using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Globalization;
using System.Text.RegularExpressions;

namespace StringExtensions
{
    public static class StringExtensions
    {
        /// <summary>
        /// Remove any non-numeric characters and then return the resultant string.
        /// Useful for parsing phone numbers.
        /// </summary>
        /// <param name="s">The text that is to be evaluated.</param>
        /// <returns>New string</returns>                 
        public static string RemoveNonNumeric(this string s)
        {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < s.Length; i++)
                if (Char.IsNumber(s[i]))
                    sb.Append(s[i]);
            return sb.ToString();
        }

        /// <summary>
        /// Returns the substring of the first argument string that follows the first occurrence
        /// of the second argument string in the first argument string, or the empty
        /// string if the first argument string does not contain the second argument string.
        /// </summary>
        /// <param name="source">The text that is to be evaluated.</param>
        /// <param name="value">String to search.</param>
        /// <returns>New string</returns>
        public static string SubstringAfter(this string source, string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                return source;
            }
            CompareInfo compareInfo = CultureInfo.InvariantCulture.CompareInfo;
            int index = compareInfo.IndexOf(source, value, CompareOptions.Ordinal);
            if (index < 0)
            {
                //No such substring
                return string.Empty;
            }
            return source.Substring(index + value.Length);
        }

        /// <summary>
        /// Returns the substring of the first argument string that precedes the first occurrence of
        /// the second argument string in the first argument string, or the empty string if
        /// the first argument string does not contain the second argument string.
        /// </summary>
        /// <param name="source">The text that is to be evaluated.</param>
        /// <param name="value">String to search.</param>
        /// <returns>New string</returns>
        public static string SubstringBefore(this string source, string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                return value;
            }
            CompareInfo compareInfo = CultureInfo.InvariantCulture.CompareInfo;
            int index = compareInfo.IndexOf(source, value, CompareOptions.Ordinal);
            if (index < 0)
            {
                //No such substring
                return string.Empty;
            }
            return source.Substring(0, index);
        }

        /// <summary>
        /// Truncate string using dots...
        /// Useful for displaying long filename paths.
        /// </summary>
        /// <param name="s">String to be truncated.</param>
        /// <param name="maxLength">Maximum string size</param>
        /// <returns>New string</returns>
        public static string Truncate(this string s, int maxLength)
        {
            if (string.IsNullOrEmpty(s) || maxLength <= 0)
                return string.Empty;
            else if (s.Length > maxLength)
                return s.Substring(0, maxLength) + "...";
            else
                return s;
        }

        /// <summary>
        /// Reverse string.
        /// </summary>
        /// <param name="s">String to be reversed.</param>
        /// <returns>Reversed string.</returns>
        public static string Reverse(this string s)
        {
            char[] c = s.ToCharArray();
            Array.Reverse(c);
            return new string(c);
        }

        /// <summary>
        /// Test if string contains only numbers.       
        /// </summary>
        /// <param name="text">The text that is to be evaluated.</param>
        /// <returns>True if text included only letters.</returns>
        public static bool IsAlpha(this string text) 
        {           
            foreach (char c in text.ToLower()) 
            { 
                if (!char.IsLetter(c))
                    return false; 
            } 
            return true; 
        }

        /// <summary>
        /// Check is string is valid email address.
        /// </summary>
        /// <param name="email">Email to be checked.</param>
        /// <returns>True if email address was ok.</returns>       
        public static bool IsValidEmailAddress(this string email)
         {             
             const string REGEX_VALID_EMAIL =
                 @"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|" +
                 @"(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$";
             bool valid = Regex.IsMatch(email, REGEX_VALID_EMAIL);
             return valid;
         }

        /// <summary>
        /// Convert string to integer.
        /// </summary>
        /// <param name="s">String to be processed.</param>
        /// <returns>Integer</returns>
        public static int ToInteger(this string s)
        {
            int integerValue = 0;
            int.TryParse(s, out integerValue);
            return integerValue;
        }

        /// <summary>
        /// Compare two strings, ignore case.
        /// </summary>
        /// <param name="s1">String </param>
        /// <param name="s2">String 2</param>
        /// <returns>If equal return true.</returns>
        public static bool Comparei(this string s1, string s2)
        {
            CompareInfo Compare = CultureInfo.InvariantCulture.CompareInfo;
            int i = Compare.IndexOf(s1, s2, CompareOptions.IgnoreCase);
            if (i != 0 )
                return true;
            else
                return false;
        }
    }
}