beets/beets/ui/commands.py

# This file is part of beets.
# Copyright 2013, Adrian Sampson.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

"""This module provides the default commands for beets' command-line
interface.
"""
from __future__ import print_function

import logging
import os
import time
import itertools
import re
import codecs

import beets
from beets import ui
from beets.ui import print_, input_, decargs
from beets import autotag
from beets.autotag import recommendation
from beets import plugins
from beets import importer
from beets.util import syspath, normpath, ancestry, displayable_path
from beets.util.functemplate import Template
from beets import library
from beets import config

# Global logger.
log = logging.getLogger('beets')

# The list of default subcommands. This is populated with Subcommand
# objects that can be fed to a SubcommandsOptionParser.
default_commands = []


# Utilities.

def _do_query(lib, query, album, also_items=True):
    """For commands that operate on matched items, performs a query
    and returns a list of matching items and a list of matching
    albums. (The latter is only nonempty when album is True.) Raises
    a UserError if no items match. also_items controls whether, when
    fetching albums, the associated items should be fetched also.
    """
    if album:
        albums = list(lib.albums(query))
        items = []
        if also_items:
            for al in albums:
                items += al.items()

    else:
        albums = []
        items = list(lib.items(query))

    if album and not albums:
        raise ui.UserError('No matching albums found.')
    elif not album and not items:
        raise ui.UserError('No matching items found.')

    return items, albums

FLOAT_EPSILON = 0.01
def _showdiff(field, oldval, newval):
    """Prints out a human-readable field difference line."""
    # Considering floats incomparable for perfect equality, introduce
    # an epsilon tolerance.
    if isinstance(oldval, float) and isinstance(newval, float) and \
            abs(oldval - newval) < FLOAT_EPSILON:
        return

    if newval != oldval:
        oldval, newval = ui.colordiff(oldval, newval)
        print_(u'  %s: %s -> %s' % (field, oldval, newval))


# fields: Shows a list of available fields for queries and format strings.

fields_cmd = ui.Subcommand('fields',
    help='show fields available for queries and format strings')
def fields_func(lib, opts, args):
    print("Available item fields:")
    print("  " + "\n  ".join([key for key in library.ITEM_KEYS]))
    print("\nAvailable album fields:")
    print("  " + "\n  ".join([key for key in library.ALBUM_KEYS]))

fields_cmd.func = fields_func
default_commands.append(fields_cmd)


# import: Autotagger and importer.

VARIOUS_ARTISTS = u'Various Artists'

PARTIAL_MATCH_MESSAGE = u'(partial match!)'

# Importer utilities and support.

def dist_string(dist):
    """Formats a distance (a float) as a colorized similarity percentage
    string.
    """
    out = '%.1f%%' % ((1 - dist) * 100)
    if dist <= config['match']['strong_rec_thresh'].as_number():
        out = ui.colorize('green', out)
    elif dist <= config['match']['medium_rec_thresh'].as_number():
        out = ui.colorize('yellow', out)
    else:
        out = ui.colorize('red', out)
    return out

def show_change(cur_artist, cur_album, match):
    """Print out a representation of the changes that will be made if an
    album's tags are changed according to `match`, which must be an AlbumMatch
    object.
    """
    def show_album(artist, album, partial=False):
        if artist:
            album_description = u'    %s - %s' % (artist, album)
        elif album:
            album_description = u'    %s' % album
        else:
            album_description = u'    (unknown album)'

        out = album_description

        # Add a suffix if this is a partial match.
        if partial:
            out += u' ' + ui.colorize('yellow', PARTIAL_MATCH_MESSAGE)

        print_(out)

    def format_index(track_info):
        """Return a string representing the track index of the given
        TrackInfo object.
        """
        if config['per_disc_numbering'].get(bool):
            if match.info.mediums > 1:
                return u'{0}-{1}'.format(track_info.medium,
                                         track_info.medium_index)
            else:
                return unicode(track_info.medium_index)
        else:
            return unicode(track_info.index)

    # Identify the album in question.
    if cur_artist != match.info.artist or \
            (cur_album != match.info.album and
             match.info.album != VARIOUS_ARTISTS):
        artist_l, artist_r = cur_artist or '', match.info.artist
        album_l,  album_r  = cur_album  or '', match.info.album
        if artist_r == VARIOUS_ARTISTS:
            # Hide artists for VA releases.
            artist_l, artist_r = u'', u''

        artist_l, artist_r = ui.colordiff(artist_l, artist_r)
        album_l, album_r   = ui.colordiff(album_l, album_r)

        print_("Correcting tags from:")
        show_album(artist_l, album_l)
        print_("To:")
        show_album(artist_r, album_r)
    else:
        message = u"Tagging: %s - %s" % (match.info.artist, match.info.album)
        if match.extra_items or match.extra_tracks:
            message += u' ' + ui.colorize('yellow', PARTIAL_MATCH_MESSAGE)
        print_(message)

    # Distance/similarity.
    print_('(Similarity: %s)' % dist_string(match.distance))

    # Tracks.
    pairs = match.mapping.items()
    pairs.sort(key=lambda (_, track_info): track_info.index)

    # Build up LHS and RHS for track difference display. The `lines`
    # list contains ``(current title, new title, width)`` tuples where
    # `width` is the length (in characters) of the uncolorized LHS.
    lines = []
    for item, track_info in pairs:
        # Titles.
        new_title = track_info.title
        if not item.title.strip():
            # If there's no title, we use the filename.
            cur_title = displayable_path(os.path.basename(item.path))
            lhs, rhs = cur_title, new_title
        else:
            cur_title = item.title.strip()
            lhs, rhs = ui.colordiff(cur_title, new_title)
        lhs_width = len(cur_title)

        # Track number change.
        if item.track not in (track_info.index, track_info.medium_index):
            cur_track, new_track = unicode(item.track), format_index(track_info)
            lhs_track, rhs_track = ui.color_diff_suffix(cur_track, new_track)
            templ = ui.colorize('red', u' (#') + u'{0}' + \
                    ui.colorize('red', u')')
            lhs += templ.format(lhs_track)
            rhs += templ.format(rhs_track)
            lhs_width += len(cur_track) + 4

        # Length change.
        if item.length and track_info.length and \
                abs(item.length - track_info.length) > \
                config['ui']['length_diff_thresh'].as_number():
            cur_length = ui.human_seconds_short(item.length)
            new_length = ui.human_seconds_short(track_info.length)
            lhs_length, rhs_length = ui.color_diff_suffix(cur_length,
                                                          new_length)
            templ = ui.colorize('red', u' (') + u'{0}' + \
                    ui.colorize('red', u')')
            lhs += templ.format(lhs_length)
            rhs += templ.format(rhs_length)
            lhs_width += len(cur_length) + 3

        if lhs != rhs:
            lines.append((lhs, rhs, lhs_width))
        elif config['import']['detail']:
            lines.append((lhs, '', lhs_width))

    # Print each track in two columns, or across two lines.
    col_width = (ui.term_width() - len(''.join([' * ', ' -> ']))) // 2
    if lines:
        max_width = max(w for _, _, w in lines)
        for lhs, rhs, lhs_width in lines:
            if not rhs:
                print_(u' * {0}'.format(lhs))
            elif max_width > col_width:
                print_(u' * %s ->\n   %s' % (lhs, rhs))
            else:
                pad = max_width - lhs_width
                print_(u' * %s%s -> %s' % (lhs, ' ' * pad, rhs))

    # Missing and unmatched tracks.
    for track_info in match.extra_tracks:
        line = u' * Missing track: {0} ({1})'.format(track_info.title,
                                                     format_index(track_info))
        line = ui.colorize('yellow', line)
        print_(line)
    for item in match.extra_items:
        line = u' * Unmatched track: {0} ({1})'.format(item.title, item.track)
        line = ui.colorize('yellow', line)
        print_(line)

def show_item_change(item, match):
    """Print out the change that would occur by tagging `item` with the
    metadata from `match`, a TrackMatch object.
    """
    cur_artist, new_artist = item.artist, match.info.artist
    cur_title, new_title = item.title, match.info.title

    if cur_artist != new_artist or cur_title != new_title:
        cur_artist, new_artist = ui.colordiff(cur_artist, new_artist)
        cur_title, new_title = ui.colordiff(cur_title, new_title)

        print_("Correcting track tags from:")
        print_("    %s - %s" % (cur_artist, cur_title))
        print_("To:")
        print_("    %s - %s" % (new_artist, new_title))

    else:
        print_("Tagging track: %s - %s" % (cur_artist, cur_title))

    print_('(Similarity: %s)' % dist_string(match.distance))

def _summary_judment(rec):
    """Determines whether a decision should be made without even asking
    the user. This occurs in quiet mode and when an action is chosen for
    NONE recommendations. Return an action or None if the user should be
    queried. May also print to the console if a summary judgment is
    made.
    """
    if config['import']['quiet']:
        if rec == recommendation.strong:
            return importer.action.APPLY
        else:
            action = config['import']['quiet_fallback'].as_choice({
                'skip': importer.action.SKIP,
                'asis': importer.action.ASIS,
            })

    elif rec == recommendation.none:
        action = config['import']['none_rec_action'].as_choice({
            'skip': importer.action.SKIP,
            'asis': importer.action.ASIS,
            'ask': None,
        })

    else:
        return None

    if action == importer.action.SKIP:
        print_('Skipping.')
    elif action == importer.action.ASIS:
        print_('Importing as-is.')
    return action

def choose_candidate(candidates, singleton, rec, cur_artist=None,
                     cur_album=None, item=None, itemcount=None):
    """Given a sorted list of candidates, ask the user for a selection
    of which candidate to use. Applies to both full albums and
    singletons  (tracks). Candidates are either AlbumMatch or TrackMatch
    objects depending on `singleton`. for albums, `cur_artist`,
    `cur_album`, and `itemcount` must be provided. For singletons,
    `item` must be provided.

    Returns the result of the choice, which may SKIP, ASIS, TRACKS, or
    MANUAL or a candidate (an AlbumMatch/TrackMatch object).
    """
    # Sanity check.
    if singleton:
        assert item is not None
    else:
        assert cur_artist is not None
        assert cur_album is not None

    # Zero candidates.
    if not candidates:
        if singleton:
            print_("No matching recordings found.")
            opts = ('Use as-is', 'Skip', 'Enter search', 'enter Id',
                    'aBort')
        else:
            print_("No matching release found for {0} tracks."
                   .format(itemcount))
            print_('For help, see: '
                   'https://github.com/sampsyo/beets/wiki/FAQ#wiki-nomatch')
            opts = ('Use as-is', 'as Tracks', 'Skip', 'Enter search',
                    'enter Id', 'aBort')
        sel = ui.input_options(opts)
        if sel == 'u':
            return importer.action.ASIS
        elif sel == 't':
            assert not singleton
            return importer.action.TRACKS
        elif sel == 'e':
            return importer.action.MANUAL
        elif sel == 's':
            return importer.action.SKIP
        elif sel == 'b':
            raise importer.ImportAbort()
        elif sel == 'i':
            return importer.action.MANUAL_ID
        else:
            assert False

    # Is the change good enough?
    bypass_candidates = False
    if rec != recommendation.none:
        match = candidates[0]
        bypass_candidates = True

    while True:
        # Display and choose from candidates.
        require = rec <= recommendation.low

        if not bypass_candidates:
            # Display list of candidates.
            if singleton:
                print_('Finding tags for track "%s - %s".' %
                       (item.artist, item.title))
                print_('Candidates:')
                for i, match in enumerate(candidates):
                    print_('%i. %s - %s (%s)' %
                           (i + 1, match.info.artist, match.info.title,
                            dist_string(match.distance)))
            else:
                print_('Finding tags for album "%s - %s".' %
                       (cur_artist, cur_album))
                print_('Candidates:')
                for i, match in enumerate(candidates):
                    line = '%i. %s - %s' % (i + 1, match.info.artist,
                                            match.info.album)

                    # Label, year and media disambiguation, if available.
                    disambig = []
                    if match.info.label:
                        disambig.append(match.info.label)
                    if match.info.year:
                        disambig.append(unicode(match.info.year))
                    if match.info.media:
                        if match.info.mediums > 1:
                            disambig.append(u'{0}x{1}'.format(
                              match.info.mediums, match.info.media))
                        else:
                            disambig.append(match.info.media)
                    if match.info.albumdisambig:
                        disambig.append(match.info.albumdisambig)
                    if disambig:
                        line += u' [{0}]'.format(u', '.join(disambig))

                    line += ' (%s)' % dist_string(match.distance)

                    # Point out the partial matches.
                    if match.extra_items or match.extra_tracks:
                        warning = PARTIAL_MATCH_MESSAGE
                        warning = ui.colorize('yellow', warning)
                        line += u' %s' % warning

                    print_(line)

            # Ask the user for a choice.
            if singleton:
                opts = ('Skip', 'Use as-is', 'Enter search', 'enter Id',
                        'aBort')
            else:
                opts = ('Skip', 'Use as-is', 'as Tracks', 'Enter search',
                        'enter Id', 'aBort')
            sel = ui.input_options(opts, numrange=(1, len(candidates)))
            if sel == 's':
                return importer.action.SKIP
            elif sel == 'u':
                return importer.action.ASIS
            elif sel == 'e':
                return importer.action.MANUAL
            elif sel == 't':
                assert not singleton
                return importer.action.TRACKS
            elif sel == 'b':
                raise importer.ImportAbort()
            elif sel == 'i':
                return importer.action.MANUAL_ID
            else:  # Numerical selection.
                match = candidates[sel - 1]
                if sel != 1:
                    # When choosing anything but the first match,
                    # disable the default action.
                    require = True
        bypass_candidates = False

        # Show what we're about to do.
        if singleton:
            show_item_change(item, match)
        else:
            show_change(cur_artist, cur_album, match)

        # Exact match => tag automatically if we're not in timid mode.
        if rec == recommendation.strong and not config['import']['timid']:
            return match

        # Ask for confirmation.
        if singleton:
            opts = ('Apply', 'More candidates', 'Skip', 'Use as-is',
                    'Enter search', 'enter Id', 'aBort')
        else:
            opts = ('Apply', 'More candidates', 'Skip', 'Use as-is',
                    'as Tracks', 'Enter search', 'enter Id', 'aBort')
        default = config['import']['default_action'].as_choice({
            'apply': 'a',
            'skip': 's',
            'asis': 'u',
            'none': None,
        })
        if default is None:
            require = True
        sel = ui.input_options(opts, require=require, default=default)
        if sel == 'a':
            return match
        elif sel == 'm':
            pass
        elif sel == 's':
            return importer.action.SKIP
        elif sel == 'u':
            return importer.action.ASIS
        elif sel == 't':
            assert not singleton
            return importer.action.TRACKS
        elif sel == 'e':
            return importer.action.MANUAL
        elif sel == 'b':
            raise importer.ImportAbort()
        elif sel == 'i':
            return importer.action.MANUAL_ID

def manual_search(singleton):
    """Input either an artist and album (for full albums) or artist and
    track name (for singletons) for manual search.
    """
    artist = input_('Artist:')
    name = input_('Track:' if singleton else 'Album:')
    return artist.strip(), name.strip()

def manual_id(singleton):
    """Input a MusicBrainz ID, either for an album ("release") or a
    track ("recording"). If no valid ID is entered, returns None.
    """
    prompt = 'Enter MusicBrainz %s ID:' % \
             ('recording' if singleton else 'release')
    entry = input_(prompt).strip()

    # Find the first thing that looks like a UUID/MBID.
    match = re.search('[a-f0-9]{8}(-[a-f0-9]{4}){3}-[a-f0-9]{12}', entry)
    if match:
        return match.group()
    else:
        log.error('Invalid MBID.')
        return None

class TerminalImportSession(importer.ImportSession):
    """An import session that runs in a terminal.
    """
    def choose_match(self, task):
        """Given an initial autotagging of items, go through an interactive
        dance with the user to ask for a choice of metadata. Returns an
        AlbumMatch object, ASIS, or SKIP.
        """
        # Show what we're tagging.
        print_()
        print_(displayable_path(task.paths, u'\n'))

        # Take immediate action if appropriate.
        action = _summary_judment(task.rec)
        if action == importer.action.APPLY:
            match = task.candidates[0]
            show_change(task.cur_artist, task.cur_album, match)
            return match
        elif action is not None:
            return action

        # Loop until we have a choice.
        candidates, rec = task.candidates, task.rec
        while True:
            # Ask for a choice from the user.
            choice = choose_candidate(candidates, False, rec, task.cur_artist,
                                    task.cur_album, itemcount=len(task.items))

            # Choose which tags to use.
            if choice in (importer.action.SKIP, importer.action.ASIS,
                        importer.action.TRACKS):
                # Pass selection to main control flow.
                return choice
            elif choice is importer.action.MANUAL:
                # Try again with manual search terms.
                search_artist, search_album = manual_search(False)
                _, _, candidates, rec = autotag.tag_album(
                    task.items, search_artist, search_album
                )
            elif choice is importer.action.MANUAL_ID:
                # Try a manually-entered ID.
                search_id = manual_id(False)
                if search_id:
                    _, _, candidates, rec = autotag.tag_album(
                        task.items, search_id=search_id
                    )
            else:
                # We have a candidate! Finish tagging. Here, choice is an
                # AlbumMatch object.
                assert isinstance(choice, autotag.AlbumMatch)
                return choice

    def choose_item(self, task):
        """Ask the user for a choice about tagging a single item. Returns
        either an action constant or a TrackMatch object.
        """
        print_()
        print_(task.item.path)
        candidates, rec = task.candidates, task.rec

        # Take immediate action if appropriate.
        action = _summary_judment(task.rec)
        if action == importer.action.APPLY:
            match = candidates[0]
            show_item_change(task.item, match)
            return match
        elif action is not None:
            return action

        while True:
            # Ask for a choice.
            choice = choose_candidate(candidates, True, rec, item=task.item)

            if choice in (importer.action.SKIP, importer.action.ASIS):
                return choice
            elif choice == importer.action.TRACKS:
                assert False # TRACKS is only legal for albums.
            elif choice == importer.action.MANUAL:
                # Continue in the loop with a new set of candidates.
                search_artist, search_title = manual_search(True)
                candidates, rec = autotag.tag_item(task.item, search_artist,
                                                search_title)
            elif choice == importer.action.MANUAL_ID:
                # Ask for a track ID.
                search_id = manual_id(True)
                if search_id:
                    candidates, rec = autotag.tag_item(task.item,
                                                    search_id=search_id)
            else:
                # Chose a candidate.
                assert isinstance(choice, autotag.TrackMatch)
                return choice

    def resolve_duplicate(self, task):
        """Decide what to do when a new album or item seems similar to one
        that's already in the library.
        """
        log.warn("This %s is already in the library!" %
                ("album" if task.is_album else "item"))

        if config['import']['quiet']:
            # In quiet mode, don't prompt -- just skip.
            log.info('Skipping.')
            sel = 's'
        else:
            sel = ui.input_options(
                ('Skip new', 'Keep both', 'Remove old')
            )

        if sel == 's':
            # Skip new.
            task.set_choice(importer.action.SKIP)
        elif sel == 'k':
            # Keep both. Do nothing; leave the choice intact.
            pass
        elif sel == 'r':
            # Remove old.
            task.remove_duplicates = True
        else:
            assert False

    def should_resume(self, path):
        return ui.input_yn(u"Import of the directory:\n{0}\n"
                           "was interrupted. Resume (Y/n)?"
                           .format(displayable_path(path)))

# The import command.

def import_files(lib, paths, query):
    """Import the files in the given list of paths or matching the
    query.
    """
    # Check the user-specified directories.
    for path in paths:
        fullpath = syspath(normpath(path))
        if not config['import']['singletons'] and not os.path.isdir(fullpath):
            raise ui.UserError('not a directory: ' + path)
        elif config['import']['singletons'] and not os.path.exists(fullpath):
            raise ui.UserError('no such file: ' + path)

    # Check parameter consistency.
    if config['import']['quiet'] and config['import']['timid']:
        raise ui.UserError("can't be both quiet and timid")

    # Open the log.
    if config['import']['log'].get() is not None:
        logpath = config['import']['log'].as_filename()
        try:
            logfile = codecs.open(syspath(logpath), 'a', 'utf8')
        except IOError:
            raise ui.UserError(u"could not open log file for writing: %s" %
                               displayable_path(logpath))
        print(u'import started', time.asctime(), file=logfile)
    else:
        logfile = None

    # Never ask for input in quiet mode.
    if config['import']['resume'].get() == 'ask' and \
            config['import']['quiet']:
        config['import']['resume'] = False

    session = TerminalImportSession(lib, logfile, paths, query)
    try:
        session.run()
    finally:
        # If we were logging, close the file.
        if logfile:
            print(u'', file=logfile)
            logfile.close()

    # Emit event.
    plugins.send('import', lib=lib, paths=paths)

import_cmd = ui.Subcommand('import', help='import new music',
    aliases=('imp', 'im'))
import_cmd.parser.add_option('-c', '--copy', action='store_true',
    default=None, help="copy tracks into library directory (default)")
import_cmd.parser.add_option('-C', '--nocopy', action='store_false',
    dest='copy', help="don't copy tracks (opposite of -c)")
import_cmd.parser.add_option('-w', '--write', action='store_true',
    default=None, help="write new metadata to files' tags (default)")
import_cmd.parser.add_option('-W', '--nowrite', action='store_false',
    dest='write', help="don't write metadata (opposite of -w)")
import_cmd.parser.add_option('-a', '--autotag', action='store_true',
    dest='autotag', help="infer tags for imported files (default)")
import_cmd.parser.add_option('-A', '--noautotag', action='store_false',
    dest='autotag',
    help="don't infer tags for imported files (opposite of -a)")
import_cmd.parser.add_option('-p', '--resume', action='store_true',
    default=None, help="resume importing if interrupted")
import_cmd.parser.add_option('-P', '--noresume', action='store_false',
    dest='resume', help="do not try to resume importing")
import_cmd.parser.add_option('-q', '--quiet', action='store_true',
    dest='quiet', help="never prompt for input: skip albums instead")
import_cmd.parser.add_option('-l', '--log', dest='log',
    help='file to log untaggable albums for later review')
import_cmd.parser.add_option('-s', '--singletons', action='store_true',
    help='import individual tracks instead of full albums')
import_cmd.parser.add_option('-t', '--timid', dest='timid',
    action='store_true', help='always confirm all actions')
import_cmd.parser.add_option('-L', '--library', dest='library',
    action='store_true', help='retag items matching a query')
import_cmd.parser.add_option('-i', '--incremental', dest='incremental',
    action='store_true', help='skip already-imported directories')
import_cmd.parser.add_option('-I', '--noincremental', dest='incremental',
    action='store_false', help='do not skip already-imported directories')
import_cmd.parser.add_option('--flat', dest='flat',
    action='store_true', help='import an entire tree as a single album')
def import_func(lib, opts, args):
    config['import'].set_args(opts)

    # Special case: --copy flag suppresses import_move (which would
    # otherwise take precedence).
    if opts.copy:
        config['import']['move'] = False

    if opts.library:
        query = decargs(args)
        paths = []
    else:
        query = None
        paths = args
        if not paths:
            raise ui.UserError('no path specified')

    import_files(lib, paths, query)
import_cmd.func = import_func
default_commands.append(import_cmd)


# list: Query and show library contents.

def list_items(lib, query, album, fmt):
    """Print out items in lib matching query. If album, then search for
    albums instead of single items.
    """
    tmpl = Template(ui._pick_format(album, fmt))
    if album:
        for album in lib.albums(query):
            ui.print_obj(album, lib, tmpl)
    else:
        for item in lib.items(query):
            ui.print_obj(item, lib, tmpl)

list_cmd = ui.Subcommand('list', help='query the library', aliases=('ls',))
list_cmd.parser.add_option('-a', '--album', action='store_true',
    help='show matching albums instead of tracks')
list_cmd.parser.add_option('-p', '--path', action='store_true',
    help='print paths for matched items or albums')
list_cmd.parser.add_option('-f', '--format', action='store',
    help='print with custom format', default=None)
def list_func(lib, opts, args):
    if opts.path:
        fmt = '$path'
    else:
        fmt = opts.format
    list_items(lib, decargs(args), opts.album, fmt)
list_cmd.func = list_func
default_commands.append(list_cmd)


# update: Update library contents according to on-disk tags.

def update_items(lib, query, album, move, pretend):
    """For all the items matched by the query, update the library to
    reflect the item's embedded tags.
    """
    with lib.transaction():
        items, _ = _do_query(lib, query, album)

        # Walk through the items and pick up their changes.
        affected_albums = set()
        for item in items:
            # Item deleted?
            if not os.path.exists(syspath(item.path)):
                ui.print_obj(item, lib)
                if not pretend:
                    lib.remove(item, True)
                affected_albums.add(item.album_id)
                continue

            # Did the item change since last checked?
            if item.current_mtime() <= item.mtime:
                log.debug(u'skipping %s because mtime is up to date (%i)' %
                        (displayable_path(item.path), item.mtime))
                continue

            # Read new data.
            old_data = dict(item.record)
            item.read()

            # Special-case album artist when it matches track artist. (Hacky
            # but necessary for preserving album-level metadata for non-
            # autotagged imports.)
            if not item.albumartist and \
                    old_data['albumartist'] == old_data['artist'] == \
                        item.artist:
                item.albumartist = old_data['albumartist']
                item.dirty['albumartist'] = False

            # Get and save metadata changes.
            changes = {}
            for key in library.ITEM_KEYS_META:
                if item.dirty[key]:
                    changes[key] = old_data[key], getattr(item, key)
            if changes:
                # Something changed.
                ui.print_obj(item, lib)
                for key, (oldval, newval) in changes.iteritems():
                    _showdiff(key, oldval, newval)

                # If we're just pretending, then don't move or save.
                if pretend:
                    continue

                # Move the item if it's in the library.
                if move and lib.directory in ancestry(item.path):
                    lib.move(item)

                lib.store(item)
                affected_albums.add(item.album_id)
            elif not pretend:
                # The file's mtime was different, but there were no changes
                # to the metadata. Store the new mtime, which is set in the
                # call to read(), so we don't check this again in the
                # future.
                lib.store(item)

        # Skip album changes while pretending.
        if pretend:
            return

        # Modify affected albums to reflect changes in their items.
        for album_id in affected_albums:
            if album_id is None:  # Singletons.
                continue
            album = lib.get_album(album_id)
            if not album: # Empty albums have already been removed.
                log.debug('emptied album %i' % album_id)
                continue
            al_items = list(album.items())

            # Update album structure to reflect an item in it.
            for key in library.ALBUM_KEYS_ITEM:
                setattr(album, key, getattr(al_items[0], key))

            # Move album art (and any inconsistent items).
            if move and lib.directory in ancestry(al_items[0].path):
                log.debug('moving album %i' % album_id)
                album.move()

update_cmd = ui.Subcommand('update',
    help='update the library', aliases=('upd','up',))
update_cmd.parser.add_option('-a', '--album', action='store_true',
    help='match albums instead of tracks')
update_cmd.parser.add_option('-M', '--nomove', action='store_false',
    default=True, dest='move', help="don't move files in library")
update_cmd.parser.add_option('-p', '--pretend', action='store_true',
    help="show all changes but do nothing")
update_cmd.parser.add_option('-f', '--format', action='store',
    help='print with custom format', default=None)
def update_func(lib, opts, args):
    update_items(lib, decargs(args), opts.album, opts.move, opts.pretend)
update_cmd.func = update_func
default_commands.append(update_cmd)


# remove: Remove items from library, delete files.

def remove_items(lib, query, album, delete):
    """Remove items matching query from lib. If album, then match and
    remove whole albums. If delete, also remove files from disk.
    """
    # Get the matching items.
    items, albums = _do_query(lib, query, album)

    # Show all the items.
    for item in items:
        ui.print_obj(item, lib)

    # Confirm with user.
    print_()
    if delete:
        prompt = 'Really DELETE %i files (y/n)?' % len(items)
    else:
        prompt = 'Really remove %i items from the library (y/n)?' % \
                 len(items)
    if not ui.input_yn(prompt, True):
        return

    # Remove (and possibly delete) items.
    with lib.transaction():
        if album:
            for al in albums:
                al.remove(delete)
        else:
            for item in items:
                lib.remove(item, delete)

remove_cmd = ui.Subcommand('remove',
    help='remove matching items from the library', aliases=('rm',))
remove_cmd.parser.add_option("-d", "--delete", action="store_true",
    help="also remove files from disk")
remove_cmd.parser.add_option('-a', '--album', action='store_true',
    help='match albums instead of tracks')
def remove_func(lib, opts, args):
    remove_items(lib, decargs(args), opts.album, opts.delete)
remove_cmd.func = remove_func
default_commands.append(remove_cmd)


# stats: Show library/query statistics.

def show_stats(lib, query, exact):
    """Shows some statistics about the matched items."""
    items = lib.items(query)

    total_size = 0
    total_time = 0.0
    total_items = 0
    artists = set()
    albums = set()

    for item in items:
        if exact:
            total_size += os.path.getsize(item.path)
        else:
            total_size += int(item.length * item.bitrate / 8)
        total_time += item.length
        total_items += 1
        artists.add(item.artist)
        albums.add(item.album)

    size_str = '' + ui.human_bytes(total_size)
    if exact:
        size_str += ' ({0} bytes)'.format(total_size)

    print_("""Tracks: {0}
Total time: {1} ({2:.2f} seconds)
Total size: {3}
Artists: {4}
Albums: {5}""".format(total_items, ui.human_seconds(total_time), total_time,
                      size_str, len(artists), len(albums)))

stats_cmd = ui.Subcommand('stats',
    help='show statistics about the library or a query')
stats_cmd.parser.add_option('-e', '--exact', action='store_true',
    help='get exact file sizes')
def stats_func(lib, opts, args):
    show_stats(lib, decargs(args), opts.exact)
stats_cmd.func = stats_func
default_commands.append(stats_cmd)


# version: Show current beets version.

def show_version(lib, opts, args):
    print_('beets version %s' % beets.__version__)
    # Show plugins.
    names = [p.name for p in plugins.find_plugins()]
    if names:
        print_('plugins:', ', '.join(names))
    else:
        print_('no plugins loaded')
version_cmd = ui.Subcommand('version',
    help='output version information')
version_cmd.func = show_version
default_commands.append(version_cmd)


# modify: Declaratively change metadata.

def modify_items(lib, mods, query, write, move, album, confirm):
    """Modifies matching items according to key=value assignments."""
    # Parse key=value specifications into a dictionary.
    allowed_keys = library.ALBUM_KEYS if album else library.ITEM_KEYS_WRITABLE
    fsets = {}
    for mod in mods:
        key, value = mod.split('=', 1)
        if key not in allowed_keys:
            raise ui.UserError('"%s" is not a valid field' % key)
        fsets[key] = value

    # Get the items to modify.
    items, albums = _do_query(lib, query, album, False)
    objs = albums if album else items

    # Preview change.
    print_('Modifying %i %ss.' % (len(objs), 'album' if album else 'item'))
    for obj in objs:
        # Identify the changed object.
        ui.print_obj(obj, lib)

        # Show each change.
        for field, value in fsets.iteritems():
            curval = getattr(obj, field)
            _showdiff(field, curval, value)

    # Confirm.
    if confirm:
        extra = ' and write tags' if write else ''
        if not ui.input_yn('Really modify%s (Y/n)?' % extra):
            return

    # Apply changes to database.
    with lib.transaction():
        for obj in objs:
            for field, value in fsets.iteritems():
                setattr(obj, field, value)

            if move:
                cur_path = obj.item_dir() if album else obj.path
                if lib.directory in ancestry(cur_path): # In library?
                    log.debug('moving object %s' % cur_path)
                    if album:
                        obj.move()
                    else:
                        lib.move(obj)

            # When modifying items, we have to store them to the database.
            if not album:
                lib.store(obj)

    # Apply tags if requested.
    if write:
        if album:
            items = itertools.chain(*(a.items() for a in albums))
        for item in items:
            item.write()

modify_cmd = ui.Subcommand('modify',
    help='change metadata fields', aliases=('mod',))
modify_cmd.parser.add_option('-M', '--nomove', action='store_false',
    default=True, dest='move', help="don't move files in library")
modify_cmd.parser.add_option('-w', '--write', action='store_true',
    default=None, help="write new metadata to files' tags (default)")
modify_cmd.parser.add_option('-W', '--nowrite', action='store_false',
    dest='write', help="don't write metadata (opposite of -w)")
modify_cmd.parser.add_option('-a', '--album', action='store_true',
    help='modify whole albums instead of tracks')
modify_cmd.parser.add_option('-y', '--yes', action='store_true',
    help='skip confirmation')
modify_cmd.parser.add_option('-f', '--format', action='store',
    help='print with custom format', default=None)
def modify_func(lib, opts, args):
    args = decargs(args)
    mods = [a for a in args if '=' in a]
    query = [a for a in args if '=' not in a]
    if not mods:
        raise ui.UserError('no modifications specified')
    write = opts.write if opts.write is not None else \
        config['import']['write'].get(bool)
    modify_items(lib, mods, query, write, opts.move, opts.album, not opts.yes)
modify_cmd.func = modify_func
default_commands.append(modify_cmd)


# move: Move/copy files to the library or a new base directory.

def move_items(lib, dest, query, copy, album):
    """Moves or copies items to a new base directory, given by dest. If
    dest is None, then the library's base directory is used, making the
    command "consolidate" files.
    """
    items, albums = _do_query(lib, query, album, False)
    objs = albums if album else items

    action = 'Copying' if copy else 'Moving'
    entity = 'album' if album else 'item'
    logging.info('%s %i %ss.' % (action, len(objs), entity))
    for obj in objs:
        old_path = obj.item_dir() if album else obj.path
        logging.debug('moving: %s' % old_path)

        if album:
            obj.move(copy, basedir=dest)
        else:
            lib.move(obj, copy, basedir=dest)
            lib.store(obj)

move_cmd = ui.Subcommand('move',
    help='move or copy items', aliases=('mv',))
move_cmd.parser.add_option('-d', '--dest', metavar='DIR', dest='dest',
    help='destination directory')
move_cmd.parser.add_option('-c', '--copy', default=False, action='store_true',
    help='copy instead of moving')
move_cmd.parser.add_option('-a', '--album', default=False, action='store_true',
    help='match whole albums instead of tracks')
def move_func(lib, opts, args):
    dest = opts.dest
    if dest is not None:
        dest = normpath(dest)
        if not os.path.isdir(dest):
            raise ui.UserError('no such directory: %s' % dest)

    move_items(lib, dest, decargs(args), opts.copy, opts.album)
move_cmd.func = move_func
default_commands.append(move_cmd)