using System;

namespace DA_Assets.Extensions
{
    public static class Levenshtein
    {
        /// <summary>
        /// Calculate percentage similarity of two strings
        /// <param name="source">Source String to Compare with</param>
        /// <param name="target">Targeted String to Compare</param>
        /// <returns>Return Similarity between two strings from 0 to 1.0</returns>
        /// <para><see cref="https://stackoverflow.com/a/2344347"/></para>
        /// </summary>
        public static float CalculateSimilarity(this string source, string target)
        {
            if ((source == null) || (target == null)) return 0.0f;
            if ((source.Length == 0) || (target.Length == 0)) return 0.0f;
            if (source == target) return 1.0f;

            int stepsToSame = ComputeLevenshteinDistance(source, target);
            return (1.0f - (stepsToSame / (float)Math.Max(source.Length, target.Length)));
        }

        /// <summary>
        /// Returns the number of steps required to transform the source string
        /// into the target string.
        /// </summary>
        private static int ComputeLevenshteinDistance(string source, string target)
        {
            if ((source == null) || (target == null)) return 0;
            if ((source.Length == 0) || (target.Length == 0)) return 0;
            if (source == target) return source.Length;

            int sourceWordCount = source.Length;
            int targetWordCount = target.Length;

            // Step 1
            if (sourceWordCount == 0)
                return targetWordCount;

            if (targetWordCount == 0)
                return sourceWordCount;

            int[,] distance = new int[sourceWordCount + 1, targetWordCount + 1];

            // Step 2
            for (int i = 0; i <= sourceWordCount; distance[i, 0] = i++) ;
            for (int j = 0; j <= targetWordCount; distance[0, j] = j++) ;

            for (int i = 1; i <= sourceWordCount; i++)
            {
                for (int j = 1; j <= targetWordCount; j++)
                {
                    // Step 3
                    int cost = (target[j - 1] == source[i - 1]) ? 0 : 1;

                    // Step 4
                    distance[i, j] = Math.Min(Math.Min(distance[i - 1, j] + 1, distance[i, j - 1] + 1), distance[i - 1, j - 1] + cost);
                }
            }

            return distance[sourceWordCount, targetWordCount];
        }
    }
}