/*
    Copyright (C) 2011-2015 de4dot@gmail.com

    This file is part of de4dot.

    de4dot is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    de4dot is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with de4dot.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.IO;
using dnlib.IO;
using dnlib.DotNet;
using dnlib.DotNet.Emit;
using de4dot.blocks;

namespace de4dot.code.deobfuscators.CodeVeil {
	class ResourceDecrypter {
		ModuleDefMD module;
		TypeDef encryptedResourceStreamType;
		TypeDef encryptedResourceSetType;
		MethodDef encryptedResourceSet_GetDefaultReader;
		TypeDef encryptedResourceReaderType;
		GenericInstSig encryptedResourceReaderTypeDict;
		TypeDef resType;
		MethodDef resTypeCtor;
		TypeDef resourceFlagsType;
		TypeDef resourceEnumeratorType;
		MethodCallRestorerBase methodsRestorer;

		public bool CanRemoveTypes {
			get {
				return EncryptedResourceStreamType != null &&
					EncryptedResourceSetType != null &&
					EncryptedResourceReaderType != null &&
					ResType != null &&
					ResourceFlagsType != null &&
					ResourceEnumeratorType != null;
			}
		}

		public TypeDef EncryptedResourceStreamType {
			get { return encryptedResourceStreamType; }
		}

		public TypeDef EncryptedResourceSetType {
			get { return encryptedResourceSetType; }
		}

		public TypeDef EncryptedResourceReaderType {
			get { return encryptedResourceReaderType; }
		}

		public TypeDef ResType {
			get { return resType; }
		}

		public TypeDef ResourceFlagsType {
			get { return resourceFlagsType; }
		}

		public TypeDef ResourceEnumeratorType {
			get { return resourceEnumeratorType; }
		}

		public ResourceDecrypter(ModuleDefMD module) {
			this.module = module;
		}

		public void Initialize() {
			methodsRestorer = new MethodCallRestorerBase(module);
			FindEncryptedResourceStreamType();
			FindEncryptedResourceSet();
			FindEncryptedResourceReader();
			FindResType();
			FindResourceFlags();
			FindResourceEnumerator();
		}

		void FindResourceEnumerator() {
			if (encryptedResourceReaderType == null)
				return;

			var resourceEnumeratorType_fields = new string[] {
				"System.Collections.DictionaryEntry",
				"System.Collections.IDictionaryEnumerator",
				"System.Boolean",
				encryptedResourceReaderType.FullName,
			};
			foreach (var type in module.Types) {
				if (type.Namespace != "")
					continue;
				if (type.BaseType == null || type.BaseType.FullName != "System.Object")
					continue;
				if (!HasInterface(type, "System.Collections.IDictionaryEnumerator"))
					continue;
				if (!new FieldTypes(type).All(resourceEnumeratorType_fields))
					continue;
				var ctor = type.FindMethod(".ctor");
				if (ctor == null)
					continue;
				var sig = ctor.MethodSig;
				if (sig == null || sig.Params.Count != 1)
					continue;
				if (sig.Params[0].TryGetTypeDef() != encryptedResourceReaderType)
					continue;

				resourceEnumeratorType = type;
				return;
			}
		}

		void FindResourceFlags() {
			if (resTypeCtor == null)
				return;
			var sig = resTypeCtor.MethodSig;
			if (sig == null || sig.Params.Count != 4)
				return;
			var type = sig.Params[2].TryGetTypeDef();
			if (type == null || !type.IsEnum)
				return;

			resourceFlagsType = type;
		}

		static string[] resType_fields = new string[] {
			"System.Int32",
			"System.Object",
			"System.String",
		};
		void FindResType() {
			if (encryptedResourceReaderTypeDict == null)
				return;
			var type = encryptedResourceReaderTypeDict.GenericArguments[1].TryGetTypeDef();
			if (type == null)
				return;
			if (type.BaseType == null || type.BaseType.FullName != "System.Object")
				return;
			var ctor = type.FindMethod(".ctor");
			if (ctor == null)
				return;
			var sig = ctor.MethodSig;
			if (sig == null || sig.Params.Count != 4)
				return;

			resTypeCtor = ctor;
			resType = type;
		}

		static string[] encryptedResourceReaderType_fields = new string[] {
			"System.Boolean",
			"System.Int32",
			"System.Int64",
			"System.IO.BinaryReader",
			"System.Runtime.Serialization.Formatters.Binary.BinaryFormatter",
		};
		void FindEncryptedResourceReader() {
			var type = GetTypeFromCode(encryptedResourceSet_GetDefaultReader);
			if (type == null)
				return;
			if (type.BaseType == null || !HasInterface(type, "System.Resources.IResourceReader"))
				return;
			if (!new FieldTypes(type).All(encryptedResourceReaderType_fields))
				return;
			var dictType = GetDlxResDict(type);
			if (dictType == null)
				return;
			if (FindXxteaMethod(type) == null)
				return;

			encryptedResourceReaderType = type;
			encryptedResourceReaderTypeDict = dictType;
		}

		static bool HasInterface(TypeDef type, string interfaceFullName) {
			foreach (var iface in type.Interfaces) {
				if (iface.Interface.FullName == interfaceFullName)
					return true;
			}
			return false;
		}

		static GenericInstSig GetDlxResDict(TypeDef type) {
			foreach (var field in type.Fields) {
				var fieldType = field.FieldSig.GetFieldType().ToGenericInstSig();
				if (fieldType == null)
					continue;
				if (fieldType.GenericType.FullName != "System.Collections.Generic.Dictionary`2")
					continue;
				if (fieldType.GenericArguments.Count != 2)
					continue;
				if (fieldType.GenericArguments[0].FullName != "System.String")
					continue;
				if (fieldType.GenericArguments[1].TryGetTypeDef() == null)
					continue;
				return fieldType;
			}
			return null;
		}

		static TypeDef GetTypeFromCode(MethodDef method) {
			if (method == null || method.Body == null)
				return null;
			foreach (var instr in method.Body.Instructions) {
				if (instr.OpCode.Code != Code.Ldtoken)
					continue;
				var type = instr.Operand as TypeDef;
				if (type != null)
					return type;
			}

			return null;
		}

		void FindEncryptedResourceSet() {
			foreach (var type in module.Types) {
				if (type.Namespace != "")
					continue;
				if (type.BaseType == null || type.BaseType.FullName != "System.Resources.ResourceSet")
					continue;
				var ctor = type.FindMethod(".ctor");
				if (!DotNetUtils.IsMethod(ctor, "System.Void", "(System.Resources.IResourceReader)"))
					continue;
				var method = type.FindMethod("GetDefaultReader");
				if (!DotNetUtils.IsMethod(method, "System.Type", "()"))
					continue;
				if (method.Body == null || method.IsStatic || !method.IsVirtual)
					continue;

				encryptedResourceSet_GetDefaultReader = method;
				encryptedResourceSetType = type;
				return;
			}
		}

		static string[] encryptedResourceStreamType_fields = new string[] {
			"System.Byte",
			"System.Byte[]",
			"System.Boolean",
			"System.Int32",
			"System.Int64",
			"System.IO.MemoryStream",
			"System.IO.Stream",
			"System.UInt32[]",
		};
		void FindEncryptedResourceStreamType() {
			foreach (var type in module.Types) {
				if (type.Namespace != "")
					continue;
				if (type.BaseType == null || type.BaseType.FullName != "System.IO.Stream")
					continue;
				var ctor = type.FindMethod(".ctor");
				if (!DotNetUtils.IsMethod(ctor, "System.Void", "(System.IO.Stream)"))
					continue;
				if (!new FieldTypes(type).All(encryptedResourceStreamType_fields))
					continue;
				if (FindXxteaMethod(type) == null)
					continue;

				MethodDef getManifestResourceStreamMethodTmp1, getManifestResourceStreamMethodTmp2;
				if (!FindManifestResourceStreamMethods(type, out getManifestResourceStreamMethodTmp1, out getManifestResourceStreamMethodTmp2))
					continue;

				methodsRestorer.CreateGetManifestResourceStream1(getManifestResourceStreamMethodTmp1);
				methodsRestorer.CreateGetManifestResourceStream2(getManifestResourceStreamMethodTmp2);
				encryptedResourceStreamType = type;
				return;
			}
		}

		static MethodDef FindXxteaMethod(TypeDef type) {
			foreach (var method in type.Methods) {
				if (!method.IsPrivate || method.IsStatic || method.Body == null)
					continue;
				if (DotNetUtils.IsMethod(method, "System.Void", "(System.UInt32[],System.UInt32[])")) {
					if (!DeobUtils.HasInteger(method, 0x9E3779B9))
						continue;
				}
				else if (DotNetUtils.IsMethod(method, "System.Void", "(System.UInt32[],System.UInt32[],System.UInt32,System.UInt32,System.UInt32,System.UInt32,System.UInt32,System.UInt32,System.UInt32,System.UInt32,System.UInt32)")) {
					// Here if 5.0. 0x9E3779B9 is passed to it as the last arg.
				}
				else
					continue;
				if (!DeobUtils.HasInteger(method, 52))
					continue;

				return method;
			}
			return null;
		}

		static bool FindManifestResourceStreamMethods(TypeDef type, out MethodDef getManifestResourceStreamMethodTmp1, out MethodDef getManifestResourceStreamMethodTmp2) {
			getManifestResourceStreamMethodTmp1 = null;
			getManifestResourceStreamMethodTmp2 = null;
			foreach (var method in type.Methods) {
				if (!method.IsStatic || method.Body == null)
					continue;
				if (DotNetUtils.IsMethod(method, "System.IO.Stream", "(System.Reflection.Assembly,System.String)"))
					getManifestResourceStreamMethodTmp1 = method;
				else if (DotNetUtils.IsMethod(method, "System.IO.Stream", "(System.Reflection.Assembly,System.Type,System.String)"))
					getManifestResourceStreamMethodTmp2 = method;
			}
			return getManifestResourceStreamMethodTmp1 != null && getManifestResourceStreamMethodTmp2 != null;
		}

		public void Decrypt() {
			for (int i = 0; i < module.Resources.Count; i++) {
				var resource = module.Resources[i] as EmbeddedResource;
				if (resource == null)
					continue;

				var decrypted = Decrypt(resource.Data);
				if (decrypted == null)
					continue;

				Logger.v("Decrypted resource {0}", Utils.ToCsharpString(resource.Name));
				module.Resources[i] = new EmbeddedResource(resource.Name, decrypted, resource.Attributes);
			}
		}

		byte[] Decrypt(IBinaryReader reader) {
			try {
				reader.Position = 0;
				uint sig = reader.ReadUInt32();
				reader.Position = 0;
				if (sig == 0xBEEFCACE)
					return DecryptBeefcace(reader);
				if (sig == 0x58455245)
					return DecryptErex(reader);
				return null;
			}
			catch (InvalidDataException) {
				return null;
			}
			catch (Exception ex) {
				Logger.w("Got an exception when decrypting resources: {0} - {1}", ex.GetType(), ex.Message);
				return null;
			}
		}

		byte[] DecryptBeefcace(IBinaryReader reader) {
			var resourceReader = new ResourceReader(reader);
			return new ResourceConverter(module, resourceReader.Read()).Convert();
		}

		byte[] DecryptErex(IBinaryReader reader) {
			return new ErexResourceReader(reader).Decrypt();
		}

		public void Deobfuscate(Blocks blocks) {
			if (encryptedResourceStreamType == null)
				return;

			methodsRestorer.Deobfuscate(blocks);
		}
	}
}
