feat: implement backend API clients for multi-marketplace integration and frontend service layer

backend/ozon_api/client.py

@@ -0,0 +1,68 @@
+import os
+import requests
+import time
+from typing import Dict, Any, Optional
+from .exceptions import OzonAPIError, OzonAuthError, OzonRateLimitError, OzonBadRequestError
+
+class OzonClient:
+    """Base client for interacting with Ozon API."""
+    
+    BASE_URL = "https://api-seller.ozon.ru"
+    
+    def __init__(self, client_id: Optional[str] = None, api_key: Optional[str] = None):
+        # Fetch from env if not provided
+        self.client_id = client_id or os.getenv('OZON_CLIENT_ID')
+        self.api_key = api_key or os.getenv('OZON_API_KEY')
+        
+        if not self.client_id or not self.api_key:
+            raise ValueError("OZON_CLIENT_ID and OZON_API_KEY must be provided")
+            
+        self.session = requests.Session()
+        self.session.headers.update({
+            "Client-Id": self.client_id,
+            "Api-Key": self.api_key,
+            "Content-Type": "application/json"
+        })
+
+    def request(self, method: str, path: str, data: Optional[Dict[str, Any]] = None, params: Optional[Dict[str, Any]] = None, retries: int = 3) -> Dict[str, Any]:
+        """Perform HTTP request to Ozon API with automatic retries."""
+        url = f"{self.BASE_URL}{path}"
+        
+        for attempt in range(retries):
+            try:
+                response = self.session.request(method, url, json=data, params=params)
+                
+                # Check rate limiting
+                if response.status_code == 429:
+                    if attempt < retries - 1:
+                        time.sleep(2 ** attempt)  # Exponential backoff
+                        continue
+                    raise OzonRateLimitError("Rate limit exceeded")
+
+                if response.status_code in (401, 403):
+                    raise OzonAuthError(f"Authentication failed: {response.text}")
+                    
+                if response.status_code == 400:
+                    raise OzonBadRequestError(f"Bad Request: {response.text}")
+                    
+                response.raise_for_status()
+                
+                # Ozon usually wraps responses in "result" key, but not always.
+                # We return the whole JSON parsed response.
+                if response.content:
+                    return response.json()
+                return {}
+
+            except requests.exceptions.RequestException as e:
+                if attempt < retries - 1:
+                    time.sleep(2 ** attempt)
+                    continue
+                raise OzonAPIError(f"Request failed: {str(e)}")
+                
+        raise OzonAPIError("Request failed after max retries")
+
+    def post(self, path: str, data: Optional[Dict[str, Any]] = None) -> Dict[str, Any]:
+        return self.request("POST", path, data=data)
+
+    def get(self, path: str, params: Optional[Dict[str, Any]] = None) -> Dict[str, Any]:
+        return self.request("GET", path, params=params)