import hashlib
import mimetypes
from collections.abc import AsyncGenerator
from datetime import datetime, timezone
from pathlib import Path

import aiofiles
from fastapi import Request
from fastapi.responses import Response, StreamingResponse

mimetypes.init()


def get_range_response(file: Path, request: Request, chunk_size: int) -> Response:
    """Get a Response for the given file, supporting range-requests, E-Tag and Last-Modified."""
    file_size = file.stat().st_size
    last_modified_time = datetime.fromtimestamp(file.stat().st_mtime, timezone.utc)
    start = 0
    end = file_size - 1
    status_code = 200
    e_tag = hashlib.md5((str(last_modified_time) + str(file_size)).encode()).hexdigest()
    if_match_header = request.headers.get('If-None-Match')
    if if_match_header and if_match_header == e_tag:
        return Response(status_code=304)  # Not Modified
    headers = {
        'E-Tag': e_tag,
        'Last-Modified': last_modified_time.strftime(r'%a, %d %b %Y %H:%M:%S GMT'),
    }
    range_header = request.headers.get('range')
    media_type = mimetypes.guess_type(str(file))[0] or 'application/octet-stream'
    if range_header is not None:
        byte1, byte2 = range_header.split('=')[1].split('-')
        start = int(byte1)
        if byte2:
            end = int(byte2)
        status_code = 206  # Partial Content
    content_length = end - start + 1
    headers.update({
        'Content-Length': str(content_length),
        'Content-Range': f'bytes {start}-{end}/{file_size}',
        'Accept-Ranges': 'bytes',
    })

    async def content_reader(file: Path, start: int, end: int) -> AsyncGenerator[bytes, None]:
        async with aiofiles.open(file, 'rb') as data:
            await data.seek(start)
            remaining_bytes = end - start + 1
            while remaining_bytes > 0:
                chunk = await data.read(min(chunk_size, remaining_bytes))
                if not chunk:
                    break
                yield chunk
                remaining_bytes -= len(chunk)
    return StreamingResponse(
        content_reader(file, start, end),
        media_type=media_type,
        headers=headers,
        status_code=status_code,
    )