from __future__ import annotations

import logging
import threading
from typing import TYPE_CHECKING, Optional

import cv2

if TYPE_CHECKING:
    import easyocr

logger = logging.getLogger("uvicorn")


def _load_reader(languages: list[str]) -> easyocr.Reader:
    """Load the OCR model. easyocr and torch are imported here: they take seconds to import.

    Args:
        languages (list[str]): The languages the reader must recognize.

    Raises:
        OSError: When the model files can't be downloaded or read.
        RuntimeError: When torch can't load the model files.

    Returns:
        easyocr.Reader: The loaded reader.
    """
    import easyocr
    import torch

    return easyocr.Reader(languages, gpu=torch.cuda.is_available())


class OCRReader:
    _instance: Optional["OCRReader"] = None
    _lock = threading.Lock()
    ocr_reader: easyocr.Reader

    def __new__(cls):
        """Return the one instance, loading the model on the first call.

        Raises:
            OSError: When the model files can't be downloaded or read.
            RuntimeError: When torch can't load the model files.

        Returns:
            OCRReader: The shared instance, with its reader loaded.
        """
        # Double-checked: once loaded the fast path takes no lock, and while
        # the model is still loading every other caller waits here for it.
        if cls._instance is None:
            with cls._lock:
                if cls._instance is None:
                    logger.info("Loading the OCR model into memory...")
                    instance = super().__new__(cls)
                    instance.ocr_reader = _load_reader(["en", "fr"])
                    # Published only once it can read: a caller racing the
                    # warm-up must never get an instance without a reader.
                    cls._instance = instance
        return cls._instance

    def read_text(self, img: cv2.typing.MatLike | None):
        res = self.ocr_reader.readtext(img, detail=0)
        if not isinstance(res, list):
            return None
        return " ".join([str(item) for item in res])