from __future__ import annotations

import logging
import mimetypes
import shutil
import subprocess
import tempfile
from pathlib import Path
from typing import TYPE_CHECKING
from typing import Final

from django.conf import settings

from documents.loggers import LoggingMixin
from documents.utils import copy_file_with_basic_stats
from documents.utils import run_subprocess
from paperless.parsers.registry import get_parser_registry

if TYPE_CHECKING:
    import datetime

logger = logging.getLogger("paperless.parsing")


def is_mime_type_supported(mime_type: str) -> bool:
    """
    Returns True if the mime type is supported, False otherwise
    """
    return get_parser_registry().get_parser_for_file(mime_type, "") is not None


def get_default_file_extension(mime_type: str) -> str:
    """
    Returns the default file extension for a mimetype, or
    an empty string if it could not be determined
    """
    parser_class = get_parser_registry().get_parser_for_file(mime_type, "")
    if parser_class is not None:
        supported = parser_class.supported_mime_types()
        if mime_type in supported:
            return supported[mime_type]

    ext = mimetypes.guess_extension(mime_type)
    return ext if ext else ""


def is_file_ext_supported(ext: str) -> bool:
    """
    Returns True if the file extension is supported, False otherwise
    TODO: Investigate why this really exists, why not use mimetype
    """
    if ext:
        return ext.lower() in get_supported_file_extensions()
    else:
        return False


def get_supported_file_extensions() -> set[str]:
    extensions = set()
    for parser_class in get_parser_registry().all_parsers():
        for mime_type, ext in parser_class.supported_mime_types().items():
            extensions.update(mimetypes.guess_all_extensions(mime_type))
            # Python's stdlib might be behind, so also add what the parser
            # says is the default extension
            # This makes image/webp supported on Python < 3.11
            extensions.add(ext)

    return extensions


def get_default_thumbnail() -> Path:
    """
    Returns the path to a generic thumbnail
    """
    return (Path(__file__).parent / "resources" / "document.webp").resolve()


_THUMBNAIL_MAX_WIDTH: Final[int] = 500
_THUMBNAIL_MAX_HEIGHT: Final[int] = 5000
# Used only when the page geometry cannot be read
_THUMBNAIL_FALLBACK_DPI: Final[int] = 150
# Applied before supersampling, so tiny pages are not enlarged
_THUMBNAIL_MAX_DPI: Final[int] = 300
# Rendering at a multiple and downsampling keeps text crisper
_THUMBNAIL_SUPERSAMPLE: Final[int] = 2


def rasterize_pdf_page_to_png(
    in_path: Path,
    out_path: Path,
    *,
    dpi: float,
    logging_group=None,
) -> None:
    """
    Rasterizes the first page of a PDF to a PNG with pdftoppm.
    """
    args = [
        "pdftoppm",
        # Only the first page is needed, first and last page are both 1
        "-f",
        "1",
        "-l",
        "1",
        # Resolution in DPI, which may be fractional
        "-r",
        str(dpi),
        # Write a PNG
        "-png",
        # Write exactly one file with no page number in its name. -png appends
        # ".png" to the output root, so the path is passed without its suffix
        "-singlefile",
        # Render the CropBox instead of the MediaBox, as a viewer would. This
        # must be the same box get_pdf_first_page_size_points measures, or the
        # DPI is computed for the wrong size
        "-cropbox",
        str(in_path),
        str(out_path.with_suffix("")),
    ]

    logger.debug("Execute: " + " ".join(args), extra={"group": logging_group})

    try:
        run_subprocess(args, logger=logger)
    except subprocess.CalledProcessError as e:
        raise ParseError(f"pdftoppm failed at {args}") from e
    except Exception as e:  # pragma: no cover
        raise ParseError("Unknown error running pdftoppm") from e


def encode_thumbnail_webp(
    png_path: Path,
    out_path: Path,
    *,
    supersample: int = 1,
) -> None:
    """
    Flattens alpha onto white, undoes supersampling, shrinks to fit and saves as WebP.
    """
    from PIL import Image

    try:
        with Image.open(png_path) as im:
            if im.mode in ("RGBA", "LA"):
                flattened = Image.new("RGB", im.size, (255, 255, 255))
                flattened.paste(im, mask=im.split()[-1])
            else:
                flattened = im.convert("RGB")

        # One resize avoids a second, softer pass: undo the supersample and
        # clamp to the bounds together, never enlarging
        scale = min(
            1 / supersample,
            _THUMBNAIL_MAX_WIDTH / flattened.width,
            _THUMBNAIL_MAX_HEIGHT / flattened.height,
        )
        if scale < 1:
            flattened = flattened.resize(
                (
                    max(1, round(flattened.width * scale)),
                    max(1, round(flattened.height * scale)),
                ),
                Image.Resampling.LANCZOS,
            )

        flattened.save(out_path, format="WEBP")
    except (OSError, Image.DecompressionBombError) as e:
        raise ParseError(f"Unable to encode thumbnail from {png_path}") from e


def _compute_thumbnail_dpi(in_path: Path, logging_group=None) -> tuple[float, int]:
    """
    Returns (dpi, supersample). Unknown geometry is not supersampled, since
    the render size cannot be bounded.

    The DPI is left fractional rather than floored at 1, so an oversized page
    still renders at about the thumbnail size instead of an unbounded raster.
    pdftoppm rounds pixel dimensions up, so the render is never short of the
    target; the shrink-only clamp in encode_thumbnail_webp trims any excess.
    """
    from paperless.parsers.utils import get_pdf_first_page_size_points

    size = get_pdf_first_page_size_points(in_path)
    if size is None:
        logger.debug(
            "Could not read PDF page size, using fallback DPI",
            extra={"group": logging_group},
        )
        return _THUMBNAIL_FALLBACK_DPI, 1

    width_pts, height_pts = size
    dpi_for_width = _THUMBNAIL_MAX_WIDTH * 72 / width_pts
    dpi_for_height = _THUMBNAIL_MAX_HEIGHT * 72 / height_pts
    return (
        min(_THUMBNAIL_MAX_DPI, dpi_for_width, dpi_for_height),
        _THUMBNAIL_SUPERSAMPLE,
    )


def _render_pdf_thumbnail(
    in_path: Path,
    png_path: Path,
    out_path: Path,
    logging_group=None,
) -> None:
    dpi, supersample = _compute_thumbnail_dpi(in_path, logging_group=logging_group)
    rasterize_pdf_page_to_png(
        in_path,
        png_path,
        dpi=dpi * supersample,
        logging_group=logging_group,
    )
    encode_thumbnail_webp(png_path, out_path, supersample=supersample)


def _repair_pdf_with_qpdf(in_path: Path, out_path: Path) -> None:
    # qpdf exits 3 after a repair; --warning-exit-0 keeps that from failing
    try:
        shutil.copy(in_path, out_path)
        run_subprocess(
            ["qpdf", "--warning-exit-0", "--replace-input", str(out_path)],
            logger=logger,
        )
    except (subprocess.CalledProcessError, OSError) as e:
        raise ParseError(f"qpdf repair failed for {in_path}") from e


def make_thumbnail_from_pdf_qpdf_fallback(
    in_path: Path,
    temp_dir: Path,
    logging_group=None,
) -> Path:
    png_path = temp_dir / "page1_repaired.png"
    out_path = temp_dir / "convert_qpdf.webp"
    repaired_path = temp_dir / "repaired.pdf"

    logger.warning(
        "Thumbnail generation with pdftoppm failed, attempting qpdf repair and retry.",
        extra={"group": logging_group},
    )

    try:
        _repair_pdf_with_qpdf(in_path, repaired_path)
        _render_pdf_thumbnail(repaired_path, png_path, out_path, logging_group)
        return out_path

    except ParseError as e:
        logger.error(f"Unable to make thumbnail after qpdf repair: {e}")
        # The caller might expect a generated thumbnail that can be moved,
        # so we need to copy it before it gets moved.
        # https://github.com/paperless-ngx/paperless-ngx/issues/3631
        default_thumbnail_path = temp_dir / "document.webp"
        copy_file_with_basic_stats(get_default_thumbnail(), default_thumbnail_path)
        return default_thumbnail_path


def make_thumbnail_from_pdf(in_path: Path, temp_dir: Path, logging_group=None) -> Path:
    """
    The thumbnail of a PDF is just a 500px wide image of the first page.
    """
    png_path: Path = temp_dir / "page1.png"
    out_path: Path = temp_dir / "convert.webp"

    try:
        _render_pdf_thumbnail(in_path, png_path, out_path, logging_group)
    except ParseError as e:
        logger.error(f"Unable to make thumbnail with pdftoppm: {e}")
        out_path = make_thumbnail_from_pdf_qpdf_fallback(
            in_path,
            temp_dir,
            logging_group,
        )

    return out_path


class ParseError(Exception):
    pass


class DocumentParser(LoggingMixin):
    """
    Subclass this to make your own parser.  Have a look at
    `paperless_tesseract.parsers` for inspiration.
    """

    logging_name = "paperless.parsing"

    def __init__(self, logging_group, progress_callback=None) -> None:
        super().__init__()
        self.renew_logging_group()
        self.logging_group = logging_group
        self.settings = self.get_settings()
        settings.SCRATCH_DIR.mkdir(parents=True, exist_ok=True)
        self.tempdir = Path(
            tempfile.mkdtemp(prefix="paperless-", dir=settings.SCRATCH_DIR),
        )

        self.archive_path = None
        self.text = None
        self.date: datetime.datetime | None = None
        self.progress_callback = progress_callback

    def progress(self, current_progress, max_progress) -> None:
        if self.progress_callback:
            self.progress_callback(current_progress, max_progress)

    def get_settings(self):  # pragma: no cover
        """
        A parser must implement this
        """
        raise NotImplementedError

    def read_file_handle_unicode_errors(self, filepath: Path) -> str:
        """
        Helper utility for reading from a file, and handling a problem with its
        unicode, falling back to ignoring the error to remove the invalid bytes
        """
        try:
            text = filepath.read_text(encoding="utf-8")
        except UnicodeDecodeError as e:
            self.log.warning(f"Unicode error during text reading, continuing: {e}")
            text = filepath.read_bytes().decode("utf-8", errors="replace")
        return text

    def extract_metadata(self, document_path, mime_type):
        return []

    def get_page_count(self, document_path, mime_type) -> None:
        return None

    def parse(self, document_path, mime_type, file_name=None):
        raise NotImplementedError

    def get_archive_path(self):
        return self.archive_path

    def get_thumbnail(self, document_path, mime_type, file_name=None):
        """
        Returns the path to a file we can use as a thumbnail for this document.
        """
        raise NotImplementedError

    def get_text(self):
        return self.text

    def get_date(self) -> datetime.datetime | None:
        return self.date

    def cleanup(self) -> None:
        self.log.debug(f"Deleting directory {self.tempdir}")
        shutil.rmtree(self.tempdir)