Flipdot-display/src/esp32/system/settings_store.cpp

#include "system/settings_store.h"

#include <Preferences.h>
#include <stddef.h>
#include <string.h>

static const char *NAMESPACE = "flipdot";
static const char *KEY = "settings";
// Increase when the Settings struct changes; old records are then ignored (defaults),
// unless OLD_VERSIONS says how to read them
static const uint16_t VERSION = 3;

// Older versions: fields were only added at the end, so the start of an old record has
// the same layout. New fields keep their defaults.
struct OldVersion
{
	uint16_t version;
	size_t fields; // bytes of Settings that version had
};
static const OldVersion OLD_VERSIONS[] = {
	{1, offsetof(Settings, off_page)},
	{2, offsetof(Settings, drive)},
};

struct StoredSettings
{
	uint16_t version;
	uint16_t size;
	Settings settings;
};

void loadSettings(Settings &settings)
{
	settings = Settings();
	StoredSettings stored;
	memset(&stored, 0, sizeof(stored));
	Preferences prefs;
	prefs.begin(NAMESPACE, true);
	size_t read = prefs.getBytes(KEY, &stored, sizeof(stored));
	prefs.end();

	Settings loaded;
	if (read == sizeof(stored) && stored.version == VERSION && stored.size == sizeof(Settings))
		loaded = stored.settings;
	else
	{
		const OldVersion *old = nullptr;
		for (const OldVersion &o : OLD_VERSIONS)
			if (o.version == stored.version)
				old = &o;
		if (!old || stored.size < old->fields || stored.size > sizeof(Settings) ||
			read != offsetof(StoredSettings, settings) + stored.size)
			return;
		memcpy((void *)&loaded, &stored.settings, old->fields);
	}
	if (validateSettings(loaded) == nullptr)
		settings = loaded;
}

void saveSettings(const Settings &settings)
{
	StoredSettings stored;
	stored.version = VERSION;
	stored.size = sizeof(Settings);
	stored.settings = settings;
	Preferences prefs;
	prefs.begin(NAMESPACE, false);
	prefs.putBytes(KEY, &stored, sizeof(stored));
	prefs.end();
}