using System;
using System.Security.Cryptography;
using System.Text;
using System.Xml.Linq;

namespace Neo.Afx.Security
{
    /// <summary>
    /// Groups some password security methods.
    /// </summary>
    public static class SecurePassword
    {
        #region Hash(string password)

        /// <summary>
        /// Uses the SHA1 algorithm to produce a hash of the given password. 
        /// </summary>
        /// <param name="password">The password to be hashed.</param>
        /// <returns>The SHA1 hash of the password.</returns>
        public static string Hash(string password)
        {
            HashAlgorithm algorithm = new SHA1Managed();
            return Convert.ToBase64String(algorithm.ComputeHash(Encoding.UTF8.GetBytes(password)));
        }

        #endregion

        #region Hash(string password, string salt)

        /// <summary>
        /// Creates a salted hash of the given value.
        /// </summary>
        /// <param name="password">The password to be hashed.</param>
        /// <param name="salt">The salt to be applied.</param>
        /// <returns>A salted hash of the given value.</returns>
        public static string Hash(string password, string salt)
        {
            return Hash(String.Concat(password, salt));
        }

        #endregion

        #region CreateSalt

        /// <summary>
        /// Creates a random salt value of size 7.
        /// </summary>
        /// <returns>A random salt value.</returns>
        public static string CreateSalt()
        {
            return CreateSalt(7);
        }

        /// <summary>
        /// Creates a random salt value.
        /// </summary>
        /// <param name="size">The size of the salt value.</param>
        /// <returns>A random salt value.</returns>
        public static string CreateSalt(int size)
        {
            // Generate a cryptographic random number
            var rng = new RNGCryptoServiceProvider();
            var buff = new byte[size];
            rng.GetBytes(buff);

            // Return a Base64 string representation of the random number
            return Convert.ToBase64String(buff);
        }

        #endregion

        #region Obfuscate(string password, string salt, string challenge)

        /// <summary>
        /// Obfuscates the specified password using the given salt and challenge values.
        /// </summary>
        /// <param name="password">The password to be obfuscated.</param>
        /// <param name="salt">The salt value to be used.</param>
        /// <param name="challenge">The challenge value to be used.</param>
        /// <returns>An obfuscated password.</returns>
        public static string Obfuscate(string password, string salt, string challenge)
        {
            string passwordHash = Hash(password, salt);
            return Hash(passwordHash, challenge);
        }

        #endregion

        #region CreateSecureCredentials

        /// <summary>
        /// Creates secure credentials from the given password and challenge token.
        /// </summary>
        /// <param name="challengeToken">The challenge token containing the salt and challenge values to be parsed.</param>
        /// <param name="password">The password to be secured.</param>
        /// <returns>The secure credentials.</returns>
        public static string CreateSecureCredentials(XElement challengeToken, string password)
        {
            var salt = challengeToken.Attribute("Salt");
            var challenge = challengeToken.Attribute("Challenge");

            if(salt == null || challenge == null)
            {
                return null;
            }

            var passwordHash = Hash(password);
            return Obfuscate(passwordHash, salt.Value, challenge.Value);
        }

        #endregion
    }
}