/**
 * The arithmetic of the sortable list shared by the shape, pixel art and tilemap lists: which row
 * shows which item, which gap a drop falls into, and what move that makes in the owner's order.
 */
import { describe, expect, it } from 'vitest';
import { dropGap, dropMove, rowOrder } from '../../src/ui/sortable';

const ROW = 30;

describe('sortable list', () => {
  it('shows a layer list upside down – the item drawn last is the top row', () => {
    expect(rowOrder(['bottom', 'middle', 'top'], true)).toEqual(['top', 'middle', 'bottom']);
    expect(rowOrder(['first', 'second'], false)).toEqual(['first', 'second']);
  });

  it('drops into the gap the pointer is nearest to', () => {
    expect(dropGap(3, 2, ROW)).toBe(0);
    expect(dropGap(3, 20, ROW)).toBe(1);
    expect(dropGap(3, 44, ROW)).toBe(1);
    expect(dropGap(3, 46, ROW)).toBe(2);
    // Outside the list there is no gap: a drop above it is the first, below it the last.
    expect(dropGap(3, 400, ROW)).toBe(3);
    expect(dropGap(3, -40, ROW)).toBe(0);
  });

  it('turns a drop into a move of the model, the top row being the last item when reversed', () => {
    // Three items, so the rows are the model indices [2, 1, 0]: the top row dropped at the
    // bottom gap becomes the first item of the model, the one drawn first.
    expect(dropMove(3, 0, 3, true)).toEqual({ from: 2, to: 0 });
    expect(dropMove(3, 2, 0, true)).toEqual({ from: 0, to: 2 });
    expect(dropMove(3, 1, 0, true)).toEqual({ from: 1, to: 2 });
  });

  it('keeps the indices as they are in a list shown in model order', () => {
    // Frames: the first row is the first frame. The top row dropped at the bottom becomes the last.
    expect(dropMove(3, 0, 3, false)).toEqual({ from: 0, to: 2 });
    expect(dropMove(3, 2, 0, false)).toEqual({ from: 2, to: 0 });
    expect(dropMove(3, 0, 2, false)).toEqual({ from: 0, to: 1 });
  });

  it('is no move when the row lands where it already is', () => {
    for (const reversed of [true, false]) {
      expect(dropMove(3, 1, 1, reversed)).toBeNull();
      expect(dropMove(3, 1, 2, reversed)).toBeNull();
      expect(dropMove(3, 5, 1, reversed)).toBeNull();
    }
  });
});