import { describe, it, expect } from 'vitest';
import { createMercatorProjection, mercatorY, MAX_MERCATOR_LAT } from './map-projection';

describe('mercatorY', () => {
  it('is zero at the equator', () => {
    // tan(pi/4) lands a float epsilon below 1, so the log is ~-1e-16, not 0.
    expect(mercatorY(0)).toBeCloseTo(0, 12);
  });

  it('grows northward and is symmetric', () => {
    expect(mercatorY(45)).toBeGreaterThan(0);
    expect(mercatorY(-45)).toBeCloseTo(-mercatorY(45), 10);
  });

  it('clamps beyond the Mercator limit instead of diverging', () => {
    expect(Number.isFinite(mercatorY(90))).toBe(true);
    expect(mercatorY(90)).toBe(mercatorY(MAX_MERCATOR_LAT));
  });
});

describe('createMercatorProjection', () => {
  // Roughly the bounding box of Rio Grande do Sul.
  const points = [
    { lat: -27.08, lng: -53.11 },
    { lat: -33.75, lng: -49.69 },
  ];

  it('returns null when there is nothing to fit', () => {
    expect(createMercatorProjection([], 800, 600)).toBeNull();
  });

  it('returns null when the container has no area', () => {
    expect(createMercatorProjection(points, 0, 0)).toBeNull();
  });

  it('keeps every projected point inside the container', () => {
    const projection = createMercatorProjection(points, 800, 600, 24)!;

    points.forEach(point => {
      const { x, y } = projection.project(point);
      expect(x).toBeGreaterThanOrEqual(0);
      expect(x).toBeLessThanOrEqual(800);
      expect(y).toBeGreaterThanOrEqual(0);
      expect(y).toBeLessThanOrEqual(600);
    });
  });

  it('puts north above south on screen', () => {
    const projection = createMercatorProjection(points, 800, 600)!;

    const north = projection.project({ lat: -27.08, lng: -51 });
    const south = projection.project({ lat: -33.75, lng: -51 });

    expect(north.y).toBeLessThan(south.y);
  });

  it('puts west left of east', () => {
    const projection = createMercatorProjection(points, 800, 600)!;

    const west = projection.project({ lat: -30, lng: -53.11 });
    const east = projection.project({ lat: -30, lng: -49.69 });

    expect(west.x).toBeLessThan(east.x);
  });

  it('scales both axes uniformly so the geography is not stretched', () => {
    // A square-ish extent in a very wide container must not fill the width.
    const square = [
      { lat: 0, lng: 0 },
      { lat: 10, lng: 10 },
    ];
    const projection = createMercatorProjection(square, 1000, 200, 0)!;

    const a = projection.project(square[0]);
    const b = projection.project(square[1]);

    const spanX = Math.abs(b.x - a.x);
    const spanY = Math.abs(b.y - a.y);

    // Mercator stretches latitude slightly, but the two spans must stay within
    // the same order — a non-uniform fit would push spanX toward 1000.
    expect(spanX).toBeLessThan(400);
    expect(spanX / spanY).toBeGreaterThan(0.5);
    expect(spanX / spanY).toBeLessThan(2);
  });

  it('centers a single point instead of dividing by zero', () => {
    const projection = createMercatorProjection([{ lat: -30, lng: -51 }], 800, 600)!;
    const { x, y } = projection.project({ lat: -30, lng: -51 });

    expect(x).toBeCloseTo(400, 5);
    expect(y).toBeCloseTo(300, 5);
  });

  it('handles a perfectly vertical line of points', () => {
    const projection = createMercatorProjection(
      [
        { lat: -27, lng: -51 },
        { lat: -33, lng: -51 },
      ],
      800,
      600
    )!;

    const a = projection.project({ lat: -27, lng: -51 });
    const b = projection.project({ lat: -33, lng: -51 });

    expect(Number.isFinite(a.x)).toBe(true);
    expect(Number.isFinite(a.y)).toBe(true);
    expect(a.x).toBeCloseTo(b.x, 5);
    expect(a.y).toBeLessThan(b.y);
  });
});