feat(reader): End of Book next-book suggestions (#2499) (#2532)

src/activities/reader/EndOfBookOptions.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <atomic>
+#include <string>
+#include <vector>
+
+class GfxRenderer;
+class MappedInputManager;
+
+// Shared End-of-Book next-book menu for the EPUB and XTC readers. Collects up to
+// MAX_SUGGESTIONS sibling books once per reader session, handles the menu input, and
+// draws the end screen. With no suggestions the end screen keeps its historical
+// plain-title look and behavior.
+class EndOfBookOptions {
+ public:
+  enum class Action { None, Redraw, OpenBook, GoHome, LastPage };
+
+  static constexpr size_t MAX_SUGGESTIONS = 3;
+
+  // Scans the book's folder for suggestions; no-op when already loaded. Call ONLY from
+  // the reader's render() (the render task, serialized by RenderLock) — the loaded flag
+  // is the release/acquire publication point that lets the main task read the finished
+  // list safely.
+  void loadOnce(const std::string& currentBookPath);
+
+  // True when the suggestion menu is showing and should own the reader's input.
+  bool menuActive() const;
+
+  // Menu input handling, following the standard list idiom: side Up/Down and front
+  // Left/Right move the selection (wrapping), Confirm opens it (or Home), and a short
+  // Back press returns to the last page of the book. Fills openPath when the result is
+  // OpenBook. Returns Action::None when nothing relevant was pressed; callers continue
+  // their normal input path (keeping long-press Back to the file browser working).
+  Action handleMenuInput(const MappedInputManager& input, std::string* openPath);
+
+  // Draws the full end screen (plain title, or the suggestion menu) onto a cleared buffer.
+  void render(GfxRenderer& renderer, const MappedInputManager& input) const;
+
+ private:
+  std::string folder;
+  // Written by the render task in loadOnce(), immutable afterwards; the main task only
+  // reads it after isLoaded is observed true (acquire), so no further locking is needed.
+  std::vector<std::string> names;
+  int selector = 0;
+  std::atomic<bool> isLoaded{false};
+
+  std::string fullPath(size_t index) const;
+};