import { describe, expect, it } from 'vitest';
import { fitView, screenToImage, zoomAt, type View } from '../src/lib/view';

describe('view transform', () => {
  it('maps screen to image coordinates', () => {
    const view: View = { scale: 2, offsetX: 10, offsetY: 20 };
    expect(screenToImage({ x: 30, y: 60 }, view)).toEqual({ x: 10, y: 20 });
  });

  it('keeps the point under the cursor fixed while zooming', () => {
    const view: View = { scale: 0.5, offsetX: 40, offsetY: -15 };
    const cursor = { x: 300, y: 200 };
    const before = screenToImage(cursor, view);
    const zoomed = zoomAt(view, cursor, 3);
    expect(zoomed.scale).toBeCloseTo(1.5);
    const after = screenToImage(cursor, zoomed);
    expect(after.x).toBeCloseTo(before.x);
    expect(after.y).toBeCloseTo(before.y);
  });

  it('clamps zoom', () => {
    expect(zoomAt({ scale: 10, offsetX: 0, offsetY: 0 }, { x: 0, y: 0 }, 100).scale).toBe(20);
    expect(zoomAt({ scale: 0.1, offsetX: 0, offsetY: 0 }, { x: 0, y: 0 }, 0.001).scale).toBe(0.05);
  });

  it('fits and centres the image in the viewport', () => {
    const view = fitView(2000, 1000, 1016, 1016, 8);
    expect(view.scale).toBeCloseTo(0.5);
    expect(view.offsetX).toBeCloseTo(8);
    expect(view.offsetY).toBeCloseTo(258);
  });
});