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

namespace TextAnalysis
{
    static class SentencesParserTask
    {
        public static List<List<string>> ParseSentences(string text)
        {
            var sentencesList = new List<List<string>>();
            var sentences = ParseSentence(text);

            foreach (var sentence in sentences)
            {
                if (sentence.Length != 0)
                {
                    sentencesList.Add(ParseWords(sentence));
                }
            }

            return sentencesList;
        }

        private static List<string> ParseWords(string sentence)
        {
            var wordsList = new List<string>();
            var sentenceBuilder = new StringBuilder();

            foreach (var symbol in sentence)
            {
                if (char.IsLetter(symbol) || symbol == '\'')
                {
                    sentenceBuilder.Append(char.ToLower(symbol));
                }
                else
                {
                    if (sentenceBuilder.Length == 0)
                    {
                        continue;
                    }

                    wordsList.Add(sentenceBuilder.ToString());
                    sentenceBuilder.Clear();
                }
            }

            return wordsList;
        }

        private static List<string> ParseSentence(string text)
        {
            var sentenceList = new List<string>();
            var sentenceArray = text.Split('.', '!', '?', ';', ':', '(', ')');

            foreach (var sentence in sentenceArray)
            {
                if (!string.IsNullOrEmpty(sentence))
                {
                    sentenceList.Add(sentence);
                }
            }

            return sentenceList;
        }
    }
}