Route app save decisions through app core

src/app_core/document_session.h

@@ -13,6 +13,20 @@ enum class CloseRequestDecision {
     wait_for_existing_prompt,
 };
 
+enum class DocumentSaveIntent {
+    save,
+    save_as,
+    save_version,
+    save_dirty_version,
+};
+
+enum class DocumentSaveDecision {
+    no_op,
+    show_save_dialog,
+    save_existing,
+    save_version,
+};
+
 [[nodiscard]] constexpr ProjectOpenDecision plan_project_open(bool has_unsaved_changes) noexcept
 {
     return has_unsaved_changes
@@ -33,4 +47,35 @@ enum class CloseRequestDecision {
         : CloseRequestDecision::show_unsaved_prompt;
 }
 
+[[nodiscard]] constexpr DocumentSaveDecision plan_document_save(
+    bool is_new_document,
+    bool has_unsaved_changes,
+    DocumentSaveIntent intent) noexcept
+{
+    switch (intent) {
+    case DocumentSaveIntent::save:
+        if (is_new_document) {
+            return DocumentSaveDecision::show_save_dialog;
+        }
+        return has_unsaved_changes
+            ? DocumentSaveDecision::save_existing
+            : DocumentSaveDecision::no_op;
+    case DocumentSaveIntent::save_as:
+        return DocumentSaveDecision::show_save_dialog;
+    case DocumentSaveIntent::save_version:
+        return is_new_document
+            ? DocumentSaveDecision::show_save_dialog
+            : DocumentSaveDecision::save_version;
+    case DocumentSaveIntent::save_dirty_version:
+        if (is_new_document) {
+            return DocumentSaveDecision::show_save_dialog;
+        }
+        return has_unsaved_changes
+            ? DocumentSaveDecision::save_version
+            : DocumentSaveDecision::no_op;
+    }
+
+    return DocumentSaveDecision::no_op;
+}
+
 }