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

namespace TextAnalysis
{
    static class FrequencyAnalysisTask
    {
        public static Dictionary<string, string> GetMostFrequentNextWords(List<List<string>> text)
        {
            var temp = new List<Tuple<string, string>>();

            foreach (var sentence in text)
            {
                if (sentence.Count == 2)
                {
                    temp.Add(Tuple.Create(sentence[0], sentence[1]));
                }
                else
                {
                    for (int i = 0; i < sentence.Count - 2; i++)
                    {
                        var ngrams = sentence.Skip(i).Take(3).ToArray();
                        temp.Add(Tuple.Create(ngrams[0], ngrams[1]));
                        temp.Add(Tuple.Create(string.Join(" ", ngrams.Take(2)), ngrams[2]));
                        if (i == sentence.Count - 3) temp.Add(Tuple.Create(ngrams[1], ngrams[2]));
                    }
                }
            }
            var result = temp.GroupBy(tuple => tuple.Item1)
                .Select(tuple => new
                {
                    tuple.Key,
                    Value = tuple.Select(item => item.Item2)
                    .GroupBy(x => x).ToList().
                    Select(y => new { y.Key, Count = y.Count() })
                .OrderByDescending(x => x.Count)
                .ThenBy(x => x.Key,StringComparer.Ordinal)
                .Select(p => p.Key)
                .First()
                }).ToDictionary(x => x.Key, x => x.Value);

            return result;
        }
   }
}