draconisplusplus/include/rfl/Literal.hpp

#ifndef RFL_LITERAL_HPP_
#define RFL_LITERAL_HPP_

#include <cstdint>
#include <functional>
#include <limits>
#include <stdexcept>
#include <string>
#include <tuple>
#include <type_traits>

#include "Result.hpp"
#include "internal/StringLiteral.hpp"
#include "internal/VisitTree.hpp"

namespace rfl {

  template <internal::StringLiteral _field>
  struct LiteralHelper {
    constexpr static internal::StringLiteral field_ = _field;
  };

  template <internal::StringLiteral... fields_>
  class Literal {
    using FieldsType = std::tuple<LiteralHelper<fields_>...>;

   public:
    using ValueType = std::conditional_t<
        sizeof...(fields_) <= std::numeric_limits<std::uint8_t>::max(),
        std::uint8_t,
        std::uint16_t>;

    /// The number of different fields or different options that the literal
    /// can assume.
    static constexpr ValueType num_fields_ = sizeof...(fields_);

    using ReflectionType = std::string;

    /// Constructs a Literal from another literal.
    Literal(const Literal<fields_...>& _other) = default;

    /// Constructs a Literal from another literal.
    Literal(Literal<fields_...>&& _other) noexcept = default;

    Literal(const std::string& _str) : value_(find_value(_str).value()) {}

    /// A single-field literal is special because it
    /// can also have a default constructor.
    template <
        ValueType num_fields = num_fields_,
        typename             = std::enable_if_t<num_fields <= 1>>
    Literal() : value_(0) {}

    ~Literal() = default;

    /// Constructs a new Literal.
    template <internal::StringLiteral _name>
    static Literal<fields_...> make() {
      return Literal(Literal<fields_...>::template value_of<_name>());
    }

    /// Constructs a new Literal, equivalent to make, for reasons of
    /// consistency.
    template <internal::StringLiteral _name>
    static Literal<fields_...> from_name() {
      return Literal<fields_...>::template make<_name>();
    }

    /// Constructs a new Literal.
    template <ValueType _value>
    static Literal<fields_...> from_value() {
      static_assert(
          _value < num_fields_, "Value cannot exceed number of fields."
      );
      return Literal<fields_...>(_value);
    }

    /// Constructs a new Literal.
    static Result<Literal<fields_...>> from_value(ValueType _value) {
      if (_value >= num_fields_) {
        return Error("Value cannot exceed number of fields.");
      }
      return Literal<fields_...>(_value);
    }

    /// Determines whether the literal contains the string.
    static bool contains(const std::string& _str) {
      bool found = false;
      has_value(_str, &found);
      return found;
    }

    /// Determines whether the literal contains the string at compile time.
    template <internal::StringLiteral _name>
    static constexpr bool contains() {
      return find_value_of<_name>() != -1;
    }

    /// Determines whether the literal contains any of the strings in the other
    /// literal at compile time.
    template <class OtherLiteralType, int _i = 0>
    static constexpr bool contains_any() {
      if constexpr (_i == num_fields_) {
        return false;
      } else {
        constexpr auto name = find_name_within_own_fields<_i>();
        return OtherLiteralType::template contains<name>() ||
               contains_any<OtherLiteralType, _i + 1>();
      }
    }

    /// Determines whether the literal contains all of the strings in the other
    /// literal at compile time.
    template <class OtherLiteralType, int _i = 0, int _n_found = 0>
    static constexpr bool contains_all() {
      if constexpr (_i == num_fields_) {
        return _n_found == OtherLiteralType::num_fields_;
      } else {
        constexpr auto name = find_name_within_own_fields<_i>();
        if constexpr (OtherLiteralType::template contains<name>()) {
          return contains_all<OtherLiteralType, _i + 1, _n_found + 1>();
        } else {
          return contains_all<OtherLiteralType, _i + 1, _n_found>();
        }
      }
    }

    /// Determines whether the literal has duplicate strings at compile time.
    /// These is useful for checking collections of strings in other contexts.
    static constexpr bool has_duplicates() { return has_duplicate_strings(); }

    /// Constructs a Literal from a string. Returns an error if the string
    /// cannot be found.
    static Result<Literal> from_string(const std::string& _str) {
      const auto to_literal = [](const auto& _v) {
        return Literal<fields_...>(_v);
      };
      return find_value(_str).transform(to_literal);
    };

    /// The name defined by the Literal.
    std::string name() const { return find_name(); }

    /// Returns all possible values of the literal as a
    /// std::vector<std::string>.
    static std::vector<std::string> names() { return allowed_strings_vec(); }

    /// Helper function to retrieve a name at compile time.
    template <int _value>
    constexpr static auto name_of() {
      constexpr auto name = find_name_within_own_fields<_value>();
      return Literal<name>();
    }

    /// Assigns from another literal.
    Literal<fields_...>& operator=(const Literal<fields_...>& _other) = default;

    /// Assigns from another literal.
    Literal<fields_...>& operator=(Literal<fields_...>&& _other
    ) noexcept = default;

    /// Assigns the literal from a string
    Literal<fields_...>& operator=(const std::string& _str) {
      value_ = find_value(_str);
      return *this;
    }

    /// <=> for other Literals with the same fields.
    auto operator<=>(const Literal<fields_...>& _other) const {
      return value() <=> _other.value();
    }

    /// <=> for other Literals with different fields.
    template <internal::StringLiteral... _fields>
    inline auto operator<=>(const Literal<_fields...>& _l2) const {
      return name() <=> _l2.name();
    }

    /// <=> for strings.
    inline auto operator<=>(const std::string& _str) const {
      return name() <=> _str;
    }

    /// <=> for const char*.
    template <internal::StringLiteral... other_fields>
    inline auto operator<=>(const char* _str) const {
      return name() <=> _str;
    }

    /// Equality operator.
    template <class Other>
    bool operator==(const Other& _other) const {
      return (*this <=> _other) == 0;
    }

    /// Alias for .name().
    std::string reflection() const { return name(); }

    /// Returns the number of fields in the Literal.
    static constexpr size_t size() { return num_fields_; }

    /// Alias for .name().
    std::string str() const { return name(); }

    /// Alias for .names().
    static std::vector<std::string> strings() { return allowed_strings_vec(); }

    /// Returns the value actually contained in the Literal.
    ValueType value() const { return value_; }

    /// Returns the value of the string literal in the template.
    template <internal::StringLiteral _name>
    static constexpr ValueType value_of() {
      constexpr auto value = find_value_of<_name>();
      static_assert(value >= 0, "String not supported.");
      return value;
    }

   private:
    /// Only the static methods are allowed to access this.
    Literal(const ValueType _value) : value_(_value) {}

    /// Returns all of the allowed fields.
    static std::string allowed_strings() {
      const auto  vec = allowed_strings_vec();
      std::string str;
      for (size_t i = 0; i < vec.size(); ++i) {
        const auto head = "'" + vec[i] + "'";
        str += i == 0 ? head : (", " + head);
      }
      return str;
    }

    /// Returns all of the allowed fields.
    template <int _i = 0>
    static std::vector<std::string> allowed_strings_vec(
        std::vector<std::string> _values = {}
    ) {
      using FieldType = typename std::tuple_element<_i, FieldsType>::type;
      const auto head = FieldType::field_.str();
      _values.push_back(head);
      if constexpr (_i + 1 < num_fields_) {
        return allowed_strings_vec<_i + 1>(std::move(_values));
      } else {
        return _values;
      }
    }

    /// Whether the Literal contains duplicate strings.
    template <int _i = 1>
    constexpr static bool has_duplicate_strings() {
      if constexpr (_i >= num_fields_) {
        return false;
      } else {
        return is_duplicate<_i>() || has_duplicate_strings<_i + 1>();
      }
    }

    template <int _i, int _j = _i - 1>
    constexpr static bool is_duplicate() {
      using FieldType1 = typename std::tuple_element<_i, FieldsType>::type;
      using FieldType2 = typename std::tuple_element<_j, FieldsType>::type;
      if constexpr (FieldType1::field_ == FieldType2::field_) {
        return true;
      } else if constexpr (_j > 0) {
        return is_duplicate<_i, _j - 1>();
      } else {
        return false;
      }
    }

    /// Finds the correct index associated with
    /// the string at run time.
    template <int _i = 0>
    std::string find_name() const {
      if (_i == value_) {
        using FieldType = typename std::tuple_element<_i, FieldsType>::type;
        return FieldType::field_.str();
      }
      if constexpr (_i + 1 == num_fields_) {
        return "";
      } else {
        return find_name<_i + 1>();
      }
    }

    /// Finds the correct index associated with
    /// the string at compile time within the Literal's own fields.
    template <int _i>
    constexpr static auto find_name_within_own_fields() {
      using FieldType = typename std::tuple_element<_i, FieldsType>::type;
      return FieldType::field_;
    }

    /// Finds the correct value associated with
    /// the string at run time.
    template <int _i = 0>
    static Result<int> find_value(const std::string& _str) {
      using FieldType = typename std::tuple_element<_i, FieldsType>::type;
      if (FieldType::field_.str() == _str) { return _i; }
      if constexpr (_i + 1 == num_fields_) {
        return Error(
            "Literal does not support string '" + _str +
            "'. The following strings are supported: " + allowed_strings() + "."
        );
      } else {
        return find_value<_i + 1>(_str);
      }
    }

    /// Finds the value of a string literal at compile time.
    template <internal::StringLiteral _name, int _i = 0>
    static constexpr int find_value_of() {
      if constexpr (_i == num_fields_) {
        return -1;
      } else {
        using FieldType = typename std::tuple_element<_i, FieldsType>::type;
        if constexpr (FieldType::field_ == _name) {
          return _i;
        } else {
          return find_value_of<_name, _i + 1>();
        }
      }
    }

    /// Whether the literal contains this string.
    template <int _i = 0>
    static void has_value(const std::string& _str, bool* _found) {
      if constexpr (_i == num_fields_) {
        *_found = false;
        return;
      } else {
        using FieldType = typename std::tuple_element<_i, FieldsType>::type;
        if (FieldType::field_.str() == _str) {
          *_found = true;
          return;
        }
        return has_value<_i + 1>(_str, _found);
      }
    }

    static_assert(
        sizeof...(fields_) <= std::numeric_limits<ValueType>::max(),
        "Too many fields."
    );

    static_assert(
        sizeof...(fields_) <= 1 || !has_duplicates(),
        "Duplicate strings are not allowed in a Literal."
    );

   private:
    /// The underlying value.
    ValueType value_;
  };

  /// Helper function to retrieve a name at compile time.
  template <class LiteralType, int _value>
  inline constexpr auto name_of() {
    return LiteralType::template name_of<_value>();
  }

  /// Helper function to retrieve a value at compile time.
  template <class LiteralType, internal::StringLiteral _name>
  inline constexpr auto value_of() {
    return LiteralType::template value_of<_name>();
  }

} // namespace rfl

namespace std {

  template <rfl::internal::StringLiteral... fields>
  struct hash<rfl::Literal<fields...>> {
    size_t operator()(const rfl::Literal<fields...>& _l) const {
      return hash<int>()(static_cast<int>(_l.value()));
    }
  };

} // namespace std

#endif // RFL_LITERAL_HPP_