#pragma once
/*
 *  Copyright (C) 2024  Brett Terpstra
 *
 *  This program 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.
 *
 *  This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef BLT_GP_PROGRAM_H
#define BLT_GP_PROGRAM_H


#include <cstddef>
#include <functional>
#include <type_traits>
#include <string_view>
#include <string>
#include <utility>
#include <iostream>
#include <random>

#include <blt/std/ranges.h>
#include <blt/std/hashmap.h>
#include <blt/std/types.h>
#include <blt/std/utility.h>
#include <blt/std/memory.h>
#include <blt/gp/fwdecl.h>
#include <blt/gp/typesystem.h>
#include <blt/gp/operations.h>
#include <blt/gp/tree.h>
#include <blt/gp/stack.h>

namespace blt::gp
{
    static constexpr blt::size_t NONE_T = 0x0;
    static constexpr blt::size_t STATIC_T = 0x1;
    static constexpr blt::size_t TERMINAL_T = 0x2;
    
    struct argc_t
    {
        blt::size_t argc = 0;
        blt::size_t argc_context = 0;
    };
    
    template<typename Context = detail::empty_t>
    class gp_operations
    {
            friend class gp_program;
            
            friend class blt::gp::detail::operator_storage_test;
        
        public:
            explicit gp_operations(type_system& system): system(system)
            {}
            
            template<typename Return, typename... Args>
            gp_operations& add_operator(const operation_t<Return(Args...)>& op, bool is_static = false)
            {
                auto return_type_id = system.get_type<Return>().id();
                auto operator_id = blt::gp::operator_id(operators.size());
                
                auto& operator_list = op.get_argc() == 0 ? terminals : non_terminals;
                operator_list[return_type_id].push_back(operator_id);
                
                if constexpr (sizeof...(Args) > 0)
                {
                    (add_non_context_argument<Args>(operator_id), ...);
                }
                
                argc_t argc;
                argc.argc_context = argc.argc = sizeof...(Args);
                
                ((std::is_same_v<detail::remove_cv_ref<Args>, Context> ? argc.argc -= 1 : (blt::size_t) nullptr), ...);
                
                BLT_ASSERT(argc.argc_context - argc.argc <= 1 && "Cannot pass multiple context as arguments!");
                
                operator_argc[operator_id] = argc;
                
                operators.push_back(op.template make_callable<Context>());
                transfer_funcs.push_back([](stack_allocator& to, stack_allocator& from) {
                    to.push(from.pop<Return>());
                });
                if (is_static)
                    static_types.insert(operator_id);
                return *this;
            }
        
        private:
            template<typename T>
            void add_non_context_argument(blt::gp::operator_id operator_id)
            {
                if constexpr (!std::is_same_v<Context, detail::remove_cv_ref<T>>)
                {
                    argument_types[operator_id].push_back(system.get_type<T>());
                }
            }
            
            type_system& system;
            
            // indexed from return TYPE ID, returns index of operator
            blt::expanding_buffer<std::vector<operator_id>> terminals;
            blt::expanding_buffer<std::vector<operator_id>> non_terminals;
            // indexed from OPERATOR ID (operator number)
            blt::expanding_buffer<std::vector<type>> argument_types;
            blt::expanding_buffer<argc_t> operator_argc;
            blt::hashset_t<operator_id> static_types;
            std::vector<detail::callable_t> operators;
            std::vector<detail::transfer_t> transfer_funcs;
    };
    
    class gp_program
    {
        public:
            /**
             * Note about context size: This is required as context is passed to every operator in the GP tree, this context will be provided by your
             * call to one of the evaluator functions. This was the nicest way to provide this as C++ lacks reflection
             *
             * @param system type system to use in tree generation
             * @param engine random engine to use throughout the program. TODO replace this with something better
             * @param context_size number of arguments which are always present as "context" to the GP system / operators
             */
            explicit gp_program(type_system& system, std::mt19937_64 engine):
                    system(system), engine(engine)
            {}
            
            void generate_tree();
            
            [[nodiscard]] inline std::mt19937_64& get_random()
            {
                return engine;
            }
            
            [[nodiscard]] inline bool choice()
            {
                static std::uniform_int_distribution dist(0, 1);
                return dist(engine);
            }
            
            /**
             * @param cutoff precent in floating point form chance of the event happening.
             * @return
             */
            [[nodiscard]] inline bool choice(double cutoff)
            {
                static std::uniform_real_distribution dist(0.0, 1.0);
                return dist(engine) < cutoff;
            }
            
            [[nodiscard]] inline type_system& get_typesystem()
            {
                return system;
            }
            
            inline operator_id select_terminal(type_id id)
            {
                std::uniform_int_distribution<blt::size_t> dist(0, terminals[id].size() - 1);
                return terminals[id][dist(engine)];
            }
            
            inline operator_id select_non_terminal(type_id id)
            {
                std::uniform_int_distribution<blt::size_t> dist(0, non_terminals[id].size() - 1);
                return non_terminals[id][dist(engine)];
            }
            
            inline std::vector<type>& get_argument_types(operator_id id)
            {
                return argument_types[id];
            }
            
            inline std::vector<operator_id>& get_type_terminals(type_id id)
            {
                return terminals[id];
            }
            
            inline std::vector<operator_id>& get_type_non_terminals(type_id id)
            {
                return non_terminals[id];
            }
            
            inline argc_t get_argc(operator_id id)
            {
                return operator_argc[id];
            }
            
            inline detail::callable_t& get_operation(operator_id id)
            {
                return operators[id];
            }
            
            inline detail::transfer_t& get_transfer_func(operator_id id)
            {
                return transfer_funcs[id];
            }
            
            inline bool is_static(operator_id id)
            {
                return static_types.contains(static_cast<blt::size_t>(id));
            }
            
            template<typename Context>
            inline void set_operations(gp_operations<Context>&& op)
            {
                terminals = std::move(op.terminals);
                non_terminals = std::move(op.non_terminals);
                argument_types = std::move(op.argument_types);
                static_types = std::move(op.static_types);
                operator_argc = std::move(op.operator_argc);
                operators = std::move(op.operators);
                transfer_funcs = std::move(op.transfer_funcs);
            }
        
        private:
            type_system& system;
            blt::gp::stack_allocator alloc;
            std::mt19937_64 engine;
            
            // indexed from return TYPE ID, returns index of operator
            blt::expanding_buffer<std::vector<operator_id>> terminals;
            blt::expanding_buffer<std::vector<operator_id>> non_terminals;
            // indexed from OPERATOR ID (operator number)
            blt::expanding_buffer<std::vector<type>> argument_types;
            blt::expanding_buffer<argc_t> operator_argc;
            blt::hashset_t<operator_id> static_types;
            std::vector<detail::callable_t> operators;
            std::vector<detail::transfer_t> transfer_funcs;
    };
    
}

#endif //BLT_GP_PROGRAM_H