Recover from merge fiasco

src/FontInstaller.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <SdCardFontRegistry.h>
+
+#include <cstddef>
+#include <cstdint>
+
+/// Shared utility for font installation (device download + browser upload).
+/// Handles directory creation, file validation, deletion, and registry refresh.
+class FontInstaller {
+ public:
+  enum class Error {
+    OK,
+    INVALID_FAMILY_NAME,
+    INVALID_FILE,
+    SD_WRITE_ERROR,
+    MAX_FAMILIES_REACHED,
+  };
+
+  explicit FontInstaller(SdCardFontRegistry& registry);
+
+  /// Validate a family name: alphanumeric + hyphen + underscore only, no path traversal.
+  static bool isValidFamilyName(const char* name);
+
+  /// Ensure /.crosspoint/fonts/<family>/ directory exists.
+  bool ensureFamilyDir(const char* familyName);
+
+  /// Validate a .cpfont file on disk (check magic bytes).
+  bool validateCpfontFile(const char* path);
+
+  /// Build the full SD path for a font file.
+  /// Writes "/.crosspoint/fonts/<family>/<filename>" to outBuf.
+  static void buildFontPath(const char* family, const char* filename, char* outBuf, size_t outBufSize);
+
+  /// Delete a family directory and all .cpfont files in it.
+  /// If the deleted family is the active reader font, clears the setting.
+  Error deleteFamily(const char* familyName);
+
+  /// Re-run registry discovery to pick up new/removed fonts.
+  void refreshRegistry();
+
+  /// Check whether a family name already exists in the registry.
+  bool isFamilyInstalled(const char* familyName) const;
+
+ private:
+  SdCardFontRegistry& registry_;
+
+  static constexpr const char* CPFONT_MAGIC = "CPFONT\0";
+  static constexpr size_t CPFONT_MAGIC_LEN = 8;
+};