using System.Collections.Generic;

namespace TextAnalysis
{
    static class FrequencyAnalysisTask
    {
        public static void GetBigrams(List<List<string>> text, Dictionary<string, Dictionary<string, int>> result)
        {
            foreach (var words in text)
            {
                for (int i = 0; i < words.Count - 1; i++)
                {
                    if (!result.ContainsKey(words[i]))
                        result.Add(words[i], new Dictionary<string, int>());
                    if (!result[words[i]].ContainsKey(words[i + 1]))
                        result[words[i]].Add(words[i + 1], 1);
                    else
                        result[words[i]][words[i + 1]]++;
                }
            }
        }

        public static void GetTrigrams(List<List<string>> text, Dictionary<string, Dictionary<string, int>> result)
        {
            foreach (var words in text)
            {
                for (int i = 0; i < words.Count - 2; i++)
                {
                    if (!result.ContainsKey(words[i] + " " + words[i + 1]))
                        result.Add(words[i] + " " + words[i + 1], new Dictionary<string, int>());
                    if (!result[words[i] + " " + words[i + 1]].ContainsKey(words[i + 2]))
                        result[words[i] + " " + words[i + 1]].Add(words[i + 2], 1);
                    else
                        result[words[i] + " " + words[i + 1]][words[i + 2]]++;
                }
            }
        }

        public static Dictionary<string, string> GetMostFrequentNextWords(List<List<string>> text)
        {
            var result = new Dictionary<string, Dictionary<string, int>>();
            var total = new Dictionary<string, string>();

            GetBigrams(text, result);
            GetTrigrams(text, result);
            return FrequencyDetermination(result, total);
        }

        private static Dictionary<string, string> FrequencyDetermination
            (Dictionary<string, Dictionary<string, int>> result, Dictionary<string, string> total)
        {
            foreach (var key in result.Keys)
            {
                string mostFrequentWord = null;
                int maxCount = 0;

                foreach (var innerKey in result[key])
                {
                    if (innerKey.Value > maxCount || innerKey.Value == maxCount &&
                             string.CompareOrdinal(innerKey.Key, mostFrequentWord) < 0)
                    {
                        maxCount = innerKey.Value;
                        mostFrequentWord = innerKey.Key;
                    }
                }
                total.Add(key, mostFrequentWord);
            }
            return total;
        }
    }
}