from starlette.applications import Starlette
from starlette.responses import StreamingResponse
from starlette.requests import Request
from starlette.routing import Route
from pathlib import Path
from typing import IO, Generator

"""
Stream a file, in this case an mp4 video, supporting range-requests using starlette

Reference: https://stackoverflow.com/questions/33208849/python-django-streaming-video-mp4-file-using-httpresponse
"""

VIDEO_PATH = '/tmp/video.mp4'

def ranged \
        (
            file: IO[bytes],
            start: int = 0,
            end: int = None,
            block_size: int = 8192,
        ) -> Generator[bytes, None, None]:
    consumed = 0

    file.seek(start)

    while True:
        data_length = min(block_size, end - start - consumed) if end else block_size

        if data_length <= 0:
            break

        data = file.read(data_length)

        if not data:
            break

        consumed += data_length

        yield data

    if hasattr(file, 'close'):
        file.close()

def homepage(request: Request) -> StreamingResponse:
    path = Path(VIDEO_PATH)

    file = path.open('rb')

    file_size = path.stat().st_size

    content_range = request.headers.get('range')

    content_length = file_size
    status_code = 200
    headers = {}

    if content_range is not None:
        content_range = content_range.strip().lower()

        content_ranges = content_range.split('=')[-1]

        range_start, range_end, *_ = map(str.strip, (content_ranges + '-').split('-'))

        range_start = max(0, int(range_start)) if range_start else 0
        range_end   = min(file_size - 1, int(range_end)) if range_end else file_size - 1

        content_length = (range_end - range_start) + 1

        file = ranged(file, start = range_start, end = range_end + 1)

        status_code = 206

        headers['Content-Range'] = f'bytes {range_start}-{range_end}/{file_size}'

    response = StreamingResponse \
    (
        file,
        media_type = 'video/mp4',
        status_code = status_code,
    )

    response.headers.update \
    ({
        'Accept-Ranges': 'bytes',
        'Content-Length': str(content_length),
        **headers,
    })

    return response


app = Starlette \
(
    routes = \
    [
        Route('/', homepage),
    ],
)