Add VK OAuth implicit flow and fix sync issues

- Replace manual community token entry with OAuth button that redirects
  to VK authorization and auto-saves token via /vk/callback
- Fix groups.get API call (was groups.getById) to correctly retrieve
  admin group id and name from user token response
- Fix price comparison: VK price.amount is in roubles, not kopecks
- Keep manual token input as fallback when VK_CLIENT_ID is not set

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

web/routes/vk.py

@@ -1,4 +1,5 @@
 from datetime import datetime
+from urllib.parse import urlencode
 
 import httpx
 
@@ -15,6 +16,57 @@ from web.models import User, VkConnection
 router = APIRouter(prefix="/vk")
 
 VK_API_URL = "https://api.vk.com/method"
+VK_OAUTH_URL = "https://oauth.vk.com/authorize"
+
+
+async def _fetch_group_info(token: str) -> tuple[str | None, str | None]:
+    """Returns (group_id, group_name) for the first admin group, or (None, None)."""
+    try:
+        async with httpx.AsyncClient() as client:
+            resp = await client.get(
+                f"{VK_API_URL}/groups.get",
+                params={
+                    "access_token": token,
+                    "v": settings.VK_API_VERSION,
+                    "filter": "admin",
+                    "extended": 1,
+                    "count": 1,
+                },
+                timeout=15,
+            )
+            if resp.status_code == 200:
+                data = resp.json()
+                if "error" not in data:
+                    items = data.get("response", {}).get("items", [])
+                    if items:
+                        return str(items[0].get("id", "")), items[0].get("name")
+    except Exception:
+        pass
+    return None, None
+
+
+def _save_connection(db: Session, user_id: int, token: str,
+                     group_id: str | None, group_name: str | None) -> None:
+    now = datetime.utcnow()
+    connection = db.query(VkConnection).filter(VkConnection.user_id == user_id).first()
+    if connection:
+        connection.access_token = token
+        connection.vk_user_id = group_id
+        connection.first_name = group_name
+        connection.last_name = None
+        connection.is_online = True
+        connection.last_checked_at = now
+    else:
+        db.add(VkConnection(
+            user_id=user_id,
+            access_token=token,
+            vk_user_id=group_id,
+            first_name=group_name,
+            last_name=None,
+            is_online=True,
+            last_checked_at=now,
+        ))
+    db.commit()
 
 
 @router.get("")
@@ -33,6 +85,46 @@ def vk_page(
         "user": user,
         "connection": connection,
         "error": error,
+        "vk_client_id": settings.VK_CLIENT_ID,
+        "callback_url": f"{settings.BASE_URL}/vk/callback",
+    })
+
+
+@router.get("/connect")
+def vk_connect(
+    request: Request,
+    user: User | None = Depends(get_current_user),
+):
+    """Redirect to VK OAuth authorization page."""
+    if not user:
+        return RedirectResponse("/login", 303)
+
+    if not settings.VK_CLIENT_ID:
+        return RedirectResponse("/vk?error=no_client_id", 303)
+
+    params = urlencode({
+        "client_id": settings.VK_CLIENT_ID,
+        "scope": "market,groups",
+        "redirect_uri": f"{settings.BASE_URL}/vk/callback",
+        "display": "page",
+        "response_type": "token",
+        "v": settings.VK_API_VERSION,
+    })
+    return RedirectResponse(f"{VK_OAUTH_URL}?{params}", 302)
+
+
+@router.get("/callback")
+def vk_callback(
+    request: Request,
+    user: User | None = Depends(get_current_user),
+):
+    """Landing page after VK OAuth. JS reads the token from the URL fragment and POSTs it."""
+    if not user:
+        return RedirectResponse("/login", 303)
+
+    return templates.TemplateResponse("vk_callback.html", {
+        "request": request,
+        "user": user,
     })
 
 
@@ -42,7 +134,7 @@ async def vk_token(
     db: Session = Depends(get_db),
     user: User | None = Depends(get_current_user),
 ):
-    """Save a manually entered VK community access token."""
+    """Save a VK user access token (from manual entry or OAuth callback)."""
     if not user:
         return RedirectResponse("/login", 303)
 
@@ -51,52 +143,11 @@ async def vk_token(
     if not token:
         return RedirectResponse("/vk?error=empty_token", 303)
 
-    # Fetch community info to validate the token and get group name/id
-    group_id = None
-    group_name = None
-    try:
-        async with httpx.AsyncClient() as client:
-            resp = await client.get(
-                f"{VK_API_URL}/groups.getById",
-                params={"access_token": token, "v": settings.VK_API_VERSION},
-                timeout=15,
-            )
-            if resp.status_code == 200:
-                data = resp.json()
-                if "error" in data:
-                    return RedirectResponse("/vk?error=invalid_token", 303)
-                response = data.get("response", [])
-                groups = response if isinstance(response, list) else response.get("groups", [])
-                if groups:
-                    group_id = str(groups[0].get("id", ""))
-                    group_name = groups[0].get("name")
-            elif resp.status_code == 401:
-                return RedirectResponse("/vk?error=invalid_token", 303)
-    except Exception:
-        pass
-
-    connection = db.query(VkConnection).filter(VkConnection.user_id == user.id).first()
-    now = datetime.utcnow()
-    if connection:
-        connection.access_token = token
-        connection.vk_user_id = group_id
-        connection.first_name = group_name
-        connection.last_name = None
-        connection.is_online = True
-        connection.last_checked_at = now
-    else:
-        connection = VkConnection(
-            user_id=user.id,
-            access_token=token,
-            vk_user_id=group_id,
-            first_name=group_name,
-            last_name=None,
-            is_online=True,
-            last_checked_at=now,
-        )
-        db.add(connection)
-    db.commit()
+    group_id, group_name = await _fetch_group_info(token)
+    if not group_id:
+        return RedirectResponse("/vk?error=invalid_token", 303)
 
+    _save_connection(db, user.id, token, group_id, group_name)
     return RedirectResponse("/connections", 303)