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

namespace TextAnalysis
{
    static class SentencesParserTask
    {
        public static List<List<string>> ParseSentences(string text)
        {
            var sentencesList = SplitToSentences(text.ToLower());
            var result = new List<List<string>>();
            foreach (var senetence in sentencesList)
            {
                var words = SplitToWords(senetence);
                if (words.Count > 0)
                {
                    result.Add(SplitToWords(senetence));
                }
            }
            return result;
        }

        private static List<string> SplitToSentences(string text)
        {
            var delimiters = ".!?;:()";
            var result = new List<string>();
            var builder = new StringBuilder();
            foreach (var ch in text)
            {
                if (!delimiters.Contains(ch))
                {
                    builder.Append(ch);
                }
                else if (builder.Length != 0)
                {
                    result.Add(builder.ToString());
                    builder = new StringBuilder();
                }
            }
            if (builder.Length != 0)
            {
                result.Add(builder.ToString());
            }
            return result;
        }

        private static List<string> SplitToWords(string text)
        {
            var result = new List<string>();
            var builder = new StringBuilder();
            foreach (var ch in text)
            {
                if (char.IsLetter(ch) || ch == '\'')
                {
                    builder.Append(ch);
                }
                else if (builder.Length != 0)
                {
                    result.Add(builder.ToString());
                    builder = new StringBuilder();
                }
            }
            if (builder.Length != 0)
            {
                result.Add(builder.ToString());
            }
            return result;
        }
    }
}