feat: add AI provider abstraction with Gemini and Anthropic support

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

backend/app/core/ai_provider.py

@@ -0,0 +1,162 @@
+"""
+AI Provider abstraction layer.
+
+Supports Gemini (google-genai) and Anthropic (anthropic) as interchangeable
+backends for JSON generation used by the AI Flow Builder.
+"""
+
+from abc import ABC, abstractmethod
+
+from app.core.config import settings
+
+
+class AIProvider(ABC):
+    """Abstract base class for AI providers."""
+
+    @abstractmethod
+    async def generate_json(
+        self,
+        system_prompt: str,
+        messages: list[dict[str, str]],
+        max_tokens: int = 4096,
+    ) -> tuple[str, int, int]:
+        """Generate a JSON response from the AI model.
+
+        Args:
+            system_prompt: System-level instruction for the model.
+            messages: List of message dicts with "role" and "content" keys.
+            max_tokens: Maximum output tokens.
+
+        Returns:
+            Tuple of (response_text, input_tokens, output_tokens).
+        """
+        ...
+
+
+class GeminiProvider(AIProvider):
+    """Google Gemini provider using the google-genai SDK."""
+
+    def __init__(self, api_key: str, model: str) -> None:
+        self._api_key = api_key
+        self._model = model
+
+    async def generate_json(
+        self,
+        system_prompt: str,
+        messages: list[dict[str, str]],
+        max_tokens: int = 4096,
+    ) -> tuple[str, int, int]:
+        from google import genai
+        from google.genai import types as genai_types
+
+        client = genai.Client(api_key=self._api_key)
+
+        # Convert messages to Gemini Content format
+        contents: list[genai_types.Content] = []
+        for msg in messages:
+            role = "model" if msg["role"] == "assistant" else "user"
+            contents.append(
+                genai_types.Content(
+                    role=role,
+                    parts=[genai_types.Part(text=msg["content"])],
+                )
+            )
+
+        config = genai_types.GenerateContentConfig(
+            system_instruction=system_prompt,
+            max_output_tokens=max_tokens,
+            response_mime_type="application/json",
+        )
+
+        response = await client.models.generate_content_async(
+            model=self._model,
+            contents=contents,
+            config=config,
+        )
+
+        text = response.text or ""
+        input_tokens = getattr(response.usage_metadata, "prompt_token_count", 0) or 0
+        output_tokens = (
+            getattr(response.usage_metadata, "candidates_token_count", 0) or 0
+        )
+
+        return text, input_tokens, output_tokens
+
+
+class AnthropicProvider(AIProvider):
+    """Anthropic Claude provider using the anthropic SDK."""
+
+    def __init__(self, api_key: str, model: str, timeout: int = 45) -> None:
+        self._api_key = api_key
+        self._model = model
+        self._timeout = timeout
+
+    async def generate_json(
+        self,
+        system_prompt: str,
+        messages: list[dict[str, str]],
+        max_tokens: int = 4096,
+    ) -> tuple[str, int, int]:
+        import anthropic
+
+        client = anthropic.AsyncAnthropic(
+            api_key=self._api_key,
+            timeout=self._timeout,
+        )
+
+        response = await client.messages.create(
+            model=self._model,
+            max_tokens=max_tokens,
+            system=system_prompt,
+            messages=messages,
+        )
+
+        text = response.content[0].text
+        input_tokens = response.usage.input_tokens
+        output_tokens = response.usage.output_tokens
+
+        return text, input_tokens, output_tokens
+
+
+def get_ai_provider() -> AIProvider:
+    """Factory that returns the configured AI provider.
+
+    Selection logic:
+    1. If AI_PROVIDER == "gemini" and GOOGLE_AI_API_KEY is set -> GeminiProvider
+    2. If AI_PROVIDER == "anthropic" and ANTHROPIC_API_KEY is set -> AnthropicProvider
+    3. Fallback: if preferred provider key missing, try the other one
+    4. If nothing configured -> raise RuntimeError
+    """
+    provider = settings.AI_PROVIDER
+
+    if provider == "gemini":
+        if settings.GOOGLE_AI_API_KEY:
+            return GeminiProvider(
+                api_key=settings.GOOGLE_AI_API_KEY,
+                model=settings.AI_MODEL_GEMINI,
+            )
+        # Fallback to Anthropic
+        if settings.ANTHROPIC_API_KEY:
+            return AnthropicProvider(
+                api_key=settings.ANTHROPIC_API_KEY,
+                model=settings.AI_MODEL_ANTHROPIC,
+                timeout=settings.AI_REQUEST_TIMEOUT_SECONDS,
+            )
+
+    elif provider == "anthropic":
+        if settings.ANTHROPIC_API_KEY:
+            return AnthropicProvider(
+                api_key=settings.ANTHROPIC_API_KEY,
+                model=settings.AI_MODEL_ANTHROPIC,
+                timeout=settings.AI_REQUEST_TIMEOUT_SECONDS,
+            )
+        # Fallback to Gemini
+        if settings.GOOGLE_AI_API_KEY:
+            return GeminiProvider(
+                api_key=settings.GOOGLE_AI_API_KEY,
+                model=settings.AI_MODEL_GEMINI,
+            )
+
+    raise RuntimeError(
+        "No AI provider configured. Set GOOGLE_AI_API_KEY or ANTHROPIC_API_KEY."
+    )