Arbutils/src/String/StringView.hpp

#ifndef ARBUTILS_STRINGVIEW_HPP
#define ARBUTILS_STRINGVIEW_HPP

#include <cstddef>
#include <cstdint>
#include <cstring>
#include <memory>
#include <string_view>
#include "BasicStringView.hpp"

#if WINDOWS
#define STDSTRINGCONSTEXPR
#else
#define STDSTRINGCONSTEXPR constexpr
#endif

namespace ArbUt {
    class __ConstStringCharHolder {
        char* _value = 0;

        __ConstStringCharHolder(const __ConstStringCharHolder& o) = delete;
        __ConstStringCharHolder& operator=(const __ConstStringCharHolder& other) = delete;

    public:
        __ConstStringCharHolder(const char* value, size_t length) noexcept : _value(new char[length + 1]) {
            strncpy(_value, value, length + 1);
        }
        ~__ConstStringCharHolder() noexcept { delete[] _value; }
        inline constexpr const char* GetValue() const noexcept { return _value; }
    };
}

inline static constexpr char charToLower(const char c) { return (c >= 'A' && c <= 'Z') ? c + ('a' - 'A') : c; }
static uint32_t constexpr Hash(char const* input) {
    return charToLower(*input) ? static_cast<uint32_t>(charToLower(*input)) + 33 * Hash(input + 1) : 5381;
};
static int constexpr CalcLength(const char* str) { return *str ? 1 + CalcLength(str + 1) : 0; }

namespace ArbUt {
    /// \ingroup Strings
    /// @brief A constant, non-editable string that allows copies to share the same string object.
    class StringView final : public BasicStringView {
    private:
        static std::shared_ptr<__ConstStringCharHolder> __emptyString;
        static inline const std::shared_ptr<__ConstStringCharHolder>& GetEmptyString() { return __emptyString; }

        std::shared_ptr<__ConstStringCharHolder> _str = GetEmptyString();

    public:
        /// @brief Instantiate a StringView using a C string.
        /// @param str A null-terminated C string.
        StringView(const char* str) noexcept
            : BasicStringView(CalcLength(str), Hash(str)), _str(new __ConstStringCharHolder(str, CalcLength(str))) {}
        /// @brief Instantiate a StringView using a C string, as well as it's length.
        /// @param str A null-terminated C string.
        /// @param length The length of the C string
        StringView(const char* str, size_t length) noexcept
            : BasicStringView(length, Hash(str)), _str(new __ConstStringCharHolder(str, length)) {}
        StringView() noexcept : BasicStringView(0, Hash("")) {}

        /* Copy operators */
        /// @brief Copy operator
        /// @param other Other StringView
        StringView(const StringView& other) noexcept : BasicStringView(other._length, other._hash), _str(other._str) {}
        /// @brief Special constructor of stringview, specifically designed for use of conversion from StringViewLiteral
        /// to StringView.
        /// @param other Other StringView
        /// @param c A null-terminated C string.
        /// @param length The length of the C string.
        StringView(const BasicStringView& other, const char* c, size_t length) noexcept
            : BasicStringView(length, other.GetHash()), _str(new __ConstStringCharHolder(c, length)) {}

        /// @brief Assignment operator.
        /// @param other Stringview to assign.
        /// @return current stringview.
        StringView& operator=(const StringView& other) noexcept {
            if (this == &other || _str == other._str) {
                return *this;
            }
            _str = other._str;
            _length = other._length;
            _hash = other._hash;
            return *this;
        }

        /// @brief Returns null-terminated C string.
        /// @return Null-terminated C string.
        [[nodiscard]] inline const char* c_str() const noexcept override { return _str->GetValue(); }
        /// @brief Returns std string_view of internal C string.
        /// @return std::string_view.
        [[nodiscard]] inline std::string_view std_str() const noexcept override { return _str->GetValue(); }

        inline constexpr bool operator==(const std::string_view& rhs) const noexcept override {
            return _hash == Hash(rhs.data());
        }
        inline constexpr bool operator!=(const std::string_view& rhs) const noexcept override {
            return _hash != Hash(rhs.data());
        }
        inline constexpr bool operator==(const char* rhs) const noexcept override { return _hash == Hash(rhs); }
        inline constexpr bool operator!=(const char* rhs) const noexcept override { return _hash != Hash(rhs); }

        /// @brief Calculates the hash for a given C string.
        /// @param val A null-terminated C string.
        /// @return A hash of the given string.
        [[maybe_unused]] [[nodiscard]] inline static constexpr uint32_t CalculateHash(const char* val) noexcept {
            return Hash(val);
        }

        /// @brief Calculates the hash for a given std string.
        /// @param val A std string.
        /// @return A hash of the given string.
        [[maybe_unused]] [[nodiscard]] inline static constexpr uint32_t
        CalculateHash(const std::string_view& val) noexcept {
            return Hash(val.data());
        }

        /// @brief Returns an empty string.
        /// @return An empty string.
        static const StringView& EmptyString();
    };
}

namespace std {
    /// @brief Helper class for hashing string views.
    template <> struct hash<ArbUt::StringView> {
        /// @brief Returns the hash of a stringview.
        /// @param s a StringView.
        /// @return The hash of the StringView.
        constexpr std::size_t operator()(ArbUt::StringView const& s) const noexcept { return s.GetHash(); }
    };
}
#endif // ARBUTILS_STRINGVIEW_HPP