/*
    Copyright (C) 2011-2012 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.Collections.Generic;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;

namespace de4dot.blocks.cflow {
	// Very simple constants folder which is all that's needed at the moment
	class ConstantsFolder {
		List<Block> allBlocks;
		Blocks blocks;
		InstructionEmulator instructionEmulator = new InstructionEmulator();
		List<ParameterDefinition> args;

		public void init(Blocks blocks, List<Block> allBlocks) {
			this.blocks = blocks;
			this.allBlocks = allBlocks;
			args = DotNetUtils.getParameters(blocks.Method);
		}

		public bool deobfuscate() {
			bool changed = false;
			foreach (var block in allBlocks) {
				instructionEmulator.init(blocks);
				var instrs = block.Instructions;
				for (int i = 0; i < instrs.Count; i++) {
					var instr = instrs[i];

					switch (instr.OpCode.Code) {
					case Code.Ldarg:
					case Code.Ldarg_0:
					case Code.Ldarg_1:
					case Code.Ldarg_2:
					case Code.Ldarg_3:
					case Code.Ldarg_S:
						changed |= fixLoadInstruction(block, i, instructionEmulator.getArg(DotNetUtils.getParameter(args, instr.Instruction)));
						break;

					case Code.Ldloc:
					case Code.Ldloc_0:
					case Code.Ldloc_1:
					case Code.Ldloc_2:
					case Code.Ldloc_3:
					case Code.Ldloc_S:
						changed |= fixLoadInstruction(block, i, instructionEmulator.getLocal(DotNetUtils.getLocalVar(blocks.Locals, instr.Instruction)));
						break;

					case Code.Ldarga:
					case Code.Ldarga_S:
						instructionEmulator.makeArgUnknown((ParameterDefinition)instr.Operand);
						break;

					case Code.Ldloca:
					case Code.Ldloca_S:
						instructionEmulator.makeLocalUnknown((VariableDefinition)instr.Operand);
						break;
					}

					try {
						instructionEmulator.emulate(instr.Instruction);
					}
					catch (System.NullReferenceException) {
						// Here if eg. invalid metadata token in a call instruction (operand is null)
						break;
					}
				}
			}
			return changed;
		}

		bool fixLoadInstruction(Block block, int index, Value value) {
			if (value.isInt32()) {
				var intValue = (Int32Value)value;
				if (!intValue.allBitsValid())
					return false;
				block.Instructions[index] = new Instr(DotNetUtils.createLdci4(intValue.value));
				return true;
			}
			else if (value.isInt64()) {
				var intValue = (Int64Value)value;
				if (!intValue.allBitsValid())
					return false;
				block.Instructions[index] = new Instr(Instruction.Create(OpCodes.Ldc_I8, intValue.value));
				return true;
			}
			return false;
		}
	}
}