qswiki/database/hdr/sqlite_modern_cpp/utility/variant.h

#pragma once

#include "../errors.h"
#include <sqlite3.h>
#include <optional>
#include <variant>

namespace sqlite::utility
{
template <typename... Options> struct VariantFirstNullable
{
	using type = void;
};
template <typename T, typename... Options> struct VariantFirstNullable<T, Options...>
{
	using type = typename VariantFirstNullable<Options...>::type;
};
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename T, typename... Options> struct VariantFirstNullable<std::optional<T>, Options...>
{
	using type = std::optional<T>;
};
#endif
template <typename T, typename... Options> struct VariantFirstNullable<std::unique_ptr<T>, Options...>
{
	using type = std::unique_ptr<T>;
};
template <typename... Options> struct VariantFirstNullable<std::nullptr_t, Options...>
{
	using type = std::nullptr_t;
};
template <typename Callback, typename... Options> inline void variant_select_null(Callback &&callback)
{
	if constexpr(std::is_same_v<typename VariantFirstNullable<Options...>::type, void>)
	{
		throw errors::mismatch("NULL is unsupported by this variant.", "", SQLITE_MISMATCH);
	}
	else
	{
		std::forward<Callback>(callback)(typename VariantFirstNullable<Options...>::type());
	}
}

template <typename... Options> struct VariantFirstIntegerable
{
	using type = void;
};
template <typename T, typename... Options> struct VariantFirstIntegerable<T, Options...>
{
	using type = typename VariantFirstIntegerable<Options...>::type;
};
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename T, typename... Options> struct VariantFirstIntegerable<std::optional<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstIntegerable<T, Options...>::type, T>,
									std::optional<T>, typename VariantFirstIntegerable<Options...>::type>;
};
#endif
template <typename T, typename... Options>
struct VariantFirstIntegerable<
	std::enable_if_t<std::is_same_v<typename VariantFirstIntegerable<T, Options...>::type, T>>, std::unique_ptr<T>,
	Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstIntegerable<T, Options...>::type, T>,
									std::unique_ptr<T>, typename VariantFirstIntegerable<Options...>::type>;
};
template <typename... Options> struct VariantFirstIntegerable<int, Options...>
{
	using type = int;
};
template <typename... Options> struct VariantFirstIntegerable<sqlite_int64, Options...>
{
	using type = sqlite_int64;
};
template <typename Callback, typename... Options> inline auto variant_select_integer(Callback &&callback)
{
	if constexpr(std::is_same_v<typename VariantFirstIntegerable<Options...>::type, void>)
	{
		throw errors::mismatch("Integer is unsupported by this variant.", "", SQLITE_MISMATCH);
	}
	else
	{
		std::forward<Callback>(callback)(typename VariantFirstIntegerable<Options...>::type());
	}
}

template <typename... Options> struct VariantFirstFloatable
{
	using type = void;
};
template <typename T, typename... Options> struct VariantFirstFloatable<T, Options...>
{
	using type = typename VariantFirstFloatable<Options...>::type;
};
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename T, typename... Options> struct VariantFirstFloatable<std::optional<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstFloatable<T, Options...>::type, T>,
									std::optional<T>, typename VariantFirstFloatable<Options...>::type>;
};
#endif
template <typename T, typename... Options> struct VariantFirstFloatable<std::unique_ptr<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstFloatable<T, Options...>::type, T>,
									std::unique_ptr<T>, typename VariantFirstFloatable<Options...>::type>;
};
template <typename... Options> struct VariantFirstFloatable<float, Options...>
{
	using type = float;
};
template <typename... Options> struct VariantFirstFloatable<double, Options...>
{
	using type = double;
};
template <typename Callback, typename... Options> inline auto variant_select_float(Callback &&callback)
{
	if constexpr(std::is_same_v<typename VariantFirstFloatable<Options...>::type, void>)
	{
		throw errors::mismatch("Real is unsupported by this variant.", "", SQLITE_MISMATCH);
	}
	else
	{
		std::forward<Callback>(callback)(typename VariantFirstFloatable<Options...>::type());
	}
}

template <typename... Options> struct VariantFirstTextable
{
	using type = void;
};
template <typename T, typename... Options> struct VariantFirstTextable<T, Options...>
{
	using type = typename VariantFirstTextable<void, Options...>::type;
};
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename T, typename... Options> struct VariantFirstTextable<std::optional<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstTextable<T, Options...>::type, T>,
									std::optional<T>, typename VariantFirstTextable<Options...>::type>;
};
#endif
template <typename T, typename... Options> struct VariantFirstTextable<std::unique_ptr<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstTextable<T, Options...>::type, T>,
									std::unique_ptr<T>, typename VariantFirstTextable<Options...>::type>;
};
template <typename... Options> struct VariantFirstTextable<std::string, Options...>
{
	using type = std::string;
};
template <typename... Options> struct VariantFirstTextable<std::u16string, Options...>
{
	using type = std::u16string;
};
template <typename Callback, typename... Options> inline void variant_select_text(Callback &&callback)
{
	if constexpr(std::is_same_v<typename VariantFirstTextable<Options...>::type, void>)
	{
		throw errors::mismatch("Text is unsupported by this variant.", "", SQLITE_MISMATCH);
	}
	else
	{
		std::forward<Callback>(callback)(typename VariantFirstTextable<Options...>::type());
	}
}

template <typename... Options> struct VariantFirstBlobable
{
	using type = void;
};
template <typename T, typename... Options> struct VariantFirstBlobable<T, Options...>
{
	using type = typename VariantFirstBlobable<Options...>::type;
};
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename T, typename... Options> struct VariantFirstBlobable<std::optional<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstBlobable<T, Options...>::type, T>,
									std::optional<T>, typename VariantFirstBlobable<Options...>::type>;
};
#endif
template <typename T, typename... Options> struct VariantFirstBlobable<std::unique_ptr<T>, Options...>
{
	using type = std::conditional_t<std::is_same_v<typename VariantFirstBlobable<T, Options...>::type, T>,
									std::unique_ptr<T>, typename VariantFirstBlobable<Options...>::type>;
};
template <typename T, typename A, typename... Options>
struct VariantFirstBlobable<std::enable_if_t<std::is_pod_v<T>>, std::vector<T, A>, Options...>
{
	using type = std::vector<T, A>;
};
template <typename Callback, typename... Options> inline auto variant_select_blob(Callback &&callback)
{
	if constexpr(std::is_same_v<typename VariantFirstBlobable<Options...>::type, void>)
	{
		throw errors::mismatch("Blob is unsupported by this variant.", "", SQLITE_MISMATCH);
	}
	else
	{
		std::forward<Callback>(callback)(typename VariantFirstBlobable<Options...>::type());
	}
}

template <typename... Options> inline auto variant_select(int type)
{
	return [type](auto &&callback) {
		using Callback = decltype(callback);
		switch(type)
		{
		case SQLITE_NULL:
			variant_select_null<Callback, Options...>(std::forward<Callback>(callback));
			break;
		case SQLITE_INTEGER:
			variant_select_integer<Callback, Options...>(std::forward<Callback>(callback));
			break;
		case SQLITE_FLOAT:
			variant_select_float<Callback, Options...>(std::forward<Callback>(callback));
			break;
		case SQLITE_TEXT:
			variant_select_text<Callback, Options...>(std::forward<Callback>(callback));
			break;
		case SQLITE_BLOB:
			variant_select_blob<Callback, Options...>(std::forward<Callback>(callback));
			break;
		default:;
			/* assert(false); */
		}
	};
}
} // namespace sqlite::utility