Add OpenAI nano fallback for HF inference outages (silent UI)

.streamlit/secrets.toml.example

@@ -25,4 +25,12 @@ HF_PROVIDER = "auto"
 
 # Compatibility: older name for the endpoint base URL. The app will treat this
 # as an alias for HF_ENDPOINT_URL if set.
-HF_INFERENCE_BASE_URL = ""
+HF_INFERENCE_BASE_URL = ""
+
+# Optional: OpenAI fallback settings used when HF Inference requests fail.
+OPENAI_API_KEY = ""
+OPENAI_FALLBACK_MODEL = "gpt-5-nano"
+# When set to a truthy value (\"true\", \"1\", \"yes\"), the app will use structured
+# JSON outputs for the fallback ({\"sql\": \"...\"}) and attempt to parse the SQL
+# field. If parsing fails, it falls back to plain text handling.
+OPENAI_FALLBACK_STRICT_JSON = "false"

app/streamlit_app.py

@@ -42,12 +42,14 @@
 
 from __future__ import annotations
 
+import json
 import logging
 import os
 from typing import Any, Mapping, NamedTuple, Optional, Tuple
 
 import streamlit as st
 from huggingface_hub import InferenceClient  # type: ignore[import]
+from openai import OpenAI  # type: ignore[import]
 
 
 logger = logging.getLogger(__name__)
@@ -130,6 +132,72 @@ def _get_from_mapping(mapping: Mapping[str, Any], key: str) -> str:
     )
 
 
+def _get_openai_settings() -> Tuple[str, str]:
+    """
+    Resolve OpenAI fallback settings from Streamlit secrets and environment variables.
+
+    Secrets take precedence over environment variables. The model name falls back
+    to "gpt-5-nano" when not configured explicitly.
+    """
+    try:
+        secrets: Mapping[str, Any] = st.secrets  # type: ignore[assignment]
+    except Exception:  # noqa: BLE001
+        secrets = {}
+
+    def _get_from_mapping(mapping: Mapping[str, Any], key: str) -> str:
+        try:
+            value = mapping.get(key)  # type: ignore[attr-defined]
+        except Exception:  # noqa: BLE001
+            value = None
+        if value is None:
+            return ""
+        return str(value).strip()
+
+    api_key = _get_from_mapping(secrets, "OPENAI_API_KEY") or os.environ.get(
+        "OPENAI_API_KEY",
+        "",
+    ).strip()
+
+    model_name = _get_from_mapping(secrets, "OPENAI_FALLBACK_MODEL") or os.environ.get(
+        "OPENAI_FALLBACK_MODEL",
+        "",
+    ).strip()
+
+    if not model_name:
+        model_name = "gpt-5-nano"
+
+    return api_key, model_name
+
+
+def _is_openai_strict_json_enabled() -> bool:
+    """
+    Return True if structured JSON mode is enabled for the OpenAI fallback.
+
+    Controlled by OPENAI_FALLBACK_STRICT_JSON in Streamlit secrets or environment
+    variables. Defaults to False.
+    """
+    try:
+        secrets: Mapping[str, Any] = st.secrets  # type: ignore[assignment]
+    except Exception:  # noqa: BLE001
+        secrets = {}
+
+    def _get_from_mapping(mapping: Mapping[str, Any], key: str) -> str:
+        try:
+            value = mapping.get(key)  # type: ignore[attr-defined]
+        except Exception:  # noqa: BLE001
+            value = None
+        if value is None:
+            return ""
+        return str(value).strip()
+
+    raw_value = _get_from_mapping(secrets, "OPENAI_FALLBACK_STRICT_JSON") or os.environ.get(
+        "OPENAI_FALLBACK_STRICT_JSON",
+        "",
+    ).strip()
+
+    return raw_value.lower() in {"1", "true", "yes", "on"}
+
+
 @st.cache_resource(show_spinner=False)
 def _get_cached_client(
     hf_token: str,
@@ -162,6 +230,157 @@ def _get_cached_client(
     )
 
 
+def _openai_response_text(resp: Any) -> str:
+    """
+    Extract text content from an OpenAI Responses API response object.
+
+    1) Prefer the convenience `output_text` attribute when present and non-empty.
+    2) Otherwise, iterate over `resp.output` and aggregate any text content blocks.
+
+    The Responses API typically exposes text as:
+        resp.output[0].content[0].text.value
+    but this helper is defensive and also supports dict-like structures.
+    """
+    # 1) Convenience attribute, when present.
+    try:
+        value = getattr(resp, "output_text", None)
+    except Exception:  # noqa: BLE001
+        value = None
+
+    if isinstance(value, str) and value.strip():
+        return value.strip()
+
+    # 2) Walk the output structure.
+    try:
+        output = getattr(resp, "output", None)
+    except Exception:  # noqa: BLE001
+        output = None
+
+    if not output:
+        return ""
+
+    chunks: list[str] = []
+
+    try:
+        for item in output:
+            # Handle both object-style and dict-style access to content.
+            content_list: Any
+            if isinstance(item, dict):
+                content_list = item.get("content")
+            else:
+                try:
+                    content_list = getattr(item, "content", None)
+                except Exception:  # noqa: BLE001
+                    content_list = None
+
+            if not content_list:
+                continue
+
+            for content in content_list:
+                # Retrieve the "text" field from the content object or dict.
+                text_obj: Any = None
+                if isinstance(content, dict):
+                    text_obj = content.get("text")
+                else:
+                    try:
+                        text_obj = getattr(content, "text", None)
+                    except Exception:  # noqa: BLE001
+                        text_obj = None
+
+                if text_obj is None:
+                    continue
+
+                # Unwrap the actual string value, handling nested objects/dicts.
+                text_val: Optional[str] = None
+                if isinstance(text_obj, str):
+                    text_val = text_obj
+                else:
+                    # Object-style: content.text.value
+                    try:
+                        inner_val = getattr(text_obj, "value", None)
+                    except Exception:  # noqa: BLE001
+                        inner_val = None
+                    if isinstance(inner_val, str):
+                        text_val = inner_val
+                    elif isinstance(text_obj, dict):
+                        # Dict-style: {"text": {"value": "..."}} or similar.
+                        inner_val = text_obj.get("value")
+                        if isinstance(inner_val, str):
+                            text_val = inner_val
+
+                if isinstance(text_val, str) and text_val:
+                    chunks.append(text_val)
+    except Exception:  # noqa: BLE001
+        logger.exception("Failed to extract text from OpenAI response.output.")
+        return ""
+
+    return "".join(chunks).strip()
+
+
+def _call_openai_fallback(
+    system_prompt: str,
+    user_prompt: str,
+) -> str:
+    """
+    Call the OpenAI Responses API as a fallback when HF inference fails.
+
+    Uses the cheapest nano model (default: gpt-5-nano) and avoids passing
+    unsupported parameters such as temperature or top_p.
+    """
+    api_key, model_name = _get_openai_settings()
+    if not api_key:
+        raise RuntimeError("OpenAI fallback not configured")
+
+    client = OpenAI(api_key=api_key)
+    full_input = f"{system_prompt}\n\n{user_prompt}"
+
+    extra_kwargs: dict[str, Any] = {}
+    strict_json = _is_openai_strict_json_enabled()
+    if strict_json:
+        extra_kwargs["response_format"] = {
+            "type": "json_schema",
+            "json_schema": {
+                "name": "sql_fallback",
+                "schema": {
+                    "type": "object",
+                    "properties": {
+                        "sql": {"type": "string"},
+                    },
+                    "required": ["sql"],
+                    "additionalProperties": False,
+                },
+                "strict": True,
+            },
+        }
+
+    response = client.responses.create(
+        model=model_name,
+        input=full_input,
+        **extra_kwargs,
+    )
+
+    raw_text = _openai_response_text(response)
+
+    if strict_json and raw_text:
+        try:
+            parsed = json.loads(raw_text)
+            if isinstance(parsed, dict):
+                sql_val = parsed.get("sql")
+                if isinstance(sql_val, str) and sql_val.strip():
+                    return sql_val.strip()
+        except Exception:  # noqa: BLE001
+            logger.exception(
+                "Failed to parse structured JSON output from OpenAI fallback; "
+                "falling back to raw text.",
+            )
+
+    if not raw_text:
+        logger.warning("OpenAI fallback returned empty text output.")
+        return ""
+
+    return raw_text.strip()
+
+
 def _build_prompt(schema: str, question: str) -> Tuple[str, str]:
     """
     Build the system and user prompt content for text-to-SQL generation.
@@ -249,6 +468,17 @@ def _create_inference_client(timeout_s: int = 45) -> Tuple[InferenceClient, HFCo
     return client, hf_config
 
 
+def _extract_sql_from_text(raw_text: str) -> str:
+    """
+    Extract SQL from model output text.
+
+    Currently implemented as a simple pass-through that returns the
+    stripped text. Defined as a separate helper so it can be extended
+    or replaced in tests without changing call sites.
+    """
+    return raw_text.strip()
+
+
 def _call_model(
     client: InferenceClient,
     schema: str,
@@ -283,14 +513,40 @@ def _call_model(
     try:
         response = client.text_generation(**generation_kwargs)
     except Exception as exc:  # noqa: BLE001
-        logger.error("Error while calling Hugging Face Inference API.", exc_info=True)
-        st.error(
-            "The Hugging Face Inference endpoint did not respond successfully. "
-            "This can happen if the endpoint is cold, overloaded, or misconfigured. "
-            "Please try again, or check your HF endpoint / model settings."
-        )
-        st.caption(f"Details: {exc}")
-        return None, user_prompt
+        message = str(exc) if exc is not None else ""
+        lower_message = message.lower()
+        if "endpoint is paused" in lower_message:
+            logger.warning(
+                "Hugging Face Inference endpoint is paused; using OpenAI fallback.",
+            )
+        else:
+            logger.exception(
+                "Error while calling Hugging Face Inference API. "
+                "Attempting OpenAI fallback if configured.",
+            )
+        try:
+            raw_text = _call_openai_fallback(
+                system_prompt=system_prompt,
+                user_prompt=user_prompt,
+            )
+        except Exception:  # noqa: BLE001
+            logger.exception("OpenAI fallback inference failed.")
+            st.error(
+                "The service is temporarily unavailable. Please try again in a moment."
+            )
+            return None, user_prompt
+
+        if not raw_text.strip():
+            sql_text = "-- Fallback provider returned empty output. Try again."
+        else:
+            extracted = _extract_sql_from_text(raw_text)
+            if extracted and extracted.strip():
+                sql_text = extracted.strip()
+            else:
+                sql_text = raw_text.strip()
+
+        st.caption("Using backup inference provider")
+        return sql_text, user_prompt
 
     # InferenceClient.text_generation may return a string, a dict, or a list.
     try:

requirements.txt

@@ -21,4 +21,7 @@ pytest>=8.0.0
 huggingface-hub>=0.36.0
 
 # --- Evaluation helpers ---
-sqlglot>=28.5.0
+sqlglot>=28.5.0
+
+# --- Inference fallbacks ---
+openai>=2.15.0