# -*- coding: utf-8 -*-
#
# gPodder - A media aggregator and podcast client
# Copyright (c) 2005-2011 Thomas Perl and the gPodder Team
#
# gPodder 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 3 of the License, or
# (at your option) any later version.
#
# gPodder 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, see <http://www.gnu.org/licenses/>.
#

#
#  util.py -- Misc utility functions
#  Thomas Perl <thp@perli.net> 2007-08-04
#

"""Miscellaneous helper functions for gPodder

This module provides helper and utility functions for gPodder that 
are not tied to any specific part of gPodder.

"""

import gpodder
from gpodder.liblogger import log

import os
import os.path
import platform
import glob
import stat
import shlex
import socket
import sys

import re
import subprocess
from htmlentitydefs import entitydefs
import time
import gzip
import datetime
import threading

import urlparse
import urllib
import urllib2
import httplib
import webbrowser
import mimetypes

import feedparser

import StringIO
import xml.dom.minidom

_ = gpodder.gettext
N_ = gpodder.ngettext


import locale
try:
    locale.setlocale(locale.LC_ALL, '')
except Exception, e:
    log('Warning: Cannot set locale (%s).', e)

# Native filesystem encoding detection
encoding = sys.getfilesystemencoding()

if encoding is None:
    if 'LANG' in os.environ and '.' in os.environ['LANG']:
        lang = os.environ['LANG']
        (language, encoding) = lang.rsplit('.', 1)
        log('Detected encoding: %s', encoding)
    elif gpodder.ui.fremantle:
        encoding = 'utf-8'
    elif gpodder.win32:
        # To quote http://docs.python.org/howto/unicode.html:
        # ,,on Windows, Python uses the name "mbcs" to refer
        #   to whatever the currently configured encoding is``
        encoding = 'mbcs'
    else:
        encoding = 'iso-8859-15'
        log('Assuming encoding: ISO-8859-15 ($LANG not set).')


# Used by file_type_by_extension()
_BUILTIN_FILE_TYPES = None


def make_directory( path):
    """
    Tries to create a directory if it does not exist already.
    Returns True if the directory exists after the function 
    call, False otherwise.
    """
    if os.path.isdir( path):
        return True

    try:
        os.makedirs( path)
    except:
        log( 'Could not create directory: %s', path)
        return False

    return True


def normalize_feed_url(url):
    """
    Converts any URL to http:// or ftp:// so that it can be 
    used with "wget". If the URL cannot be converted (invalid
    or unknown scheme), "None" is returned.

    This will also normalize feed:// and itpc:// to http://.

    >>> normalize_feed_url('itpc://example.org/podcast.rss')
    'http://example.org/podcast.rss'

    If no URL scheme is defined (e.g. "curry.com"), we will
    simply assume the user intends to add a http:// feed.

    >>> normalize_feed_url('curry.com')
    'http://curry.com/'

    There are even some more shortcuts for advanced users
    and lazy typists (see the source for details).

    >>> normalize_feed_url('fb:43FPodcast')
    'http://feeds.feedburner.com/43FPodcast'

    It will also take care of converting the domain name to
    all-lowercase (because domains are not case sensitive):

    >>> normalize_feed_url('http://Example.COM/')
    'http://example.com/'

    Some other minimalistic changes are also taken care of,
    e.g. a ? with an empty query is removed:

    >>> normalize_feed_url('http://example.org/test?')
    'http://example.org/test'
    """
    if not url or len(url) < 8:
        return None

    # This is a list of prefixes that you can use to minimize the amount of
    # keystrokes that you have to use.
    # Feel free to suggest other useful prefixes, and I'll add them here.
    PREFIXES = {
            'fb:': 'http://feeds.feedburner.com/%s',
            'yt:': 'http://www.youtube.com/rss/user/%s/videos.rss',
            'sc:': 'http://soundcloud.com/%s',
            'fm4od:': 'http://onapp1.orf.at/webcam/fm4/fod/%s.xspf',
    }

    for prefix, expansion in PREFIXES.iteritems():
        if url.startswith(prefix):
            url = expansion % (url[len(prefix):],)
            break

    # Assume HTTP for URLs without scheme
    if not '://' in url:
        url = 'http://' + url

    scheme, netloc, path, query, fragment = urlparse.urlsplit(url)

    # Schemes and domain names are case insensitive
    scheme, netloc = scheme.lower(), netloc.lower()

    # Normalize empty paths to "/"
    if path == '':
        path = '/'

    # feed://, itpc:// and itms:// are really http://
    if scheme in ('feed', 'itpc', 'itms'):
        scheme = 'http'

    if scheme not in ('http', 'https', 'ftp', 'file'):
        return None

    # urlunsplit might return "a slighty different, but equivalent URL"
    return urlparse.urlunsplit((scheme, netloc, path, query, fragment))


def username_password_from_url(url):
    r"""
    Returns a tuple (username,password) containing authentication
    data from the specified URL or (None,None) if no authentication
    data can be found in the URL.

    See Section 3.1 of RFC 1738 (http://www.ietf.org/rfc/rfc1738.txt)

    >>> username_password_from_url('https://@host.com/')
    ('', None)
    >>> username_password_from_url('telnet://host.com/')
    (None, None)
    >>> username_password_from_url('ftp://foo:@host.com/')
    ('foo', '')
    >>> username_password_from_url('http://a:b@host.com/')
    ('a', 'b')
    >>> username_password_from_url(1)
    Traceback (most recent call last):
      ...
    ValueError: URL has to be a string or unicode object.
    >>> username_password_from_url(None)
    Traceback (most recent call last):
      ...
    ValueError: URL has to be a string or unicode object.
    >>> username_password_from_url('http://a@b:c@host.com/')
    Traceback (most recent call last):
      ...
    ValueError: "@" must be encoded for username/password (RFC1738).
    >>> username_password_from_url('ftp://a:b:c@host.com/')
    Traceback (most recent call last):
      ...
    ValueError: ":" must be encoded for username/password (RFC1738).
    >>> username_password_from_url('http://i%2Fo:P%40ss%3A@host.com/')
    ('i/o', 'P@ss:')
    >>> username_password_from_url('ftp://%C3%B6sterreich@host.com/')
    ('\xc3\xb6sterreich', None)
    >>> username_password_from_url('http://w%20x:y%20z@example.org/')
    ('w x', 'y z')
    """
    if type(url) not in (str, unicode):
        raise ValueError('URL has to be a string or unicode object.')

    (username, password) = (None, None)

    (scheme, netloc, path, params, query, fragment) = urlparse.urlparse(url)

    if '@' in netloc:
        (authentication, netloc) = netloc.rsplit('@', 1)
        if ':' in authentication:
            (username, password) = authentication.split(':', 1)
            # RFC1738 dictates that we should not allow these unquoted
            # characters in the username and password field (Section 3.1).
            for c in (':', '@', '/'):
                if c in username or c in password:
                    raise ValueError('"%c" must be encoded for username/password (RFC1738).' % c)
            username = urllib.unquote(username)
            password = urllib.unquote(password)
        else:
            username = urllib.unquote(authentication)

    return (username, password)


def directory_is_writable( path):
    """
    Returns True if the specified directory exists and is writable
    by the current user.
    """
    return os.path.isdir( path) and os.access( path, os.W_OK)


def calculate_size( path):
    """
    Tries to calculate the size of a directory, including any 
    subdirectories found. The returned value might not be 
    correct if the user doesn't have appropriate permissions 
    to list all subdirectories of the given path.
    """
    if path is None:
        return 0L

    if os.path.dirname( path) == '/':
        return 0L

    if os.path.isfile( path):
        return os.path.getsize( path)

    if os.path.isdir( path) and not os.path.islink( path):
        sum = os.path.getsize( path)

        try:
            for item in os.listdir(path):
                try:
                    sum += calculate_size(os.path.join(path, item))
                except:
                    log('Cannot get size for %s', path)
        except:
            log('Cannot access: %s', path)

        return sum

    return 0L


def file_modification_datetime(filename):
    """
    Returns the modification date of the specified file
    as a datetime.datetime object or None if the modification
    date cannot be determined.
    """
    if filename is None:
        return None

    if not os.access(filename, os.R_OK):
        return None

    try:
        s = os.stat(filename)
        timestamp = s[stat.ST_MTIME]
        return datetime.datetime.fromtimestamp(timestamp)
    except:
        log('Cannot get modification timestamp for %s', filename)
        return None


def file_modification_timestamp(filename):
    """
    Returns the modification date of the specified file as a number
    or -1 if the modification date cannot be determined.
    """
    if filename is None:
        return -1
    try:
        s = os.stat(filename)
        return s[stat.ST_MTIME]
    except:
        log('Cannot get modification timestamp for %s', filename)
        return -1


def file_age_in_days(filename):
    """
    Returns the age of the specified filename in days or
    zero if the modification date cannot be determined.
    """
    dt = file_modification_datetime(filename)
    if dt is None:
        return 0
    else:
        return (datetime.datetime.now()-dt).days


def file_age_to_string(days):
    """
    Converts a "number of days" value to a string that
    can be used in the UI to display the file age.

    >>> file_age_to_string(0)
    ''
    >>> file_age_to_string(1)
    u'1 day ago'
    >>> file_age_to_string(2)
    u'2 days ago'
    """
    if days < 1:
        return ''
    else:
        return N_('%(count)d day ago', '%(count)d days ago', days) % {'count':days}


def get_free_disk_space_win32(path):
    """
    Win32-specific code to determine the free disk space remaining
    for a given path. Uses code from:

    http://mail.python.org/pipermail/python-list/2003-May/203223.html
    """

    drive, tail = os.path.splitdrive(path)

    try:
        import win32file
        userFree, userTotal, freeOnDisk = win32file.GetDiskFreeSpaceEx(drive)
        return userFree
    except ImportError:
        log('Warning: Running on Win32 but win32api/win32file not installed.')

    # Cannot determine free disk space
    return 0


def get_free_disk_space(path):
    """
    Calculates the free disk space available to the current user
    on the file system that contains the given path.

    If the path (or its parent folder) does not yet exist, this
    function returns zero.
    """

    if not os.path.exists(path):
        return 0

    if gpodder.win32:
        return get_free_disk_space_win32(path)

    s = os.statvfs(path)

    return s.f_bavail * s.f_bsize


def format_date(timestamp):
    """
    Converts a UNIX timestamp to a date representation. This
    function returns "Today", "Yesterday", a weekday name or
    the date in %x format, which (according to the Python docs)
    is the "Locale's appropriate date representation".

    Returns None if there has been an error converting the
    timestamp to a string representation.
    """
    if timestamp is None:
        return None

    seconds_in_a_day = 60*60*24

    today = time.localtime()[:3]
    yesterday = time.localtime(time.time() - seconds_in_a_day)[:3]
    try:
        timestamp_date = time.localtime(timestamp)[:3]
    except ValueError, ve:
        log('Warning: Cannot convert timestamp', traceback=True)
        return None
    
    if timestamp_date == today:
       return _('Today')
    elif timestamp_date == yesterday:
       return _('Yesterday')
   
    try:
        diff = int( (time.time() - timestamp)/seconds_in_a_day )
    except:
        log('Warning: Cannot convert "%s" to date.', timestamp, traceback=True)
        return None

    try:
        timestamp = datetime.datetime.fromtimestamp(timestamp)
    except:
        return None

    if diff < 7:
        # Weekday name
        return str(timestamp.strftime('%A').decode(encoding))
    else:
        # Locale's appropriate date representation
        return str(timestamp.strftime('%x'))


def format_filesize(bytesize, use_si_units=False, digits=2):
    """
    Formats the given size in bytes to be human-readable, 

    Returns a localized "(unknown)" string when the bytesize
    has a negative value.
    """
    si_units = (
            ( 'kB', 10**3 ),
            ( 'MB', 10**6 ),
            ( 'GB', 10**9 ),
    )

    binary_units = (
            ( 'KiB', 2**10 ),
            ( 'MiB', 2**20 ),
            ( 'GiB', 2**30 ),
    )

    try:
        bytesize = float( bytesize)
    except:
        return _('(unknown)')

    if bytesize < 0:
        return _('(unknown)')

    if use_si_units:
        units = si_units
    else:
        units = binary_units

    ( used_unit, used_value ) = ( 'B', bytesize )

    for ( unit, value ) in units:
        if bytesize >= value:
            used_value = bytesize / float(value)
            used_unit = unit

    return ('%.'+str(digits)+'f %s') % (used_value, used_unit)


def delete_file(filename):
    """Delete a file from the filesystem

    Errors (permissions errors or file not found)
    are silently ignored.
    """
    try:
        os.remove(filename)
    except:
        pass


def remove_html_tags(html):
    """
    Remove HTML tags from a string and replace numeric and
    named entities with the corresponding character, so the 
    HTML text can be displayed in a simple text view.
    """
    if html is None:
        return None

    # If we would want more speed, we could make these global
    re_strip_tags = re.compile('<[^>]*>')
    re_unicode_entities = re.compile('&#(\d{2,4});')
    re_html_entities = re.compile('&(.{2,8});')
    re_newline_tags = re.compile('(<br[^>]*>|<[/]?ul[^>]*>|</li>)', re.I)
    re_listing_tags = re.compile('<li[^>]*>', re.I)

    result = html
    
    # Convert common HTML elements to their text equivalent
    result = re_newline_tags.sub('\n', result)
    result = re_listing_tags.sub('\n * ', result)
    result = re.sub('<[Pp]>', '\n\n', result)

    # Remove all HTML/XML tags from the string
    result = re_strip_tags.sub('', result)

    # Convert numeric XML entities to their unicode character
    result = re_unicode_entities.sub(lambda x: unichr(int(x.group(1))), result)

    # Convert named HTML entities to their unicode character
    result = re_html_entities.sub(lambda x: unicode(entitydefs.get(x.group(1),''), 'iso-8859-1'), result)
    
    # Convert more than two newlines to two newlines
    result = re.sub('([\r\n]{2})([\r\n])+', '\\1', result)

    return result.strip()


def wrong_extension(extension):
    """
    Determine if a given extension looks like it's
    wrong (e.g. empty, extremely long or spaces)

    Returns True if the extension most likely is a
    wrong one and should be replaced.

    >>> wrong_extension('.mp3')
    False
    >>> wrong_extension('.divx')
    False
    >>> wrong_extension('mp3')
    True
    >>> wrong_extension('')
    True
    >>> wrong_extension('.12 - Everybody')
    True
    >>> wrong_extension('.mp3 ')
    True
    >>> wrong_extension('.')
    True
    >>> wrong_extension('.42')
    True
    """
    if not extension:
        return True
    elif len(extension) > 5:
        return True
    elif ' ' in extension:
        return True
    elif extension == '.':
        return True
    elif not extension.startswith('.'):
        return True
    else:
        try:
            # ".<number>" is an invalid extension
            float(extension)
            return True
        except:
            pass

    return False


def extension_from_mimetype(mimetype):
    """
    Simply guesses what the file extension should be from the mimetype
    """
    MIMETYPE_EXTENSIONS = {
            # This is required for YouTube downloads on Maemo 5
            'video/x-flv': '.flv',
            'video/mp4': '.mp4',
    }
    if mimetype in MIMETYPE_EXTENSIONS:
        return MIMETYPE_EXTENSIONS[mimetype]
    return mimetypes.guess_extension(mimetype) or ''


def extension_correct_for_mimetype(extension, mimetype):
    """
    Check if the given filename extension (e.g. ".ogg") is a possible
    extension for a given mimetype (e.g. "application/ogg") and return
    a boolean value (True if it's possible, False if not). Also do

    >>> extension_correct_for_mimetype('.ogg', 'application/ogg')
    True
    >>> extension_correct_for_mimetype('.ogv', 'video/ogg')
    True
    >>> extension_correct_for_mimetype('.ogg', 'audio/mpeg')
    False
    >>> extension_correct_for_mimetype('mp3', 'audio/mpeg')
    Traceback (most recent call last):
      ...
    ValueError: "mp3" is not an extension (missing .)
    >>> extension_correct_for_mimetype('.mp3', 'audio mpeg')
    Traceback (most recent call last):
      ...
    ValueError: "audio mpeg" is not a mimetype (missing /)
    """
    if not '/' in mimetype:
        raise ValueError('"%s" is not a mimetype (missing /)' % mimetype)
    if not extension.startswith('.'):
        raise ValueError('"%s" is not an extension (missing .)' % extension)

    # Create a "default" extension from the mimetype, e.g. "application/ogg"
    # becomes ".ogg", "audio/mpeg" becomes ".mpeg", etc...
    default = ['.'+mimetype.split('/')[-1]]

    return extension in default+mimetypes.guess_all_extensions(mimetype)


def filename_from_url(url):
    """
    Extracts the filename and (lowercase) extension (with dot)
    from a URL, e.g. http://server.com/file.MP3?download=yes
    will result in the string ("file", ".mp3") being returned.

    This function will also try to best-guess the "real" 
    extension for a media file (audio, video) by
    trying to match an extension to these types and recurse
    into the query string to find better matches, if the 
    original extension does not resolve to a known type.

    http://my.net/redirect.php?my.net/file.ogg => ("file", ".ogg")
    http://server/get.jsp?file=/episode0815.MOV => ("episode0815", ".mov")
    http://s/redirect.mp4?http://serv2/test.mp4 => ("test", ".mp4")
    """
    (scheme, netloc, path, para, query, fragid) = urlparse.urlparse(url)
    (filename, extension) = os.path.splitext(os.path.basename( urllib.unquote(path)))

    if file_type_by_extension(extension) is not None and not \
        query.startswith(scheme+'://'):
        # We have found a valid extension (audio, video)
        # and the query string doesn't look like a URL
        return ( filename, extension.lower() )

    # If the query string looks like a possible URL, try that first
    if len(query.strip()) > 0 and query.find('/') != -1:
        query_url = '://'.join((scheme, urllib.unquote(query)))
        (query_filename, query_extension) = filename_from_url(query_url)

        if file_type_by_extension(query_extension) is not None:
            return os.path.splitext(os.path.basename(query_url))

    # No exact match found, simply return the original filename & extension
    return ( filename, extension.lower() )


def file_type_by_extension(extension):
    """
    Tries to guess the file type by looking up the filename 
    extension from a table of known file types. Will return 
    "audio", "video" or None.

    >>> file_type_by_extension('.aif')
    'audio'
    >>> file_type_by_extension('.3GP')
    'video'
    >>> file_type_by_extension('.txt') is None
    True
    >>> file_type_by_extension(None) is None
    True
    >>> file_type_by_extension('ogg')
    Traceback (most recent call last):
      ...
    ValueError: Extension does not start with a dot: ogg
    """
    if not extension:
        return None

    if not extension.startswith('.'):
        raise ValueError('Extension does not start with a dot: %s' % extension)

    global _BUILTIN_FILE_TYPES
    if _BUILTIN_FILE_TYPES is None:
        # List all types that are not in the default mimetypes.types_map
        # (even if they might be detected by mimetypes.guess_type)
        # For OGG, see http://wiki.xiph.org/MIME_Types_and_File_Extensions
        audio_types = ('.ogg', '.oga', '.spx', '.flac', '.axa', \
                       '.aac', '.m4a', '.m4b', '.wma')
        video_types = ('.ogv', '.axv', '.mp4', \
                       '.mkv', '.m4v', '.divx', '.flv', '.wmv', '.3gp')
        _BUILTIN_FILE_TYPES = {}
        _BUILTIN_FILE_TYPES.update((ext, 'audio') for ext in audio_types)
        _BUILTIN_FILE_TYPES.update((ext, 'video') for ext in video_types)

    extension = extension.lower()

    if extension in _BUILTIN_FILE_TYPES:
        return _BUILTIN_FILE_TYPES[extension]

    # Need to prepend something to the extension, so guess_type works
    type, encoding = mimetypes.guess_type('file'+extension)

    if type is not None and '/' in type:
        filetype, rest = type.split('/', 1)
        if filetype in ('audio', 'video', 'image'):
            return filetype
    
    return None


def get_first_line( s):
    """
    Returns only the first line of a string, stripped so
    that it doesn't have whitespace before or after.
    """
    return s.strip().split('\n')[0].strip()


def object_string_formatter( s, **kwargs):
    """
    Makes attributes of object passed in as keyword 
    arguments available as {OBJECTNAME.ATTRNAME} in 
    the passed-in string and returns a string with 
    the above arguments replaced with the attribute 
    values of the corresponding object.

    Example:

    e = Episode()
    e.title = 'Hello'
    s = '{episode.title} World'
    
    print object_string_formatter( s, episode = e)
          => 'Hello World'
    """
    result = s
    for ( key, o ) in kwargs.items():
        matches = re.findall( r'\{%s\.([^\}]+)\}' % key, s)
        for attr in matches:
            if hasattr( o, attr):
                try:
                    from_s = '{%s.%s}' % ( key, attr )
                    to_s = getattr( o, attr)
                    result = result.replace( from_s, to_s)
                except:
                    log( 'Could not replace attribute "%s" in string "%s".', attr, s)

    return result


def format_desktop_command(command, filenames):
    """
    Formats a command template from the "Exec=" line of a .desktop
    file to a string that can be invoked in a shell.

    Handled format strings: %U, %u, %F, %f and a fallback that
    appends the filename as first parameter of the command.

    See http://standards.freedesktop.org/desktop-entry-spec/1.0/ar01s06.html

    Returns a list of commands to execute, either one for
    each filename if the application does not support multiple
    file names or one for all filenames (%U, %F or unknown).
    """
    # Replace backslashes with slashes to fix win32 issues
    # (even on win32, "/" works, but "\" does not)
    command = command.replace('\\', '/')

    command = shlex.split(command)

    command_before = command
    command_after = []
    multiple_arguments = True
    for fieldcode in ('%U', '%F', '%u', '%f'):
        if fieldcode in command:
            command_before = command[:command.index(fieldcode)]
            command_after = command[command.index(fieldcode)+1:]
            multiple_arguments = fieldcode in ('%U', '%F')
            break

    if multiple_arguments:
        return [command_before + filenames + command_after]

    commands = []
    for filename in filenames:
        commands.append(command_before+[filename]+command_after)

    return commands

def url_strip_authentication(url):
    """
    Strips authentication data from an URL. Returns the URL with
    the authentication data removed from it.

    >>> url_strip_authentication('https://host.com/')
    'https://host.com/'
    >>> url_strip_authentication('telnet://foo:bar@host.com/')
    'telnet://host.com/'
    >>> url_strip_authentication('ftp://billy@example.org')
    'ftp://example.org'
    >>> url_strip_authentication('ftp://billy:@example.org')
    'ftp://example.org'
    >>> url_strip_authentication('http://aa:bc@localhost/x')
    'http://localhost/x'
    >>> url_strip_authentication('http://i%2Fo:P%40ss%3A@blubb.lan/u.html')
    'http://blubb.lan/u.html'
    >>> url_strip_authentication('http://c:d@x.org/')
    'http://x.org/'
    >>> url_strip_authentication('http://P%40%3A:i%2F@cx.lan')
    'http://cx.lan'
    """
    url_parts = list(urlparse.urlsplit(url))
    # url_parts[1] is the HOST part of the URL

    # Remove existing authentication data
    if '@' in url_parts[1]:
        url_parts[1] = url_parts[1].split('@', 2)[1]

    return urlparse.urlunsplit(url_parts)


def url_add_authentication(url, username, password):
    """
    Adds authentication data (username, password) to a given
    URL in order to construct an authenticated URL.

    >>> url_add_authentication('https://host.com/', '', None)
    'https://host.com/'
    >>> url_add_authentication('http://example.org/', None, None)
    'http://example.org/'
    >>> url_add_authentication('telnet://host.com/', 'foo', 'bar')
    'telnet://foo:bar@host.com/'
    >>> url_add_authentication('ftp://example.org', 'billy', None)
    'ftp://billy@example.org'
    >>> url_add_authentication('ftp://example.org', 'billy', '')
    'ftp://billy:@example.org'
    >>> url_add_authentication('http://localhost/x', 'aa', 'bc')
    'http://aa:bc@localhost/x'
    >>> url_add_authentication('http://blubb.lan/u.html', 'i/o', 'P@ss:')
    'http://i%2Fo:P%40ss%3A@blubb.lan/u.html'
    >>> url_add_authentication('http://a:b@x.org/', 'c', 'd')
    'http://c:d@x.org/'
    >>> url_add_authentication('http://i%2F:P%40%3A@cx.lan', 'P@:', 'i/')
    'http://P%40%3A:i%2F@cx.lan'
    >>> url_add_authentication('http://x.org/', 'a b', 'c d')
    'http://a%20b:c%20d@x.org/'
    """
    if username is None or username == '':
        return url

    username = urllib.quote(username, safe='')

    if password is not None:
        password = urllib.quote(password, safe='')
        auth_string = ':'.join((username, password))
    else:
        auth_string = username

    url = url_strip_authentication(url)

    url_parts = list(urlparse.urlsplit(url))
    # url_parts[1] is the HOST part of the URL
    url_parts[1] = '@'.join((auth_string, url_parts[1]))

    return urlparse.urlunsplit(url_parts)


def urlopen(url):
    """
    An URL opener with the User-agent set to gPodder (with version)
    """
    username, password = username_password_from_url(url)
    if username is not None or password is not None:
        url = url_strip_authentication(url)
        password_mgr = urllib2.HTTPPasswordMgrWithDefaultRealm()
        password_mgr.add_password(None, url, username, password)
        handler = urllib2.HTTPBasicAuthHandler(password_mgr)
        opener = urllib2.build_opener(handler)
    else:
        opener = urllib2.build_opener()

    headers = {'User-agent': gpodder.user_agent}
    request = urllib2.Request(url, headers=headers)
    return opener.open(request)

def get_real_url(url):
    """
    Gets the real URL of a file and resolves all redirects.
    """
    try:
        return urlopen(url).geturl()
    except:
        log('Error getting real url for %s', url, traceback=True)
        return url


def find_command( command):
    """
    Searches the system's PATH for a specific command that is
    executable by the user. Returns the first occurence of an
    executable binary in the PATH, or None if the command is 
    not available.
    """

    if 'PATH' not in os.environ:
        return None

    for path in os.environ['PATH'].split( os.pathsep):
        command_file = os.path.join( path, command)
        if os.path.isfile( command_file) and os.access( command_file, os.X_OK):
            return command_file
        
    return None


def http_get_and_gunzip(uri):
    """
    Does a HTTP GET request and tells the server that we accept
    gzip-encoded data. This is necessary, because the Apple iTunes
    server will always return gzip-encoded data, regardless of what
    we really request.

    Returns the uncompressed document at the given URI.
    """
    request = urllib2.Request(uri)
    request.add_header("Accept-encoding", "gzip")
    usock = urllib2.urlopen(request)
    data = usock.read()
    if usock.headers.get('content-encoding', None) == 'gzip':
        data = gzip.GzipFile(fileobj=StringIO.StringIO(data)).read()
    return data


def idle_add(func, *args):
    """
    This is a wrapper function that does the Right
    Thing depending on if we are running a GTK+ GUI or
    not. If not, we're simply calling the function.

    If we are a GUI app, we use gobject.idle_add() to
    call the function later - this is needed for
    threads to be able to modify GTK+ widget data.
    """
    if gpodder.ui.desktop or gpodder.ui.fremantle:
        import gobject
        def x(f, *a):
            f(*a)
            return False

        gobject.idle_add(func, *args)
    else:
        func(*args)


def bluetooth_available():
    """
    Returns True or False depending on the availability
    of bluetooth functionality on the system.
    """
    if find_command('bluetooth-sendto') or \
            find_command('gnome-obex-send'):
        return True
    else:
        return False

def bluetooth_send_files_maemo(filenames):
    """Maemo implementation of Bluetooth file transfer

    Takes a list of (absolute and local) filenames that are
    submitted to the Maemo Bluetooth UI for file transfer.
    """
    import dbus
    bus = dbus.SystemBus()
    o = bus.get_object('com.nokia.bt_ui', '/com/nokia/bt_ui', False)
    i = dbus.Interface(o, 'com.nokia.bt_ui')
    i.show_send_file_dlg(['file://'+f for f in filenames])
    return True


def bluetooth_send_file(filename):
    """
    Sends a file via bluetooth.

    This function tries to use "bluetooth-sendto", and if
    it is not available, it also tries "gnome-obex-send".
    """
    command_line = None

    if find_command('bluetooth-sendto'):
        command_line = ['bluetooth-sendto']
    elif find_command('gnome-obex-send'):
        command_line = ['gnome-obex-send']

    if command_line is not None:
        command_line.append(filename)
        return (subprocess.Popen(command_line).wait() == 0)
    else:
        log('Cannot send file. Please install "bluetooth-sendto" or "gnome-obex-send".')
        return False


def format_time(value):
    """Format a seconds value to a string

    >>> format_time(0)
    '00:00'
    >>> format_time(20)
    '00:20'
    >>> format_time(3600)
    '01:00:00'
    >>> format_time(10921)
    '03:02:01'
    """
    dt = datetime.datetime.utcfromtimestamp(value)
    if dt.hour == 0:
        return dt.strftime('%M:%S')
    else:
        return dt.strftime('%H:%M:%S')


def parse_time(value):
    """Parse a time string into seconds
    >>> parse_time('00:00')
    0
    >>> parse_time('00:00:00')
    0
    >>> parse_time('00:20')
    20
    >>> parse_time('00:00:20')
    20
    >>> parse_time('01:00:00')
    3600
    >>> parse_time('03:02:01')
    10921
    """
    if not value:
        raise ValueError('Invalid value: %s' % (str(value),))

    for format in ('%H:%M:%S', '%M:%S'):
        try:
            t = time.strptime(value, format)
            return (t.tm_hour * 60 + t.tm_min) * 60 + t.tm_sec
        except ValueError, ve:
            continue

    return int(value)


def format_seconds_to_hour_min_sec(seconds):
    """
    Take the number of seconds and format it into a
    human-readable string (duration).

    >>> format_seconds_to_hour_min_sec(3834)
    u'1 hour, 3 minutes and 54 seconds'
    >>> format_seconds_to_hour_min_sec(3600)
    u'1 hour'
    >>> format_seconds_to_hour_min_sec(62)
    u'1 minute and 2 seconds'
    """

    if seconds < 1:
        return N_('%(count)d second', '%(count)d seconds', seconds) % {'count':seconds}

    result = []

    seconds = int(seconds)

    hours = seconds/3600
    seconds = seconds%3600

    minutes = seconds/60
    seconds = seconds%60

    if hours:
        result.append(N_('%(count)d hour', '%(count)d hours', hours) % {'count':hours})

    if minutes:
        result.append(N_('%(count)d minute', '%(count)d minutes', minutes) % {'count':minutes})

    if seconds:
        result.append(N_('%(count)d second', '%(count)d seconds', seconds) % {'count':seconds})

    if len(result) > 1:
        return (' '+_('and')+' ').join((', '.join(result[:-1]), result[-1]))
    else:
        return result[0]

def http_request(url, method='HEAD'):
    (scheme, netloc, path, parms, qry, fragid) = urlparse.urlparse(url)
    conn = httplib.HTTPConnection(netloc)
    start = len(scheme) + len('://') + len(netloc)
    conn.request(method, url[start:])
    return conn.getresponse()

def get_episode_info_from_url(url):
    """
    Try to get information about a podcast episode by sending
    a HEAD request to the HTTP server and parsing the result.

    The return value is a dict containing all fields that 
    could be parsed from the URL. This currently contains:
    
      "length": The size of the file in bytes
      "pubdate": The unix timestamp for the pubdate

    If there is an error, this function returns {}. This will
    only function with http:// and https:// URLs.
    """
    if not (url.startswith('http://') or url.startswith('https://')):
        return {}

    r = http_request(url)
    result = {}

    log('Trying to get metainfo for %s', url)

    if 'content-length' in r.msg:
        try:
            length = int(r.msg['content-length'])
            result['length'] = length
        except ValueError, e:
            log('Error converting content-length header.')

    if 'last-modified' in r.msg:
        try:
            parsed_date = feedparser._parse_date(r.msg['last-modified'])
            pubdate = time.mktime(parsed_date)
            result['pubdate'] = pubdate
        except:
            log('Error converting last-modified header.')

    return result


def gui_open(filename):
    """
    Open a file or folder with the default application set
    by the Desktop environment. This uses "xdg-open" on all
    systems with a few exceptions:

       on Win32, os.startfile() is used
       on Maemo, osso is used to communicate with Nokia Media Player
    """
    try:
        if gpodder.ui.fremantle:
            try:
                import osso
            except ImportError, ie:
                log('Cannot import osso module on maemo.')
                return False

            log('Using Nokia Media Player to open %s', filename)
            context = osso.Context('gPodder', gpodder.__version__, False)
            filename = filename.encode('utf-8')

            # Fix for Maemo bug 7162 (for local files with "#" in filename)
            if filename.startswith('/'):
                filename = 'file://' + urllib.quote(filename)

            rpc = osso.Rpc(context)
            app = 'mediaplayer'

            _unneeded, extension = os.path.splitext(filename.lower())

            # Fix for Maemo bug 5588 (use PDF viewer and images app)
            if extension == '.pdf':
                app = 'osso_pdfviewer'
            elif extension in ('.jpg', '.jpeg', '.png'):
                app = 'image_viewer'

            svc, path = (x % app for x in ('com.nokia.%s', '/com/nokia/%s'))
            rpc.rpc_run(svc, path, svc, 'mime_open', (filename,))
        elif gpodder.win32:
            os.startfile(filename)
        else:
            subprocess.Popen(['xdg-open', filename])
        return True
    except:
        log('Cannot open file/folder: "%s"', filename, traceback=True)
        return False


def open_website(url):
    """
    Opens the specified URL using the default system web
    browser. This uses Python's "webbrowser" module, so
    make sure your system is set up correctly.
    """
    if gpodder.ui.fremantle:
        import osso
        context = osso.Context('gPodder', gpodder.__version__, False)
        rpc = osso.Rpc(context)
        rpc.rpc_run_with_defaults('osso_browser', \
                                  'open_new_window', \
                                  (url,))
    else:
        threading.Thread(target=webbrowser.open, args=(url,)).start()

def sanitize_encoding(filename):
    r"""
    Generate a sanitized version of a string (i.e.
    remove invalid characters and encode in the
    detected native language encoding).

    >>> sanitize_encoding('\x80')
    ''
    >>> sanitize_encoding(u'unicode')
    'unicode'
    """
    global encoding
    if not isinstance(filename, unicode):
        filename = filename.decode(encoding, 'ignore')
    return filename.encode(encoding, 'ignore')


def sanitize_filename(filename, max_length=0, use_ascii=False):
    """
    Generate a sanitized version of a filename that can
    be written on disk (i.e. remove/replace invalid
    characters and encode in the native language) and
    trim filename if greater than max_length (0 = no limit).

    If use_ascii is True, don't encode in the native language,
    but use only characters from the ASCII character set.
    """
    global encoding
    if use_ascii:
        e = 'ascii'
    else:
        e = encoding

    if not isinstance(filename, unicode):
        filename = filename.decode(encoding, 'ignore')

    if max_length > 0 and len(filename) > max_length:
        log('Limiting file/folder name "%s" to %d characters.', filename, max_length)
        filename = filename[:max_length]

    return re.sub('[/|?*<>:+\[\]\"\\\]', '_', filename.strip().encode(e, 'ignore'))


def find_mount_point(directory):
    """
    Try to find the mount point for a given directory.
    If the directory is itself a mount point, return
    it. If not, remove the last part of the path and
    re-check if it's a mount point. If the directory
    resides on your root filesystem, "/" is returned.

    >>> find_mount_point('/')
    '/'

    >>> find_mount_point(u'/something')
    Traceback (most recent call last):
      ...
    ValueError: Convert unicode objects to str first.

    >>> find_mount_point(None)
    Traceback (most recent call last):
      ...
    ValueError: Directory names should be of type str.

    >>> find_mount_point(42)
    Traceback (most recent call last):
      ...
    ValueError: Directory names should be of type str.

    >>> from minimock import mock, restore
    >>> mocked_mntpoints = ('/', '/home', '/media/usbdisk', '/media/cdrom')
    >>> mock('os.path.ismount', returns_func=lambda x: x in mocked_mntpoints)
    >>>
    >>> # For mocking os.getcwd(), we simply use a lambda to avoid the
    >>> # massive output of "Called os.getcwd()" lines in this doctest
    >>> os.getcwd = lambda: '/home/thp'
    >>>
    >>> find_mount_point('.')
    Called os.path.ismount('/home/thp')
    Called os.path.ismount('/home')
    '/home'
    >>> find_mount_point('relativity')
    Called os.path.ismount('/home/thp/relativity')
    Called os.path.ismount('/home/thp')
    Called os.path.ismount('/home')
    '/home'
    >>> find_mount_point('/media/usbdisk/')
    Called os.path.ismount('/media/usbdisk')
    '/media/usbdisk'
    >>> find_mount_point('/home/thp/Desktop')
    Called os.path.ismount('/home/thp/Desktop')
    Called os.path.ismount('/home/thp')
    Called os.path.ismount('/home')
    '/home'
    >>> find_mount_point('/media/usbdisk/Podcasts/With Spaces')
    Called os.path.ismount('/media/usbdisk/Podcasts/With Spaces')
    Called os.path.ismount('/media/usbdisk/Podcasts')
    Called os.path.ismount('/media/usbdisk')
    '/media/usbdisk'
    >>> find_mount_point('/home/')
    Called os.path.ismount('/home')
    '/home'
    >>> find_mount_point('/media/cdrom/../usbdisk/blubb//')
    Called os.path.ismount('/media/usbdisk/blubb')
    Called os.path.ismount('/media/usbdisk')
    '/media/usbdisk'
    >>> restore()
    """
    if isinstance(directory, unicode):
        # We do not accept unicode strings, because they could fail when
        # trying to be converted to some native encoding, so fail loudly
        # and leave it up to the callee to encode into the proper encoding.
        raise ValueError('Convert unicode objects to str first.')

    if not isinstance(directory, str):
        raise ValueError('Directory names should be of type str.')

    directory = os.path.abspath(directory)

    while directory != '/':
        if os.path.ismount(directory):
            return directory
        else:
            (directory, tail_data) = os.path.split(directory)

    return '/'


# matches http:// and ftp:// and mailto://
protocolPattern = re.compile(r'^\w+://')

def isabs(string):
    """
    @return true if string is an absolute path or protocoladdress
    for addresses beginning in http:// or ftp:// or ldap:// -
    they are considered "absolute" paths.
    Source: http://code.activestate.com/recipes/208993/
    """
    if protocolPattern.match(string): return 1
    return os.path.isabs(string)

def rel2abs(path, base = os.curdir):
    """ converts a relative path to an absolute path.

    @param path the path to convert - if already absolute, is returned
    without conversion.
    @param base - optional. Defaults to the current directory.
    The base is intelligently concatenated to the given relative path.
    @return the relative path of path from base
    Source: http://code.activestate.com/recipes/208993/
    """
    if isabs(path): return path
    retval = os.path.join(base,path)
    return os.path.abspath(retval)

def commonpath(l1, l2, common=[]):
    """
    helper functions for relpath
    Source: http://code.activestate.com/recipes/208993/
    """
    if len(l1) < 1: return (common, l1, l2)
    if len(l2) < 1: return (common, l1, l2)
    if l1[0] != l2[0]: return (common, l1, l2)
    return commonpath(l1[1:], l2[1:], common+[l1[0]])

def relpath(p1, p2):
    """
    Finds relative path from p1 to p2
    Source: http://code.activestate.com/recipes/208993/
    """
    pathsplit = lambda s: s.split(os.path.sep)

    (common,l1,l2) = commonpath(pathsplit(p1), pathsplit(p2))
    p = []
    if len(l1) > 0:
        p = [ ('..'+os.sep) * len(l1) ]
    p = p + l2
    if len(p) is 0:
        return "."

    return os.path.join(*p)


def run_external_command(command_line):
    """
    This is the function that will be called in a separate
    thread that will call an external command (specified by
    command_line). In case of problem (i.e. the command has
    not been found or there has been another error), we will
    call the notification function with two arguments - the
    first being the error message and the second being the
    title to be used for the error message.
    """

    def open_process(command_line):
        log('Running external command: %s', command_line)
        p = subprocess.Popen(command_line, shell=True)
        result = p.wait()
        if result == 127:
            log('Command not found: %s', command_line)
        elif result == 126:
            log('Command permission denied: %s', command_line)
        elif result > 0:
            log('Command returned an error (%d): %s', result, command_line)
        else:
            log('Command finished successfully: %s', command_line)

    threading.Thread(target=open_process, args=(command_line,)).start()

def get_hostname():
    """Return the hostname of this computer

    This can be implemented in a different way on each
    platform and should yield a unique-per-user device ID.
    """
    nodename = platform.node()

    if nodename:
        return nodename

    # Fallback - but can this give us "localhost"?
    return socket.gethostname()

def detect_device_type():
    """Device type detection for gpodder.net

    This function tries to detect on which
    kind of device gPodder is running on.

    Possible return values:
    desktop, laptop, mobile, server, other
    """
    if gpodder.ui.fremantle:
        return 'mobile'
    elif glob.glob('/proc/acpi/battery/*'):
        # Linux: If we have a battery, assume Laptop
        return 'laptop'

    return 'desktop'


def write_m3u_playlist(m3u_filename, episodes, extm3u=True):
    """Create an M3U playlist from a episode list

    If the parameter "extm3u" is False, the list of
    episodes should be a list of filenames, and no
    extended information will be written into the
    M3U files (#EXTM3U / #EXTINF).

    If the parameter "extm3u" is True (default), then the
    list of episodes should be PodcastEpisode objects,
    as the extended metadata will be taken from them.
    """
    f = open(m3u_filename, 'w')

    if extm3u:
        # Mandatory header for extended playlists
        f.write('#EXTM3U\n')

    for episode in episodes:
        if not extm3u:
            # Episode objects are strings that contain file names
            f.write(episode+'\n')
            continue

        if episode.was_downloaded(and_exists=True):
            filename = episode.local_filename(create=False)
            assert filename is not None

            if os.path.dirname(filename).startswith(os.path.dirname(m3u_filename)):
                filename = filename[len(os.path.dirname(m3u_filename)+os.sep):]
            f.write('#EXTINF:0,'+episode.playlist_title()+'\n')
            f.write(filename+'\n')

    f.close()