Add duplicate file detection with skip/overwrite options

When uploading a file that already exists in a shared space (same filename),
the UI now shows the existing file info with Overwrite and Skip buttons
instead of silently creating a duplicate.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

portal/templates/portal/shared_space/home.html

@@ -67,6 +67,43 @@
         border-color: var(--error);
     }
 
+    .result-item.duplicate {
+        border-color: #f59e0b;
+    }
+
+    .duplicate-actions {
+        display: flex;
+        gap: 0.5rem;
+    }
+
+    .duplicate-actions button {
+        border: none;
+        padding: 0.35rem 0.85rem;
+        border-radius: 4px;
+        cursor: pointer;
+        font-size: 0.8rem;
+        font-weight: 500;
+    }
+
+    .btn-overwrite {
+        background: var(--primary);
+        color: white;
+    }
+
+    .btn-overwrite:hover {
+        background: var(--primary-hover);
+    }
+
+    .btn-skip {
+        background: var(--border);
+        color: var(--text);
+    }
+
+    .btn-skip:hover {
+        background: var(--text-muted);
+        color: white;
+    }
+
     .result-info {
         flex: 1;
     }
@@ -249,9 +286,7 @@ function formatBytes(bytes) {
     return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
 }
 
-function uploadFile(file) {
+function uploadFile(file, action) {
-    const itemId = 'upload-' + Date.now() + Math.random().toString(36).substr(2, 9);
-
     // Check file size before upload (skip if unlimited)
     if (maxSize > 0 && file.size > maxSize) {
         const item = document.createElement('div');
@@ -266,10 +301,15 @@ function uploadFile(file) {
         return;
     }
 
-    // Create result item
+    // Create or reuse result item
-    const item = document.createElement('div');
+    let item = action ? document.getElementById('dup-' + file.name) : null;
-    item.className = 'result-item';
+    if (!item) {
-    item.id = itemId;
+        item = document.createElement('div');
+        item.className = 'result-item';
+        results.insertBefore(item, results.firstChild);
+    } else {
+        item.className = 'result-item';
+    }
     item.innerHTML = `
         <div class="result-info">
             <h3>${file.name}</h3>
@@ -277,11 +317,10 @@ function uploadFile(file) {
             <div class="progress-bar"><div class="progress" style="width: 0%"></div></div>
         </div>
     `;
-    results.insertBefore(item, results.firstChild);
 
-    // Upload
     const formData = new FormData();
     formData.append('file', file);
+    if (action) formData.append('action', action);
 
     const xhr = new XMLHttpRequest();
 
@@ -306,6 +345,32 @@ function uploadFile(file) {
                     <button class="copy-btn" onclick="copyLink(this, '${data.share.url}')">Copy</button>
                 </div>
             `;
+        } else if (xhr.status === 409) {
+            const data = JSON.parse(xhr.responseText);
+            item.id = 'dup-' + file.name;
+            item.classList.add('duplicate');
+            const existingSize = data.existing_file.size ? formatBytes(data.existing_file.size) : 'unknown size';
+            item.innerHTML = `
+                <div class="result-info">
+                    <h3>${file.name}</h3>
+                    <div class="meta">"${data.existing_file.title}" already exists (${existingSize})</div>
+                </div>
+                <div class="duplicate-actions">
+                    <button class="btn-overwrite" data-action="overwrite">Overwrite</button>
+                    <button class="btn-skip" data-action="skip">Skip</button>
+                </div>
+            `;
+            item.querySelector('.btn-overwrite').addEventListener('click', () => uploadFile(file, 'overwrite'));
+            item.querySelector('.btn-skip').addEventListener('click', () => {
+                item.classList.remove('duplicate');
+                item.classList.add('error');
+                item.innerHTML = `
+                    <div class="result-info">
+                        <h3>${file.name}</h3>
+                        <div class="meta">Skipped (duplicate)</div>
+                    </div>
+                `;
+            });
         } else {
             let errorMsg = 'Upload failed';
             try {
@@ -314,14 +379,16 @@ function uploadFile(file) {
             } catch(e) {}
             item.classList.add('error');
             item.querySelector('.meta').textContent = errorMsg;
-            item.querySelector('.progress-bar').remove();
+            const pb = item.querySelector('.progress-bar');
+            if (pb) pb.remove();
         }
     });
 
     xhr.addEventListener('error', () => {
         item.classList.add('error');
         item.querySelector('.meta').textContent = 'Upload failed - network error';
-        item.querySelector('.progress-bar').remove();
+        const pb = item.querySelector('.progress-bar');
+        if (pb) pb.remove();
     });
 
     xhr.open('POST', '{% url "shared_space_upload" %}');

portal/views_shared_space.py

@@ -71,6 +71,32 @@ class SharedSpaceUploadAPIView(View):
                     'error': f'File too large. Maximum size is {space.max_file_size_mb}MB'
                 }, status=400)
 
+        action = request.POST.get('action', '')
+
+        # Check for duplicate filename in this space
+        existing = MediaFile.objects.filter(
+            shared_space=space,
+            original_filename=uploaded_file.name,
+        ).first()
+
+        if existing and action != 'overwrite':
+            existing_share = existing.public_shares.filter(is_active=True).first()
+            return JsonResponse({
+                'duplicate': True,
+                'existing_file': {
+                    'id': str(existing.id),
+                    'title': existing.title,
+                    'filename': existing.original_filename,
+                    'size': existing.file_size,
+                    'share_url': existing_share.get_public_url() if existing_share else None,
+                },
+            }, status=409)
+
+        # Overwrite: delete the old file and its shares
+        if existing and action == 'overwrite':
+            existing.file.delete(save=False)
+            existing.delete()
+
         title = request.POST.get('title', '') or uploaded_file.name
         description = request.POST.get('description', '')