// Copyright (c) 2020 Can Boluk and contributors of the VTIL Project   
// All rights reserved.   
//    
// Redistribution and use in source and binary forms, with or without   
// modification, are permitted provided that the following conditions are met: 
//    
// 1. Redistributions of source code must retain the above copyright notice,   
//    this list of conditions and the following disclaimer.   
// 2. Redistributions in binary form must reproduce the above copyright   
//    notice, this list of conditions and the following disclaimer in the   
//    documentation and/or other materials provided with the distribution.   
// 3. Neither the name of mosquitto nor the names of its   
//    contributors may be used to endorse or promote products derived from   
//    this software without specific prior written permission.   
//    
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE   
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE  
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE   
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR   
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF   
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS   
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN   
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)   
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE  
// POSSIBILITY OF SUCH DAMAGE.        
//
#include "simplifier.hpp"
#include "directives.hpp"
#include "boolean_directives.hpp"
#include "../expressions/expression.hpp"
#include "../directives/transformer.hpp"
#include <vtil/io>

namespace vtil::symbolic
{
	struct join_depth_exception : std::exception
	{
		const char* what() const throw()
		{
			return "Reached the maximum join depth limit.";
		}
	};

	// Simplifier cache and its accessor.
	//
	static thread_local simplifier_cache_t simplifier_cache;
	simplifier_cache_t& ref_simplifier_cache() { return simplifier_cache; }

	// Attempts to prettify the expression given.
	//
	static bool prettify_expression( expression::reference& exp )
	{
		using namespace logger;
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
		scope_padding _p( 1 );
		log<CON_CYN>( "[Prettify]  = %s\n", *exp );
#endif

		// Prettify each operand.
		//
		auto pexp = +exp;
		for ( auto* op_ptr : { &pexp->lhs, &pexp->rhs } )
		{
			if ( !op_ptr->is_valid() ) continue;
			
			// If successful, recurse.
			//
			if ( prettify_expression( *op_ptr ) )
			{
				pexp->update( false );
				simplify_expression( exp, true, -1, false );
				return true;
			}
		}

		// Update the expression.
		//
		pexp->update( false );
		
		// Enumerate each pack descriptor:
		//
		for ( auto [dir_src, dir_dst] : directive::get_pack_descriptors( exp->op )  )
		{
			// If we can transform the expression by the directive set:
			//
			if ( auto exp_new = transform( exp, dir_src, dir_dst, {}, -1 ) )
			{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
				log<CON_PRP>( "[Pack] %s => %s\n", dir_src, dir_dst );
				log<CON_GRN>( "= %s\n", *exp );
#endif
				exp = exp_new;
				return true;
			}
		}

#if VTIL_SYMEX_SIMPLIFY_VERBOSE
		log<CON_YLW>( "= %s\n", *exp );
#endif
		return false;
	}

	// Attempts to simplify the expression given, returns whether the simplification
	// succeeded or not.
	//
	bool simplify_expression( expression::reference& exp, bool pretty, int64_t max_depth, bool unpack )
	{
		using namespace logger;

		if ( max_depth == 0 )
			throw join_depth_exception{};

		// If not an expression, we cannot simplify further.
		//
		if ( !exp->is_expression() )
			return false;

		// If simplify hint is set, only call prettify if requested and return.
		//
		if ( exp->simplify_hint )
		{
			if ( pretty )
				prettify_expression( exp );
			return false;
		}

		// If expression has known value, return as is.
		//
		if ( exp->value.is_known() )
		{
			*+exp = expression{ exp->value.known_one(), exp->value.size() };
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
			log<CON_CYN>( "= %s [By evaluation]\n", *exp );
#endif
			return true;
		}

#if VTIL_SYMEX_SIMPLIFY_VERBOSE
		// Log the input.
		//
		scope_padding _p( 1 );
		if ( !state::get()->padding ) log( "\n" );
		log( "[Input]  = %s ", *exp );
		log( "(Hash: %s)\n", exp->hash() );
#endif

		// If we resolved a valid cache entry:
		//
		auto cache_it = simplifier_cache.find( ( boxed_expression& ) *exp );
		if ( cache_it != simplifier_cache.end() )
		{
			// Replace with the cached entry if simplifies.
			//
			if ( cache_it->second.first.is_valid() && cache_it->second.second )
			{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
				log<CON_YLW>( "= %s (From cache, Success: %d)\n", *cache_it->second.first, cache_it->second.second );
#endif
				exp = *cache_it->second.first;
				return true;
			}
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
			log<CON_RED>( "Failed as directed by cache...\n" );
#endif
			return false;
		}

		// Otherwise create a new cache entry with {invalid, false} by default.
		//
		cache_it = simplifier_cache.insert( { ( boxed_expression& ) *exp, { {}, false } } ).first;
		auto& [cache_entry, success_flag] = cache_it->second;

		// If trying to simplify resizing:
		//
		if ( exp->op == math::operator_id::ucast ||
			 exp->op == math::operator_id::cast )
		{
			// If the temporary disable flag to prevent stack overflow is set:
			//
			static thread_local bool temp_disable = false;
			if ( temp_disable )
			{
				// Toggle temporary disable bit.
				//
				temp_disable = false;

				// If left hand side simplifies:
				//
				expression::reference op_ref = exp->lhs;
				if ( simplify_expression( op_ref, pretty, max_depth - 1, unpack ) )
				{
					// Own the reference and relocate the pointer.
					//
					auto [exp_new, op_new] = exp.own( &exp->lhs );

					// Update the expression and indicate success.
					//
					*op_new = op_ref;
					exp_new->update( false );
					success_flag = true;
				}

				// Toggle temporary disable bit.
				//
				temp_disable = true;
			}
			else
			{
				// Simplify left hand side with the exact same arguments.
				//
				expression::reference exp_new = exp->lhs;
				bool simplified = simplify_expression( exp_new, pretty, max_depth - 1, unpack );

				// Toggle temporary disable bit and invoke resize.
				//
				temp_disable = true;
				( +exp_new )->resize( math::narrow_cast<bitcnt_t>( *exp->rhs->get() ), exp->op == math::operator_id::cast );
				temp_disable = false;

				// If operand was simplified or if the complexity reduced, indicate success. 
				//
				if ( simplified || exp_new->complexity < exp->complexity )
				{
					exp = exp_new;
					success_flag = true;
				}
			}
			cache_entry = *exp;
			( +exp )->simplify_hint = true;
			return success_flag;
		}

		// Simplify operands first if not done already.
		//
		for ( auto* op_ptr : { &exp->lhs, &exp->rhs } )
		{
			// If invalid or is simplified, skip.
			//
			if ( !op_ptr->is_valid() || op_ptr->get()->simplify_hint )
				continue;

			// If we could simplify the operand:
			//
			expression::reference op_ref = *op_ptr;
			if ( simplify_expression( op_ref, false, max_depth - 1 ) )
			{
				// Own the reference and relocate the pointer.
				//
				auto [exp_new, op_new] = exp.own( op_ptr );

				// Update the expression.
				//
				*op_new = op_ref;
				exp_new->update( false );

				// Recurse, and indicate success.
				//
				simplify_expression( exp, pretty, max_depth - 1 );
				( +exp )->simplify_hint = true;
				cache_entry = *exp;
				success_flag = true;
				return true;
			}
		}

#if VTIL_SYMEX_SIMPLIFY_VERBOSE
		// Log the bit states.
		//
		log( "[Vector] = %s\n", exp->value );
#endif

		// If reduced to a constant, replace it.
		//
		if ( exp->value.is_known() )
		{
			cache_entry = expression{ exp->value.known_one(), exp->value.size() };
			success_flag = true;
			exp = cache_entry;
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
			log<CON_CYN>( "= %s [By evaluation]\n", *exp );
#endif
			return success_flag;
		}

		// Declare the filter.
		//
		expression_filter_t filter;

		// If no maximum depth was set:
		//
		if ( max_depth < 0 )
		{
			filter = [ & ] ( auto& exp_new )
			{
				// If complexity was reduced already, pass.
				//
				if ( exp_new->complexity < exp->complexity )
					return true;

				// Save current cache iterator.
				//
				auto it0 = simplifier_cache.end();

				// Try simplifying with maximum depth set as expression's
				// depth times two and pass if complexity was reduced.
				//
				try
				{
					simplify_expression( exp_new, false, exp_new->depth * 2 );
					return exp_new->complexity < exp->complexity;
				}
				// If maximum depth was reached, revert any changes to the cache
				// and fail the join directive.
				//
				catch ( join_depth_exception& )
				{
					simplifier_cache.erase( it0, simplifier_cache.end() );
					return false;
				}
			};
		}
		// Else:
		//
		else
		{
			filter = [ & ] ( auto& exp_new )
			{
				// If complexity was reduced already, pass.
				//
				if ( exp_new->complexity < exp->complexity )
					return true;

				// Attempt simplifying with maximum depth decremented by one,
				// fail if complexity was not reduced.
				//
				simplify_expression( exp_new, false, max_depth - 1 );
				return exp_new->complexity < exp->complexity;
			};
		}

		// Enumerate each universal simplifier:
		//
		for ( auto [dir_src, dir_dst] : directive::get_universal_simplifiers( exp->op ) )
		{
			// If we can transform the expression by the directive set:
			//
			if ( auto exp_new = transform( exp, dir_src, dir_dst, {}, max_depth ) )
			{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
				log<CON_GRN>( "[Simplify] %s => %s\n", dir_src->to_string(), dir_dst->to_string() );
				log<CON_GRN>( "= %s [By simplify directive]\n", *exp_new );
#endif
				// Recurse, set the hint and return the simplified instance.
				//
				simplify_expression( exp_new, pretty, max_depth );
				( +exp_new )->simplify_hint = true;
				cache_entry = exp_new;
				success_flag = true;
				exp = exp_new;
				return success_flag;
			}
		}

		// If it is a boolean expression:
		//
		if ( exp->size() == 1 )
		{
			// Enumerate each universal simplifier:
			//
			for ( auto [dir_src, dir_dst] : directive::get_boolean_simplifiers( exp->op ) )
			{
				// If we can transform the expression by the directive set:
				//
				if ( auto exp_new = transform( exp, dir_src, dir_dst, {}, max_depth ) )
				{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
					log<CON_GRN>( "[Simplify] %s => %s\n", dir_src->to_string(), dir_dst->to_string() );
					log<CON_GRN>( "= %s [By simplify directive]\n", *exp_new );
#endif
					// Recurse, set the hint and return the simplified instance.
					//
					simplify_expression( exp_new, pretty, max_depth );
					( +exp_new )->simplify_hint = true;
					cache_entry = exp_new;
					success_flag = true;
					exp = exp_new;
					return success_flag;
				}
			}
		}

		// Enumerate each join descriptor:
		//
		for ( auto [dir_src, dir_dst] : directive::get_join_descriptors( exp->op ) )
		{
			// If we can transform the expression by the directive set:
			//
			if ( auto exp_new = transform( exp, dir_src, dir_dst, filter, max_depth ) )
			{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
				log<CON_GRN>( "[Join] %s => %s\n", dir_src->to_string(), dir_dst->to_string() );
				log<CON_GRN>( "= %s [By join directive]\n", *exp_new );
				log<CON_YLW>( "Complexity: %lf => %lf\n", exp->complexity, exp_new->complexity );
#endif
				// Recurse, set the hint and return the simplified instance.
				//
				simplify_expression( exp_new, pretty, max_depth - 1 );
				( +exp_new )->simplify_hint = true;
				cache_entry = exp_new;
				success_flag = true;
				exp = exp_new;
				return success_flag;
			}
		}

		// If it is a boolean expression:
		//
		if ( exp->size() == 1 )
		{
			// Enumerate each join descriptor:
			//
			for ( auto [dir_src, dir_dst] : directive::get_boolean_joiners( exp->op ) )
			{
				// If we can transform the expression by the directive set:
				//
				if ( auto exp_new = transform( exp, dir_src, dir_dst, filter, max_depth ) )
				{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
					log<CON_GRN>( "[Join] %s => %s\n", dir_src->to_string(), dir_dst->to_string() );
					log<CON_GRN>( "= %s [By join directive]\n", *exp_new );
					log<CON_YLW>( "Complexity: %lf => %lf\n", exp->complexity, exp_new->complexity );
#endif
					// Recurse, set the hint and return the simplified instance.
					//
					simplify_expression( exp_new, pretty, max_depth - 1 );
					( +exp_new )->simplify_hint = true;
					cache_entry = exp_new;
					success_flag = true;
					exp = exp_new;
					return success_flag;
				}
			}
		}

		// Unpack the expression if requested:
		//
		if ( unpack )
		{
			// Enumerate each unpack descriptor:
			//
			for ( auto [dir_src, dir_dst] : directive::get_unpack_descriptors( exp->op ) )
			{
				// If we can transform the expression by the directive set:
				//
				if ( auto exp_new = transform( exp, dir_src, dir_dst, 
					 [ & ] ( auto& exp_new ) { simplify_expression( exp_new, true, max_depth - 1 ); return exp_new->complexity < exp->complexity; }, max_depth ) )
				{
#if VTIL_SYMEX_SIMPLIFY_VERBOSE
					log<CON_YLW>( "[Unpack] %s => %s\n", dir_src->to_string(), dir_dst->to_string() );
					log<CON_GRN>( "= %s [By unpack directive]\n", *exp_new );
#endif

					// Set the hint and return the simplified instance.
					//
					( +exp_new )->simplify_hint = true;
					cache_entry = exp_new;
					success_flag = true;
					exp = exp_new;
					return success_flag;
				}
			}
		}

		// Prettify the expression if requested.
		//
		if ( pretty )
			prettify_expression( exp );

#if VTIL_SYMEX_SIMPLIFY_VERBOSE
		// Log the output.
		//
		log( "= %s\n\n", *exp );
#endif
		return false;
	}
};