Source

beets / beets / library.py

Full commit
   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
# This file is part of beets.
# Copyright 2011, 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.

import sqlite3
import os
import re
import shutil
import sys
from string import Template
import logging
from beets.mediafile import MediaFile
from beets import plugins
from beets import util
from beets.util import bytestring_path, syspath, normpath

MAX_FILENAME_LENGTH = 200

# Fields in the "items" database table; all the metadata available for
# items in the library. These are used directly in SQL; they are
# vulnerable to injection if accessible to the user.
# Each tuple has the following values:
# - The name of the field.
# - The (SQLite) type of the field.
# - Is the field writable?
# - Does the field reflect an attribute of a MediaFile?
ITEM_FIELDS = [
    ('id',          'integer primary key', False, False),
    ('path',        'blob', False, False),
    ('album_id',    'int',  False, False),

    ('title',            'text', True, True),
    ('artist',           'text', True, True),
    ('album',            'text', True, True),
    ('albumartist',      'text', True, True),
    ('genre',            'text', True, True),
    ('composer',         'text', True, True),
    ('grouping',         'text', True, True),
    ('year',             'int',  True, True),
    ('month',            'int',  True, True),
    ('day',              'int',  True, True),
    ('track',            'int',  True, True),
    ('tracktotal',       'int',  True, True),
    ('disc',             'int',  True, True),
    ('disctotal',        'int',  True, True),
    ('lyrics',           'text', True, True),
    ('comments',         'text', True, True),
    ('bpm',              'int',  True, True),
    ('comp',             'bool', True, True),
    ('mb_trackid',       'text', True, True),
    ('mb_albumid',       'text', True, True),
    ('mb_artistid',      'text', True, True),
    ('mb_albumartistid', 'text', True, True),
    ('albumtype',        'text', True, True),

    ('length',      'real', False, True),
    ('bitrate',     'int',  False, True),
    ('format',      'text', False, True),
]
ITEM_KEYS_WRITABLE = [f[0] for f in ITEM_FIELDS if f[3] and f[2]]
ITEM_KEYS_META     = [f[0] for f in ITEM_FIELDS if f[3]]
ITEM_KEYS          = [f[0] for f in ITEM_FIELDS]

# Database fields for the "albums" table.
# The third entry in each tuple indicates whether the field reflects an
# identically-named field in the items table.
ALBUM_FIELDS = [
    ('id',      'integer primary key', False),
    ('artpath', 'blob',                False),

    ('albumartist',      'text', True),
    ('album',            'text', True),
    ('genre',            'text', True),
    ('year',             'int',  True),
    ('month',            'int',  True),
    ('day',              'int',  True),
    ('tracktotal',       'int',  True),
    ('disctotal',        'int',  True),
    ('comp',             'bool', True),
    ('mb_albumid',       'text', True),
    ('mb_albumartistid', 'text', True),
    ('albumtype',        'text', True),
]
ALBUM_KEYS = [f[0] for f in ALBUM_FIELDS]
ALBUM_KEYS_ITEM = [f[0] for f in ALBUM_FIELDS if f[2]]

# Default search fields for various granularities.
ARTIST_DEFAULT_FIELDS = ('artist',)
ALBUM_DEFAULT_FIELDS = ('album', 'albumartist', 'genre')
ITEM_DEFAULT_FIELDS = ARTIST_DEFAULT_FIELDS + ALBUM_DEFAULT_FIELDS + \
    ('title', 'comments')

# Logger.
log = logging.getLogger('beets')
if not log.handlers:
    log.addHandler(logging.StreamHandler())


# Exceptions.

class InvalidFieldError(Exception):
    pass


# Library items (songs).

class Item(object):
    def __init__(self, values):
        self.dirty = {}
        self._fill_record(values)
        self._clear_dirty()
        
    @classmethod
    def from_path(cls, path):
        """Creates a new item from the media file at the specified path.
        """
        # Initiate with values that aren't read from files.
        i = cls({
            'album_id': None,
        })
        i.read(path)
        return i

    def _fill_record(self, values):
        self.record = {}
        for key in ITEM_KEYS:
            try:
                setattr(self, key, values[key])
            except KeyError:
                setattr(self, key, None)

    def _clear_dirty(self):
        self.dirty = {}
        for key in ITEM_KEYS:
            self.dirty[key] = False

    def __repr__(self):
        return 'Item(' + repr(self.record) + ')'


    # Item field accessors.

    def __getattr__(self, key):
        """If key is an item attribute (i.e., a column in the database),
        returns the record entry for that key.
        """
        if key in ITEM_KEYS:
            return self.record[key]
        else:
            raise AttributeError(key + ' is not a valid item field')

    def __setattr__(self, key, value):
        """If key is an item attribute (i.e., a column in the database),
        sets the record entry for that key to value. Note that to change
        the attribute in the database or in the file's tags, one must
        call store() or write().
        
        Otherwise, performs an ordinary setattr.
        """
        # Encode unicode paths and read buffers.
        if key == 'path':
            if isinstance(value, unicode):
                value = bytestring_path(value)
            elif isinstance(value, buffer):
                value = str(value)

        if key in ITEM_KEYS:
            if (not (key in self.record)) or (self.record[key] != value):
                # don't dirty if value unchanged
                self.record[key] = value
                self.dirty[key] = True
        else:
            super(Item, self).__setattr__(key, value)
    
    
    # Interaction with file metadata.
    
    def read(self, read_path=None):
        """Read the metadata from the associated file. If read_path is
        specified, read metadata from that file instead.
        """
        if read_path is None:
            read_path = self.path
        else:
            read_path = normpath(read_path)
        f = MediaFile(syspath(read_path))

        for key in ITEM_KEYS_META:
            setattr(self, key, getattr(f, key))
        self.path = read_path
    
    def write(self):
        """Writes the item's metadata to the associated file.
        """
        f = MediaFile(syspath(self.path))
        for key in ITEM_KEYS_WRITABLE:
            setattr(f, key, getattr(self, key))
        f.save()
    
    
    # Dealing with files themselves.
    
    def move(self, library, copy=False, in_album=False):
        """Move the item to its designated location within the library
        directory (provided by destination()). Subdirectories are
        created as needed. If the operation succeeds, the item's path
        field is updated to reflect the new location.
        
        If copy is True, moving the file is copied rather than moved.
        
        If in_album is True, then the track is treated as part of an
        album even if it does not yet have an album_id associated with
        it. (This allows items to be moved before they are added to the
        database, a performance optimization.)

        Passes on appropriate exceptions if directories cannot be created
        or moving/copying fails.
        
        Note that one should almost certainly call store() and
        library.save() after this method in order to keep on-disk data
        consistent.
        """
        dest = library.destination(self, in_album=in_album)
        
        # Create necessary ancestry for the move.
        util.mkdirall(dest)
        
        if not shutil._samefile(syspath(self.path), syspath(dest)):
            if copy:
                # copyfile rather than copy will not copy permissions
                # bits, thus possibly making the copy writable even when
                # the original is read-only.
                shutil.copyfile(syspath(self.path), syspath(dest))
            else:
                shutil.move(syspath(self.path), syspath(dest))
            
        # Either copying or moving succeeded, so update the stored path.
        self.path = dest


# Library queries.

class Query(object):
    """An abstract class representing a query into the item database.
    """
    def clause(self):
        """Returns (clause, subvals) where clause is a valid sqlite
        WHERE clause implementing the query and subvals is a list of
        items to be substituted for ?s in the clause.
        """
        raise NotImplementedError

    def match(self, item):
        """Check whether this query matches a given Item. Can be used to
        perform queries on arbitrary sets of Items.
        """
        raise NotImplementedError

    def statement(self, columns='*'):
        """Returns (query, subvals) where clause is a sqlite SELECT
        statement to enact this query and subvals is a list of values
        to substitute in for ?s in the query.
        """
        clause, subvals = self.clause()
        return ('SELECT ' + columns + ' FROM items WHERE ' + clause, subvals)

    def count(self, library):
        """Returns `(num, length)` where `num` is the number of items in
        the library matching this query and `length` is their total
        length in seconds.
        """
        clause, subvals = self.clause()
        statement = 'SELECT COUNT(id), SUM(length) FROM items WHERE ' + clause
        c = library.conn.cursor()
        result = c.execute(statement, subvals).fetchone()
        return (result[0], result[1] or 0.0)

    def execute(self, library):
        """Runs the query in the specified library, returning a
        ResultIterator.
        """
        c = library.conn.cursor()
        stmt, subs = self.statement()
        log.debug('Executing query: %s' % stmt)
        c.execute(stmt, subs)
        return ResultIterator(c, library)

class FieldQuery(Query):
    """An abstract query that searches in a specific field for a
    pattern.
    """
    def __init__(self, field, pattern):
        if field not in ITEM_KEYS:
            raise InvalidFieldError(field + ' is not an item key')
        self.field = field
        self.pattern = pattern
        
class MatchQuery(FieldQuery):
    """A query that looks for exact matches in an item field."""
    def clause(self):
        pattern = self.pattern
        if self.field == 'path' and isinstance(pattern, str):
            pattern = buffer(pattern)
        return self.field + " = ?", [pattern]

    def match(self, item):
        return self.pattern == getattr(item, self.field)

class SubstringQuery(FieldQuery):
    """A query that matches a substring in a specific item field."""
    def clause(self):
        search = '%' + (self.pattern.replace('\\','\\\\').replace('%','\\%')
                            .replace('_','\\_')) + '%'
        clause = self.field + " like ? escape '\\'"
        subvals = [search]
        return clause, subvals

    def match(self, item):
        return self.pattern.lower() in getattr(item, self.field).lower()

class BooleanQuery(MatchQuery):
    """Matches a boolean field. Pattern should either be a boolean or a
    string reflecting a boolean.
    """
    def __init__(self, field, pattern):
        super(BooleanQuery, self).__init__(field, pattern)
        if isinstance(pattern, basestring):
            self.pattern = util.str2bool(pattern)
        self.pattern = int(self.pattern)

class SingletonQuery(Query):
    """Matches either singleton or non-singleton items."""
    def __init__(self, sense):
        self.sense = sense

    def clause(self):
        if self.sense:
            return "album_id ISNULL", ()
        else:
            return "NOT album_id ISNULL", ()

    def match(self, item):
        return (not item.album_id) == self.sense

class CollectionQuery(Query):
    """An abstract query class that aggregates other queries. Can be
    indexed like a list to access the sub-queries.
    """
    def __init__(self, subqueries = ()):
        self.subqueries = subqueries
    
    # is there a better way to do this?
    def __len__(self): return len(self.subqueries)
    def __getitem__(self, key): return self.subqueries[key]
    def __iter__(self): iter(self.subqueries)
    def __contains__(self, item): item in self.subqueries

    def clause_with_joiner(self, joiner):
        """Returns a clause created by joining together the clauses of
        all subqueries with the string joiner (padded by spaces).
        """
        clause_parts = []
        subvals = []
        for subq in self.subqueries:
            subq_clause, subq_subvals = subq.clause()
            clause_parts.append('(' + subq_clause + ')')
            subvals += subq_subvals
        clause = (' ' + joiner + ' ').join(clause_parts)
        return clause, subvals
    
    # regular expression for _parse_query, below
    _pq_regex = re.compile(r'(?:^|(?<=\s))' # zero-width match for whitespace
                                            # or beginning of string
       
                           # non-grouping optional segment for the keyword
                           r'(?:'
                                r'(\S+?)'   # the keyword
                                r'(?<!\\):' # unescaped :
                           r')?'
       
                           r'(\S+)',        # the term itself
                           re.I)            # case-insensitive
    @classmethod
    def _parse_query(cls, query_string):
        """Takes a query in the form of a whitespace-separated list of
        search terms that may be preceded with a key followed by a
        colon. Returns a list of pairs (key, term) where key is None if
        the search term has no key.

        For instance,
        parse_query('stapler color:red') ==
            [(None, 'stapler'), ('color', 'red')]

        Colons may be 'escaped' with a backslash to disable the keying
        behavior.
        """
        out = []
        for match in cls._pq_regex.finditer(query_string):
            out.append((match.group(1), match.group(2).replace(r'\:',':')))
        return out

    @classmethod
    def from_string(cls, query_string, default_fields=None):
        """Creates a query from a string in the format used by
        _parse_query. If default_fields are specified, they are the
        fields to be searched by unqualified search terms. Otherwise,
        all fields are searched for those terms.
        """
        subqueries = []
        for key, pattern in cls._parse_query(query_string):
            if key is None: # no key specified; match any field
                subqueries.append(AnySubstringQuery(pattern, default_fields))
            elif key.lower() == 'comp': # a boolean field
                subqueries.append(BooleanQuery(key.lower(), pattern))
            elif key.lower() in ITEM_KEYS: # ignore unrecognized keys
                subqueries.append(SubstringQuery(key.lower(), pattern))
            elif key.lower() == 'singleton':
                subqueries.append(SingletonQuery(util.str2bool(pattern)))
        if not subqueries: # no terms in query
            subqueries = [TrueQuery()]
        return cls(subqueries)

class AnySubstringQuery(CollectionQuery):
    """A query that matches a substring in any of a list of metadata
    fields.
    """
    def __init__(self, pattern, fields=None):
        """Create a query for pattern over the sequence of fields
        given. If no fields are given, all available fields are
        used.
        """
        self.pattern = pattern
        self.fields = fields or ITEM_KEYS_WRITABLE

        subqueries = []
        for field in self.fields:
            subqueries.append(SubstringQuery(field, pattern))
        super(AnySubstringQuery, self).__init__(subqueries)

    def clause(self):
        return self.clause_with_joiner('or')

    def match(self, item):
        for fld in self.fields:
            try:
                val = getattr(item, fld)
            except KeyError:
                continue
            if isinstance(val, basestring) and \
               self.pattern.lower() in val.lower():
                return True
        return False

class MutableCollectionQuery(CollectionQuery):
    """A collection query whose subqueries may be modified after the
    query is initialized.
    """
    def __setitem__(self, key, value): self.subqueries[key] = value
    def __delitem__(self, key): del self.subqueries[key]

class AndQuery(MutableCollectionQuery):
    """A conjunction of a list of other queries."""
    def clause(self):
        return self.clause_with_joiner('and')

    def match(self, item):
        return all([q.match(item) for q in self.subqueries])

class TrueQuery(Query):
    """A query that always matches."""
    def clause(self):
        return '1', ()

    def match(self, item):
        return True

class ResultIterator(object):
    """An iterator into an item query result set."""
    
    def __init__(self, cursor, library):
        self.cursor = cursor
        self.library = library
    
    def __iter__(self): return self
    
    def next(self):
        try:
            row = self.cursor.next()
        except StopIteration:
            self.cursor.close()
            raise
        return Item(row)


# An abstract library.

class BaseLibrary(object):
    """Abstract base class for music libraries, which are loosely
    defined as sets of Items.
    """
    def __init__(self):
        raise NotImplementedError


    # Helpers.

    @classmethod
    def _get_query(cls, val=None, default_fields=None):
        """Takes a value which may be None, a query string, or a Query
        object, and returns a suitable Query object. If default_fields
        is specified, then it restricts the list of fields to search
        for unqualified terms in query strings.
        """
        if val is None:
            return TrueQuery()
        elif isinstance(val, basestring):
            return AndQuery.from_string(val, default_fields)
        elif isinstance(val, Query):
            return val
        elif not isinstance(val, Query):
            raise ValueError('query must be None or have type Query or str')


    # Basic operations.

    def add(self, item, copy=False): #FIXME copy should default to true
        """Add the item as a new object to the library database. The id
        field will be updated; the new id is returned. If copy, then
        each item is copied to the destination location before it is
        added.
        """
        raise NotImplementedError

    def get(self, query=None, default_fields=None):
        """Returns a sequence of the items matching query, which may
        be None (match the entire library), a Query object, or a query
        string. If default_fields is specified, it restricts the fields
        that may be matched by unqualified query string terms.
        """
        raise NotImplementedError

    def save(self):
        """Ensure that the library is consistent on disk. A no-op by
        default.
        """
        pass

    def load(self, item, load_id=None):
        """Refresh the item's metadata from the library database. If
        fetch_id is not specified, use the item's current id.
        """
        raise NotImplementedError

    def store(self, item, store_id=None, store_all=False):
        """Save the item's metadata into the library database. If
        store_id is specified, use it instead of the item's current id.
        If store_all is true, save the entire record instead of just
        the dirty fields.
        """
        raise NotImplementedError

    def remove(self, item):
        """Removes the item from the database (leaving the file on
        disk).
        """
        raise NotImplementedError


    # Browsing operations.
    # Naive implementations are provided, but these methods should be
    # overridden if a better implementation exists.

    def artists(self, query=None):
        """Returns a sorted sequence of artists in the database,
        possibly filtered by a query. Unqualified query string terms
        only match the artist field.
        """
        out = set()
        for item in self.get(query, ARTIST_DEFAULT_FIELDS):
            out.add(item.artist)
        return sorted(out)

    def albums(self, artist=None, query=None):
        """Returns a sorted list of BaseAlbum objects, possibly filtered
        by an artist name or an arbitrary query. Unqualified query
        string terms only match fields that apply at an album
        granularity: artist, album, and genre.
        """
        # Gather the unique album/artist names and associated example
        # Items.
        specimens = {}
        for item in self.get(query, ALBUM_DEFAULT_FIELDS):
            if (artist is None or item.artist == artist):
                key = (item.artist, item.album)
                if key not in specimens:
                    specimens[key] = item

        # Build album objects.
        for k in sorted(specimens.keys()):
            item = specimens[k]
            record = {}
            for key in ALBUM_KEYS_ITEM:
                record[key] = getattr(item, key)
            yield BaseAlbum(self, record)

    def items(self, artist=None, album=None, title=None, query=None):
        """Returns a sequence of the items matching the given artist,
        album, title, and query (if present). Sorts in such a way as to
        group albums appropriately. Unqualified query string terms only
        match intuitively relevant fields: artist, album, genre, title,
        and comments.
        """
        out = []
        for item in self.get(query, ITEM_DEFAULT_FIELDS):
            if (artist is None or item.artist == artist) and \
               (album is None  or item.album == album) and \
               (title is None  or item.title == title):
                out.append(item)

        # Sort by: artist, album, disc, track.
        def compare(a, b):
            return cmp(a.artist, b.artist) or \
                   cmp(a.album, b.album) or \
                   cmp(a.disc, b.disc) or \
                   cmp(a.track, b.track)
        return sorted(out, compare)

class BaseAlbum(object):
    """Represents an album in the library, which in turn consists of a
    collection of items in the library.

    This base version just reflects the metadata of the album's items
    and therefore isn't particularly useful. The items are referenced
    by the record's album and artist fields. Implementations can add
    album-level metadata or use distinct backing stores.
    """
    def __init__(self, library, record):
        super(BaseAlbum, self).__setattr__('_library', library)
        super(BaseAlbum, self).__setattr__('_record', record)

    def __getattr__(self, key):
        """Get the value for an album attribute."""
        if key in self._record:
            return self._record[key]
        else:
            raise AttributeError('no such field %s' % key)

    def __setattr__(self, key, value):
        """Set the value of an album attribute, modifying each of the
        album's items.
        """
        if key in self._record:
            # Reflect change in this object.
            self._record[key] = value
            # Modify items.
            if key in ALBUM_KEYS_ITEM:
                items = self._library.items(albumartist=self.albumartist,
                                            album=self.album)
                for item in items:
                    setattr(item, key, value)
                self._library.store(item)
        else:
            super(BaseAlbum, self).__setattr__(key, value)

    def load(self):
        """Refresh this album's cached metadata from the library.
        """
        items = self._library.items(artist=self.artist, album=self.album)
        item = iter(items).next()
        for key in ALBUM_KEYS_ITEM:
            self._record[key] = getattr(item, key)


# Concrete DB-backed library.

class Library(BaseLibrary):
    """A music library using an SQLite database as a metadata store."""
    def __init__(self, path='library.blb',
                       directory='~/Music',
                       path_formats=None,
                       art_filename='cover',
                       item_fields=ITEM_FIELDS,
                       album_fields=ALBUM_FIELDS):
        self.path = bytestring_path(path)
        self.directory = bytestring_path(directory)
        if path_formats is None:
            path_formats = {'default': '$artist/$album/$track $title'}
        elif isinstance(path_formats, basestring):
            path_formats = {'default': path_formats}
        self.path_formats = path_formats
        self.art_filename = bytestring_path(art_filename)
        
        self.conn = sqlite3.connect(self.path)
        self.conn.row_factory = sqlite3.Row
            # this way we can access our SELECT results like dictionaries
        
        self._make_table('items', item_fields)
        self._make_table('albums', album_fields)
    
    def _make_table(self, table, fields):
        """Set up the schema of the library file. fields is a list of
        all the fields that should be present in the indicated table.
        Columns are added if necessary.
        """
        # Get current schema.
        cur = self.conn.cursor()
        cur.execute('PRAGMA table_info(%s)' % table)
        current_fields = set([row[1] for row in cur])
        
        field_names = set([f[0] for f in fields])
        if current_fields.issuperset(field_names):
            # Table exists and has all the required columns.
            return
            
        if not current_fields:
            # No table exists.        
            setup_sql =  'CREATE TABLE %s (' % table
            setup_sql += ', '.join(['%s %s' % f[:2] for f in fields])
            setup_sql += ');\n'
            
        else:
            # Table exists but is missing fields.
            setup_sql = ''
            for fname in field_names - current_fields:
                for field in fields:
                    if field[0] == fname:
                        break
                else:
                    assert False
                setup_sql += 'ALTER TABLE %s ' % table
                setup_sql += 'ADD COLUMN %s %s;\n' % field[:2]

        # Special case. If we're moving from a version without
        # albumartist, copy all the "artist" values to "albumartist"
        # values on the album data structure.
        if table == 'albums' and 'artist' in current_fields and \
                    'albumartist' not in current_fields:
            setup_sql += "UPDATE ALBUMS SET albumartist=artist;\n"
        
        self.conn.executescript(setup_sql)
        self.conn.commit()
    
    def destination(self, item, pathmod=None, in_album=False):
        """Returns the path in the library directory designated for item
        item (i.e., where the file ought to be). in_album forces the
        item to be treated as part of an album.
        """
        pathmod = pathmod or os.path
        
        # Use a path format based on the album type, if available.
        if not item.album_id and not in_album:
            # Singleton track. Never use the "album" formats.
            if 'singleton' in self.path_formats:
                path_format = self.path_formats['singleton']
            else:
                path_format = self.path_formats['default']
        elif item.albumtype and item.albumtype in self.path_formats:
            path_format = self.path_formats[item.albumtype]
        elif item.comp and 'comp' in self.path_formats:
            path_format = self.path_formats['comp']
        else:
            path_format = self.path_formats['default']
        subpath_tmpl = Template(path_format)
        
        # Get the item's Album if it has one.
        album = self.get_album(item)
        
        # Build the mapping for substitution in the path template,
        # beginning with the values from the database.
        mapping = {}
        for key in ITEM_KEYS_META:
            # Get the values from either the item or its album.
            if key in ALBUM_KEYS_ITEM and album is not None:
                # From album.
                value = getattr(album, key)
            else:
                # From Item.
                value = getattr(item, key)
            mapping[key] = util.sanitize_for_path(value, pathmod, key)
        
        # Use the album artist if the track artist is not set and
        # vice-versa.
        if not mapping['artist']:
            mapping['artist'] = mapping['albumartist']
        if not mapping['albumartist']:
            mapping['albumartist'] = mapping['artist']
        
        # Perform substitution.
        subpath = subpath_tmpl.substitute(mapping)
        
        # Encode for the filesystem, dropping unencodable characters.
        if isinstance(subpath, unicode):
            encoding = sys.getfilesystemencoding() or sys.getdefaultencoding()
            subpath = subpath.encode(encoding, 'replace')
        
        # Truncate components and remove forbidden characters.
        subpath = util.sanitize_path(subpath)
        
        # Preserve extension.
        _, extension = pathmod.splitext(item.path)
        subpath += extension
        
        return normpath(os.path.join(self.directory, subpath))   

    
    # Main interface.

    def add(self, item, copy=False):
        #FIXME make a deep copy of the item?
        item.library = self
        if copy:
            item.move(self, copy=True)

        # build essential parts of query
        columns = ','.join([key for key in ITEM_KEYS if key != 'id'])
        values = ','.join( ['?'] * (len(ITEM_KEYS)-1) )
        subvars = []
        for key in ITEM_KEYS:
            if key != 'id':
                value = getattr(item, key)
                if key == 'path' and isinstance(value, str):
                    value = buffer(value)
                subvars.append(value)
        
        # issue query
        c = self.conn.cursor()
        query = 'INSERT INTO items (' + columns + ') VALUES (' + values + ')'
        c.execute(query, subvars)
        new_id = c.lastrowid
        c.close()
        
        item._clear_dirty()
        item.id = new_id
        return new_id
    
    def get(self, query=None):
        return self._get_query(query).execute(self)
    
    def save(self):
        """Writes the library to disk (completing an sqlite
        transaction).
        """
        self.conn.commit()
        plugins.send('save', lib=self)

    def load(self, item, load_id=None):
        if load_id is None:
            load_id = item.id
        
        c = self.conn.execute(
                'SELECT * FROM items WHERE id=?', (load_id,) )
        item._fill_record(c.fetchone())
        item._clear_dirty()
        c.close()

    def store(self, item, store_id=None, store_all=False):
        if store_id is None:
            store_id = item.id
 
        # build assignments for query
        assignments = ''
        subvars = []
        for key in ITEM_KEYS:
            if (key != 'id') and (item.dirty[key] or store_all):
                assignments += key + '=?,'
                value = getattr(item, key)
                # Wrap path strings in buffers so they get stored
                # "in the raw".
                if key == 'path' and isinstance(value, str):
                    value = buffer(value)
                subvars.append(value)
        
        if not assignments:
            # nothing to store (i.e., nothing was dirty)
            return
        
        assignments = assignments[:-1] # knock off last ,

        # finish the query
        query = 'UPDATE items SET ' + assignments + ' WHERE id=?'
        subvars.append(store_id)

        self.conn.execute(query, subvars)
        item._clear_dirty()

    def remove(self, item, delete=False, with_album=True):
        """Removes this item. If delete, then the associated file is
        removed from disk. If with_album, then the item's album (if any)
        is removed if it the item was the last in the album.
        """
        album = self.get_album(item) if with_album else None

        self.conn.execute('DELETE FROM items WHERE id=?', (item.id,))

        if album:
            item_iter = album.items()
            try:
                item_iter.next()
            except StopIteration:
                # Album is empty.
                album.remove(delete, False)

        if delete:
            util.soft_remove(item.path)
            util.prune_dirs(os.path.dirname(item.path), self.directory)


    # Browsing.

    def artists(self, query=None):
        query = self._get_query(query, ARTIST_DEFAULT_FIELDS)
        where, subvals = query.clause()
        sql = "SELECT DISTINCT artist FROM items " + \
              "WHERE " + where + \
              " ORDER BY artist"
        c = self.conn.execute(sql, subvals)
        return [res[0] for res in c.fetchall()]

    def albums(self, artist=None, query=None):
        query = self._get_query(query, ALBUM_DEFAULT_FIELDS)
        if artist is not None:
            # "Add" the artist to the query.
            query = AndQuery((query, MatchQuery('albumartist', artist)))
        where, subvals = query.clause()
        sql = "SELECT * FROM albums " + \
              "WHERE " + where + \
              " ORDER BY albumartist, album"
        c = self.conn.execute(sql, subvals)
        return [Album(self, dict(res)) for res in c.fetchall()]

    def items(self, artist=None, album=None, title=None, query=None):
        queries = [self._get_query(query, ITEM_DEFAULT_FIELDS)]
        if artist is not None:
            queries.append(MatchQuery('artist', artist))
        if album is not None:
            queries.append(MatchQuery('album', album))
        if title is not None:
            queries.append(MatchQuery('title', title))
        super_query = AndQuery(queries)
        where, subvals = super_query.clause()

        sql = "SELECT * FROM items " + \
              "WHERE " + where + \
              " ORDER BY artist, album, disc, track"
        log.debug('Getting items with SQL: %s' % sql)
        c = self.conn.execute(sql, subvals)
        return ResultIterator(c, self)


    # Convenience accessors.

    def get_item(self, id):
        """Fetch an Item by its ID. Returns None if no match is found.
        """
        c = self.conn.execute("SELECT * FROM items WHERE id=?", (id,))
        it = ResultIterator(c, self)
        try:
            return it.next()
        except StopIteration:
            return None
    
    def get_album(self, item_or_id):
        """Given an album ID or an item associated with an album,
        return an Album object for the album. If no such album exists,
        returns None.
        """
        if isinstance(item_or_id, int):
            album_id = item_or_id
        else:
            album_id = item_or_id.album_id
        if album_id is None:
            return None

        record = self.conn.execute(
            'SELECT * FROM albums WHERE id=?',
            (album_id,)
        ).fetchone()
        if record:
            return Album(self, dict(record))

    def add_album(self, items, infer_aa=False):
        """Create a new album in the database with metadata derived
        from its items. The items are added to the database if they
        don't yet have an ID. Returns an Album object. If the
        infer_aa flag is set, then the album artist field will be
        guessed from artist fields when not present.
        """
        # Set the metadata from the first item.
        #fixme: check for consensus?
        item_values = dict(
            (key, getattr(items[0], key)) for key in ALBUM_KEYS_ITEM)
        if infer_aa:
            namemap = {
                'albumartist': 'artist',
                'mb_albumartistid': 'mb_artistid',
            }
            for field, itemfield in namemap.iteritems():
                if not item_values[field]:
                    item_values[field] = getattr(items[0], itemfield)

        sql = 'INSERT INTO albums (%s) VALUES (%s)' % \
              (', '.join(ALBUM_KEYS_ITEM),
               ', '.join(['?'] * len(ALBUM_KEYS_ITEM)))
        subvals = [item_values[key] for key in ALBUM_KEYS_ITEM]
        c = self.conn.execute(sql, subvals)
        album_id = c.lastrowid

        # Construct the new Album object.
        record = {}
        for key in ALBUM_KEYS:
            if key in ALBUM_KEYS_ITEM:
                record[key] = item_values[key]
            else:
                # Non-item fields default to None.
                record[key] = None
        record['id'] = album_id
        album = Album(self, record)

        # Add the items to the library.
        for item in items:
            item.album_id = album_id
            if item.id is None:
                self.add(item)
            else:
                self.store(item)

        return album

class Album(BaseAlbum):
    """Provides access to information about albums stored in a
    library. Reflects the library's "albums" table, including album
    art.
    """
    def __init__(self, lib, record):
        # Decode Unicode paths in database.
        if 'artpath' in record and isinstance(record['artpath'], unicode):
            record['artpath'] = bytestring_path(record['artpath'])
        super(Album, self).__init__(lib, record)

    def __setattr__(self, key, value):
        """Set the value of an album attribute."""
        if key == 'id':
            raise AttributeError("can't modify album id")

        elif key in ALBUM_KEYS:
            # Make sure paths are bytestrings.
            if key == 'artpath' and isinstance(value, unicode):
                value = bytestring_path(value)

            # Reflect change in this object.
            self._record[key] = value

            # Store art path as a buffer.
            if key == 'artpath' and isinstance(value, str):
                value = buffer(value)

            # Change album table.
            sql = 'UPDATE albums SET %s=? WHERE id=?' % key
            self._library.conn.execute(sql, (value, self.id))

            # Possibly make modification on items as well.
            if key in ALBUM_KEYS_ITEM:
                for item in self.items():
                    setattr(item, key, value)
                    self._library.store(item)

        else:
            object.__setattr__(self, key, value)

    def __getattr__(self, key):
        value = super(Album, self).__getattr__(key)

        # Unwrap art path from buffer object.
        if key == 'artpath' and isinstance(value, buffer):
            value = str(value)

        return value

    def items(self):
        """Returns an iterable over the items associated with this
        album.
        """
        c = self._library.conn.execute(
            'SELECT * FROM items WHERE album_id=?',
            (self.id,)
        )
        return ResultIterator(c, self._library)

    def remove(self, delete=False, with_items=True):
        """Removes this album and all its associated items from the
        library. If delete, then the items' files are also deleted
        from disk, along with any album art. The directories
        containing the album are also removed (recursively) if empty.
        Set with_items to False to avoid removing the album's items.
        """
        if with_items:
            # Remove items.
            for item in self.items():
                self._library.remove(item, delete, False)
        
        if delete:
            # Delete art file.
            artpath = self.artpath
            if artpath:
                util.soft_remove(artpath)
        
        # Remove album from database.
        self._library.conn.execute(
            'DELETE FROM albums WHERE id=?',
            (self.id,)
        )

    def move(self, copy=False):
        """Moves (or copies) all items to their destination. Any
        album art moves along with them.
        """
        # Move items.
        items = list(self.items())
        for item in items:
            item.move(self._library, copy)
        newdir = os.path.dirname(items[0].path)

        # Move art.
        old_art = self.artpath
        if old_art:
            new_art = self.art_destination(old_art, newdir)
            if new_art != old_art:
                if copy:
                    shutil.copy(syspath(old_art), syspath(new_art))
                else:
                    shutil.move(syspath(old_art), syspath(new_art))
                self.artpath = new_art

        # Store new item paths. We do this at the end to avoid
        # locking the database for too long while files are copied.
        for item in items:
            self._library.store(item)

    def art_destination(self, image, item_dir=None):
        """Returns a path to the destination for the album art image
        for the album. `image` is the path of the image that will be
        moved there (used for its extension).

        The path construction uses the existing path of the album's
        items, so the album must contain at least one item or
        item_dir must be provided.
        """
        image = bytestring_path(image)
        if item_dir is None:
            item = self.items().next()
            item_dir = os.path.dirname(item.path)
        _, ext = os.path.splitext(image)
        dest = os.path.join(item_dir, self._library.art_filename + ext)
        return dest
    
    def set_art(self, path):
        """Sets the album's cover art to the image at the given path.
        The image is copied into place, replacing any existing art.
        """
        path = bytestring_path(path)
        oldart = self.artpath
        artdest = self.art_destination(path)
        if oldart == artdest:
            util.soft_remove(oldart)
        
        shutil.copyfile(syspath(path), syspath(artdest))
        self.artpath = artdest