"""
HTTP views dedicated to LocalFiles storage download operations.
"""
import logging
import mimetypes
import os
import posixpath
from pathlib import Path
from typing import Optional

from django.conf import settings
from django.db.models import CharField, F, Value
from django.http import HttpRequest, HttpResponse, HttpResponseForbidden, HttpResponseNotFound, HttpResponseNotModified
from django.utils._os import safe_join
from drf_spectacular.utils import extend_schema
from io_storages.localfiles.models import LocalFilesImportStorage
from ranged_fileresponse import RangedFileResponse
from rest_framework.decorators import api_view, permission_classes
from rest_framework.permissions import IsAuthenticated

logger = logging.getLogger(__name__)


"""
Utility helpers for LocalFiles storage operations.
"""


def _if_none_match_satisfied(header_value: Optional[str], etag: str) -> bool:
    """Return True if the client's cached representation matches the current file."""
    if not header_value:
        return False
    etag_candidates = [candidate.strip() for candidate in header_value.split(',') if candidate.strip()]
    return '*' in etag_candidates or etag in etag_candidates


def build_localfile_response(
    request: HttpRequest,
    full_path: str,
    if_none_match_header: Optional[str],
) -> HttpResponse:
    """
    Stream the requested file and attach a weak ETag so browsers can cache it.

    We also honor `If-None-Match` headers to short-circuit the response with 304
    when the client's cached representation is still valid.
    """
    try:
        file_handle = open(full_path, mode='rb')
    except OSError as exc:
        logger.error('Error opening file %s: %s', full_path, exc)
        return HttpResponseNotFound(f'Error opening file {full_path}')

    # Weak ETag keeps the implementation simple while still invalidating on file edits.
    stat_result = os.fstat(file_handle.fileno())
    mtime_ns = getattr(stat_result, 'st_mtime_ns', int(stat_result.st_mtime * 1_000_000_000))
    etag = f'W/"{mtime_ns:x}-{stat_result.st_size:x}"'

    # Check if the client's cached representation matches the current file
    if _if_none_match_satisfied(if_none_match_header, etag):
        file_handle.close()
        not_modified = HttpResponseNotModified()
        not_modified['ETag'] = etag
        return not_modified

    # Detect mime type and encoding
    content_type, _ = mimetypes.guess_type(str(full_path))
    content_type = content_type or 'application/octet-stream'

    response = RangedFileResponse(request, file_handle, content_type=content_type)
    response['ETag'] = etag  # Enables client-side caching for unchanged files.
    return response


"""
Main view for serving files residing under LocalFilesImportStorage roots with ETag support
"""


@extend_schema(exclude=True)
@api_view(['GET'])
@permission_classes([IsAuthenticated])
def localfiles_data(request):
    """Serve files residing under LocalFilesImportStorage roots with ETag support."""
    path = request.GET.get('d')
    if settings.LOCAL_FILES_SERVING_ENABLED is False:
        return HttpResponseForbidden(
            "Serving local files can be dangerous, so it's disabled by default. "
            'You can enable it with LOCAL_FILES_SERVING_ENABLED environment variable, '
            'please check docs: https://labelstud.io/guide/storage.html#Local-storage'
        )

    local_serving_document_root = settings.LOCAL_FILES_DOCUMENT_ROOT
    if path and request.user.is_authenticated:
        # Normalize the incoming relative path so we don't depend on trailing slashes
        path = posixpath.normpath(path).lstrip('/')
        full_path = Path(safe_join(local_serving_document_root, path))
        user_has_permissions = False

        # Storage paths are normalized on save/migration, so prefix matches using the
        # directory that contains the requested file stay consistent across OSes.
        full_path_dir = os.path.normpath(os.path.dirname(str(full_path)))
        localfiles_storage = LocalFilesImportStorage.objects.annotate(
            _full_path=Value(full_path_dir, output_field=CharField())
        ).filter(_full_path__startswith=F('path'))
        if localfiles_storage.exists():
            user_has_permissions = any(storage.project.has_permission(request.user) for storage in localfiles_storage)

        # Check user permissions for this file and if it exists
        if user_has_permissions and os.path.exists(full_path):
            # Detect mime type and encoding
            return build_localfile_response(
                request=request,
                full_path=str(full_path),
                if_none_match_header=request.META.get('HTTP_IF_NONE_MATCH'),
            )
        else:
            return HttpResponseNotFound()

    return HttpResponseForbidden()