//
// interpreter.cpp
// curly
//
// Created by Bob Polis at 2020-09-05
// Copyright (c) 2020 SwiftCoder. All rights reserved.
//

#include "interpreter.hpp"
#include <cctype>
#include <algorithm>
#include <sstream>

void interpreter::reset() {
    _prog.clear();
    _values.clear();
    _labels.clear();
    _vars.clear();
    _calls.clear();
    _pc_offsets.clear();
    _pc = 0;
}

std::string interpreter::eval(std::istream& in, bool& done) {
    std::string result;
    reset();
    done = false;

    // first pass: read program & resolve labels, ignore comments
    for (std::string line; std::getline(in, line);) {
        if (line[0] == ':') { // check label definition
            _labels.emplace(line.substr(1), _prog.size());
            _pc_offsets.push_back(_prog.size());
        } else if (line[0] == '#') { // check comment
            _pc_offsets.push_back(_prog.size());
        } else {
            _prog.push_back(line);
        }
    }

    // second pass: run program
    while (_pc < _prog.size() && !done) {
        // fetch next instruction
        std::string code {_prog[_pc]};

        if (std::isdigit(code[0])) { // check literal int
            _values.push_back(code);
            _pc++;
        } else if (code[0] == '\\' || code[0] == '>') { // check literal string or label ref
            _values.push_back(code.substr(1));
            _pc++;
        } else if (code[0] == '=') { // check var assignment
            _vars[code.substr(1)] = _values.back();
            _values.pop_back();
            _pc++;
        } else if (code[0] == '$') { // check var ref
            _values.push_back(_vars[code.substr(1)]);
            _pc++;
        } else {
            exec_instruction(code, done);
        }
    }

    if (_values.size()) {
        result = _values.back();
    }
    return result;
}

void interpreter::exec_instruction(const std::string& code, bool& done) {
    if (code == "end") done = true;
    else if (code == "add") add();
    else if (code == "sub") sub();
    else if (code == "mul") mul();
    else if (code == "div") div();
    else if (code == "mod") mod();
    else if (code == "abs") abs();
    else if (code == "neg") neg();
    else if (code == "dup") dup();
    else if (code == "inc") inc();
    else if (code == "dec") dec();
    else if (code == "rev") rev();
    else if (code == "slc") slc();
    else if (code == "idx") idx();
    else if (code == "cat") cat();
    else if (code == "len") len();
    else if (code == "rot") rot();
    else if (code == "gto") gto();
    else if (code == "geq") geq();
    else if (code == "gne") gne();
    else if (code == "glt") glt();
    else if (code == "gle") gle();
    else if (code == "ggt") ggt();
    else if (code == "gge") gge();
    else if (code == "fun") fun();
    else if (code == "ret") ret();
    else if (code == "enl") enl();
    else if (code == "inp") inp();
    else if (code == "out") out();
    else if (code == "err") err();
    else {
        auto it = std::upper_bound(_pc_offsets.begin(), _pc_offsets.end(), _pc);
        long num_removed_source_lines {it - _pc_offsets.begin()};
        size_t lineno {num_removed_source_lines + _pc + 1};
        throw syntax_error {code, lineno};
    }
}

inline int interpreter::pop_int() {
    std::istringstream iss {pop_str()};
    int result;
    iss >> result;
    return result;
}

inline std::string interpreter::pop_str() {
    auto val = _values.back();
    _values.pop_back();
    return val;
}

// integer operations -----------------------------------------------------

void interpreter::add() {
    auto val2 = pop_int();
    auto val1 = pop_int();
    _values.push_back(std::to_string(val1 + val2));
    _pc++;
}

void interpreter::sub() {
    auto val2 = pop_int();
    auto val1 = pop_int();
    _values.push_back(std::to_string(val1 - val2));
    _pc++;
}

void interpreter::mul() {
    auto val2 = pop_int();
    auto val1 = pop_int();
    _values.push_back(std::to_string(val1 * val2));
    _pc++;
}

void interpreter::div() {
    auto val2 = pop_int();
    auto val1 = pop_int();
    _values.push_back(std::to_string(val1 / val2));
    _pc++;
}

void interpreter::mod() {
    auto val2 = pop_int();
    auto val1 = pop_int();
    _values.push_back(std::to_string(val1 % val2));
    _pc++;
}

void interpreter::abs() {
    auto val = pop_int();
    _values.push_back(std::to_string(val < 0 ? -val : val));
    _pc++;
}

void interpreter::neg() {
    auto val = pop_int();
    _values.push_back(std::to_string(-val));
    _pc++;
}

void interpreter::inc() {
    auto val = pop_int();
    _values.push_back(std::to_string(val + 1));
    _pc++;
}

void interpreter::dec() {
    auto val = pop_int();
    _values.push_back(std::to_string(val - 1));
    _pc++;
}

// string operations ------------------------------------------------------

void interpreter::dup() {
    _values.push_back(_values.back());
    _pc++;
}

void interpreter::rev() {
    auto val = pop_str();
    std::string result;
    for (auto it = val.rbegin(); it != val.rend(); ++it) {
        result += *it;
    }
    _values.push_back(result);
    _pc++;
}

void interpreter::slc() {
    auto to = pop_int();
    auto from = pop_int();
    auto val = pop_str();
    _values.push_back(val.substr(from, to - from));
    _pc++;
}

void interpreter::idx() {
    auto idx = pop_int();
    auto val = pop_str();
    val = val[idx];
    _values.emplace_back(val);
    _pc++;
}

void interpreter::cat() {
    auto val2 = pop_str();
    auto val1 = pop_str();
    _values.emplace_back(val1 + val2);
    _pc++;
}

void interpreter::len() {
    auto val = pop_str();
    _values.push_back(std::to_string(val.size()));
    _pc++;
}

void interpreter::rot() {
    auto val = pop_str();
    std::transform(val.begin(), val.end(), val.begin(), [](char ch) -> char {
        if (ch >= 'a' && ch <= 'm') {
            return ch + 13;
        } else if (ch >= 'n' && ch <= 'z') {
            return ch - 13;
        } else if (ch >= 'A' && ch <= 'M') {
            return ch + 13;
        } else if (ch >= 'N' && ch <= 'Z') {
            return ch - 13;
        }
        return ch;
    });
    _values.push_back(val);
    _pc++;
}

void interpreter::enl() {
    auto val = pop_str();
    _values.emplace_back(val + '\n');
    _pc++;
}

// tests & jumps ----------------------------------------------------------

void interpreter::gto() {
    _pc = _labels[pop_str()];
}

void interpreter::geq() {
    auto label = pop_str();
    auto val2 = pop_str();
    auto val1 = pop_str();
    if (val1 == val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gne() {
    auto label = pop_str();
    auto val2 = pop_str();
    auto val1 = pop_str();
    if (val1 != val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::glt() {
    auto label = pop_str();
    auto val2 = pop_int();
    auto val1 = pop_int();
    if (val1 < val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gle() {
    auto label = pop_str();
    auto val2 = pop_int();
    auto val1 = pop_int();
    if (val1 <= val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::ggt() {
    auto label = pop_str();
    auto val2 = pop_int();
    auto val1 = pop_int();
    if (val1 > val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gge() {
    auto label = pop_str();
    auto val2 = pop_int();
    auto val1 = pop_int();
    if (val1 >= val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

// subroutines ------------------------------------------------------------

void interpreter::fun() {
    _calls.push_back(_pc + 1); // push return address
    gto();
}

void interpreter::ret() {
    _pc = _calls.back();
    _calls.pop_back();
}

// I/O --------------------------------------------------------------------

void interpreter::inp() {
    std::string val;
    std::cin >> val;
    _values.push_back(val);
    _pc++;
}

void interpreter::out() {
    std::cout << _values.back() << '\n';
    _pc++;
}

void interpreter::err() {
    std::cerr << _values.back() << '\n';
    _pc++;
}