chore: Refactor stores to use PersistableStore CRTP template (#2464)

lib/Serialization/PersistableStore.cpp

@@ -0,0 +1,45 @@
+#include "PersistableStore.h"
+
+#include <HalStorage.h>
+#include <Logging.h>
+#include <ObfuscationUtils.h>
+
+bool PersistableStoreBase::writeDocToFile(const char* path, const JsonDocument& doc) {
+  Storage.mkdir("/.crosspoint");
+  String json;
+  serializeJson(doc, json);
+  if (!Storage.writeFile(path, json)) {
+    LOG_ERR("PERSIST", "Failed to write %s", path);
+    return false;
+  }
+  return true;
+}
+
+bool PersistableStoreBase::readDocFromFile(const char* path, JsonDocument& doc) {
+  if (!Storage.exists(path)) {
+    return false;  // Expected on first boot — not an error.
+  }
+  String json = Storage.readFile(path);
+  if (json.isEmpty()) {
+    LOG_ERR("PERSIST", "Failed to read %s (empty)", path);
+    return false;
+  }
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("PERSIST", "JSON parse error in %s: %s", path, error.c_str());
+    return false;
+  }
+  return true;
+}
+
+std::string PersistableStoreBase::extractPassword(JsonVariantConst doc, bool& needsResave) {
+  bool ok = false;
+  std::string pass = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
+  if (!ok) {
+    // Deobfuscation failed — fall back to legacy plaintext password.
+    pass = doc["password"] | "";
+    if (!pass.empty()) needsResave = true;
+  }
+  // A successfully decoded empty string is a legitimate value; preserve as-is.
+  return pass;
+}

lib/Serialization/PersistableStore.h

@@ -0,0 +1,82 @@
+#pragma once
+
+#include <Arduino.h>
+#include <ArduinoJson.h>
+
+#include <string>
+
+/**
+ * @brief Non-template core of PersistableStore.
+ *
+ * All ArduinoJson parse/serialize machinery is instantiated once here (in
+ * PersistableStore.cpp) instead of in every store's translation unit. GCC
+ * emits the JSON serializer/parser templates as local .isra clones per TU
+ * (~0.5KB each), so keeping serializeJson/deserializeJson out of the stores
+ * is what makes the abstraction flash-neutral.
+ */
+class PersistableStoreBase {
+ protected:
+  PersistableStoreBase() = default;
+  ~PersistableStoreBase() = default;
+
+  // Serializes doc and writes it to path (ensures /.crosspoint exists). Logs on failure.
+  static bool writeDocToFile(const char* path, const JsonDocument& doc);
+
+  // Reads path and parses it into doc. Returns false silently when the file
+  // does not exist (expected on first boot); logs on read/parse failure.
+  static bool readDocFromFile(const char* path, JsonDocument& doc);
+
+  /**
+   * Helper function for extracting an obfuscated password from a JSON value.
+   * Accepts JsonVariantConst so callers can pass either a whole JsonDocument
+   * or a JsonObject element (e.g. inside an array iteration).
+   * If the decoded password requires a resave (e.g. from plaintext fallback), `needsResave` is set to true.
+   */
+  static std::string extractPassword(JsonVariantConst doc, bool& needsResave);
+};
+
+/**
+ * @brief Base class for persistable singletons using CRTP.
+ *
+ * Derived classes must provide:
+ * - A private default constructor
+ * - friend class PersistableStore<Derived>;
+ * - static const char* getFilePath();
+ * - void toJson(JsonDocument& doc) const;
+ * - bool fromJson(JsonVariantConst doc);
+ *
+ * Note for implementers: read string values as `const char*` (e.g.
+ * `obj["name"] | ""`), never as `| std::string("")` — ArduinoJson's
+ * std::string converter drags a per-TU copy of the whole JSON serializer
+ * into flash via its serializeJson fallback.
+ */
+template <typename T>
+class PersistableStore : public PersistableStoreBase {
+ protected:
+  PersistableStore() = default;
+  ~PersistableStore() = default;
+
+ public:
+  // Delete copy constructor and assignment
+  PersistableStore(const PersistableStore&) = delete;
+  PersistableStore& operator=(const PersistableStore&) = delete;
+
+  static T& getInstance() {
+    static T instance;
+    return instance;
+  }
+
+  bool saveToFile() const {
+    JsonDocument doc;
+    static_cast<const T*>(this)->toJson(doc);
+    return writeDocToFile(T::getFilePath(), doc);
+  }
+
+  bool loadFromFile() {
+    JsonDocument doc;
+    if (!readDocFromFile(T::getFilePath(), doc)) {
+      return false;
+    }
+    return static_cast<T*>(this)->fromJson(doc.as<JsonVariantConst>());
+  }
+};