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

namespace Developpez.Dotnet.Security
{
    /// <summary>
    /// Password
    /// </summary>
    public class Password
    {
        /// <summary>
        /// Value of the password
        /// </summary>
        public string Value { get; set; }

        /// <summary>
        /// Validate a password
        /// </summary>
        /// <param name="rule">Rule applying to the validation</param>
        public void Validate(PasswordSecurityRule rule)
        {
            rule.Validate(this);
        }
    }

    /// <summary>
    /// Password strategy
    /// </summary>
    public class PasswordSecurityRule
    {
        /// <summary>
        /// Minimal number of digits
        /// </summary>
        public int? MinNbDigits { get; set; }
        /// <summary>
        /// Minimal number of letters
        /// </summary>
        public int? MinNbLetters { get; set; }
        /// <summary>
        /// Minimal number of special characters
        /// </summary>
        public int? MinNbSpecialChars { get; set; }
        /// <summary>
        /// Minimal number of lowercase
        /// </summary>
        public int? MinNbLowerCase { get; set; }
        /// <summary>
        /// Minimal number of uppercase
        /// </summary>
        public int? MinNbUpperCase { get; set; }
        /// <summary>
        /// Minimal number of characters
        /// </summary>
        public int? MinTotalLength { get; set; }
        /// <summary>
        /// Maximal number of characters
        /// </summary>
        public int? MaxTotalLength { get; set; }

        /// <summary>
        /// Validate the rule
        /// </summary>
        internal void Validate(Password password)
        {
            var errors = new StringBuilder();

            // Digits
            if (MinNbDigits.IsApplicable() && password.Value.ToCharArray().Count(i => char.IsDigit(i)) < MinNbDigits)
                errors.AppendLine(string.Format("\t- Minimum {0} digits.", MinNbDigits));

            // Letters
            if (MinNbLetters.IsApplicable() && password.Value.ToCharArray().Count(i => char.IsLetter(i)) < MinNbLetters)
                errors.AppendLine(string.Format("\t- Minimum {0} letters.", MinNbLetters));

            // Special chars
            if (MinNbSpecialChars.IsApplicable() && password.Value.ToCharArray().Count(i => !char.IsLetterOrDigit(i)) < MinNbSpecialChars)
                errors.AppendLine(string.Format("\t- Minimum {0} special characters.", MinNbSpecialChars));

            // Lower case
            if (MinNbLowerCase.IsApplicable() && password.Value.ToCharArray().Count(i => char.IsLower(i)) < MinNbLowerCase)
                errors.AppendLine(string.Format("\t- Minimum {0} lowercase characters.", MinNbLowerCase));

            // Upper case
            if (MinNbUpperCase.IsApplicable() && password.Value.ToCharArray().Count(i => char.IsUpper(i)) < MinNbUpperCase)
                errors.AppendLine(string.Format("\t- Minimum {0} uppercase characters.", MinNbUpperCase));

            // Min length
            if (MinTotalLength.IsApplicable() && password.Value.Length < MinTotalLength)
                errors.AppendLine(string.Format("\t- The length must be minimum {0}.", MinTotalLength));

            // Max length
            if (MaxTotalLength.IsApplicable() && password.Value.Length > MaxTotalLength)
                errors.AppendLine(string.Format("\t- The length must be maximum {0}.", MaxTotalLength));

            if (errors.Length > 0)
            {
                errors.Insert(0, "Your password is not valid, please corect the following:");
                throw new PasswordValidationException(errors.ToString());
            }
        }
    }

    /// <summary>
    /// Extensions for password strategy
    /// </summary>
    internal static class PasswordRuleExtensions
    {
        /// <summary>
        /// Check if the parameter is applicable to the rule
        /// </summary>
        public static bool IsApplicable(this int? nb)
        {
            if (nb == null) return false;
            if (nb == 0) return false;
            return true;
        }
    }

    /// <summary>
    /// Exception thrown by a password validation
    /// </summary>
    public class PasswordValidationException : Exception
    {
        /// <summary>
        /// Constructor for PasswordValidationException
        /// </summary>
        public PasswordValidationException(string exeption)
            : base(exeption)
        {
        }
    }
}