import os
import uuid
import time
import logging
import shutil
import tempfile
from typing import Optional, List
from enum import Enum
from pathlib import Path
from contextvars import ContextVar
import uvicorn
import pytesseract
from fastapi import (
    FastAPI, File, UploadFile, Depends, 
    HTTPException, Request, status
)
from fastapi.middleware.cors import CORSMiddleware
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
from fastapi.responses import JSONResponse
from fastapi.concurrency import run_in_threadpool
from pydantic import BaseModel
from dotenv import load_dotenv
from PIL import Image
from pdf2image import convert_from_path

# ==========================================
# 1. CONFIGURATION & LOGGING SETUP
# ==========================================
load_dotenv()

# ContextVar for thread-safe Request ID tracking
request_id_ctx: ContextVar[str] = ContextVar("request_id", default="system")

class Config:
    APP_NAME = os.getenv("APP_NAME", "OCR API")
    API_TOKEN = os.getenv("API_BEARER_TOKEN")
    MAX_SIZE = int(os.getenv("MAX_FILE_SIZE", 52428800)) # 50MB
    ALLOWED_ORIGINS = [o.strip() for o in os.getenv("ALLOWED_ORIGINS", "").split(",") if o.strip()]
    ALLOWED_TYPES = ["image/jpeg", "image/png", "image/bmp", "image/webp", "application/pdf"]

class RequestIdFilter(logging.Filter):
    def filter(self, record):
        # Automatically pull request_id from the context variable
        record.request_id = request_id_ctx.get()
        return True

logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s | %(levelname)s | ReqID:%(request_id)s | %(message)s',
    datefmt='%Y-%m-%d %H:%M:%S',
    force=True # Ensures our config is applied
)
logger = logging.getLogger("ocr_api")
logger.addFilter(RequestIdFilter())

# ==========================================
# 2. MODELS
# ==========================================
class StatusEnum(str, Enum):
    SUCCESS = "success"
    ERROR = "error"

class BaseResponse(BaseModel):
    request_id: str
    process_time_ms: float
    status: StatusEnum
    message: Optional[str] = None

class PageResult(BaseModel):
    index: int
    page_number: int
    text: str

class OCRResult(BaseModel):
    filename: str
    content_type: str
    saved_file_path: str
    total_pages: int
    pages_content: List[PageResult]

class APIResponse(BaseResponse):
    data: Optional[OCRResult] = None
    error_message: Optional[str] = None

# ==========================================
# 3. SERVICES
# ==========================================

class SecurityService:
    security_scheme = HTTPBearer()

    @staticmethod
    async def validate_token(credentials: HTTPAuthorizationCredentials = Depends(security_scheme)):
        if credentials.credentials != Config.API_TOKEN:
            logger.warning("Auth Failed: Invalid Token")
            raise HTTPException(status_code=401, detail="Invalid Bearer Token")
        return credentials.credentials

class FileValidator:
    @staticmethod
    def validate(file: UploadFile):
        if file.content_type not in Config.ALLOWED_TYPES:
            raise HTTPException(400, f"Invalid file type: {file.content_type}")

    @staticmethod
    def check_size_and_save(file: UploadFile) -> str:
        suffix = Path(file.filename).suffix
        with tempfile.NamedTemporaryFile(delete=False, suffix=suffix) as buffer:
            shutil.copyfileobj(file.file, buffer)
            tmp_path = os.path.abspath(buffer.name)
        
        if os.path.getsize(tmp_path) > Config.MAX_SIZE:
            os.remove(tmp_path)
            raise HTTPException(413, "File too large")
        return tmp_path

class OCRProcessor:
    @classmethod
    def process_file(cls, file_path: str, content_type: str) -> dict:
        """Note: No longer passing request_id; logger picks it up from contextvars automatically."""
        start = time.perf_counter()
        pages_content = []
        
        try:
            logger.info(f"Processing File: {file_path}")

            if content_type == "application/pdf":
                logger.info("Converting PDF to Images...")
                images = convert_from_path(file_path)
                total = len(images)
                
                for idx, img in enumerate(images):
                    page_num = idx + 1
                    logger.info(f"Scanning Page {page_num}/{total}")
                    text = pytesseract.image_to_string(img).strip()
                    pages_content.append({"index": idx, "page_number": page_num, "text": text})
            else:
                logger.info("Scanning Single Image...")
                img = Image.open(file_path)
                text = pytesseract.image_to_string(img).strip()
                pages_content.append({"index": 0, "page_number": 1, "text": text})

            logger.info(f"OCR Complete in {(time.perf_counter()-start)*1000:.2f}ms")
            return {"total_pages": len(pages_content), "pages_content": pages_content}

        except Exception as e:
            logger.error(f"OCR Logic Failure: {str(e)}")
            raise ValueError(str(e))

# ==========================================
# 4. APP & MIDDLEWARE
# ==========================================
app = FastAPI(title=Config.APP_NAME)

app.add_middleware(
    CORSMiddleware,
    allow_origins=Config.ALLOWED_ORIGINS if Config.ALLOWED_ORIGINS else ["*"],
    allow_methods=["*"],
    allow_headers=["*"],
)

@app.middleware("http")
async def request_context_middleware(request: Request, call_next):
    # 1. Generate ID
    req_id = str(uuid.uuid4())
    # 2. Set Context (Crucial for thread logging)
    token = request_id_ctx.set(req_id)
    request.state.request_id = req_id

    start_time = time.perf_counter()
    logger.info(f"Start: {request.method} {request.url.path}")

    try:
        response = await call_next(request)
        duration = (time.perf_counter() - start_time) * 1000
        response.headers["X-Request-ID"] = req_id
        logger.info(f"Finish: {response.status_code} in {duration:.2f}ms")
        return response
    except Exception as e:
        logger.exception("Middleware caught crash")
        return JSONResponse(status_code=500, content={"status":"error","message":"Internal Server Error","request_id":req_id})
    finally:
        # 3. Clean up Context
        request_id_ctx.reset(token)

# ==========================================
# 5. ENDPOINTS
# ==========================================

@app.get("/")
async def root(request: Request):
    return {
        "request_id": request.state.request_id,
        "process_time_ms": 0,
        "status": StatusEnum.SUCCESS,
        "message": "OCR API Active"
    }

@app.post("/api/v1/get_data", response_model=APIResponse)
async def extract_data(
    request: Request,
    file: UploadFile = File(...),
    token: str = Depends(SecurityService.validate_token)
):
    start_ts = time.perf_counter()
    tmp_path = None
    req_id = request.state.request_id

    try:
        FileValidator.validate(file)
        tmp_path = FileValidator.check_size_and_save(file)
        
        # CPU heavy task run in thread pool. 
        # ContextVars are automatically copied to the thread.
        result = await run_in_threadpool(
            OCRProcessor.process_file,
            tmp_path,
            file.content_type
        )

        return {
            "request_id": req_id,
            "process_time_ms": (time.perf_counter() - start_ts) * 1000,
            "status": StatusEnum.SUCCESS,
            "message": "OCR Extraction Successful",
            "data": {
                "filename": file.filename,
                "content_type": file.content_type,
                "saved_file_path": tmp_path,
                "total_pages": result["total_pages"],
                "pages_content": result["pages_content"]
            }
        }

    except Exception as e:
        logger.error(f"Request failed: {str(e)}")
        status_code = getattr(e, "status_code", 500)
        return JSONResponse(
            status_code=status_code,
            content={
                "request_id": req_id,
                "process_time_ms": (time.perf_counter() - start_ts) * 1000,
                "status": StatusEnum.ERROR,
                "error_message": getattr(e, "detail", str(e))
            }
        )
    finally:
        if tmp_path:
            logger.info(f"File preserved at: {tmp_path}")
            try:
              os.remove(tmp_path)
              logger.info(f"Temporary file deleted: {tmp_path}")
            except Exception as e:
              logger.warning(f"Failed to delete temp file: {str(e)}")