#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange
//
// Copyright (c) 2005-2017 empira Software GmbH, Cologne Area (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

// With this define each iref object gets a unique number (uid) to make them distinguishable in the debugger
#define UNIQUE_IREF_

using System;
using System.Collections.Generic;
using System.Diagnostics;
using PdfSharp.Pdf.IO;

namespace PdfSharp.Pdf.Advanced
{
    /// <summary>
    /// Represents an indirect reference to a PdfObject.
    /// </summary>
    [DebuggerDisplay("iref({ObjectNumber}, {GenerationNumber})")]
    public sealed class PdfReference : PdfItem
    {
        // About PdfReference 
        // 
        // * A PdfReference holds either the ObjectID or the PdfObject or both.
        // 
        // * Each PdfObject has a PdfReference if and only if it is an indirect object. Direct objects have
        //   no PdfReference, because they are embedded in a parent objects.
        //
        // * PdfReference objects are used to reference PdfObject instances. A value in a PDF dictionary
        //   or array that is a PdfReference represents an indirect reference. A value in a PDF dictionary or
        //   or array that is a PdfObject represents a direct (or embeddded) object.
        //
        // * When a PDF file is imported, the PdfXRefTable is filled with PdfReference objects keeping the
        //   ObjectsIDs and file positions (offsets) of all indirect objects.
        //
        // * Indirect objects can easily be renumbered because they do not rely on their ObjectsIDs.
        //
        // * During modification of a document the ObjectID of an indirect object has no meaning,
        //   except that they must be different in pairs.

        /// <summary>
        /// Initializes a new PdfReference instance for the specified indirect object.
        /// </summary>
        public PdfReference(PdfObject pdfObject)
        {
            if (pdfObject.Reference != null)
                throw new InvalidOperationException("Must not create iref for an object that already has one.");
            _value = pdfObject;
            pdfObject.Reference = this;
#if UNIQUE_IREF && DEBUG
            _uid = ++s_counter;
#endif
        }

        /// <summary>
        /// Initializes a new PdfReference instance from the specified object identifier and file position.
        /// </summary>
        public PdfReference(PdfObjectID objectID, int position)
        {
            _objectID = objectID;
            _position = position;
#if UNIQUE_IREF && DEBUG
            _uid = ++s_counter;
#endif
        }

        /// <summary>
        /// Gets or sets the object identifier.
        /// </summary>
        public PdfObjectID ObjectID
        {
            get { return _objectID; }
            set
            {
                // Ignore redundant invokations.
                if (_objectID == value)
                    return;

                _objectID = value;
                if (Document != null)
                {
                    //PdfXRefTable table = Document.xrefTable;
                    //table.Remove(this);
                    //objectID = value;
                    //table.Add(this);
                }
            }
        }
        PdfObjectID _objectID;

        /// <summary>
        /// Gets the object number of the object identifier.
        /// </summary>
        public int ObjectNumber
        {
            get { return _objectID.ObjectNumber; }
        }

        /// <summary>
        /// Gets the generation number of the object identifier.
        /// </summary>
        public int GenerationNumber
        {
            get { return _objectID.GenerationNumber; }
        }

        /// <summary>
        /// Gets or sets the file position of the related PdfObject.
        /// </summary>
        public int Position
        {
            get { return _position; }
            set { _position = value; }
        }
        int _position;  // I know it should be long, but I have never seen a 2GB PDF file.

        //public bool InUse
        //{
        //  get {return inUse;}
        //  set {inUse = value;}
        //}
        //bool inUse;

        /// <summary>
        /// Gets or sets the referenced PdfObject.
        /// </summary>
        public PdfObject Value
        {
            get { return _value; }
            set
            {
                Debug.Assert(value != null, "The value of a PdfReference must never be null.");
                Debug.Assert(value.Reference == null || ReferenceEquals(value.Reference, this), "The reference of the value must be null or this.");
                _value = value;
                // value must never be null
                value.Reference = this;
            }
        }
        PdfObject _value;

        /// <summary>
        /// Hack for dead objects.
        /// </summary>
        internal void SetObject(PdfObject value)
        {
            _value = value;
        }

        /// <summary>
        /// Gets or sets the document this object belongs to.
        /// </summary>
        public PdfDocument Document
        {
            get { return _document; }
            set { _document = value; }
        }
        PdfDocument _document;

        /// <summary>
        /// Gets a string representing the object identifier.
        /// </summary>
        public override string ToString()
        {
            return _objectID + " R";
        }

        internal static PdfReferenceComparer Comparer
        {
            get { return new PdfReferenceComparer(); }
        }

        /// <summary>
        /// Implements a comparer that compares PdfReference objects by their PdfObjectID.
        /// </summary>
        internal class PdfReferenceComparer : IComparer<PdfReference>
        {
            public int Compare(PdfReference x, PdfReference y)
            {
                PdfReference l = x;
                PdfReference r = y;
                if (l != null)
                {
                    if (r != null)
                        return l._objectID.CompareTo(r._objectID);
                    return -1;
                }
                if (r != null)
                    return 1;
                return 0;
            }
        }

#if UNIQUE_IREF && DEBUG
        static int s_counter = 0;
        int _uid;
#endif
    }
}
