z-bar-qt/Plugins/ZShell/Settings/codecs.hpp

#pragma once

#include <qhash.h>
#include <qjsonvalue.h>
#include <qlist.h>
#include <qmetaobject.h>
#include <qvariant.h>

#include <optional>

#include "common.hpp"

namespace ZShell::settings {

struct DecodeResult {
	QVariant value;
	std::optional<Diagnostic> error;
	QList<qsizetype>
		indexPath; // Index path of the failing element, outermost list first
};

class ValueCodec {
	public:
	explicit ValueCodec(const QMetaType& type, ExpectedType expected);
	virtual ~ValueCodec() = default;

	// Returns the shared codec for a type, or nullptr if the type is unsupported
	static ValueCodec* codecFor(const QMetaType& type);

	// Returns the shared codec for a union of types, or nullptr if any of them is unsupported
	static ValueCodec* unionFor(const QList<QMetaType>& types);

	[[nodiscard]] QMetaType type() const;
	[[nodiscard]] ExpectedType expected()
		const; // The JSON type this decodes from
	[[nodiscard]] virtual QJsonValue encode(const QVariant& value) const = 0;
	[[nodiscard]] virtual DecodeResult decode(const QJsonValue& value) const = 0;

	protected:
	const QMetaType m_type;
	const ExpectedType m_expected;

	Q_DISABLE_COPY_MOVE(ValueCodec)
};

#define CODEC(Type, Expected)                                                  \
	class Type##Codec : public ValueCodec {                                    \
		public:                                                                \
		explicit Type##Codec(const QMetaType& type)                            \
			: ValueCodec(type, ExpectedType::Expected) {}                      \
                                                                               \
		[[nodiscard]] QJsonValue encode(const QVariant& value) const override; \
		[[nodiscard]] DecodeResult decode(                                     \
			const QJsonValue& value) const override;                           \
	};

CODEC(Bool, Bool)
CODEC(Int, Int)
CODEC(Real, Real)
CODEC(String, String)
CODEC(VariantList, Array)
CODEC(VariantMap, Object)

#undef CODEC

class EnumCodec : public ValueCodec {
	public:
	explicit EnumCodec(const QMetaType& type, const QMetaEnum& metaEnum);

	[[nodiscard]] QJsonValue encode(const QVariant& value) const override;
	[[nodiscard]] DecodeResult decode(const QJsonValue& value) const override;

	private:
	const QMetaEnum m_metaEnum;
};

template <typename Container> class ListCodec : public ValueCodec {
	using Value = Container::value_type;

	public:
	explicit ListCodec(const QMetaType& type, const ValueCodec* elementCodec);

	[[nodiscard]] QJsonValue encode(const QVariant& value) const override;
	[[nodiscard]] DecodeResult decode(const QJsonValue& value) const override;

	private:
	const ValueCodec* m_elementCodec;
};

// Decodes any one of several types, for options that accept more than one shape
class UnionCodec : public ValueCodec {
	public:
	explicit UnionCodec(const QList<const ValueCodec*>& alternatives);

	[[nodiscard]] QJsonValue encode(const QVariant& value) const override;
	[[nodiscard]] DecodeResult decode(const QJsonValue& value) const override;

	private:
	const QList<const ValueCodec*>
		m_alternatives; // Tried in order, so the first to accept a value wins
	const QList<ExpectedType>
		m_expectedTypes; // Types of the alternatives, for diagnostics
	QHash<int, const ValueCodec*>
		m_byType; // Type id to alternative, for encoding
};

} // namespace ZShell::settings