# Copyright (C) 2011-2014 Bastian Kleineidam
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
"""
Function to check for updates.
"""

import os
from .configuration import Version as CurrentVersion
from .url import get_content
from distutils.version import StrictVersion

# Use the Freecode submit file as source since that file gets updated
# only when releasing a new version.
UPDATE_URL = "https://raw.github.com/linkchecker/linkchecker/master/linkchecker.freecode"
VERSION_TAG = 'Version:'
if os.name == 'nt':
    URL_TAG = 'Windows-installer-URL:'
else:
    URL_TAG = 'Source-Package-URL:'


def check_update():
    """Return the following values:
       (False, errmsg) - online version could not be determined
       (True, None) - user has newest version
       (True, (version, url string)) - update available
       (True, (version, None)) - current version is newer than online version
    """
    version, value = get_online_version()
    if version is None:
        # value is an error message
        return False, value
    if version == CurrentVersion:
        # user has newest version
        return True, None
    if is_newer_version(version):
        # value is an URL linking to the update package
        return True, (version, value)
    # user is running a local or development version
    return True, (version, None)


def get_online_version():
    """Download update info and parse it."""
    # prevent getting a cached answer
    headers = {'Pragma': 'no-cache', 'Cache-Control': 'no-cache'}
    content, info = get_content(UPDATE_URL, addheaders=headers)
    if content is None:
        return content, info
    version, url = None, None
    for line in content.splitlines():
        if line.startswith(VERSION_TAG):
            version = line.split(':', 1)[1].strip()
        elif line.startswith(URL_TAG):
            url = line.split(':', 1)[1].strip()
            url = url.replace('${version}', version)
    return version, url


def is_newer_version(version):
    """Check if given version is newer than current version."""
    return StrictVersion(version) > StrictVersion(CurrentVersion)