"""Bounded, dependency-free validation for supported upload formats."""

from __future__ import annotations

import codecs
import zipfile
from pathlib import Path


class UploadContentError(ValueError):
    """Raised when bytes do not match the declared file extension."""


_OLE_MAGIC = b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1"
_PNG_MAGIC = b"\x89PNG\r\n\x1a\n"
_MAX_ZIP_ENTRIES = 10_000
_MAX_ZIP_UNCOMPRESSED_BYTES = 200 * 1024 * 1024
_MAX_ZIP_RATIO = 500


def _validate_text(path: Path) -> None:
    with path.open("rb") as handle:
        sample = handle.read(64 * 1024)
    if not sample:
        return
    if sample.startswith((b"\xff\xfe", b"\xfe\xff")):
        try:
            codecs.getincrementaldecoder("utf-16")(errors="strict").decode(sample, final=False)
        except UnicodeDecodeError as exc:
            raise UploadContentError("Text file has an invalid UTF-16 encoding") from exc
        return
    if b"\x00" in sample:
        raise UploadContentError("Text file contains binary NUL bytes")
    control_bytes = sum(byte < 9 or 13 < byte < 32 for byte in sample)
    if control_bytes / len(sample) > 0.10:
        raise UploadContentError("Text file contains too many binary control bytes")
    for encoding in ("utf-8-sig", "gb18030"):
        try:
            codecs.getincrementaldecoder(encoding)(errors="strict").decode(sample, final=False)
            return
        except UnicodeDecodeError:
            continue
    raise UploadContentError("Text file encoding is not supported")


def _validate_ooxml(path: Path, expected_prefix: str) -> None:
    try:
        with zipfile.ZipFile(path) as archive:
            infos = archive.infolist()
            if len(infos) > _MAX_ZIP_ENTRIES:
                raise UploadContentError("Office archive contains too many entries")
            names = {info.filename.replace("\\", "/") for info in infos}
            if "[Content_Types].xml" not in names or not any(name.startswith(expected_prefix) for name in names):
                raise UploadContentError("Office archive content does not match its extension")
            total_uncompressed = sum(max(0, info.file_size) for info in infos)
            total_compressed = sum(max(0, info.compress_size) for info in infos)
            if total_uncompressed > _MAX_ZIP_UNCOMPRESSED_BYTES:
                raise UploadContentError("Office archive expands beyond the safety limit")
            if (
                total_uncompressed > 10 * 1024 * 1024
                and total_uncompressed > max(1, total_compressed) * _MAX_ZIP_RATIO
            ):
                raise UploadContentError("Office archive compression ratio is unsafe")
    except (zipfile.BadZipFile, OSError) as exc:
        raise UploadContentError("Office file is not a valid ZIP container") from exc


def validate_upload_content(path: Path, extension: str) -> None:
    """Check the supported format's signature without reading the whole file."""

    extension = extension.lower()
    with path.open("rb") as handle:
        header = handle.read(1024)
    if extension in {".txt", ".md", ".csv"}:
        _validate_text(path)
        return
    if extension == ".pdf":
        if b"%PDF-" not in header:
            raise UploadContentError("PDF signature does not match the .pdf extension")
        return
    if extension == ".png":
        if not header.startswith(_PNG_MAGIC):
            raise UploadContentError("PNG signature does not match the .png extension")
        return
    if extension in {".jpg", ".jpeg"}:
        if not header.startswith(b"\xff\xd8\xff"):
            raise UploadContentError("JPEG signature does not match the image extension")
        return
    if extension in {".doc", ".ppt", ".xls"}:
        if not header.startswith(_OLE_MAGIC):
            raise UploadContentError("Legacy Office signature does not match the extension")
        return
    if extension == ".docx":
        _validate_ooxml(path, "word/")
        return
    if extension == ".pptx":
        _validate_ooxml(path, "ppt/")
        return
    if extension == ".xlsx":
        _validate_ooxml(path, "xl/")
        return
    raise UploadContentError(f"Unsupported file extension: {extension or '(none)'}")