app.py

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
import torch
import re
import os

# --- Import Libraries ---
from transformers import AutoTokenizer, AutoModelForCausalLM
from peft import PeftModel

# --- Model Paths ---
GENDER_MODEL_PATH = "google/gemma-3-270m-qat-q4_0-unquantized"
BASE_MODEL_PATH = "unsloth/gemma-2b-it"
# This correctly points to your model on the Hugging Face Hub.
LORA_ADAPTER_PATH = "enoch10jason/gemma-grammar-lora"

# --- Global variables for models ---
grammar_model = None
grammar_tokenizer = None
gender_model = None
gender_tokenizer = None
device = "cpu"

print("--- Starting Model Loading ---")

try:
    # Models are loaded from the pre-downloaded cache in the image.
    # No token is needed at runtime because the files are already cached.
    print(f"Loading gender model from cache: {GENDER_MODEL_PATH}")
    gender_tokenizer = AutoTokenizer.from_pretrained(GENDER_MODEL_PATH)
    gender_model = AutoModelForCausalLM.from_pretrained(GENDER_MODEL_PATH).to(device)
    print("✅ Gender verifier model loaded successfully!")

    print(f"Loading base model for grammar correction from cache: {BASE_MODEL_PATH}")
    base_model = AutoModelForCausalLM.from_pretrained(
        BASE_MODEL_PATH,
        dtype=torch.float32,
    ).to(device)
    grammar_tokenizer = AutoTokenizer.from_pretrained(BASE_MODEL_PATH)

    print(f"Applying LoRA adapter from cache: {LORA_ADAPTER_PATH}")
    grammar_model = PeftModel.from_pretrained(base_model, LORA_ADAPTER_PATH).to(device)
    print("✅ Grammar correction model loaded successfully!")

    if grammar_tokenizer.pad_token is None:
        grammar_tokenizer.pad_token = grammar_tokenizer.eos_token
    if gender_tokenizer.pad_token is None:
        gender_tokenizer.pad_token = gender_tokenizer.eos_token

except Exception as e:
    print(f"❌ Critical error during model loading: {e}")
    grammar_model = None
    gender_model = None

print("--- Model Loading Complete ---")


# --- FastAPI Application Setup ---
app = FastAPI(title="Text Correction API")

class CorrectionRequest(BaseModel):
    text: str

class CorrectionResponse(BaseModel):
    original_text: str
    corrected_text: str

# --- Helper Functions ---
def clean_grammar_response(text: str) -> str:
    if "Response:" in text:
        parts = text.split("Response:")
        if len(parts) > 1: return parts[1].strip()
    return text.strip()

def clean_gender_response(text: str) -> str:
    if "Response:" in text:
        parts = text.split("Response:")
        if len(parts) > 1: text = parts[1].strip()
    text = re.sub(r'^(Corrected sentence:|Correct:|Prompt:)\s*', '', text, flags=re.IGNORECASE)
    return text.strip().strip('"')

def correct_gender_rules(text: str) -> str:
    corrections = {
        r'\bher wife\b': 'her husband', r'\bhis husband\b': 'his wife',
        r'\bhe is a girl\b': 'he is a boy', r'\bshe is a boy\b': 'she is a girl'
    }
    for pattern, replacement in corrections.items():
        text = re.sub(pattern, replacement, text, flags=re.IGNORECASE)
    return text

# --- API Endpoints ---
@app.post("/correct_grammar", response_model=CorrectionResponse)
async def handle_grammar_correction(request: CorrectionRequest):
    if not grammar_model or not grammar_tokenizer:
        raise HTTPException(status_code=503, detail="Grammar model is not available.")
    prompt_text = request.text
    input_text = f"Prompt: {prompt_text}\nResponse:"
    inputs = grammar_tokenizer(input_text, return_tensors="pt").to(device)
    output_ids = grammar_model.generate(**inputs, max_new_tokens=64, do_sample=False)
    output_text = grammar_tokenizer.decode(output_ids[0], skip_special_tokens=True)
    corrected = clean_grammar_response(output_text)
    return CorrectionResponse(original_text=prompt_text, corrected_text=corrected)

@app.post("/correct_gender", response_model=CorrectionResponse)
async def handle_gender_correction(request: CorrectionRequest):
    if not gender_model or not gender_tokenizer:
        raise HTTPException(status_code=503, detail="Gender model is not available.")
    prompt_text = request.text
    input_text = f"Prompt: Please rewrite the sentence with correct grammar and gender. Output ONLY the corrected sentence:\n{prompt_text}\nResponse:"
    inputs = gender_tokenizer(input_text, return_tensors="pt").to(device)
    output_ids = gender_model.generate(
        **inputs, max_new_tokens=64, temperature=0.0,
        do_sample=False, eos_token_id=gender_tokenizer.eos_token_id
    )
    output_text = gender_tokenizer.decode(output_ids[0], skip_special_tokens=True)
    cleaned_from_model = clean_gender_response(output_text)
    final_correction = correct_gender_rules(cleaned_from_model)
    return CorrectionResponse(original_text=prompt_text, corrected_text=final_correction)

@app.get("/")
def read_root():
    return {"status": "Text Correction API is running."}