Extract image import route planning

src/app_core/document_import.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "foundation/result.h"
+
+namespace pp::app {
+
+enum class DocumentImageImportAction {
+    import_equirectangular,
+    place_transform,
+};
+
+struct DocumentImageImportPlan {
+    int width = 0;
+    int height = 0;
+    DocumentImageImportAction action = DocumentImageImportAction::place_transform;
+    bool imports_equirectangular = false;
+    bool enters_transform_mode = false;
+};
+
+[[nodiscard]] inline pp::foundation::Result<DocumentImageImportPlan> plan_document_image_import(
+    int width,
+    int height) noexcept
+{
+    if (width <= 0 || height <= 0) {
+        return pp::foundation::Result<DocumentImageImportPlan>::failure(
+            pp::foundation::Status::invalid_argument("image dimensions must be positive"));
+    }
+
+    const auto wide_equirect = static_cast<long long>(width) == static_cast<long long>(height) * 2LL;
+    const auto vertical_cube_strip = width == height / 6;
+
+    DocumentImageImportPlan plan;
+    plan.width = width;
+    plan.height = height;
+    plan.imports_equirectangular = wide_equirect || vertical_cube_strip;
+    plan.enters_transform_mode = !plan.imports_equirectangular;
+    plan.action = plan.imports_equirectangular
+        ? DocumentImageImportAction::import_equirectangular
+        : DocumentImageImportAction::place_transform;
+    return pp::foundation::Result<DocumentImageImportPlan>::success(plan);
+}
+
+} // namespace pp::app