//
// 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>

int to_int(const std::string& val) {
    std::istringstream iss {val};
    int result;
    iss >> result;
    return result;
}

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

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

    // first pass: read program & resolve labels
    for (std::string line; std::getline(in, line); ++_pc) {
        if (line[0] == ':') {
            _labels.emplace(line.substr(1), _pc);
        } else {
            _prog.push_back(line);
        }
    }

    // second pass: run program
    _pc = 0;
    while (_pc < _prog.size() && !done) {
        // fetch next instruction
        std::string code {_prog[_pc]};
        
        // check literal int
        if (std::isdigit(code[0])) {
            _stack.push_back(code);
            _pc++;
            continue;
        }

        // check literal string
        if (code[0] == '\\') {
            _stack.push_back(code.substr(1));
            _pc++;
            continue;
        }

        // check label ref
        if (code[0] == '>') {
            _stack.push_back(code.substr(1));
            _pc++;
            continue;
        }

        // check var assignment
        if (code[0] == '=') {
            _vars[code.substr(1)] = _stack.back();
            _stack.pop_back();
            _pc++;
            continue;
        }

        // check var ref
        if (code[0] == '$') {
            _stack.push_back(_vars[code.substr(1)]);
            _pc++;
            continue;
        }
        
        // exec instruction
        exec_instruction(code, done);
    }

    if (_stack.size()) {
        result = _stack.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 throw syntax_error {code};
}

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

void interpreter::add() {
    int val2 {to_int(_stack.back())};
    _stack.pop_back();
    int val1 {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val1 + val2));
    _pc++;
}

void interpreter::sub() {
    int val2 {to_int(_stack.back())};
    _stack.pop_back();
    int val1 {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val1 - val2));
    _pc++;
}

void interpreter::mul() {
    int val2 {to_int(_stack.back())};
    _stack.pop_back();
    int val1 {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val1 * val2));
    _pc++;
}

void interpreter::div() {
    int val2 {to_int(_stack.back())};
    _stack.pop_back();
    int val1 {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val1 / val2));
    _pc++;
}

void interpreter::mod() {
    int val2 {to_int(_stack.back())};
    _stack.pop_back();
    int val1 {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val1 % val2));
    _pc++;
}

void interpreter::abs() {
    int val {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(val < 0 ? -val : val));
    _pc++;
}

void interpreter::neg() {
    int val {to_int(_stack.back())};
    _stack.pop_back();
    _stack.push_back(std::to_string(-val));
    _pc++;
}

void interpreter::inc() {
    int val {to_int(_stack.back()) + 1};
    _stack.pop_back();
    _stack.push_back(std::to_string(val));
    _pc++;
}

void interpreter::dec() {
    int val {to_int(_stack.back()) - 1};
    _stack.pop_back();
    _stack.push_back(std::to_string(val));
    _pc++;
}

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

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

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

void interpreter::slc() {
    int to {to_int(_stack.back())};
    _stack.pop_back();
    int from {to_int(_stack.back())};
    _stack.pop_back();
    std::string val {_stack.back()};
    _stack.pop_back();
    _stack.push_back(val.substr(from, to - from));
    _pc++;
}

void interpreter::idx() {
    int idx {to_int(_stack.back())};
    _stack.pop_back();
    std::string val {_stack.back()};
    _stack.pop_back();
    val = val[idx];
    _stack.emplace_back(val);
    _pc++;
}

void interpreter::cat() {
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    _stack.emplace_back(val1 + val2);
    _pc++;
}

void interpreter::len() {
    std::string val {_stack.back()};
    _stack.pop_back();
    _stack.push_back(std::to_string(val.size()));
    _pc++;
}

void interpreter::rot() {
    std::string val {_stack.back()};
    _stack.pop_back();
    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;
    });
    _stack.push_back(val);
    _pc++;
}

void interpreter::enl() {
    std::string val {_stack.back()};
    _stack.pop_back();
    val += '\n';
    _stack.push_back(val);
    _pc++;
}

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

void interpreter::gto() {
    _pc = _labels[_stack.back()];
    _stack.pop_back();
}

void interpreter::geq() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    if (val1 == val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gne() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    if (val1 != val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::glt() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    if (val1 < val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gle() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    if (val1 <= val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::ggt() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    if (val1 > val2) {
        _pc = _labels[label];
    } else {
        _pc++;
    }
}

void interpreter::gge() {
    std::string label {_stack.back()};
    _stack.pop_back();
    std::string val2 {_stack.back()};
    _stack.pop_back();
    std::string val1 {_stack.back()};
    _stack.pop_back();
    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();
}