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

namespace MarkovGrams
{
	/// <summary>
	/// A collection of methods to generate various different types of n-grams.
	/// </summary>
	public static class NGrams
	{
		/// <summary>
		/// Generates a unique list of n-grams that the given list of words.
		/// </summary>
		/// <param name="words">The words to turn into n-grams.</param>
		/// <param name="order">The order of n-gram to generate..</param>
		/// <returns>A unique list of n-grams found in the given list of words.</returns>
		public static IEnumerable<string> GenerateFlat(IEnumerable<string> words, int order)
		{
			List<string> results = new List<string>();
			foreach(string word in words)
			{
				results.AddRange(GenerateFlat(word, order));
			}
			return results.Distinct();
		}

		/// <summary>
		/// Generates a unique list of n-grams from the given string.
		/// </summary>
		/// <param name="str">The string to n-gram-ise.</param>
		/// <param name="order">The order of n-gram to generate.</param>
		/// <returns>A unique list of n-grams found in the specified string.</returns>
		public static IEnumerable<string> GenerateFlat(string str, int order)
		{
			List<string> results = new List<string>();
			for(int i = 0; i < str.Length - order; i++)
			{
				results.Add(str.Substring(i, order));
			}
			return results.Distinct();
		}

		/// <summary>
		/// Generates a dictionary of weighted n-grams from the given list of words.
		/// The key is the ngram itself, and the value is the linear weight of the ngram.
		/// </summary>
		/// <param name="words">The words to n-gram-ise.</param>
		/// <param name="order">The order of ngrams to generate.</param>
		/// <returns>The weighted dictionary of ngrams.</returns>
		public static Dictionary<string, int> GenerateWeighted(IEnumerable<string> words, int order)
		{
			Dictionary<string, int> results = new Dictionary<string, int>();
			foreach(string word in words)
			{
				Dictionary<string, int> wordNgrams = GenerateWeighted(word, order);
				foreach(KeyValuePair<string, int> ngram in wordNgrams)
				{
					if(!results.ContainsKey(ngram.Key))
						results[ngram.Key] = 0;
					results[ngram.Key] += ngram.Value;
				}
			}
			return results;
		}
		/// <summary>
		/// Generates a dictionary of weighted n-grams from the specified string.
		/// </summary>
		/// <param name="str">The string to n-gram-ise.</param>
		/// <param name="order">The order of n-grams to generate.</param>
		/// <returns>The weighted dictionary of ngrams.</returns>
		public static Dictionary<string, int> GenerateWeighted(string str, int order)
		{
			Dictionary<string, int> results = new Dictionary<string, int>();
			for(int i = 0; i < str.Length - order; i++)
			{
				string ngram = str.Substring(i, order);
				if(!results.ContainsKey(ngram))
					results[ngram] = 0;
				results[ngram]++;
			}
			return results;
		}
	}
}