quarter circle, endpoints exact, all points on the circle', () => {
    // centre (0,0), radius 10, from (10,0) CCW to (0,10)
    const pts = flattenArc([10, 0], [0, 10], [0, 0], false, 0.1);
    expect(pts[0]).toEqual([10, 0]);
    expect(pts[pts.length - 1]).toEqual([0, 10]);
    expect(pts.length).toBeGreaterThan(2);
    for (const p of pts) expect(onCircle(p, [0, 0], 10)).toBe(true);
  });

  it('CW arc sweeps the other way (midpoint has negative y)', () => {
    // centre (0,0), radius 10, from (10,0) CW to (0,10) → goes the long way through y<0
    const pts = flattenArc([10, 0], [0, 10], [0, 0], true, 0.1);
    const mid = pts[Math.floor(pts.length / 2)];
    expect(mid[1]).toBeLessThan(0);
  });

  it('treats start==end as a full circle', () => {
    const pts = flattenArc([10, 0], [10, 0], [0, 0], false, 0.5);
    // a point roughly opposite the start should exist
    expect(pts.some((p) => p[0] < -9)).toBe(true);
  });

  it('respects chord tolerance (tighter tolerance → more points)', () => {
    const coarse = flattenArc([10, 0], [0, 10], [0, 0], false, 1.0);
    const fine = flattenArc([10, 0], [0, 10], [0, 0], false, 0.01);
    expect(fine.length).toBeGreaterThan(coarse.length);
  });
});