refactor

backend/src/documents/metadata.rs

@@ -0,0 +1,52 @@
+use serde_json::{map::Entry, Map, Value};
+
+use crate::error::{AppError, AppResult};
+
+pub fn merge_document_metadata(existing: Value, updates: Value) -> AppResult<Value> {
+    let mut base = match existing {
+        Value::Object(map) => map,
+        Value::Null => Map::new(),
+        _ => {
+            return Err(AppError::bad_request(
+                "existing metadata is not an object; set replace=true to overwrite",
+            ));
+        }
+    };
+
+    let incoming = match updates {
+        Value::Object(map) => map,
+        _ => {
+            return Err(AppError::bad_request(
+                "metadata value must be a JSON object when replace is false",
+            ));
+        }
+    };
+
+    merge_metadata_maps(&mut base, incoming);
+    Ok(Value::Object(base))
+}
+
+fn merge_metadata_maps(target: &mut Map<String, Value>, updates: Map<String, Value>) {
+    for (key, value) in updates {
+        match target.entry(key) {
+            Entry::Occupied(mut entry) => {
+                let existing = entry.get_mut();
+                match value {
+                    Value::Object(update_map) => {
+                        if let Value::Object(existing_map) = existing {
+                            merge_metadata_maps(existing_map, update_map);
+                        } else {
+                            *existing = Value::Object(update_map);
+                        }
+                    }
+                    other => {
+                        *existing = other;
+                    }
+                }
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(value);
+            }
+        }
+    }
+}