using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;

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

public partial class UserDefinedFunctions
{
    /// <summary>
    /// Calculates a similarity ranking value for the two specified strings
    /// </summary>
    /// <returns></returns>
    [Microsoft.SqlServer.Server.SqlFunction]
    public static SqlDouble SimilarityRank(string strValue1, string strValue2)
    {
        IList<string> pairs1 = WordLetterPairs(strValue1);
        IList<string> pairs2 = WordLetterPairs(strValue2);

        int intersection = 0;
        int union = pairs1.Count + pairs2.Count;

        foreach(string pair1 in pairs1){
            for (int j = 0; j < pairs2.Count; j++)
            {
                string pair2 = pairs2[j];
                if (pair1.Equals(pair2))
                {
                    intersection++;
                    pairs2.RemoveAt(j);
                    break;
                }
            }
        }

        return new SqlDouble((2.0 * intersection) / union);
    }

    /// <summary>
    /// Splits the input into "words" and collects all character pairs
    /// </summary>
    /// <param name="str"></param>
    /// <returns></returns>
    private static IList<string> WordLetterPairs(string str)
    {
        List<string> allPairs = new List<string>();
        // Tokenize the string and put the tokens/words into an array 
        string[] words = str.Split(' ', '\n', '\t');
        // For each word
        foreach (string word in words)
            foreach (string pairInWord in LetterPairs(word))
                allPairs.Add(pairInWord);

        return allPairs;
    }

    /// <summary>
    /// Retrieves all the character pairs in the given string
    /// </summary>
    /// <param name="str"></param>
    /// <returns></returns>
    private static string[] LetterPairs(string str)
    {
        int numPairs = str.Length - 1;
        string[] pairs = new string[numPairs];
        for (int i = 0; i < numPairs; i++)
        {
            pairs[i] = str.Substring(i, 2);
        }
        return pairs;
    }
};