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

namespace JD.Kernel.Structs
{
    /// <summary>
    /// Encapsulate a flag enum and contains helper functions to manipulate it.
    /// </summary>
    public struct Flags<T> : IEquatable<T>
        where T : IComparable, IFormattable
    {
        #region Variables

        private T m_value;

        #endregion

        #region Constructor

        static Flags()
        {
            Type type = typeof (T);

            if (!type.IsEnum)
            {
                throw new InvalidCastException($"The flags type cannot be used with the non enum type {typeof(T).Name}");
            }
            
            if (!type.IsDefined(typeof(FlagsAttribute), true))
            {
                throw new InvalidCastException($"The enum type {typeof(T).Name} should be decorated with the flags attribute. Consider using a BitArray");
            }
            
            if (Enum.GetUnderlyingType(type) != typeof(int))
            {
                throw new NotSupportedException("Flags class only support int enums.");
            }
        }

        public Flags(T value)
        {
            m_value = value;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Returns the actual wrapped value.
        /// </summary>
        public T Value
        {
            get { return m_value; }
        }

        private int IntValue
        {
            get { return ToInt(m_value); }
        }

        /// <summary>
        /// Gets/Sets the value of the given flagKey.
        /// </summary>
        /// <param name="flagKey">Flag to access.</param>
        /// <returns>The value of the flag.</returns>
        public bool this[T flagKey]
        {
            get { return Contains(flagKey); }
            set
            {
                if (value)
                {
                    Add(flagKey);
                }
                else
                {
                    Remove(flagKey);
                }
            }
        }

        #endregion

        #region Functions

        private static int ToInt(T value)
        {
            return (int)(object)value;
        }

        /// <summary>
        /// Removes the given flag from the enum value.
        /// </summary>
        /// <param name="flag"></param>
        /// <returns>True if the flag has been removed.</returns>
        public bool Remove(T flag)
        {
            int value = IntValue;
            int flagToExtract = ToInt(flag);
            int newValue = value & ~flagToExtract;

            m_value = (T)(object)newValue;

            return value != newValue;
        }

        /// <summary>
        /// Adds the given flag to the internal value.
        /// </summary>
        /// <param name="flag"></param>
        /// <returns>True if the flag has been added. (false if it was already present)</returns>
        public bool Add(T flag)
        {
            int value = IntValue;
            int flagToAdd = ToInt(flag);
            int newValue = value | flagToAdd;

            m_value = (T)(object)newValue;

            return value != newValue;
        }

        /// <summary>
        /// True if the flag contains that given value.
        /// </summary>
        /// <param name="value">Value to test for</param>
        /// <returns>True if the flag contains that given value.</returns>
        public bool Contains(T value)
        {
            int flag = ToInt(value);
            return (IntValue & flag) == flag;
        }

        /// <summary>
        /// True if the flag contains EVERY values.
        /// </summary>
        /// <param name="value">First value to test for</param>
        /// <param name="otherValues">Additional values to test for.</param>
        /// <returns>True if the flag contains EVERY values.</returns>
        public bool Contains(T value, params T[] otherValues)
        {
            if (!Contains(value))
            {
                return false;
            }

            foreach (T t in otherValues)
            {
                if (!Contains(t))
                {
                    return false;
                }
            }

            return true;
        }

        /// <summary>
        /// True if any of the given values are contained in the flag.
        /// </summary>
        /// <param name="value">First value to test for</param>
        /// <param name="otherValues">Additional values to test for.</param>
        /// <returns>True if any of the given values are contained in the flag.</returns>
        public bool ContainsAny(T value, params T[] otherValues)
        {
            if (Contains(value))
            {
                return true;
            }

            foreach (T other in otherValues)
            {
                if (Contains(other))
                {
                    return true;
                }
            }

            return false;
        }

        /// <summary>
        /// True if the flag has any overlap with the given <paramref name="value"/>.
        /// </summary>
        /// <param name="value">Value to test for.</param>
        /// <returns>True if the flag has any overlap with the given <paramref name="value"/>.</returns>
        public bool Intersects(T value)
        {
            int flag = ToInt(value);
            return (IntValue & flag) != 0;
        }

        #endregion

        #region Comparison

        /// <summary>
        /// True if the enum equals our value.
        /// </summary>
        /// <param name="other"></param>
        /// <returns></returns>
        public bool Equals(T other)
        {
            return Equals(m_value, other);
        }

        /// <summary>
        /// True if the enum equals our value.
        /// </summary>
        public override bool Equals(object obj)
        {
            if (obj is Flags<T>)
            {
                return Equals(((Flags<T>)obj).m_value, m_value);
            }

            return Equals(m_value, obj);
        }

        /// <summary>
        /// Hashcode.
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
            return m_value.GetHashCode();
        }

        /// <summary>
        /// True if the flag value is any of the given values.
        /// </summary>
        /// <param name="first"></param>
        /// <param name="other"></param>
        /// <returns>True if the flag value is any of the given values.</returns>
        public bool EqualsAny(T first, params T[] other)
        {
            if (Equals(first))
            {
                return true;
            }

            return other.Any(Equals);
        }

        #endregion

        #region Operators

        /// <summary>
        /// == Operator.
        /// </summary>
        public static bool operator ==(Flags<T> a, Flags<T> b)
        {
            return Equals((T)a, (T)b);
        }

        /// <summary>
        /// != Operator.
        /// </summary>
        public static bool operator !=(Flags<T> a, Flags<T> b)
        {
            return !Equals((T)a, (T)b);
        }

        /// <summary>
        /// Implicit cast Operator.
        /// </summary>
        public static implicit operator T(Flags<T> value)
        {
            return value.m_value;
        }

        /// <summary>
        /// Implicit cast Operator.
        /// </summary>
        public static implicit operator Flags<T>(T value)
        {
            return new Flags<T>(value);
        }

        public static Flags<T> operator |(Flags<T> a, Flags<T> b)
        {
            a.Add(b);
            return a;
        }

        #endregion

        #region ToString

        /// <summary>
        /// Returns the display of the inner Value.
        /// </summary>
    
        public override string ToString()
        {
            return $"Flags '{m_value}'";
        }

        #endregion

        #region Utilities

        /// <summary>
        /// All the defined flags defined in the enum.
        /// </summary>
        public static IEnumerable<T> Values
        {
            get { return Enum.GetValues(typeof (T)).Cast<T>(); }
        }

        #endregion
    }
}