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

namespace TextAnalysis
{
    static class FrequencyAnalysisTask
    {
        public static Dictionary<string, string> GetMostFrequentNextWords(List<List<string>> text)
        {
            var result = new Dictionary<string, string>();
            return SetBigram(text).Concat(SetTrigram(text)).ToDictionary(x => x.Key, x => x.Value);
        }
        public static Dictionary<string, string> SetBigram(List<List<string>> text)
        {
            var bigramFrequency = new Dictionary<string, Dictionary<string, int>>();
            var fistWord = new StringBuilder();
            var bigramEnding = new StringBuilder();
            foreach (var sentence in text)
            {
                if (sentence.Count > 1)
                    for (int i = 0; i < sentence.Count - 1; i++)
                    {
                        fistWord.Clear().Append(sentence[i]);
                        bigramEnding.Clear().Append(sentence[i + 1]);
                        if (!bigramFrequency.ContainsKey(sentence[i]))
                            bigramFrequency[fistWord.ToString()] = new Dictionary<string, int>();
                        if (!bigramFrequency[fistWord.ToString()].ContainsKey(bigramEnding.ToString()))
                            bigramFrequency[fistWord.ToString()][bigramEnding.ToString()] = 0;
                        bigramFrequency[fistWord.ToString()][bigramEnding.ToString()]++;
                    }
            }
            return MakeNgramDictionary(bigramFrequency);
        }

        public static Dictionary<string, string> SetTrigram(List<List<string>> text)
        {
            var trigramFrequency = new Dictionary<string, Dictionary<string, int>>();
            var bigram = new StringBuilder();
            var trigramEnding = new StringBuilder();
            foreach (var sentence in text)
            {
                if (sentence.Count > 2)
                    for (int i = 0; i < sentence.Count - 2; i++)
                    {
                        bigram.Clear().Append(sentence[i] + " " + sentence[i + 1]);
                        trigramEnding.Clear().Append(sentence[i + 2]);
                        if (!trigramFrequency.ContainsKey(bigram.ToString()))
                            trigramFrequency[bigram.ToString()] = new Dictionary<string, int>();
                        if (!trigramFrequency[bigram.ToString()].ContainsKey(sentence[i + 2]))
                            trigramFrequency[bigram.ToString()][trigramEnding.ToString()] = 0;
                        trigramFrequency[bigram.ToString()][trigramEnding.ToString()]++;
                    }
            }
            return MakeNgramDictionary(trigramFrequency);
        }
        private static Dictionary<string, string> MakeNgramDictionary(
Dictionary<string, Dictionary<string, int>> ngramFrequency)
        {
            var ngramDictionary = new Dictionary<string, string>();
            var maxFrequency = 0;
            var ngramEnding = new StringBuilder();
            foreach (var ngram in ngramFrequency)
            {
                foreach (var ngramEndingFrequency in ngram.Value)
                {
                    if (ngramEndingFrequency.Value == maxFrequency &&
                    string.CompareOrdinal(ngramEndingFrequency.Key, ngramEnding.ToString()) < 0)
                        ngramEnding.Clear().Append(ngramEndingFrequency.Key);
                    if (ngramEndingFrequency.Value > maxFrequency)
                    {
                        maxFrequency = ngramEndingFrequency.Value;
                        ngramEnding.Clear().Append(ngramEndingFrequency.Key);
                    }
                }
                ngramDictionary.Add(ngram.Key, ngramEnding.ToString());
                ngramEnding.Clear();
                maxFrequency = 0;
            }
            return ngramDictionary;
        }
    }
}