using System;
using System.Collections.Generic;
using System.Data.Entity.Design.PluralizationServices;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;

/// <summary>
/// Contains <see cref="String"/> extension methods.
/// </summary>
public static class StringExtensions
{
    private static Regex titleRegEx;

    /// <summary>
    /// Initializes the <see cref="StringExtensions"/> class.
    /// </summary>
    static StringExtensions()
    {
        titleRegEx = new Regex(@"
                (?<=[A-Z])(?=[A-Z][a-z]) |
                 (?<=[^A-Z])(?=[A-Z]) |
                 (?<=[A-Za-z])(?=[^A-Za-z])", RegexOptions.IgnorePatternWhitespace);
    }

    /// <summary>
    /// Converts the object to string. If the object is null, will return null.
    /// </summary>
    /// <param name="obj">The object.</param>
    /// <returns></returns>
    public static String ToStringSafe(this object obj)
    {
        return obj != null ? obj.ToString() : String.Empty;
    }

    /// <summary>
    /// Splits the string to lines.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static List<String> ToLines(this String str)
    {
        //return str.Split(new[] { '\r', '\n' }).ToList();
        if (str == null) return new List<string>();
        return str.Split(new[] { "\r\n", "\r", "\n" }, StringSplitOptions.None).ToList();
    }

    /// <summary>
    /// Formats the string as title style.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static String ToTitle(this String str)
    {
        return titleRegEx.Replace(str, " ");
    }

    /// <summary>
    ///  Formats the string as title case.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static String ToTitleCase(this String str)
    {
        return Thread.CurrentThread.CurrentCulture.TextInfo.ToTitleCase(str.ToLower());
    }

    /// <summary>
    /// Converts the specified database conventional name to the observables conventional name.
    /// </summary>
    /// <param name="dalName">DAL name.</param>
    /// <returns></returns>
    public static String FromDalNameToTitleCase(this String dalName)
    {
        return String.Join("", dalName.Split('_').Select(x => ToTitleCase(x)));
    }

    /// <summary>
    /// Singularizes the string.
    /// </summary>
    /// <param name="text">The text.</param>
    /// <returns></returns>
    public static String SingularizeMVC(this String text)
    {
        var serv = PluralizationService.CreateService(new System.Globalization.CultureInfo("en-us"));
        return serv.Singularize(text);
    }

    /// <summary>
    /// Pluralizes the string.
    /// </summary>
    /// <param name="text">The text.</param>
    /// <returns></returns>
    public static String PluralizeMVC(this String text)
    {
        var serv = PluralizationService.CreateService(new System.Globalization.CultureInfo("en-us"));
        return serv.Pluralize(text);
    }

    /// <summary>
    /// Truncates the specified string to the specified max length and appends ellipsis.
    /// </summary>
    /// <param name="text">The text.</param>
    /// <param name="maxLength">Max length</param>
    /// <returns></returns>
    public static String Ellipsis(this String text, int maxLength)
    {
        return text.Length <= maxLength ? text : text.Substring(0, maxLength) + "...";
    }

    /// <summary>
    /// Converts the string to camel case string.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static String ToCamelCase(this String str)
    {
        if (String.IsNullOrEmpty(str) || Char.IsLower(str, 0))
            return str;

        return Char.ToLowerInvariant(str[0]) + str.Substring(1);
    }

    /// <summary>
    /// Compares the two strings based on letter pair matches
    /// </summary>
    /// <param name="str1"></param>
    /// <param name="str2"></param>
    /// <returns>The percentage match from 0.0 to 1.0 where 1.0 is 100%</returns>
    public static double CompareSimilarity(this string str1, string str2)
    {
        List<string> pairs1 = WordLetterPairs(str1.ToUpper());
        List<string> pairs2 = WordLetterPairs(str2.ToUpper());

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

        for (int i = 0; i < pairs1.Count; i++)
        {
            for (int j = 0; j < pairs2.Count; j++)
            {
                if (pairs1[i] == pairs2[j])
                {
                    intersection++;
                    pairs2.RemoveAt(j);//Must remove the match to prevent "GGGG" from appearing to match "GG" with 100% success

                    break;
                }
            }
        }

        return (2.0 * intersection) / union;
    }

    /// <summary>
    /// Gets all letter pairs for each
    /// individual word in the string
    /// </summary>
    /// <param name="str"></param>
    /// <returns></returns>
    private static List<string> WordLetterPairs(string str)
    {
        List<string> AllPairs = new List<string>();

        // Tokenize the string and put the tokens/words into an array
        string[] Words = Regex.Split(str, @"\s");

        // For each word
        for (int w = 0; w < Words.Length; w++)
        {
            if (!string.IsNullOrEmpty(Words[w]))
            {
                // Find the pairs of characters
                String[] PairsInWord = LetterPairs(Words[w]);

                for (int p = 0; p < PairsInWord.Length; p++)
                {
                    AllPairs.Add(PairsInWord[p]);
                }
            }
        }

        return AllPairs;
    }

    /// <summary>
    /// Generates an array containing every 
    /// two consecutive letters in the input 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;
    }

    /// <summary>
    /// Splits the camel case sentence to words.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static string ToWords(this string str)
    {
        return Regex.Replace(
            Regex.Replace(
                str,
                @"(\P{Ll})(\P{Ll}\p{Ll})",
                "$1 $2"
            ),
            @"(\p{Ll})(\P{Ll})",
            "$1 $2"
        );
    }

    /// <summary>
    /// Removes any invalid file name characters from the string.
    /// </summary>
    /// <param name="str">The string.</param>
    /// <returns></returns>
    public static string ToValidFileName(this string str)
    {
        char[] _invalidChars = System.IO.Path.GetInvalidFileNameChars();

        String validFileName = str;

        if (validFileName != null)
        {
            foreach (var c in _invalidChars)
            {
                validFileName = validFileName.Replace(c.ToString(), "");
            }
        }

        return validFileName;
    }

    public static String ToStringOrEmpty(this String str)
    {
        return str != null ? str : String.Empty;
    }

    public static String ToNullIfEmpty(this String str)
    {
        return String.IsNullOrEmpty(str) ? null : str;
    }

    public static bool IsNotNullOrEmpty(this String str)
    {
        return !String.IsNullOrWhiteSpace(str);
    }

    public static String ToOneLine(this String str)
    {
        return str.Replace(Environment.NewLine, " ");
    }

    public static List<T> ToEnumValues<T>(this String str, char splitChar) where T : struct
    {
        if (!String.IsNullOrWhiteSpace(str))
        {
            return str.Split(splitChar).Select(x => (T)(object)int.Parse(x)).ToList();
        }
        else
        {
            return new List<T>();
        }
    }

    public static IEnumerable<int> AllIndexesOf(this string str, string searchstring)
    {
        int minIndex = str.IndexOf(searchstring);
        while (minIndex != -1)
        {
            yield return minIndex;
            minIndex = str.IndexOf(searchstring, minIndex + searchstring.Length);
        }
    }
}