import { describe, expect, it } from 'vitest';

import { columnHasInk, keptColumns, tighten, type Greyscale } from './tighten';

/** Builds an image from a picture: '#' is ink, '.' is paper. */
function image(row: string, height = 2): Greyscale {
  const width = row.length;
  const data = Buffer.alloc(width * height, 255);
  for (let y = 0; y < height; y += 1) {
    [...row].forEach((cell, x) => {
      data[y * width + x] = cell === '#' ? 0 : 255;
    });
  }
  return { data, width, height };
}

describe('columnHasInk', () => {
  it('finds ink anywhere down the column', () => {
    const grid: Greyscale = { data: Buffer.from([255, 255, 0, 255]), width: 2, height: 2 };
    expect(columnHasInk(grid, 0)).toBe(true);
    expect(columnHasInk(grid, 1)).toBe(false);
  });
});

describe('keptColumns', () => {
  it('shortens a gap to the allowance', () => {
    expect(keptColumns(image('#.....#'), 2)).toEqual([0, 1, 2, 6]);
  });

  it('leaves a gap already within the allowance alone', () => {
    expect(keptColumns(image('#.#'), 2)).toEqual([0, 1, 2]);
  });

  it('drops the margins, which are not spacing', () => {
    expect(keptColumns(image('..#.#..'), 2)).toEqual([2, 3, 4]);
  });

  it('handles several gaps independently', () => {
    expect(keptColumns(image('#....#....#'), 1)).toEqual([0, 1, 5, 6, 10]);
  });

  it('returns nothing for a blank image', () => {
    expect(keptColumns(image('.....'), 2)).toEqual([]);
  });

  it('keeps solid ink untouched', () => {
    expect(keptColumns(image('####'), 0)).toEqual([0, 1, 2, 3]);
  });
});

describe('tighten', () => {
  it('narrows the image by the width it removed', () => {
    const result = tighten(image('#.....#'), 2);
    expect(result.width).toBe(4);
    expect(result.height).toBe(2);
  });

  it('preserves the letterforms, only the space between them', () => {
    const result = tighten(image('##....##'), 1);
    const row = Array.from({ length: result.width }, (_, x) => (result.data[x] === 0 ? '#' : '.'));
    expect(row.join('')).toBe('##.##');
  });

  it('copies every row, not just the first', () => {
    const source = image('#..#', 3);
    const result = tighten(source, 1);
    for (let y = 0; y < 3; y += 1) {
      expect(result.data[y * result.width]).toBe(0);
    }
  });
});