app.py

"""
Hugging Face Spaces에서 돌리는 Reranker API (ONNX 최적화 버전).

모델은 HF Hub에서 로드 (환경변수 HF_MODEL_ID, 예: cross-encoder/ms-marco-MiniLM-L-6-v2).
ONNX Runtime으로 변환하여 CPU 추론 속도 2-3배 향상.

환경변수:
- HF_MODEL_ID: 모델 ID (필수)
- HF_TOKEN: 비공개 리포 접근용 토큰 (선택)
- USE_ONNX: "true"면 ONNX Runtime 사용 (기본: true)
- ONNX_PROVIDER: "CPUExecutionProvider" 또는 "CUDAExecutionProvider" (기본: CPU)
"""
import os
import time
from typing import List, Optional

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel

MODEL_ID = (os.environ.get("HF_MODEL_ID") or "").strip()
HF_TOKEN = (os.environ.get("HF_TOKEN") or "").strip() or None
USE_ONNX = os.environ.get("USE_ONNX", "true").lower() == "true"
ONNX_PROVIDER = os.environ.get("ONNX_PROVIDER", "CPUExecutionProvider")

model = None
tokenizer = None
is_onnx_mode = False

app = FastAPI(title="Reranker API (ONNX)")
app.add_middleware(CORSMiddleware, allow_origins=["*"], allow_methods=["*"], allow_headers=["*"])


class RerankerRequest(BaseModel):
    query: str
    passages: List[str]


class RerankerResponse(BaseModel):
    scores: List[float]
    latency_ms: Optional[float] = None
    mode: Optional[str] = None
    error: Optional[str] = None


def load_onnx_model():
    """ONNX Runtime으로 모델 로드. 최초 실행 시 자동 변환."""
    global model, tokenizer, is_onnx_mode
    try:
        from optimum.onnxruntime import ORTModelForSequenceClassification
        from transformers import AutoTokenizer
        
        print(f"[ONNX] 모델 로딩 중: {MODEL_ID} (provider={ONNX_PROVIDER})")
        tokenizer = AutoTokenizer.from_pretrained(MODEL_ID, token=HF_TOKEN)
        model = ORTModelForSequenceClassification.from_pretrained(
            MODEL_ID,
            export=True,  # PyTorch → ONNX 자동 변환
            provider=ONNX_PROVIDER,
            token=HF_TOKEN,
        )
        is_onnx_mode = True
        print("[ONNX] 로드 완료.")
    except Exception as e:
        print(f"[ONNX] 로드 실패, fallback to CrossEncoder: {e}")
        load_crossencoder_model()


def load_crossencoder_model():
    """기존 CrossEncoder 모델 로드 (fallback)."""
    global model, is_onnx_mode
    from sentence_transformers import CrossEncoder
    print(f"[CrossEncoder] 모델 로딩 중: {MODEL_ID}")
    model = CrossEncoder(MODEL_ID, token=HF_TOKEN)
    is_onnx_mode = False
    print("[CrossEncoder] 로드 완료.")


@app.on_event("startup")
def startup_load_model():
    global model
    if not MODEL_ID:
        raise RuntimeError("Space 설정에서 HF_MODEL_ID 를 지정하세요")
    
    if USE_ONNX:
        load_onnx_model()
    else:
        load_crossencoder_model()


def predict_onnx(query: str, passages: List[str]) -> List[float]:
    """ONNX 모델로 batch predict."""
    import torch
    pairs = [[query, p] for p in passages]
    inputs = tokenizer(
        pairs,
        padding=True,
        truncation=True,
        max_length=512,
        return_tensors="pt",
    )
    outputs = model(**inputs)
    # logits shape: (batch_size, num_labels) - 보통 1개 label (relevance score)
    logits = outputs.logits
    if logits.shape[-1] == 1:
        scores = logits.squeeze(-1)
    else:
        # 2개 label이면 softmax 후 positive class 확률
        scores = torch.softmax(logits, dim=-1)[:, 1]
    return scores.tolist()


def predict_crossencoder(query: str, passages: List[str]) -> List[float]:
    """CrossEncoder 모델로 predict."""
    pairs = [(query, p) for p in passages]
    scores = model.predict(pairs)
    if hasattr(scores, "tolist"):
        scores = scores.tolist()
    return [float(s) for s in scores]


@app.get("/")
def root():
    """브라우저/App 탭 접속 시 안내."""
    return {
        "message": "CertWeb Reranker API (ONNX Optimized)",
        "model": MODEL_ID,
        "mode": "onnx" if is_onnx_mode else "crossencoder",
        "usage": "POST / with JSON body: {\"query\": \"질문\", \"passages\": [\"문단1\", \"문단2\", ...]}",
        "response": "{\"scores\": [0.9, 0.2, ...], \"latency_ms\": 123.4, \"mode\": \"onnx\"}",
    }


@app.post("/", response_model=RerankerResponse)
def score(request: RerankerRequest):
    query = request.query
    passages = request.passages
    
    if not query or not passages or model is None:
        return RerankerResponse(scores=[], error="Empty query/passages or model not loaded")
    
    try:
        start = time.perf_counter()
        if is_onnx_mode:
            scores = predict_onnx(query, passages)
        else:
            scores = predict_crossencoder(query, passages)
        latency_ms = (time.perf_counter() - start) * 1000
        
        return RerankerResponse(
            scores=scores,
            latency_ms=round(latency_ms, 2),
            mode="onnx" if is_onnx_mode else "crossencoder",
        )
    except Exception as e:
        return RerankerResponse(scores=[], error=str(e))


@app.get("/health")
def health():
    """Health check endpoint."""
    return {
        "status": "ok",
        "model_loaded": model is not None,
        "mode": "onnx" if is_onnx_mode else "crossencoder",
    }