Plan cube export face targets in app core

src/app_core/document_export.h

@@ -1,8 +1,11 @@
 #pragma once
 
 #include "app_core/app_dialog.h"
+#include "document/document.h"
 #include "foundation/result.h"
 
+#include <array>
+#include <cstddef>
 #include <string>
 #include <string_view>
 #include <utility>
@@ -23,6 +26,16 @@ struct DocumentExportStemTarget {
     std::string stem_path;
 };
 
+struct DocumentCubeFaceExportFileTarget {
+    std::string face_name;
+    std::string path;
+};
+
+struct DocumentCubeFaceExportTarget {
+    std::array<DocumentCubeFaceExportFileTarget, pp::document::cube_face_count> faces;
+    std::size_t face_count = 0;
+};
+
 struct DocumentExportSuggestedName {
     std::string name;
 };
@@ -535,6 +548,51 @@ public:
     return pp::foundation::Result<DocumentExportStemTarget>::success(std::move(target));
 }
 
+[[nodiscard]] constexpr std::array<std::string_view, pp::document::cube_face_count>
+document_cube_face_export_names() noexcept
+{
+    return {
+        "front",
+        "right",
+        "back",
+        "left",
+        "top",
+        "bottom",
+    };
+}
+
+[[nodiscard]] inline pp::foundation::Result<DocumentCubeFaceExportTarget> make_document_cube_face_export_target(
+    std::string_view work_directory,
+    std::string_view document_name)
+{
+    if (work_directory.empty()) {
+        return pp::foundation::Result<DocumentCubeFaceExportTarget>::failure(
+            pp::foundation::Status::invalid_argument("work directory must not be empty"));
+    }
+
+    if (document_name.empty()) {
+        return pp::foundation::Result<DocumentCubeFaceExportTarget>::failure(
+            pp::foundation::Status::invalid_argument("document name must not be empty"));
+    }
+
+    DocumentCubeFaceExportTarget target;
+    const auto face_names = document_cube_face_export_names();
+    target.face_count = face_names.size();
+    for (std::size_t face_index = 0; face_index < face_names.size(); ++face_index) {
+        auto& face = target.faces[face_index];
+        face.face_name = face_names[face_index];
+        face.path.reserve(work_directory.size() + document_name.size() + face_names[face_index].size() + 6);
+        face.path += work_directory;
+        face.path += "/";
+        face.path += document_name;
+        face.path += "-";
+        face.path += face_names[face_index];
+        face.path += ".png";
+    }
+
+    return pp::foundation::Result<DocumentCubeFaceExportTarget>::success(std::move(target));
+}
+
 [[nodiscard]] inline pp::foundation::Result<DocumentExportSuggestedName> make_document_export_suggested_name(
     std::string_view document_name,
     std::string_view suffix)