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

namespace TextAnalysis
{
    static class SentencesParserTask
    {
        public static List<List<string>> ParseSentences(string text)
        {
            var listOfSentences = new List<List<string>>();
            if (text == null) return null;
            text = text.ToLower();
            string[] sentences = text.Split('.', '!', '?', ';', ':', '(', ')');
            foreach (var sentence in sentences)
            {
                if (sentence.Length > 0)
                {
                    var words = ParseToList(sentence);
                    if (words.Count > 0) listOfSentences.Add(words);
                }
            }
            return listOfSentences;
        }

        public static List<string> ParseToList(string sentence)
        {
            var word = new List<string>();
            string temp = "";
            string tempSentence = sentence + " ";
            for (int i = 0; i < tempSentence.Length; i++)
                if (char.IsLetter(tempSentence[i]) || tempSentence[i] == '\'')
                    temp += tempSentence[i];
                else
                    if (temp.Length > 0)
                {
                    word.Add(temp);
                    temp = "";
                }

            return word;
        }
    }
}