update filename on title change

backend/src/routes/documents.rs

@@ -9,7 +9,7 @@ use axum::http::StatusCode;
 use axum::response::IntoResponse;
 use chrono::{DateTime, NaiveDateTime, Utc};
 use diesel::dsl::exists;
-use diesel::{prelude::*, select, PgConnection};
+use diesel::{prelude::*, result::DatabaseErrorKind, select, PgConnection};
 use serde::{Deserialize, Serialize};
 use serde_json::{json, Value};
 use sha2::{Digest, Sha256};
@@ -726,9 +726,24 @@ pub async fn update_document(
 
     if let Some(title) = new_title {
         let now = Utc::now().naive_utc();
-        diesel::update(documents::table.find(document_id))
-            .set((documents::title.eq(title), documents::updated_at.eq(now)))
-            .execute(&mut conn)?;
+        let new_filename = filename_with_retained_extension(&title, &document.filename);
+
+        let update_result = diesel::update(documents::table.find(document_id)).set((
+            documents::title.eq(&title),
+            documents::filename.eq(&new_filename),
+            documents::updated_at.eq(now),
+        ));
+
+        match update_result.execute(&mut conn) {
+            Ok(_) => {}
+            Err(diesel::result::Error::DatabaseError(DatabaseErrorKind::UniqueViolation, _)) => {
+                return Err(AppError::bad_request(
+                    "another document in this folder already uses that filename",
+                ));
+            }
+            Err(err) => return Err(AppError::from(err)),
+        }
+
         document = documents::table.find(document_id).first(&mut conn)?;
     }
 
@@ -1515,6 +1530,26 @@ fn derive_document_title(original: &str) -> String {
     stem.unwrap_or_else(|| trimmed.to_string())
 }
 
+fn filename_with_retained_extension(title: &str, current_filename: &str) -> String {
+    let extension = FsPath::new(current_filename)
+        .extension()
+        .and_then(|ext| ext.to_str());
+
+    if let Some(ext) = extension {
+        if title
+            .rsplit_once('.')
+            .map(|(_, existing_ext)| existing_ext.eq_ignore_ascii_case(ext))
+            .unwrap_or(false)
+        {
+            title.to_string()
+        } else {
+            format!("{title}.{ext}")
+        }
+    } else {
+        title.to_string()
+    }
+}
+
 async fn load_asset_responses(
     state: &AppState,
     version_id: Uuid,