import { describe, it, expect } from 'vitest';
import { splitMessage } from './utils.js';

describe('splitMessage', () => {
  it('returns single chunk for empty string', () => {
    const result = splitMessage('', 100);
    // empty string never enters the while loop → returns empty array
    expect(result).toEqual([]);
  });

  it('returns single chunk when text is under maxLength', () => {
    const result = splitMessage('hello world', 100);
    expect(result).toEqual(['hello world']);
  });

  it('returns single chunk when text equals maxLength', () => {
    const text = 'a'.repeat(50);
    const result = splitMessage(text, 50);
    expect(result).toEqual([text]);
  });

  it('splits at newline when possible', () => {
    const text = 'line one\nline two\nline three';
    // maxLength 18 → "line one\nline two\n" is 18 chars, lastIndexOf('\n', 18) = 17
    const result = splitMessage(text, 18);
    expect(result).toEqual(['line one\nline two', 'line three']);
  });

  it('splits at space when no newline available', () => {
    const text = 'word1 word2 word3 word4';
    // maxLength 12 → "word1 word2 " lastIndexOf(' ', 12) = 11
    const result = splitMessage(text, 12);
    expect(result[0]).toBe('word1 word2');
    expect(result.length).toBeGreaterThanOrEqual(2);
  });

  it('hard-cuts when no whitespace available', () => {
    const text = 'abcdefghijklmnop';
    const result = splitMessage(text, 5);
    expect(result[0]).toBe('abcde');
    expect(result[1]).toBe('fghij');
    expect(result[2]).toBe('klmno');
    expect(result[3]).toBe('p');
  });

  it('produces multiple chunks for long text', () => {
    const text = 'chunk one\nchunk two\nchunk three\nchunk four';
    const result = splitMessage(text, 20);
    expect(result.length).toBeGreaterThan(1);
    // Every chunk respects the limit
    for (const chunk of result) {
      expect(chunk.length).toBeLessThanOrEqual(20);
    }
  });

  it('preserves all content (joined chunks equal original minus trimmed whitespace)', () => {
    const text = 'The quick brown fox jumps over the lazy dog. ' +
      'Pack my box with five dozen liquor jugs. ' +
      'How vexingly quick daft zebras jump.';
    const result = splitMessage(text, 30);

    // Reassemble: since trimStart() removes leading whitespace between chunks,
    // we verify all words are preserved
    const originalWords = text.split(/\s+/);
    const resultWords = result.join(' ').split(/\s+/);
    expect(resultWords).toEqual(originalWords);
  });

  it('prefers newline split over space split', () => {
    // Place newline at a good position and space later
    const text = 'first part\nsecond part of the message';
    // maxLength 15: lastIndexOf('\n', 15) = 10, which is >= 15/2 = 7.5 → splits at newline
    const result = splitMessage(text, 15);
    expect(result[0]).toBe('first part');
  });

  it('falls back to space when newline is too early', () => {
    // Newline at position 2, which is < maxLength/2 for maxLength=14
    const text = 'ab\ncdefghij klmnopqrst';
    // lastIndexOf('\n', 14) = 2, but 2 < 14/2=7 → falls back to space
    // lastIndexOf(' ', 14) = 11, which is >= 7 → splits at space
    const result = splitMessage(text, 14);
    expect(result[0]).toBe('ab\ncdefghij');
    expect(result[1]).toBe('klmnopqrst');
  });
});