namespace System.ComponentModel.DataAnnotations {
    using System;
    using System.ComponentModel.DataAnnotations.Resources;
    using System.Text.RegularExpressions;
 
    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
    public sealed class PhoneAttribute : DataTypeAttribute {
        // see unit tests for examples
        private static Regex _regex = CreateRegEx();
        private const string _additionalPhoneNumberCharacters = "-.()";
 
        public PhoneAttribute()
            : base(DataType.PhoneNumber) {
            
            // DevDiv 468241: set DefaultErrorMessage not ErrorMessage, allowing user to set
            // ErrorMessageResourceType and ErrorMessageResourceName to use localized messages.
            DefaultErrorMessage = DataAnnotationsResources.PhoneAttribute_Invalid;
        }
 
        public override bool IsValid(object value) {
            if (value == null) {
                return true;
            }
 
            string valueAsString = value as string;
 
            // Use RegEx implementation if it has been created, otherwise use a non RegEx version.
            if (_regex != null) { 
                return valueAsString != null && _regex.Match(valueAsString).Length > 0;
            }
            else {
                if (valueAsString == null) {
                    return false;
                }
 
                valueAsString = valueAsString.Replace("+", string.Empty).TrimEnd();
                valueAsString = RemoveExtension(valueAsString);
 
                bool digitFound = false;
                foreach (char c in valueAsString) {
                    if (Char.IsDigit(c)) {
                        digitFound = true;
                        break;
                    }
                }
 
                if (!digitFound) {
                    return false;
                }
 
                foreach (char c in valueAsString)
                {
                    if (!(Char.IsDigit(c) 
                        || Char.IsWhiteSpace(c)
                        || _additionalPhoneNumberCharacters.IndexOf(c) != -1)) {
                        return false;
                    }
                }
                return true;
            }
        }
 
        private static Regex CreateRegEx() {
            // We only need to create the RegEx if this switch is enabled.
            if (AppSettings.DisableRegEx) {
                return null;
            }
 
            const string pattern = @"^(\+\s?)?((?<!\+.*)\(\+?\d+([\s\-\.]?\d+)?\)|\d+)([\s\-\.]?(\(\d+([\s\-\.]?\d+)?\)|\d+))*(\s?(x|ext\.?)\s?\d+)?$";
            const RegexOptions options = RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.ExplicitCapture;
            
            // Set explicit regex match timeout, sufficient enough for phone parsing
            // Unless the global REGEX_DEFAULT_MATCH_TIMEOUT is already set
            TimeSpan matchTimeout = TimeSpan.FromSeconds(2);
            
            try {
                if (AppDomain.CurrentDomain.GetData("REGEX_DEFAULT_MATCH_TIMEOUT") == null) {
                    return new Regex(pattern, options, matchTimeout);
                }
            }
            catch {
                // Fallback on error
            }
            
            // Legacy fallback (without explicit match timeout)
            return new Regex(pattern, options);
        }
 
        private static string RemoveExtension(string potentialPhoneNumber) {
            int lastIndexOfExtension = potentialPhoneNumber
                .LastIndexOf("ext.", StringComparison.InvariantCultureIgnoreCase);
            if (lastIndexOfExtension >= 0)  {
                string extension = potentialPhoneNumber.Substring(lastIndexOfExtension + 4);
                if (MatchesExtension(extension)) {
                    return potentialPhoneNumber.Substring(0, lastIndexOfExtension);
                }
            }
 
            lastIndexOfExtension = potentialPhoneNumber
                .LastIndexOf("ext", StringComparison.InvariantCultureIgnoreCase);
            if (lastIndexOfExtension >= 0) {
                string extension = potentialPhoneNumber.Substring(lastIndexOfExtension + 3);
                if (MatchesExtension(extension)) {
                    return potentialPhoneNumber.Substring(0, lastIndexOfExtension);
                }
            }
 
 
            lastIndexOfExtension = potentialPhoneNumber
                .LastIndexOf("x", StringComparison.InvariantCultureIgnoreCase);
            if (lastIndexOfExtension >= 0) {
                string extension = potentialPhoneNumber.Substring(lastIndexOfExtension + 1);
                if (MatchesExtension(extension)) {
                    return potentialPhoneNumber.Substring(0, lastIndexOfExtension);
                }
            }
 
            return potentialPhoneNumber;
        }
 
        private static bool MatchesExtension(string potentialExtension)  {
            potentialExtension = potentialExtension.TrimStart();
            if (potentialExtension.Length == 0) {
                return false;
            }
 
            foreach (char c in potentialExtension) {
                if (!Char.IsDigit(c)) {
                    return false;
                }
            }
 
            return true;
        }
    }
}