#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

// ReSharper disable InconsistentNaming

namespace PdfSharp.Pdf.Security
{
    /// <summary>
    /// Represents the base of all security handlers.
    /// </summary>
    public abstract class PdfSecurityHandler : PdfDictionary
    {
        internal PdfSecurityHandler(PdfDocument document)
            : base(document)
        { }

        internal PdfSecurityHandler(PdfDictionary dict)
            : base(dict)
        { }

        /// <summary>
        /// Predefined keys of this dictionary.
        /// </summary>
        internal class Keys : KeysBase
        {
            /// <summary>
            /// (Required) The name of the preferred security handler for this document. Typically,
            /// it is the name of the security handler that was used to encrypt the document. If 
            /// SubFilter is not present, only this security handler should be used when opening 
            /// the document. If it is present, consumer applications can use any security handler
            /// that implements the format specified by SubFilter.
            /// Standard is the name of the built-in password-based security handler. Names for other
            /// security handlers can be registered by using the procedure described in Appendix E.
            /// </summary>
            [KeyInfo(KeyType.Name | KeyType.Required)]
            public const string Filter = "/Filter";

            /// <summary>
            /// (Optional; PDF 1.3) A name that completely specifies the format and interpretation of
            /// the contents of the encryption dictionary. It is needed to allow security handlers other
            /// than the one specified by Filter to decrypt the document. If this entry is absent, other
            /// security handlers should not be allowed to decrypt the document.
            /// </summary>
            [KeyInfo("1.3", KeyType.Name | KeyType.Optional)]
            public const string SubFilter = "/SubFilter";

            /// <summary>
            /// (Optional but strongly recommended) A code specifying the algorithm to be used in encrypting
            /// and decrypting the document:
            /// 0 An algorithm that is undocumented and no longer supported, and whose use is strongly discouraged.
            /// 1 Algorithm 3.1, with an encryption key length of 40 bits.
            /// 2 (PDF 1.4) Algorithm 3.1, but permitting encryption key lengths greater than 40 bits.
            /// 3 (PDF 1.4) An unpublished algorithm that permits encryption key lengths ranging from 40 to 128 bits.
            /// 4 (PDF 1.5) The security handler defines the use of encryption and decryption in the document, using
            ///             the rules specified by the CF, StmF, and StrF entries.
            /// The default value if this entry is omitted is 0, but a value of 1 or greater is strongly recommended.
            /// </summary>
            [KeyInfo(KeyType.Integer | KeyType.Optional)]
            public const string V = "/V";

            /// <summary>
            /// (Optional; PDF 1.4; only if V is 2 or 3) The length of the encryption key, in bits.
            /// The value must be a multiple of 8, in the range 40 to 128. Default value: 40.
            /// </summary>
            [KeyInfo("1.4", KeyType.Integer | KeyType.Optional)]
            public const string Length = "/Length";

            /// <summary>
            /// (Optional; meaningful only when the value of V is 4; PDF 1.5)
            /// A dictionary whose keys are crypt filter names and whose values are the corresponding
            /// crypt filter dictionaries. Every crypt filter used in the document must have an entry
            /// in this dictionary, except for the standard crypt filter names.
            /// </summary>
            [KeyInfo(KeyType.Dictionary | KeyType.Optional)]
            public const string CF = "/CF";

            /// <summary>
            /// (Optional; meaningful only when the value of V is 4; PDF 1.5)
            /// The name of the crypt filter that is used by default when decrypting streams.
            /// The name must be a key in the CF dictionary or a standard crypt filter name. All streams
            /// in the document, except for cross-reference streams or streams that have a Crypt entry in
            /// their Filter array, are decrypted by the security handler, using this crypt filter.
            /// Default value: Identity.
            /// </summary>
            [KeyInfo("1.5", KeyType.Name | KeyType.Optional)]
            public const string StmF = "/StmF";

            /// <summary>
            /// (Optional; meaningful only when the value of V is 4; PDF 1.)
            /// The name of the crypt filter that is used when decrypting all strings in the document.
            /// The name must be a key in the CF dictionary or a standard crypt filter name.
            /// Default value: Identity.
            /// </summary>
            [KeyInfo("1.5", KeyType.Name | KeyType.Optional)]
            public const string StrF = "/StrF";

            /// <summary>
            /// (Optional; meaningful only when the value of V is 4; PDF 1.6)
            /// The name of the crypt filter that should be used by default when encrypting embedded
            /// file streams; it must correspond to a key in the CF dictionary or a standard crypt
            /// filter name. This entry is provided by the security handler. Applications should respect
            /// this value when encrypting embedded files, except for embedded file streams that have
            /// their own crypt filter specifier. If this entry is not present, and the embedded file
            /// stream does not contain a crypt filter specifier, the stream should be encrypted using
            /// the default stream crypt filter specified by StmF.
            /// </summary>
            [KeyInfo("1.6", KeyType.Name | KeyType.Optional)]
            public const string EFF = "/EFF";
        }
    }
}