Plan new document creation in app core

src/app_core/document_session.h

@@ -3,6 +3,7 @@
 #include "app_core/document_route.h"
 #include "foundation/result.h"
 
+#include <array>
 #include <cctype>
 #include <cstdio>
 #include <string>
@@ -65,6 +66,12 @@ struct DocumentVersionTarget {
     std::string path;
 };
 
+struct NewDocumentPlan {
+    DocumentFileTarget target;
+    int resolution = 0;
+    DocumentFileWriteDecision write_decision = DocumentFileWriteDecision::save_now;
+};
+
 [[nodiscard]] constexpr ProjectOpenDecision plan_project_open(bool has_unsaved_changes) noexcept
 {
     return has_unsaved_changes
@@ -175,6 +182,41 @@ struct DocumentVersionTarget {
         : DocumentFileWriteDecision::save_now;
 }
 
+[[nodiscard]] constexpr pp::foundation::Result<int> document_resolution_from_index(int index) noexcept
+{
+    constexpr std::array<int, 6> resolutions{ 512, 1024, 1536, 2048, 4096, 8192 };
+    if (index < 0 || static_cast<std::size_t>(index) >= resolutions.size()) {
+        return pp::foundation::Result<int>::failure(
+            pp::foundation::Status::out_of_range("document resolution index is out of range"));
+    }
+
+    return pp::foundation::Result<int>::success(resolutions[static_cast<std::size_t>(index)]);
+}
+
+template <typename ExistsPredicate>
+[[nodiscard]] pp::foundation::Result<NewDocumentPlan> plan_new_document(
+    std::string_view work_directory,
+    std::string_view document_name,
+    int resolution_index,
+    ExistsPredicate&& exists)
+{
+    const auto resolution = document_resolution_from_index(resolution_index);
+    if (!resolution) {
+        return pp::foundation::Result<NewDocumentPlan>::failure(resolution.status());
+    }
+
+    auto target = make_document_file_target(work_directory, document_name);
+    if (!target) {
+        return pp::foundation::Result<NewDocumentPlan>::failure(target.status());
+    }
+
+    NewDocumentPlan plan;
+    plan.target = std::move(target.value());
+    plan.resolution = resolution.value();
+    plan.write_decision = plan_document_file_write(exists(plan.target.path));
+    return pp::foundation::Result<NewDocumentPlan>::success(std::move(plan));
+}
+
 [[nodiscard]] inline bool has_legacy_two_character_version_suffix(std::string_view document_name) noexcept
 {
     const auto dot = document_name.rfind('.');