#include <iostream>
#include <string>
#include <vector>
#include <unordered_map>
#include <variant>
#include <exception>
#include <memory>
#include <sstream>
#include <functional>
#include "pilang.hpp"


static inline bool is_sep(const char character) {
    return character == ' ' or character == '\t' or character == '\n';
}


namespace Pilang3 {
    std::unordered_map<std::string, Cmddesc> builtinCmds;

    Condition::Condition(const std::string& expression) {

        for (auto characterit = expression.begin(); characterit < expression.end(); characterit++) {
            if (*characterit == ',') {
                exprlen = std::distance(expression.begin(), characterit);
                break;
            }
        }
    }

    Evaluation::Evaluation(SharedEnvironment env, const std::string& expression, const bool autoeval, const bool autoderef) {
        // Count off trailing spaces
        ssize_t tspaces = 0;
        for (const auto& character : expression) {
            if (is_sep(character)) {
                tspaces++;
            } else {
                break;
            }
        }
        // Get scope
        auto &scope = env->currScope();
        // Parse arguments if any
        if (not expression.empty() and static_cast<ssize_t>(expression.size()) != tspaces) {
            Variable thisarg;
            bool in_command_name = true;
            bool in_string = false;
            bool newarg = false;
            bool escapenext = false;
            std::string cache;
            for (auto characterit = expression.begin() + tspaces; characterit < expression.end(); characterit++) {
                char character = *characterit;
                // Start new command name
                if (in_command_name) {
                    if (not is_sep(character) and character != ';') {
                        cache.push_back(character);
                    } else {
                        command_name = cache;
                        cache.clear();
                        if (character == ';') {
                            exprlen = std::distance(expression.begin(), characterit);
                            break;
                        } else {
                            in_command_name = false;
                            newarg = true;
                        }
                    }
                }
                // Start new argument
                else if (newarg) {
                    // Skip spaces
                    if (is_sep(character)) continue;
                    // Guess type by first character
                    newarg = false;
                    if (std::isdigit(character) or character == '-' or character == '+') {
                        // Integer
                        thisarg.type = Variable::id_integer;
                        goto parsechar;
                    } else if (character == '"') {
                        // String
                        in_string = true;
                        thisarg.type = Variable::id_string;
                    } else if (character == '&') {
                        // Expression
                        thisarg.type = Variable::id_evaluation;
                    } else if (character == '{' or character == '(') {
                        // Function
                        thisarg.type = Variable::id_function;
                        goto parsechar;
                    } else if (character == '!') {
                        // Function
                        thisarg.type = Variable::id_condition;
                        goto parsechar;
                    } else {
                        // Reference
                        thisarg.type = Variable::id_reference;
                        goto parsechar;
                    }
                } else {
                    parsechar:
                    bool maybe_end_of_arg = character == ',' or character == ';';
                    // Do whatever (depends on type)
                    switch (thisarg.type) {
                    case Variable::id_integer: {
                        // Integer
                        if (is_sep(character)) continue;
                        else if (maybe_end_of_arg) {
                            // End argument
                            try {
                                thisarg.data = integer_type(std::stoi(cache));
                            } catch (std::invalid_argument&) {
                                throw exceptions::BadInteger();
                            }
                            newarg = true;
                        } else {
                            cache.push_back(character);
                        }
                    } break;
                    case Variable::id_string: {
                        // String
                        if (character == '"' and not escapenext) {
                            std::get<std::string>(thisarg.data).append(cache);
                            cache.clear();
                            in_string = not in_string;
                        } else if (in_string and character == '\\' and not escapenext) {
                            escapenext = true;
                        } else if (in_string) {
                            cache.push_back(character);
                        } else if (maybe_end_of_arg) {
                            newarg = true;
                        }
                    } break;
                    case Variable::id_reference: {
                        // Reference
                        if (maybe_end_of_arg) {
                            if (autoderef) {
                                auto res = scope.find(cache);
                                if (res == scope.end()) {
                                    throw exceptions::NoSuchVariable();
                                }
                                thisarg = *res->second;
                            } else {
                                thisarg.data = cache;
                            }
                            newarg = true;
                        } else {
                            cache.push_back(character);
                        }
                    } break;
                    case Variable::id_evaluation: {
                        // Check for exclaimation mark
                        bool noexec = *characterit == '!';
                        if (noexec) {
                            // Skip exclaimation mark if required
                            characterit++;
                        }
                        // Evaluate
                        auto evaluation = std::make_shared<Evaluation>(env, std::string(characterit, expression.end()), autoeval, autoderef);
                        // Execute if possible
                        if (autoeval and not noexec) {
                            thisarg = evaluation->execute(env);
                        } else {
                            thisarg.data = SharedEvaluationWBool{evaluation, not noexec};
                        }
                        // Skip over expression in iteration
                        character = *(characterit += evaluation->exprlen + 1);
                        newarg = true;
                    } break;
                    case Variable::id_function: {
                        auto thisfunc = std::make_shared<Function>();
                        if (character == '(') {
                            thisfunc->new_scope = true;
                            // Parse
                            while (++characterit != expression.end()) {
                                if (*characterit == ',' or *characterit == ')') {
                                    if (not cache.empty()) {
                                        thisfunc->argumentNames.push_back(cache);
                                        cache.clear();
                                    }
                                    if (*characterit == ')') {
                                        break;
                                    } else {
                                        continue;
                                    }
                                } else if (is_sep(*characterit)) {
                                    // Check if seperator is after ( or ,
                                    if (cache.empty()) {
                                        // If yes; ignore character
                                        continue;
                                    } else {
                                        // If no, go on
                                    }
                                }
                                cache.push_back(*characterit);
                            }
                            // Skip spaces
                            while (characterit + 1 != expression.end() and is_sep(*(++characterit)));
                            // Check for {
                            if (*characterit != '{') {
                                throw exceptions::UnexpectedEndOfExpression();
                            }
                        }
                        // Parse expression itself
                        characterit++;
                        while (*characterit != '}') {
                            // Evaluate
                            SharedEvaluation evaluation;
                            try {
                                evaluation = std::make_shared<Evaluation>(env, std::string(characterit, expression.end()), false, false);
                            }  catch (exceptions::emptyExpr&) {
                                throw exceptions::UnexpectedEndOfExpression();
                            }
                            thisfunc->evalChain.push_back(evaluation);
                            // Skip over expression in iteration
                            characterit += evaluation->exprlen + 1;
                            if (characterit == expression.end()) {
                                throw exceptions::UnexpectedEndOfExpression();
                            }
                        }
                        // Append
                        character = *(++characterit);
                        thisarg.data = thisfunc;
                        newarg = true;
                    } break;
                    case Variable::id_condition: {
                        //TODO
                    } break;
                    }
                    // Check if argument might be a condition
                    //TODO
                    // Actually end argument if required
                    if (newarg) {
                        arguments.push_back(thisarg);
                        cache.clear();
                        // Check if end of command was reached
                        if (character == ';') {
                            exprlen = std::distance(expression.begin(), characterit);
                            break;
                        }
                    }
                }
            }
            // Check exprlen
            if (exprlen < 0) {
                throw exceptions::UnexpectedEndOfExpression();
            }
            // Find command
            auto res = Pilang3::builtinCmds.find(command_name);
            if (res == Pilang3::builtinCmds.end()) {
                // Find function
                auto res = scope.find(command_name);
                if (res == scope.end() or res->second->type != Variable::id_function) {
                    command = {command_name, {nullptr, {}, false}};
                } else {
                    auto fnc = std::get<SharedFunction>(res->second->data);
                    // Create argument list
                    std::vector<Variable::Type> argtype_list;
                    argtype_list.reserve(fnc->argumentNames.size());
                    for (auto counter = fnc->argumentNames.size(); counter != 0; counter--) {
                        argtype_list.push_back(Variable::id_any);
                    }
                    // Command is function executor
                    command = {"", {
                        [fnc] (SharedEnvironment env, Cmdargs& args) {
                            return fnc->execute(env, args);
                        }, argtype_list, false
                    }};
                }
            } else {
                std::get<1>(command) = res->second;
            }
        } else {
            throw exceptions::emptyExpr();
        }
    }

    void Evaluation::derefer(SharedEnvironment env) {
        for (auto& arg : arguments) {
            switch (arg.type) {
                case Variable::id_evaluation: {
                    SharedEvaluation evaluation;
                    bool exec;
                    std::tie(evaluation, exec) = std::get<SharedEvaluationWBool>(arg.data);
                    // Execute evaluation only if allowed (ie not &!)
                    if (exec) {
                        evaluation->derefer(env);
                        arg = evaluation->execute(env);
                    }
                } break;
                case Variable::id_reference: {
                    auto &scope = env->currScope();
                    auto res = scope.find(std::get<std::string>(arg.data));
                    if (res == scope.end()) {
                        throw exceptions::NoSuchVariable();
                    }
                    arg = *res->second;
                } break;
                default: continue;
            }
        }
    }

    Variable Evaluation::execute(SharedEnvironment env) {
        std::vector<Variable::Type> argstypes;
        bool anymoreopts;
        Cmdfnc func;
        Cmddesc desc;
        std::string name;
        std::tie(name, desc) = command;
        std::tie(func, argstypes, anymoreopts) = desc;
        if (func) {
            // Check args
            if ((arguments.size() > argstypes.size() and not anymoreopts) or (arguments.size() < argstypes.size())) {
                throw exceptions::BadArgs();
            }
            for (uint16_t argidx = 0; argidx != argstypes.size(); argidx++) {
                if (argstypes[argidx] != Variable::id_any and argstypes[argidx] != arguments[argidx].type) {
                    throw exceptions::BadArgs();
                }
            }
            // Run
            return func(env, arguments);
        } else {
            // Find function
            auto &scope = env->currScope();
            auto res = scope.find(command_name);
            if (res == scope.end() or res->second->type != Variable::id_function) {
                throw exceptions::NoSuchCommand();
            } else {
                // Execute function
                return std::get<SharedFunction>(res->second->data)->execute(env, arguments);
            }
        }
    }

    Variable Function::execute(SharedEnvironment env, Cmdargs& args) {
        // Check if enough arguments were given
        if (args.size() != argumentNames.size()) {
            throw exceptions::BadArgs();
        }
        // Go on
        Variable fres;
        // Apply arguments to new scope
        if (new_scope) {
            auto scope = env->currScope();
            scope.reserve(args.size());
            for (auto args_idx = args.size(); args_idx != 0; args_idx--) {
                scope[argumentNames[args_idx - 1]] = std::make_shared<Variable>(args[args_idx - 1]);
            }
            env->variableScope.push(std::move(scope)); // Start new scope
        }
        // Copy, derefer and execute all evaluations
        for (auto& evaluation : evalChain) {
            auto thiseval = Evaluation(*evaluation);
            thiseval.derefer(env);
            fres = thiseval.execute(env);
            // Return on return
            if (fres.type == Variable::id_retval and new_scope) {
                auto fresdata = std::get<SharedVariable>(fres.data);
                if (new_scope) env->variableScope.pop(); // End scope
                return *fresdata;
            }
        }
        if (new_scope) env->variableScope.pop(); // End scope
        return Variable({
            Variable::id_null,
            0
        });
    }
};