Route prepared file targets through platform services

docs/modernization/build-inventory.md

@@ -544,8 +544,9 @@ Known local toolchain state:
   hooks, render debug callback hooks, per-frame platform hooks, picker
   callbacks, recording cleanup, exported-image publishing, persistent storage
   flushing, document browse roots, native UI/window state saving, live
-  asset/layout reload policy, diagnostic stacktrace/crash hooks, prepared-file
-  save/download handoff;
+  asset/layout reload policy, diagnostic stacktrace/crash hooks,
+  prepared-file writable target selection, and prepared-file save/download
+  handoff;
   Windows
   live app execution now uses injected
   `WindowsPlatformServices` from

docs/modernization/debt.md

@@ -70,6 +70,7 @@ agent or engineer to remove them without reconstructing context from chat.
 | DEBT-0050 | Open | Modernization | iOS exported-image photo-library publishing and WebGL persistent-storage flushing now dispatch through `PlatformServices`, but non-Windows execution still lives in `src/platform_legacy/legacy_platform_services.*` and forwards to retained `save_image_library`/`webgl_sync` bridges | Preserve current iOS/Web export and save behavior while the Apple/Web platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; platform package smoke once Apple/Web root builds exist | Exported-image publishing and persistent-storage flushing are owned by injected Apple/Web `pp_platform_*` services with no legacy adapter branch |
 | DEBT-0051 | Open | Modernization | Document browser search roots now dispatch through `PlatformServices`, but iOS `Inbox` inclusion still lives in `src/platform_legacy/legacy_platform_services.*` | Preserve current iOS document import/browse behavior while Apple platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; Apple package smoke once root Apple builds exist | Document browse roots are owned by injected Apple and desktop `pp_platform_*` services with no legacy adapter branch |
 | DEBT-0052 | Open | Modernization | Native UI/window state saving now dispatches through `PlatformServices`, but macOS execution still lives in `src/platform_legacy/legacy_platform_services.*` and forwards to the retained Objective-C app bridge | Preserve current Windows/macOS UI persistence while platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; Windows app build; Apple package smoke once root Apple builds exist | UI/window state persistence is owned by injected platform services with no legacy adapter branch |
+| DEBT-0053 | Open | Modernization | Prepared-file writable target selection now dispatches through `PlatformServices`, but iOS/Web target selection still lives in `src/platform_legacy/legacy_platform_services.*` | Preserve mobile/Web export handoff behavior while platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; Windows app build; Apple/Web package smoke once root package builds exist | Prepared-file target selection and save/download handoff are owned by injected platform services with no legacy adapter branch |
 
 ## Closed Debt
 

docs/modernization/roadmap.md

@@ -639,6 +639,10 @@ is preserved while their platform shell implementations are extracted.
 Prepared-file save/download handoff is now also part of the service contract,
 so iOS/Web export completion routes through `PlatformServices` after the app
 writes the temporary/exported payload.
+Prepared-file writable target selection now also dispatches through
+`PlatformServices`, preserving the existing iOS temporary background-write path
+and Web data-path synchronous write path while removing those platform branches
+from `App::pick_file_save`.
 Canvas image export publishing and explicit persistent-storage flushes now
 dispatch through `PlatformServices` too, preserving iOS photo-library export
 publication and WebGL filesystem sync behavior in the legacy adapter while
@@ -1692,7 +1696,8 @@ Results:
   dispatch, render debug callback dispatch, render-capture frame hook dispatch,
   recording cleanup dispatch, exported-image publish dispatch, persistent
   storage flush dispatch, document browse-root dispatch,
-  native UI/window state save dispatch, live asset/layout reload policy dispatch,
+  native UI/window state save dispatch, prepared-file writable target dispatch,
+  live asset/layout reload policy dispatch,
   diagnostic hook dispatch, per-frame platform hook dispatch, picker callback
   dispatch, and prepared-file save/download callback dispatch. The live Windows
   app now

src/app.h

@@ -181,12 +181,9 @@ public:
     bool clipboard_set_text(const std::string& s);
     void pick_image(std::function<void(std::string path)> callback);
     void pick_file(std::vector<std::string> types, std::function<void(std::string path)> callback);
-#if __IOS__ || __WEB__
     void pick_file_save(const std::string& type, const std::string& default_name,
         std::function<void(std::string path)> writer, std::function<void(const std::string& path, bool saved)> callback);
-#else
     void pick_file_save(std::vector<std::string> types, std::function<void(std::string path)> callback);
-#endif
     void pick_dir(std::function<void(std::string path)> callback);
     void display_file(std::string path);
     void share_file(std::string path);

src/app_events.cpp

@@ -152,35 +152,34 @@ void App::pick_file(std::vector<std::string> types, std::function<void (std::str
     active_platform_services().pick_file(std::move(types), std::move(callback));
 }
 
-#if __IOS__
 void App::pick_file_save(const std::string& type, const std::string& default_name,
     std::function<void(std::string)> writer, std::function<void(const std::string& path, bool saved)> callback)
 {
     redraw = true;
-    std::string ext = "." + type;
-    std::string path = tmp_path + "/" + default_name + ext;
-    std::thread([=]{
-        writer(path);
-        save_prepared_file(path, default_name + ext, callback);
-    }).detach();
+    const auto target = active_platform_services().prepare_writable_file(type, default_name, data_path, tmp_path);
+    if (target.path.empty())
+    {
+        callback({}, false);
+        return;
+    }
+
+    LOG("App::pick_file_save %s", target.path.c_str());
+    auto write_and_save = [=] {
+        writer(target.path);
+        save_prepared_file(target.path, target.suggested_name, callback);
+    };
+
+    if (target.write_on_background_thread)
+        std::thread(write_and_save).detach();
+    else
+        write_and_save();
 }
-#elif __WEB__
-void App::pick_file_save(const std::string& type, const std::string& default_name,
-    std::function<void(std::string)> writer, std::function<void(const std::string& path, bool saved)> callback)
-{
-    redraw = true;
-    auto path = data_path + "/" + default_name + "." + type;
-    LOG("App::pick_file_save %s", path.c_str());
-    writer(path);
-    save_prepared_file(path, default_name + "." + type, std::move(callback));
-}
-#else
+
 void App::pick_file_save(std::vector<std::string> types, std::function<void(std::string)> callback)
 {
     redraw = true;
     active_platform_services().pick_save_file(std::move(types), std::move(callback));
 }
-#endif
 
 void App::pick_dir(std::function<void(std::string path)> callback)
 {

src/platform_api/platform_services.h

@@ -10,6 +10,12 @@ namespace pp::platform {
 using PickedPathCallback = std::function<void(std::string path)>;
 using PreparedFileCallback = std::function<void(std::string path, bool saved)>;
 
+struct PreparedFileTarget {
+    std::string path;
+    std::string suggested_name;
+    bool write_on_background_thread = false;
+};
+
 struct PlatformStoragePaths {
     std::string data_path;
     std::string work_path;
@@ -57,6 +63,11 @@ public:
     virtual void pick_file(std::vector<std::string> file_types, PickedPathCallback callback) = 0;
     virtual void pick_save_file(std::vector<std::string> file_types, PickedPathCallback callback) = 0;
     virtual void pick_directory(PickedPathCallback callback) = 0;
+    [[nodiscard]] virtual PreparedFileTarget prepare_writable_file(
+        std::string_view type,
+        std::string_view default_name,
+        std::string_view data_path,
+        std::string_view temporary_path) = 0;
     virtual void save_prepared_file(
         std::string_view path,
         std::string_view suggested_name,

src/platform_legacy/legacy_platform_services.cpp

@@ -431,6 +431,34 @@ public:
 #endif
     }
 
+    [[nodiscard]] pp::platform::PreparedFileTarget prepare_writable_file(
+        std::string_view type,
+        std::string_view default_name,
+        std::string_view data_path,
+        std::string_view temporary_path) override
+    {
+        const std::string name = std::string(default_name) + "." + std::string(type);
+#ifdef __IOS__
+        (void)data_path;
+        return {
+            std::string(temporary_path) + "/" + name,
+            name,
+            true,
+        };
+#elif __WEB__
+        (void)temporary_path;
+        return {
+            std::string(data_path) + "/" + name,
+            name,
+            false,
+        };
+#else
+        (void)data_path;
+        (void)temporary_path;
+        return {};
+#endif
+    }
+
     void display_file(std::string_view path) override
     {
         const std::string value(path);

src/platform_windows/windows_platform_services.cpp

@@ -448,6 +448,19 @@ public:
         invoke_selected_path(path, callback);
     }
 
+    [[nodiscard]] pp::platform::PreparedFileTarget prepare_writable_file(
+        std::string_view type,
+        std::string_view default_name,
+        std::string_view data_path,
+        std::string_view temporary_path) override
+    {
+        (void)type;
+        (void)default_name;
+        (void)data_path;
+        (void)temporary_path;
+        return {};
+    }
+
     void save_prepared_file(
         std::string_view path,
         std::string_view suggested_name,

tests/platform_api/platform_services_tests.cpp

@@ -210,6 +210,20 @@ public:
         callback(directory_path);
     }
 
+    [[nodiscard]] pp::platform::PreparedFileTarget prepare_writable_file(
+        std::string_view type,
+        std::string_view default_name,
+        std::string_view data_path,
+        std::string_view temporary_path) override
+    {
+        ++prepare_writable_file_requests;
+        writable_file_type.assign(type);
+        writable_file_default_name.assign(default_name);
+        writable_file_data_path.assign(data_path);
+        writable_file_temporary_path.assign(temporary_path);
+        return writable_file_target;
+    }
+
     void save_prepared_file(
         std::string_view path,
         std::string_view suggested_name,
@@ -255,6 +269,7 @@ public:
     int pick_file_requests = 0;
     int pick_save_file_requests = 0;
     int pick_directory_requests = 0;
+    int prepare_writable_file_requests = 0;
     int save_prepared_file_requests = 0;
     bool cursor_visible = false;
     bool keyboard_visible = false;
@@ -271,6 +286,10 @@ public:
     std::string exported_image_path;
     std::string browse_work_path;
     std::string browse_data_path;
+    std::string writable_file_type;
+    std::string writable_file_default_name;
+    std::string writable_file_data_path;
+    std::string writable_file_temporary_path;
     std::string picker_path = "D:/Paint/import.png";
     std::string save_path = "D:/Paint/export.ppi";
     std::string directory_path = "D:/Paint";
@@ -286,6 +305,11 @@ public:
         "D:/Paint/work",
         "D:/Paint/Inbox",
     };
+    pp::platform::PreparedFileTarget writable_file_target{
+        "D:/Paint/tmp/export.mp4",
+        "export.mp4",
+        true,
+    };
 
 private:
     std::string clipboard_value_;
@@ -542,6 +566,23 @@ void platform_services_dispatch_prepared_file_save(pp::tests::Harness& harness)
     PP_EXPECT(harness, saved);
 }
 
+void platform_services_dispatch_writable_file_target(pp::tests::Harness& harness)
+{
+    FakePlatformServices fake("unused");
+    pp::platform::PlatformServices& services = fake;
+
+    const auto target = services.prepare_writable_file("mp4", "export", "D:/Paint", "D:/Paint/tmp");
+
+    PP_EXPECT(harness, fake.prepare_writable_file_requests == 1);
+    PP_EXPECT(harness, fake.writable_file_type == "mp4");
+    PP_EXPECT(harness, fake.writable_file_default_name == "export");
+    PP_EXPECT(harness, fake.writable_file_data_path == "D:/Paint");
+    PP_EXPECT(harness, fake.writable_file_temporary_path == "D:/Paint/tmp");
+    PP_EXPECT(harness, target.path == "D:/Paint/tmp/export.mp4");
+    PP_EXPECT(harness, target.suggested_name == "export.mp4");
+    PP_EXPECT(harness, target.write_on_background_thread);
+}
+
 }
 
 int main()
@@ -564,5 +605,6 @@ int main()
     harness.run("platform services dispatch file actions", platform_services_dispatch_file_actions);
     harness.run("platform services dispatch picker callbacks", platform_services_dispatch_picker_callbacks);
     harness.run("platform services dispatch prepared file save", platform_services_dispatch_prepared_file_save);
+    harness.run("platform services dispatch writable file target", platform_services_dispatch_writable_file_target);
     return harness.finish();
 }