//! \file       ArcMED.cs
//! \date       Mon May 30 12:35:24 2016
//! \brief      DxLib resource archive.
//
// Copyright (C) 2016 by morkt
//
// 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.
//

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.IO;
using GameRes.Formats.Properties;
using GameRes.Formats.Strings;
using GameRes.Utility;

namespace GameRes.Formats.DxLib
{
    public interface IScriptEncryption
    {
        int StartOffset { get; }

        bool IsEncrypted (byte[] data);
        void Decrypt (byte[] data, int offset, int length);
    }

    [Serializable]
    public class FudegakiEncryption : IScriptEncryption
    {
        readonly byte[] Key;

        public FudegakiEncryption (string keyword)
        {
            Key = Encodings.cp932.GetBytes (keyword);
        }

        public int StartOffset { get { return 0x10; } }

        public bool IsEncrypted (byte[] data)
        {
            return LittleEndian.ToInt32 (data, 0) + 0x10 == data.Length && Key.Length > 0;
        }

        public void Decrypt (byte[] data, int offset, int length)
        {
            for (int i = 0; i < length; ++i)
            {
                data[offset+i] += Key[(offset+i) % Key.Length];
            }
        }
    }

    [Serializable]
    public class MedOptions : ResourceOptions
    {
        public IScriptEncryption Encryption;
    }

    [Serializable]
    public class ScrMedScheme : ResourceScheme
    {
        public Dictionary<string, IScriptEncryption> KnownSchemes;
    }

    internal class ScrMedArchive : ArcFile
    {
        public readonly IScriptEncryption Encryption;

        public ScrMedArchive (ArcView arc, ArchiveFormat impl, ICollection<Entry> dir, IScriptEncryption enc)
            : base (arc, impl, dir)
        {
            Encryption = enc;
        }
    }

    [Export(typeof(ArchiveFormat))]
    public class MedOpener : ArchiveFormat
    {
        public override string         Tag { get { return "MED"; } }
        public override string Description { get { return "DxLib engine resource archive"; } }
        public override uint     Signature { get { return 0; } }
        public override bool  IsHierarchic { get { return false; } }
        public override bool     CanCreate { get { return false; } }

        static readonly Lazy<ImageFormat> PrsFormat = new Lazy<ImageFormat> (() => ImageFormat.FindByTag ("PRS"));

        public static Dictionary<string, IScriptEncryption> KnownSchemes = new Dictionary<string, IScriptEncryption>();

        public override ResourceScheme Scheme
        {
            get { return new ScrMedScheme { KnownSchemes = KnownSchemes }; }
            set { KnownSchemes = ((ScrMedScheme)value).KnownSchemes; }
        }

        public override ArcFile TryOpen (ArcView file)
        {
            if (!file.View.AsciiEqual (0, "MD"))
                return null;
            uint entry_length = file.View.ReadUInt16 (4);
            int count = file.View.ReadUInt16 (6);
            if (entry_length <= 8 || !IsSaneCount (count))
                return null;

            uint name_length = entry_length - 8;
            uint index_offset = 0x10;
            var dir = new List<Entry> (count);
            for (int i = 0; i < count; ++i)
            {
                var name = file.View.ReadString (index_offset, name_length);
                index_offset += name_length;
                uint offset = file.View.ReadUInt32 (index_offset+4);

                var entry = new AutoEntry (name, () => {
                    uint signature = file.View.ReadUInt32 (offset);
                    if (0x4259 == (signature & 0xFFFF)) // 'YB'
                        return PrsFormat.Value;
                    return AutoEntry.DetectFileType (signature);
                });
                entry.Size   = file.View.ReadUInt32 (index_offset);
                entry.Offset = offset;
                if (!entry.CheckPlacement (file.MaxOffset))
                    return null;
                dir.Add (entry);
                index_offset += 8;
            }
            var base_name = Path.GetFileNameWithoutExtension (file.Name);
            if (base_name.EndsWith ("_scr", StringComparison.InvariantCultureIgnoreCase)
                && KnownSchemes.Count > 0)
            {
                var options = Query<MedOptions> (arcStrings.ArcEncryptedNotice);
                if (options.Encryption != null)
                    return new ScrMedArchive (file, this, dir, options.Encryption);
            }
            return new ArcFile (file, this, dir);
        }

        public override Stream OpenEntry (ArcFile arc, Entry entry)
        {
            var scr_arc = arc as ScrMedArchive;
            if (null == scr_arc || entry.Size <= scr_arc.Encryption.StartOffset)
                return base.OpenEntry (arc, entry);
            var data = arc.File.View.ReadBytes (entry.Offset, entry.Size);
            if (scr_arc.Encryption.IsEncrypted (data))
            {
                var offset = scr_arc.Encryption.StartOffset;
                scr_arc.Encryption.Decrypt (data, offset, data.Length-offset);
            }
            return new MemoryStream (data);
        }

        public override ResourceOptions GetDefaultOptions ()
        {
            return new MedOptions {
                Encryption = GetEncryption (Settings.Default.MEDScriptScheme),
            };
        }

        public override object GetAccessWidget ()
        {
            return new GUI.WidgetSCR();
        }

        public static IScriptEncryption GetEncryption (string scheme)
        {
            IScriptEncryption enc;
            if (string.IsNullOrEmpty (scheme) || !KnownSchemes.TryGetValue (scheme, out enc))
                return null;
            return enc;
        }
    }
}