handle merging tag categories

src/lib/tags.ts

@@ -98,6 +98,62 @@ export function deleteCategoryForce(id: string): void {
   if (result.changes === 0) throw new Error(`Category not found: ${id}`)
 }
 
+/**
+ * Merge all tags from `sourceId` category into `targetId` category, then
+ * delete the source category. Tags with conflicting names (case-insensitive)
+ * are combined: their media_tags and tag_mappings rows are re-pointed to the
+ * target tag, and the source tag is deleted.
+ */
+export function mergeCategories(sourceId: string, targetId: string): void {
+  const db = getDb()
+
+  const source = db.prepare('SELECT id, name FROM tag_categories WHERE id = ?').get(sourceId) as TagCategory | undefined
+  if (!source) throw new Error(`Source category not found: ${sourceId}`)
+  const target = db.prepare('SELECT id, name FROM tag_categories WHERE id = ?').get(targetId) as TagCategory | undefined
+  if (!target) throw new Error(`Target category not found: ${targetId}`)
+
+  const sourceTags = db
+    .prepare('SELECT id, name, category_id as categoryId FROM tags WHERE category_id = ?')
+    .all(sourceId) as Tag[]
+  const targetTags = db
+    .prepare('SELECT id, name, category_id as categoryId FROM tags WHERE category_id = ?')
+    .all(targetId) as Tag[]
+
+  const targetTagsByNameLower = new Map(targetTags.map((t) => [t.name.toLowerCase(), t]))
+
+  const txn = db.transaction(() => {
+    for (const srcTag of sourceTags) {
+      const conflict = targetTagsByNameLower.get(srcTag.name.toLowerCase())
+      if (conflict) {
+        // Re-point media_tags from source tag to target tag (ignore duplicates)
+        db.prepare(
+          `INSERT OR IGNORE INTO media_tags (item_key, tag_id)
+           SELECT item_key, ? FROM media_tags WHERE tag_id = ?`
+        ).run(conflict.id, srcTag.id)
+        db.prepare('DELETE FROM media_tags WHERE tag_id = ?').run(srcTag.id)
+
+        // Re-point tag_mappings from source tag to target tag (ignore duplicates)
+        db.prepare(
+          `UPDATE OR IGNORE tag_mappings SET tag_id = ? WHERE tag_id = ?`
+        ).run(conflict.id, srcTag.id)
+        // Delete any remaining (were duplicates that couldn't be updated)
+        db.prepare('DELETE FROM tag_mappings WHERE tag_id = ?').run(srcTag.id)
+
+        // Delete the source tag
+        db.prepare('DELETE FROM tags WHERE id = ?').run(srcTag.id)
+      } else {
+        // No conflict — just move the tag to the target category
+        db.prepare('UPDATE tags SET category_id = ? WHERE id = ?').run(targetId, srcTag.id)
+      }
+    }
+
+    // Delete the now-empty source category
+    db.prepare('DELETE FROM tag_categories WHERE id = ?').run(sourceId)
+  })
+
+  txn()
+}
+
 // ─── Tags ─────────────────────────────────────────────────────────────────────
 
 export function getTags(categoryId?: string): Tag[] {