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

import { diffMarkdown } from './text-diff';

/** Concatenate the segments of one type back into a string. */
function only(
  segments: ReturnType<typeof diffMarkdown>,
  type: 'added' | 'removed' | 'equal',
): string {
  return segments
    .filter((s) => s.type === type)
    .map((s) => s.value)
    .join('');
}

describe('diffMarkdown (issue #42)', () => {
  it('marks added and removed words against a fixture pair', () => {
    const before = 'The quick brown fox';
    const after = 'The slow brown fox jumps';
    const segments = diffMarkdown(before, after);

    expect(only(segments, 'removed')).toContain('quick');
    expect(only(segments, 'added')).toContain('slow');
    expect(only(segments, 'added')).toContain('jumps');
    // Unchanged words stay in the equal channel.
    expect(only(segments, 'equal')).toContain('brown');
    expect(only(segments, 'equal')).toContain('fox');
  });

  it('round-trips: equal+removed reconstructs before, equal+added reconstructs after', () => {
    const before = '# Title\n\nHello world, this is old.';
    const after = '# Title\n\nHello brave world, this is new.';
    const segments = diffMarkdown(before, after);

    const reconstructedBefore = segments
      .filter((s) => s.type !== 'added')
      .map((s) => s.value)
      .join('');
    const reconstructedAfter = segments
      .filter((s) => s.type !== 'removed')
      .map((s) => s.value)
      .join('');
    expect(reconstructedBefore).toBe(before);
    expect(reconstructedAfter).toBe(after);
  });

  it('returns only equal segments for identical text', () => {
    const text = 'nothing changed here';
    const segments = diffMarkdown(text, text);
    expect(segments.every((s) => s.type === 'equal')).toBe(true);
    expect(only(segments, 'equal')).toBe(text);
  });

  it('handles empty before (pure insert) and empty after (pure delete)', () => {
    expect(diffMarkdown('', 'brand new')).toEqual([{ type: 'added', value: 'brand new' }]);
    expect(diffMarkdown('all gone', '')).toEqual([{ type: 'removed', value: 'all gone' }]);
  });
});