cpp_drawing/input_file.cpp

#include "input_file.hpp"

#include <functional>
#include <iostream>
#include <map>
#include <string>
#include <format>

#include "shapes/circle.hpp"
#include "shapes/line.hpp"
#include "shapes/rectangle.hpp"

#include "math/constants.hpp"

InputFile::InputFile(const std::filesystem::path& path) : m_file(path), m_cmdsProcessed(0)
{
    if (m_file.bad())
    {
        throw std::runtime_error("Cannot open " + path.string() + " for reading");
    }
}

// istream >> operator for math::Vector
static std::istream& operator>>(std::istream& is, math::Vector& vec)
{
    return is >> vec.x >> vec.y;
}

// command name -> command handler map
using CommandMap = std::map<std::string, std::function<void(std::istream&)>>;

/**
 * @brief Get the type name as a string
 *
 * @tparam T Type
 * @return Type name
 */
template <class T>
static const char* GetTypeName()
{
    return typeid(T).name();
}

template <>
const char* GetTypeName<int>()
{
    return "integer";
}

template <>
const char* GetTypeName<float>()
{
    return "float";
}

template <>
const char* GetTypeName<math::Vector>()
{
    return "vector";
}

template <>
const char* GetTypeName<std::string>()
{
    return "string";
}

/**
 * @brief Read a value from an `istream` and check for errors
 *
 * @tparam T Type of the value to read
 * @param is Input stream
 * @return Read value
 */
template <class T>
static T ReadVal(std::istream& is)
{
    T v;
    is >> v;

    if (is.bad())
        throw std::runtime_error(std::format("Could not parse {} from stream", GetTypeName<T>()));

    return v;
}

/**
 * @brief Register a command in a command map
 *
 * @tparam TArgs Argument types
 * @tparam THandler Handler type
 * @param cmdMap Command map
 * @param cmd Command name
 * @param handler Command handler
 */
template <class... TArgs, class THandler>
static void RegisterCommand(CommandMap& cmdMap, const std::string& cmd, THandler&& handler)
{
    cmdMap[cmd] = [handler = std::forward<THandler>(handler)](std::istream& is) {
        std::apply(handler, std::tuple<TArgs...>{ReadVal<TArgs>(is)...}); // tuple because of order of evaluation...
    };
}

shapes::Group InputFile::Parse()
{
    shapes::Group shapes;

    CommandMap cmds;

    /* SHAPES */

    RegisterCommand<int, int, int, int>(cmds, "line", [&shapes](int x1, int y1, int x2, int y2) {
        shapes.AddShape<shapes::Line>(math::Vector{x1, y1}, math::Vector{x2, y2});
    });

    RegisterCommand<int, int, int>(cmds, "circle", [&shapes](int x, int y, int r) {
        if (r <= 0)
            throw std::runtime_error("Circle radius must be a positive integer");

        shapes.AddShape<shapes::Circle>(math::Vector{x, y}, static_cast<float>(r));
    });

    RegisterCommand<int, int, int, int>(cmds, "rect", [&shapes](int x, int y, int w, int h) {
        if (w <= 0 || h <= 0)
            throw std::runtime_error("Rect dimensions must be positive integers");

        shapes.AddShape<shapes::Rectangle>(math::Vector{x, y}, math::Vector{w, h});
    });

    /* TRANSFORMS */

    RegisterCommand<int, int>(cmds, "translate", [&shapes](int ox, int oy) { shapes.Translate(math::Vector{ox, oy}); });

    RegisterCommand<int, int, float>(cmds, "rotate", [&shapes](int cx, int cy, float deg) {
        shapes.Rotate(math::Vector{cx, cy}, deg * math::DEG_TO_RAD);
    });

    RegisterCommand<int, int, float>(cmds, "scale", [&shapes](int cx, int cy, float factor) {
        if (factor < std::numeric_limits<decltype(factor)>().epsilon())
            throw std::runtime_error("Scale factor must be a non-zero real number");

        shapes.Scale(math::Vector{cx, cy}, factor);
    });

    /* ---------------------------- */

    std::string line;
    size_t lineNum = 0;

    try
    {
        while (std::getline(m_file, line))
        {
            ++lineNum;

            if (line.empty() || line[0] == '#')
                continue;

            auto commentPos = line.find('#');
            if (commentPos != std::string::npos)
                line = line.substr(0, commentPos);

            std::istringstream iss(line);
            std::string cmdName = ReadVal<std::string>(iss);

            auto cmd = cmds.find(cmdName);

            if (cmd == cmds.end())
                throw std::runtime_error("Unknown command: " + cmdName);

            cmd->second(iss);
            ++m_cmdsProcessed;
        }
    }
    catch (const std::exception& e)
    {
        throw std::runtime_error(std::format("Line {}: {}", lineNum, e.what()));
    }

    return shapes;
}