using System.Collections.Generic;

namespace TextAnalysis
{
    static class FrequencyAnalysisTask
    {
        public static void GramCountDictionary(
            List<string> sentence,
            int n,
            Dictionary<string, Dictionary<string, int>> gramDictionary
            )
        {
            for (var i = 0; i < sentence.Count - n + 1; i++)
            {
                var firstHalfGram = n == 2 ? sentence[i] : sentence[i] + ' ' + sentence[i + 1];
                var secondHalfGram = n == 2 ? sentence[i + 1] : sentence[i + 2];
                if (!gramDictionary.ContainsKey(firstHalfGram))
                {
                    gramDictionary.Add(firstHalfGram, new Dictionary<string, int>());
                }
                if (gramDictionary[firstHalfGram].ContainsKey(secondHalfGram))
                {
                    gramDictionary[firstHalfGram][secondHalfGram]++;
                }
                else
                {
                    gramDictionary[firstHalfGram][secondHalfGram] = 1;
                }
            }
        }

        public static void AddMaxFrequentGramInResult(
            Dictionary<string, Dictionary<string, int>> gramDictionary,
            Dictionary<string, string> result
            )
        {
            foreach (var firstHalfGram in gramDictionary)
            {
                var firstHalfGramKey = firstHalfGram.Key;
                var maxCount = -1;
                var secondHalfMaxFrequentGramKey = "";
                foreach (var secondHalfGram in gramDictionary[firstHalfGramKey])
                {
                    if (secondHalfGram.Value > maxCount ||
                        secondHalfGram.Value == maxCount &&
                        string.CompareOrdinal(secondHalfGram.Key, secondHalfMaxFrequentGramKey) < 0
                        )
                    {
                        maxCount = secondHalfGram.Value;
                        secondHalfMaxFrequentGramKey = secondHalfGram.Key;
                    }
                }
                result.Add(firstHalfGramKey, secondHalfMaxFrequentGramKey);
            }
        }

        public static Dictionary<string, string> GetMostFrequentNextWords(List<List<string>> text)
        {
            var result = new Dictionary<string, string>();
            var twoGramDictionary = new Dictionary<string, Dictionary<string, int>>();
            var threeGramDictionary = new Dictionary<string, Dictionary<string, int>>();
            foreach (var sentence in text)
            {
                GramCountDictionary(sentence, 2, twoGramDictionary);
                GramCountDictionary(sentence, 3, threeGramDictionary);
            }
            AddMaxFrequentGramInResult(twoGramDictionary, result);
            AddMaxFrequentGramInResult(threeGramDictionary, result);
            return result;
        }
    }
}