#pragma once
#include <stack>
#include <map>
#include "UserScript.h"
#include "UserScript/parser.h"

namespace scripting {
	class ByteCodeInterpreter final : public UserScript {
		std::map<std::string, script_value> variables;
		std::map<std::string, function> functions;
		std::vector<argument> execution_stack;
	
	public:
		struct function_tag {
			std::string name;
			size_t arity;
			std::shared_ptr<const code_location> location;
		};
		
		struct variable_tag {
			std::string name;
			std::shared_ptr<const code_location> location;
		};
		
		enum class operator_t : uint8_t {
			logical_not,
			binary_not,
			unary_plus,
			unary_minus,
			divide,
			modulo,
			multiply,
			subtract,
			add,
			bitshift_left,
			bitshift_right,
			rotate_left,
			rotate_right,
			less_than,
			greater_than,
			less_or_equal_than,
			greater_or_equal_than,
			equals,
			different,
			binary_and,
			binary_or,
			binary_xor,
			logical_and,
			logical_or,
			INTERNAL_jump,
			INTERNAL_jump_if,
			INTERNAL_stack_cls,
		};
		
		struct operand {
			std::variant<script_value, function_tag, variable_tag, operator_t> element;
			std::shared_ptr<const code_location> location;
		};
		
		std::optional<std::reference_wrapper<script_value>> getValue(const std::string &name) {
			if (auto var = variables.find(name); var != variables.end()) {
				return var->second;
			} else {
				return std::nullopt;
			}
		}
		
		bool setValue(const std::string &name, script_value value) {
			if (auto var = variables.find(name); var != variables.end()) {
				var->second = value;
				return true;
			} else {
				variables.emplace(std::make_pair(name, value));
				return false;
			}
		}
		
		std::vector<operand> bytecode;
		size_t instruction_ptr;
		
		script_value resolve(const std::string &name) final {
			auto it = variables.find(name);
			if (it == variables.end()) {
				return script_value{};
			}
			return (*it).second;
		}
		
		script_value resolve_and_pop() {
			if (execution_stack.empty()) return script_value{};
			auto value = std::move(execution_stack.back());
			auto resolved = std::visit([&](auto v) -> script_value {
				if constexpr (std::is_same_v<script_variable, decltype(v)>) {
					auto it = variables.find(v.name);
					if (it == variables.end()) {
						return script_value{};
					}
					return (*it).second;
				} else {
					return v;
				}
			}, value);
			execution_stack.pop_back();
			return resolved;
		}
		
		void big_f_ing_switch(operand &op, std::optional<script_error> &error);
		
		std::vector<ByteCodeInterpreter::operand>
		generate(std::vector<script_error> &errors, ast::block &tree, bool loop = true);
		
		void registerFunction(std::string name, function fn) final {
			functions.insert_or_assign(name, std::move(fn));
		}
		
		void clear_variables() final {
			variables.clear();
		}
		
		int32_t op_count() final {
			return bytecode.size();
		}
		
		int32_t var_count() final {
			return variables.size();
		}
		
		void var_clear() final {
			variables.clear();
		}
		
		std::optional<script_value> var_by_idx(int32_t idx) final {
			if(idx >= var_count() || idx < 0) return std::nullopt;
			for(auto& val : variables) {
				if(not idx--) {
					return val.second;
				}
			}
			return std::nullopt;
		}
		
		std::optional<script_value> varname_by_idx(int32_t idx) final {
			if(idx >= var_count() || idx < 0) return std::nullopt;
			for(auto& val : variables) {
				if(not idx--) {
					return val.first;
				}
			}
			return std::nullopt;
		}
		
		std::variant<script_value, std::vector<script_error>> executeAtOnce(std::string code) final {
			std::vector<script_error> errors;
			auto lexed = ast::lex(code, errors);
			auto parsed = ast::parse(lexed, errors);
			if (not errors.empty()) return errors;
			bytecode = generate(errors, parsed, false);
			if (not errors.empty()) return errors;
			std::optional<script_error> maybe_error;
			instruction_ptr = 0;
			while (instruction_ptr < bytecode.size()) {
				step(maybe_error);
				if (maybe_error) return std::vector<script_error>({maybe_error.value()});
			}
			auto v = resolve_and_pop();
			execution_stack.clear();
			return v;
		}
		
		std::vector<script_error> prepare(std::string code) final {
			std::vector<script_error> errors;
			auto lexed = ast::lex(code, errors);
			auto parsed = ast::parse(lexed, errors);
			if (errors.empty()) {
				bytecode = generate(errors, parsed, true);
			}
			
			return errors;
		}
		
		std::optional<script_error> stepOnce() final {
			std::optional<script_error> error;
			while (not step(error));
			return error;
		}
		
		bool step(std::optional<script_error> &error);
		
		~ByteCodeInterpreter() final {}
	};
}