#region Using

using System;

#endregion

namespace SharpCompress.Compressor.PPMd.I1
{
    /// <summary>
    /// A structure containing a single address representing a position in the <see cref="Memory"/> array.  This
    /// is intended to mimic the behaviour of a pointer in C/C++.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This must be a structure rather than a class because several places in the associated code assume that
    /// <see cref="Pointer"/> is a value type (meaning that assignment creates a completely new copy of the
    /// instance rather than just copying a reference to the same instance).
    /// </para>
    /// <para>
    /// Note that <see cref="Address"/> is a field rather than a property for performance reasons.
    /// </para>
    /// </remarks>
    internal struct Pointer
    {
        public uint Address;
        public byte[] Memory;
        public static readonly Pointer Zero = new Pointer(0, null);
        public const int Size = 1;

        /// <summary>
        /// Initializes a new instance of the <see cref="Pointer"/> structure.
        /// </summary>
        public Pointer(uint address, byte[] memory)
        {
            Address = address;
            Memory = memory;
        }

        /// <summary>
        /// Gets or sets the byte at the given <paramref name="offset"/>.
        /// </summary>
        /// <param name="offset"></param>
        /// <returns></returns>
        public byte this[int offset]
        {
            get
            {
                #if DEBUG
                if (Address == 0)
                    throw new InvalidOperationException("The pointer being indexed is a null pointer.");
                #endif
                return Memory[Address + offset];
            }
            set
            {
                #if DEBUG
                if (Address == 0)
                    throw new InvalidOperationException("The pointer being indexed is a null pointer.");
                #endif
                Memory[Address + offset] = value;
            }
        }

        /// <summary>
        /// Allow a <see cref="MemoryNode"/> to be implicitly converted to a <see cref="Pointer"/>.
        /// </summary>
        /// <param name="memoryNode"></param>
        /// <returns></returns>
        public static implicit operator Pointer(MemoryNode memoryNode)
        {
            return new Pointer(memoryNode.Address, memoryNode.Memory);
        }

        /// <summary>
        /// Allow a <see cref="Model.PpmContext"/> to be implicitly converted to a <see cref="Pointer"/>.
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        public static implicit operator Pointer(Model.PpmContext context)
        {
            return new Pointer(context.Address, context.Memory);
        }

        /// <summary>
        /// Allow a <see cref="PpmState"/> to be implicitly converted to a <see cref="Pointer"/>.
        /// </summary>
        /// <param name="state"></param>
        /// <returns></returns>
        public static implicit operator Pointer(PpmState state)
        {
            return new Pointer(state.Address, state.Memory);
        }

        /// <summary>
        /// Increase the address of a pointer by the given number of bytes.
        /// </summary>
        /// <param name="pointer"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        public static Pointer operator +(Pointer pointer, int offset)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer is a null pointer.");
            #endif
            pointer.Address = (uint) (pointer.Address + offset);
            return pointer;
        }

        /// <summary>
        /// Increase the address of a pointer by the given number of bytes.
        /// </summary>
        /// <param name="pointer"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        public static Pointer operator +(Pointer pointer, uint offset)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer is a null pointer.");
            #endif
            pointer.Address += offset;
            return pointer;
        }

        /// <summary>
        /// Increment the address of a pointer.
        /// </summary>
        /// <param name="pointer"></param>
        /// <returns></returns>
        public static Pointer operator ++(Pointer pointer)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer being incremented is a null pointer.");
            #endif
            pointer.Address++;
            return pointer;
        }

        /// <summary>
        /// Decrease the address of a pointer by the given number of bytes.
        /// </summary>
        /// <param name="pointer"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        public static Pointer operator -(Pointer pointer, int offset)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer is a null pointer.");
            #endif
            pointer.Address = (uint) (pointer.Address - offset);
            return pointer;
        }

        /// <summary>
        /// Decrease the address of a pointer by the given number of bytes.
        /// </summary>
        /// <param name="pointer"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        public static Pointer operator -(Pointer pointer, uint offset)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer is a null pointer.");
            #endif
            pointer.Address -= offset;
            return pointer;
        }

        /// <summary>
        /// Decrement the address of a pointer.
        /// </summary>
        /// <param name="pointer"></param>
        /// <returns></returns>
        public static Pointer operator --(Pointer pointer)
        {
            #if DEBUG
            if (pointer.Address == 0)
                throw new InvalidOperationException("The pointer being decremented is a null pointer.");
            #endif
            pointer.Address--;
            return pointer;
        }

        /// <summary>
        /// Subtract two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns>The number of bytes between the two pointers.</returns>
        public static uint operator -(Pointer pointer1, Pointer pointer2)
        {
            #if DEBUG
            if (pointer1.Address == 0)
                throw new InvalidOperationException("The pointer to the left of the subtraction operator is a null pointer.");
            if (pointer2.Address == 0)
                throw new InvalidOperationException("The pointer to the right of the subtraction operator is a null pointer.");
            #endif
            return pointer1.Address - pointer2.Address;
        }

        /// <summary>
        /// Compare pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator <(Pointer pointer1, Pointer pointer2)
        {
            #if DEBUG
            if (pointer1.Address == 0)
                throw new InvalidOperationException("The pointer to the left of the less than operator is a null pointer.");
            if (pointer2.Address == 0)
                throw new InvalidOperationException("The pointer to the right of the less than operator is a null pointer.");
            #endif
            return pointer1.Address < pointer2.Address;
        }

        /// <summary>
        /// Compare two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator <=(Pointer pointer1, Pointer pointer2)
        {
            #if DEBUG
            if (pointer1.Address == 0)
                throw new InvalidOperationException("The pointer to the left of the less than or equal to operator is a null pointer.");
            if (pointer2.Address == 0)
                throw new InvalidOperationException("The pointer to the right of the less than or equal to operator is a null pointer.");
            #endif
            return pointer1.Address <= pointer2.Address;
        }

        /// <summary>
        /// Compare two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator >(Pointer pointer1, Pointer pointer2)
        {
            #if DEBUG
            if (pointer1.Address == 0)
                throw new InvalidOperationException("The pointer to the left of the greater than operator is a null pointer.");
            if (pointer2.Address == 0)
                throw new InvalidOperationException("The pointer to the right of the greater than operator is a null pointer.");
            #endif
            return pointer1.Address > pointer2.Address;
        }

        /// <summary>
        /// Compare two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator >=(Pointer pointer1, Pointer pointer2)
        {
            #if DEBUG
            if (pointer1.Address == 0)
                throw new InvalidOperationException("The pointer to the left of the greater than or equal to operator is a null pointer.");
            if (pointer2.Address == 0)
                throw new InvalidOperationException("The pointer to the right of the greater than or equal to operator is a null pointer.");
            #endif
            return pointer1.Address >= pointer2.Address;
        }

        /// <summary>
        /// Compare two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator ==(Pointer pointer1, Pointer pointer2)
        {
            return pointer1.Address == pointer2.Address;
        }

        /// <summary>
        /// Compare two pointers.
        /// </summary>
        /// <param name="pointer1"></param>
        /// <param name="pointer2"></param>
        /// <returns></returns>
        public static bool operator !=(Pointer pointer1, Pointer pointer2)
        {
            return pointer1.Address != pointer2.Address;
        }

        /// <summary>
        /// Indicates whether this instance and a specified object are equal.
        /// </summary>
        /// <returns>true if obj and this instance are the same type and represent the same value; otherwise, false.</returns>
        /// <param name="obj">Another object to compare to.</param>
        public override bool Equals(object obj)
        {
            if (obj is Pointer)
            {
                Pointer pointer = (Pointer) obj;
                return pointer.Address == Address;
            }
            return base.Equals(obj);
        }

        /// <summary>
        /// Returns the hash code for this instance.
        /// </summary>
        /// <returns>A 32-bit signed integer that is the hash code for this instance.</returns>
        public override int GetHashCode()
        {
            return Address.GetHashCode();
        }
    }
}