#!/usr/bin/env python3
#
# net.py - part of the FDroid server tools
# Copyright (C) 2015 Hans-Christoph Steiner <hans@eds.org>
# Copyright (C) 2022 FC Stegerman <flx@obfusk.net>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import logging
import os
import requests
import time
import urllib
from requests.adapters import HTTPAdapter, Retry
from requests.exceptions import ChunkedEncodingError

HEADERS = {'User-Agent': 'F-Droid'}


def download_file(url, local_filename=None, dldir='tmp', retries=3, backoff_factor=0.1):
    filename = urllib.parse.urlparse(url).path.split('/')[-1]
    if local_filename is None:
        local_filename = os.path.join(dldir, filename)
    # Retry applies to failed DNS lookups, socket connections and connection
    # timeouts, never to requests where data has made it to the server; so we
    # handle ChunkedEncodingError during transfer ourselves.
    for i in range(retries + 1):
        if retries:
            max_retries = Retry(total=retries - i, backoff_factor=backoff_factor)
            adapter = HTTPAdapter(max_retries=max_retries)
            session = requests.Session()
            session.mount('http://', adapter)
            session.mount('https://', adapter)
        else:
            session = requests
        # the stream=True parameter keeps memory usage low
        r = session.get(
            url, stream=True, allow_redirects=True, headers=HEADERS, timeout=300
        )
        r.raise_for_status()
        try:
            with open(local_filename, 'wb') as f:
                for chunk in r.iter_content(chunk_size=1024):
                    if chunk:  # filter out keep-alive new chunks
                        f.write(chunk)
                        f.flush()
            return local_filename
        except ChunkedEncodingError as err:
            if i == retries:
                raise err
            logging.warning('Download interrupted, retrying...')
            time.sleep(backoff_factor * 2**i)
    raise ValueError("retries must be >= 0")


def http_get(url, etag=None, timeout=600):
    """Download the content from the given URL by making a GET request.

    If an ETag is given, it will do a HEAD request first, to see if the content changed.

    Parameters
    ----------
    url
      The URL to download from.
    etag
      The last ETag to be used for the request (optional).

    Returns
    -------
    A tuple consisting of:
      - The raw content that was downloaded or None if it did not change
      - The new eTag as returned by the HTTP request
    """
    # TODO disable TLS Session IDs and TLS Session Tickets
    #      (plain text cookie visible to anyone who can see the network traffic)
    if etag:
        r = requests.head(url, headers=HEADERS, timeout=timeout)
        r.raise_for_status()
        if 'ETag' in r.headers and etag == r.headers['ETag']:
            return None, etag

    r = requests.get(url, headers=HEADERS, timeout=timeout)
    r.raise_for_status()

    new_etag = None
    if 'ETag' in r.headers:
        new_etag = r.headers['ETag']

    return r.content, new_etag