[add] i18n support zh,en

api/app/i18n/middleware.py

@@ -0,0 +1,202 @@
+"""
+Language detection middleware for i18n system.
+
+This middleware determines the language to use for each request based on:
+1. Query parameter (?lang=en)
+2. Accept-Language HTTP header
+3. User language preference (from database)
+4. Tenant default language
+5. System default language
+
+The detected language is injected into request.state.language and
+added to the response Content-Language header.
+"""
+
+import logging
+import re
+from typing import Optional
+
+from fastapi import Request
+from starlette.middleware.base import BaseHTTPMiddleware
+
+logger = logging.getLogger(__name__)
+
+
+class LanguageMiddleware(BaseHTTPMiddleware):
+    """
+    Language detection middleware.
+    
+    Determines the language for each request based on multiple sources
+    with a clear priority order, validates the language is supported,
+    and injects it into the request context.
+    """
+
+    async def dispatch(self, request: Request, call_next):
+        """
+        Process the request and determine the language.
+        
+        Args:
+            request: The incoming request
+            call_next: The next middleware/handler in the chain
+            
+        Returns:
+            Response with Content-Language header added
+        """
+        # Determine the language for this request
+        language = await self._determine_language(request)
+        
+        # Validate language is supported
+        from app.core.config import settings
+        if language not in settings.I18N_SUPPORTED_LANGUAGES:
+            logger.warning(
+                f"Unsupported language '{language}' requested, "
+                f"falling back to default: {settings.I18N_DEFAULT_LANGUAGE}"
+            )
+            language = settings.I18N_DEFAULT_LANGUAGE
+        
+        # Inject language into request state
+        request.state.language = language
+        
+        # Also set in context variable for exception handling
+        from app.i18n.exceptions import set_current_locale
+        set_current_locale(language)
+        
+        logger.debug(f"Request language set to: {language}")
+        
+        # Process the request
+        response = await call_next(request)
+        
+        # Add Content-Language header to response
+        response.headers["Content-Language"] = language
+        
+        return response
+
+    async def _determine_language(self, request: Request) -> str:
+        """
+        Determine the language to use based on priority order.
+        
+        Priority:
+        1. Query parameter (?lang=en)
+        2. Accept-Language HTTP header
+        3. User language preference (from database)
+        4. Tenant default language
+        5. System default language
+        
+        Args:
+            request: The incoming request
+            
+        Returns:
+            Language code (e.g., "zh", "en")
+        """
+        from app.core.config import settings
+        
+        # 1. Check query parameter (?lang=en)
+        if "lang" in request.query_params:
+            lang = request.query_params["lang"].strip().lower()
+            if lang:
+                logger.debug(f"Language from query parameter: {lang}")
+                return lang
+        
+        # 2. Check Accept-Language HTTP header
+        if "Accept-Language" in request.headers:
+            lang = self._parse_accept_language(
+                request.headers["Accept-Language"]
+            )
+            if lang:
+                logger.debug(f"Language from Accept-Language header: {lang}")
+                return lang
+        
+        # 3. Check user language preference (requires authentication)
+        # Note: This assumes user is already loaded into request.state by auth middleware
+        if hasattr(request.state, "user") and request.state.user:
+            user = request.state.user
+            if hasattr(user, "preferred_language") and user.preferred_language:
+                logger.debug(
+                    f"Language from user preference: {user.preferred_language}"
+                )
+                return user.preferred_language
+        
+        # 4. Check tenant default language
+        # Note: This assumes tenant is already loaded into request.state
+        if hasattr(request.state, "tenant") and request.state.tenant:
+            tenant = request.state.tenant
+            if hasattr(tenant, "default_language") and tenant.default_language:
+                logger.debug(
+                    f"Language from tenant default: {tenant.default_language}"
+                )
+                return tenant.default_language
+        
+        # 5. Fall back to system default language
+        logger.debug(
+            f"Using system default language: {settings.I18N_DEFAULT_LANGUAGE}"
+        )
+        return settings.I18N_DEFAULT_LANGUAGE
+
+    def _parse_accept_language(self, header: str) -> Optional[str]:
+        """
+        Parse the Accept-Language HTTP header.
+        
+        The Accept-Language header format:
+        Accept-Language: zh-CN,zh;q=0.9,en;q=0.8,en-US;q=0.7
+        
+        This method:
+        1. Parses all language codes and their quality values
+        2. Extracts the base language code (zh-CN -> zh)
+        3. Sorts by quality value (higher first)
+        4. Returns the first supported language
+        
+        Args:
+            header: Accept-Language header value
+            
+        Returns:
+            Language code if found and supported, None otherwise
+            
+        Examples:
+            _parse_accept_language("zh-CN,zh;q=0.9,en;q=0.8")
+            # => "zh" (if zh is supported)
+            
+            _parse_accept_language("en-US,en;q=0.9")
+            # => "en" (if en is supported)
+        """
+        from app.core.config import settings
+        
+        if not header:
+            return None
+        
+        # Parse language preferences with quality values
+        languages = []
+        
+        for item in header.split(","):
+            item = item.strip()
+            if not item:
+                continue
+            
+            # Split language code and quality value
+            parts = item.split(";")
+            lang_code = parts[0].strip()
+            
+            # Extract base language code (zh-CN -> zh, en-US -> en)
+            base_lang = lang_code.split("-")[0].lower()
+            
+            # Extract quality value (default: 1.0)
+            quality = 1.0
+            if len(parts) > 1:
+                # Look for q=0.9 pattern
+                q_match = re.search(r"q=([\d.]+)", parts[1])
+                if q_match:
+                    try:
+                        quality = float(q_match.group(1))
+                    except ValueError:
+                        quality = 1.0
+            
+            languages.append((base_lang, quality))
+        
+        # Sort by quality value (descending)
+        languages.sort(key=lambda x: x[1], reverse=True)
+        
+        # Return the first supported language
+        for lang_code, _ in languages:
+            if lang_code in settings.I18N_SUPPORTED_LANGUAGES:
+                return lang_code
+        
+        return None