using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TextAnalysis
{
    internal static class SentencesParserTask
    {
        public static List<List<string>> ParseSentences(string text)
        {
            var sentences = text.Split('.', '!', '?', ';', ':', '(', ')');

            return sentences
                .Select(GetWordsInSentence)
                .Where(words => words.Count > 0)
                .ToList();
        }

        private static List<string> GetWordsInSentence(string sentence)
        {
            var words = new List<string>();
            var wordBuilder = new StringBuilder();
            sentence += ' '; // Для сброса в лист последнего слова
            foreach (var letter in sentence)
            {
                if (char.IsLetter(letter) || letter == '\'')
                    wordBuilder.Append(letter);
                else
                    DropWordToList(wordBuilder, words);
            }

            return words;
        }

        private static void DropWordToList(StringBuilder wordBuilder, List<string> words)
        {
            if (wordBuilder.Length > 0)
            {
                words.Add(wordBuilder.ToString().ToLower());
                wordBuilder.Clear();
            }
        }
    }
}