"""PDF page classifier — public factory with HuggingFace auto-download.

Standalone usage (files downloaded from HF repo):
    from classifiers import load_classifier
    clf = load_classifier(".")          # local directory with model files
    result = clf.predict("page.png")

HuggingFace usage:
    from classifiers import load_classifier
    clf = load_classifier("Wikit/pdf-pages-classifier")
    result = clf.predict("page.png")
"""

from __future__ import annotations

import os
from pathlib import Path
from typing import Any


# INT8 preferred over FP32 for both backends — matches classifier lookup order
_HF_ONNX_INT8_FILES = ["model_int8.onnx", "config.json"]
_HF_ONNX_FP32_FILES = ["model.onnx", "config.json"]

_HF_OV_INT8_FILES = ["openvino_model_int8.xml", "openvino_model_int8.bin", "config.json"]
_HF_OV_FP32_FILES = ["openvino_model.xml", "openvino_model.bin", "config.json"]


def _is_hf_repo_id(path: str) -> bool:
    """Return True if path looks like 'owner/repo' rather than a local path."""
    if os.path.exists(path):
        return False
    # HF repo IDs have exactly one '/' and no OS path separators or leading dots
    normalized = path.replace("\\", "/")
    if normalized.startswith((".", "/", "~")):
        return False
    parts = normalized.split("/")
    return len(parts) == 2 and all(p.strip() for p in parts)


def _download_from_hf(repo_id: str, filenames: list[str], cache_dir: str | None) -> Path:
    """Download specific files from a HF repo and return the local snapshot directory."""
    try:
        from huggingface_hub import hf_hub_download
    except ImportError as e:
        raise ImportError(
            "huggingface_hub is required to load from a HuggingFace repo.\n"
            "Install with: pip install huggingface-hub"
        ) from e

    last: Path | None = None
    for filename in filenames:
        last = Path(hf_hub_download(repo_id=repo_id, filename=filename, cache_dir=cache_dir))

    assert last is not None
    return last.parent


def _download_with_int8_fallback(
    repo_id: str,
    int8_files: list[str],
    fp32_files: list[str],
    cache_dir: str | None,
) -> Path:
    """Download files from HF, preferring INT8 over FP32 when available."""
    try:
        from huggingface_hub import EntryNotFoundError
    except ImportError as e:
        raise ImportError(
            "huggingface_hub is required to load from a HuggingFace repo.\n"
            "Install with: pip install huggingface-hub"
        ) from e

    try:
        return _download_from_hf(repo_id, int8_files, cache_dir)
    except EntryNotFoundError:
        return _download_from_hf(repo_id, fp32_files, cache_dir)


def load_classifier(
    repo_or_dir: str = "Wikit/pdf-pages-classifier",
    backend: str = "auto",
    device: str = "CPU",
    cache_dir: str | None = None,
) -> Any:
    """Load a PDF page classifier with automatic backend selection.

    Args:
        repo_or_dir: HuggingFace repo ID (e.g. ``"Wikit/pdf-pages-classifier"``)
            or local directory containing ``config.json`` and model files.
        backend: ``"auto"`` tries OpenVINO first, falls back to ONNX.
            Pass ``"openvino"`` or ``"onnx"`` to force a specific backend.
        device: OpenVINO device string (``"CPU"``, ``"GPU"``, ``"AUTO"``).
            Ignored for ONNX.
        cache_dir: Custom cache directory for HuggingFace downloads.

    Returns:
        A classifier instance exposing ``predict(images)``.

    Example::

        clf = load_classifier("Wikit/pdf-pages-classifier")
        result = clf.predict("page.png")
        print(result["needs_image_embedding"], result["predicted_classes"])
    """
    if backend not in ("auto", "onnx", "openvino"):
        raise ValueError(f"Unknown backend {backend!r}. Choose 'auto', 'onnx', or 'openvino'.")

    is_hf = _is_hf_repo_id(repo_or_dir)

    if backend in ("auto", "openvino"):
        try:
            return _load_openvino(repo_or_dir, device=device, cache_dir=cache_dir, is_hf=is_hf)
        except (ImportError, FileNotFoundError):
            if backend == "openvino":
                raise

    return _load_onnx(repo_or_dir, cache_dir=cache_dir, is_hf=is_hf)


def _load_onnx(repo_or_dir: str, cache_dir: str | None, is_hf: bool) -> Any:
    try:
        from .classifier_onnx import PDFPageClassifierONNX
    except ImportError:
        from classifier_onnx import PDFPageClassifierONNX  # type: ignore[no-redef]

    model_dir = (
        _download_with_int8_fallback(repo_or_dir, _HF_ONNX_INT8_FILES, _HF_ONNX_FP32_FILES, cache_dir)
        if is_hf else Path(repo_or_dir)
    )
    return PDFPageClassifierONNX.from_pretrained(str(model_dir))


def _load_openvino(repo_or_dir: str, device: str, cache_dir: str | None, is_hf: bool) -> Any:
    try:
        from .classifier_ov import PDFPageClassifierOV
    except ImportError:
        from classifier_ov import PDFPageClassifierOV  # type: ignore[no-redef]

    model_dir = (
        _download_with_int8_fallback(repo_or_dir, _HF_OV_INT8_FILES, _HF_OV_FP32_FILES, cache_dir)
        if is_hf else Path(repo_or_dir)
    )
    return PDFPageClassifierOV.from_pretrained(str(model_dir), device=device)