"""
Migration runner built on the playhouse.migrate helpers.

Migrations are plain python scripts in a directory, applied in numeric
order and recorded by name in a history table. Each script defines
``up(migrator, db)`` and (optionally) ``down(migrator, db)``:

    # migrations/0002_add_karma.py
    from peewee import *

    def up(migrator, db):
        migrator.migrate(
            migrator.add_column('user', 'karma', IntegerField(default=0)))

    def down(migrator, db):
        migrator.migrate(migrator.drop_column('user', 'karma'))

Nothing is introspected at runtime or auto-detected. New tables need no special
support: declare the model inline (a frozen copy, deliberately independent of
the application models) and call ``db.create_tables()`` from ``up()``.

Set ``atomic = False`` at module scope to disable transaction wrapping.
"""
import argparse
import datetime
import decimal
import enum
import glob
import importlib.util
import logging
import os
import re
import sys
import time
import traceback
import uuid
from collections import namedtuple

from peewee import *
from peewee import is_model
from peewee import sort_models
from playhouse.migrate import SchemaMigrator
from playhouse.migrate import make_index_name

__all__ = ['Migration', 'MigrationError', 'Runner', 'run', 'template']

logger = logging.getLogger('peewee.migrations')

TEMPLATE = '''\
"""%s"""
from peewee import *


def up(migrator, db):
    # migrator.migrate(
    #     migrator.add_column('tbl', 'col', TextField(default='')))
    pass


# def down(migrator, db):
#     pass
'''

class MigrationError(Exception): pass

def _index(name):
    match = re.match(r'\d+', name)
    return int(match.group()) if match is not None else -1

class Migration(namedtuple('Migration', ('idx', 'name', 'path', 'applied'))):
    __slots__ = ()

    @classmethod
    def load_directory(cls, directory):
        accum = []
        for path in glob.glob(os.path.join(directory, '[0-9]*.py')):
            name = os.path.basename(path)[:-3]
            accum.append(Migration(_index(name), name, path, None))
        return sorted(accum)

    def load(self):
        # Execute the file at the exact path, bypassing sys.path and the
        # sys.modules cache (migration names collide across projects).
        spec = importlib.util.spec_from_file_location(self.name, self.path)
        module = importlib.util.module_from_spec(spec)
        spec.loader.exec_module(module)
        return module


class Runner(object):
    def __init__(self, database, directory='migrations',
                 table_name='schema_migration'):
        self.database = database
        self.directory = directory
        self.table_name = table_name
        self.migrator = SchemaMigrator.from_database(database)

        class History(database.Model):
            name = CharField(unique=True)
            applied = DateTimeField(default=datetime.datetime.now)
            class Meta:
                legacy_table_names = False
                table_name = self.table_name

        self.History = History

    def migrations(self):
        return Migration.load_directory(self.directory)

    def applied(self):
        if not self.History.table_exists():
            return {}

        return {h.name: h.applied for h in self.History.select()}

    def status(self):
        """
        Files and history merged as Migration tuples, in numeric order.
        ``applied`` is None for pending files, ``path`` is None for rows
        whose files are gone.
        """
        applied = self.applied()
        accum = [m._replace(applied=applied.get(m.name))
                 for m in self.migrations()]
        gone = set(applied) - {m.name for m in accum}
        accum.extend(Migration(_index(n), n, None, applied[n]) for n in gone)
        return sorted(accum)

    def up(self, target=None, fake=False):
        """
        Apply all pending migrations in order, or, given a target, stop
        after applying it. Returns the applied names.
        """
        rows = [m for m in self.status() if m.path is not None]
        if target is not None and target not in {m.name for m in rows}:
            raise MigrationError('unknown migration "%s".' % target)

        plan = []
        for migration in rows:
            if not migration.applied:
                module = migration.load()
                if getattr(module, 'up', None) is None:
                    raise MigrationError('%s does not define up().'
                                         % migration.name)
                plan.append((migration.name, module))
            if migration.name == target:
                break

        self.History.create_table()

        accum = []
        for name, module in plan:
            self._run(name, module, 'up', fake=fake)
            accum.append(name)

        return accum

    def down(self, target=None):
        """
        Revert the most recently-applied migration, or, given a target,
        every applied migration back through the target.
        """
        rows = [m for m in self.status() if m.applied]
        if target is not None and target not in {m.name for m in rows}:
            raise MigrationError('"%s" is not an applied migration.' % target)

        plan = []
        for migration in reversed(rows):
            if migration.path is None:
                raise MigrationError('cannot revert "%s": migration file '
                                     'is missing.' % migration.name)
            module = migration.load()
            if getattr(module, 'down', None) is None:
                raise MigrationError('%s does not define down().'
                                     % migration.name)

            plan.append((migration.name, module))
            if target is None or migration.name == target:
                break

        accum = []
        for name, module in plan:
            self._run(name, module, 'down')
            accum.append(name)

        return accum

    def fake(self, target=None):
        """
        Record pending migrations as applied without running them,
        stopping after the target if given. Returns the recorded names.
        """
        return self.up(target, fake=True)

    def create(self, name='', body=None):
        """Write a numbered skeleton migration file. Returns its path."""
        os.makedirs(self.directory, exist_ok=True)
        idx = max((m.idx for m in self.migrations()), default=0) + 1
        slug = re.sub(r'[^\w]+', '_', name.strip()).strip('_').lower()
        path = os.path.join(self.directory,
                            '%04d_%s.py' % (idx, slug or 'migration'))
        with open(path, 'w') as fh:
            fh.write(body or (TEMPLATE % name))
        return path

    def _run(self, name, module, direction, fake=False):
        # The plan was validated as it was built. Run it blind.
        logger.info('%s: %s%s', direction, name, ' [FAKE]' if fake else '')
        if fake:
            self.History.create(name=name)
            return

        with self.migrator.migration_context(getattr(module, 'atomic', True)):
            getattr(module, direction)(self.migrator, self.database)
            if direction == 'up':
                self.History.create(name=name)
            else:
                (self.History.delete()
                 .where(self.History.name == name)
                 .execute())

def run(database, directory='migrations', **kwargs):
    return Runner(database, directory, **kwargs).up()


_COMMON_DEFAULTS = (
    (datetime.datetime.now, 'datetime.datetime.now', 'import datetime'),
    (datetime.datetime.utcnow, 'datetime.datetime.utcnow', 'import datetime'),
    (datetime.date.today, 'datetime.date.today', 'import datetime'),
    (time.time, 'time.time', 'import time'),
    (time.time_ns, 'time.time_ns', 'import time'),
    (uuid.uuid4, 'uuid.uuid4', 'import uuid'),
    (dict, 'dict', None),
    (list, 'list', None))

def _handle_common_default(default, args, imports):
    for value, source, imp in _COMMON_DEFAULTS:
        if default == value:
            args.append('default=%s' % source)
            if imp:
                imports.add(imp)
            return True
    if isinstance(default, decimal.Decimal):
        args.append('default=decimal.Decimal(%r)' % str(default))
        imports.add('import decimal')
        return True
    return False

def _build_field_args(field, imports, todos, targets=None, unbound=False):
    args = []

    # Populate FK-only attrs first.
    if isinstance(field, ForeignKeyField):
        rel_model = field.rel_model
        # 'self' only means something inside a class body.
        if not unbound and rel_model is field.model:
            rel_name = "'self'"
        else:
            rel_name = targets[rel_model]
        args.append(rel_name)
        if unbound or field.rel_field is not rel_model._meta.primary_key:
            # Destination field needs to be explicitly specified when the
            # field is unbound (add_column calls) or if FK is not to the
            # rel's PK.
            args.append('field=%s.%s' % (rel_name, field.rel_field.name))

    if field.primary_key and not isinstance(field, AutoField):
        args.append('primary_key=True')
    if field.unique:
        args.append('unique=True')
    elif field.index and not isinstance(field, ForeignKeyField):
        args.append('index=True')
    if field.null:
        args.append('null=True')

    if isinstance(field, CharField) and field.max_length != 255:
        args.append('max_length=%r' % field.max_length)
    elif isinstance(field, DecimalField):
        if field.max_digits != 10:
            args.append('max_digits=%r' % field.max_digits)
        if field.decimal_places != 5:
            args.append('decimal_places=%r' % field.decimal_places)

    # Basic `default=` handling.
    if field.default is not None:
        default = field.default
        if isinstance(default, enum.Enum):
            # IntEnum passes the isinstance() below but %r is not valid source.
            default = default.value
        if isinstance(default, (str, int, float, bool)):
            args.append('default=%r' % default)
        elif not _handle_common_default(default, args, imports):
            todos.append('%s: default %r must be added by hand' %
                         (field.name, field.default))

    # Specify column-name if necessary.
    if isinstance(field, ForeignKeyField):
        default_colname = (field.name if field.name.endswith('_id')
                           else field.name + '_id')
        if field.column_name != default_colname:
            args.append('column_name=%r' % field.column_name)
        if field.on_delete: args.append('on_delete=%r' % field.on_delete)
        if field.on_update: args.append('on_update=%r' % field.on_update)
    elif field.column_name != field.name:
        args.append('column_name=%r' % field.column_name)

    return args

def _build_field(field, imports, todos, targets=None, unbound=False):
    cls = type(field)
    if cls.__module__ != 'peewee':
        imports.add('from %s import %s' % (cls.__module__, cls.__name__))

    args = _build_field_args(field, imports, todos, targets, unbound)
    return '%s(%s)' % (cls.__name__, ', '.join(args))

def _is_implicit_id(field):
    return (type(field) is AutoField and field.name == 'id' and
            field.column_name == 'id')

def _build_model(model, imports, todos, targets):
    meta = model._meta
    lines = ['class %s(Model):' % model.__name__]
    for field in meta.sorted_fields:
        if _is_implicit_id(field):
            continue
        lines.append('    %s = %s' % (
            field.name,
            _build_field(field, imports, todos, targets)))

    lines.append('    class Meta:')
    lines.append('        database = db')
    lines.append('        table_name = %r' % meta.table_name)
    if meta.schema:
        lines.append('        schema = %r' % meta.schema)
    pk = meta.primary_key
    if isinstance(pk, CompositeKey):
        lines.append('        primary_key = CompositeKey(%s)' %
                     ', '.join(repr(f) for f in pk.field_names))
    elif not pk:
        lines.append('        primary_key = False')

    indexes = []
    for index in (meta.indexes or ()):
        if isinstance(index, (list, tuple)):
            columns, unique = index
            indexes.append((tuple(columns), unique))
        else:
            idx_name = getattr(index, '_name', None) or repr(index)
            todos.append('%s: index %s must be added by hand' %
                         (meta.table_name, idx_name))
    if indexes:
        lines.append('        indexes = %r' % (tuple(indexes),))

    return lines

def _build_stub(model, fields, imports):
    # A frozen stand-in for an existing table: its name plus whichever
    # referenced columns are not the implicit id.
    meta = model._meta
    lines = ['class %s(Model):' % model.__name__]
    for field in fields:
        if isinstance(field, ForeignKeyField):
            # A pk that is itself a fk stores a plain integer.
            source = 'IntegerField(primary_key=True, column_name=%r)' % (
                field.column_name)
        else:
            source = _build_field(field, imports, [])
        lines.append('    %s = %s' % (field.name, source))
    lines.append('    class Meta:')
    lines.append('        database = db')
    lines.append('        table_name = %r' % meta.table_name)
    if meta.schema:
        lines.append('        schema = %r' % meta.schema)
    return lines

def _build_add_index(idx):
    return 'migrator.migrate(migrator.add_index(%r, %r%s))' % (
        idx.table,
        idx.columns,
        ', unique=True' if idx.unique else '')

def _block(fn, lines):
    while lines and not lines[-1]:
        lines.pop()
    if not lines:
        return 'def %s(migrator, db):\n    pass' % fn

    indented = ['    %s' % line if line else '' for line in lines]
    return 'def %s(migrator, db):\n%s' % (fn, '\n'.join(indented))


def template(diff):
    """
    Render a playhouse.schema_diff.SchemaDiff as a migration-file body.
    Fully-determined changes render as runnable code. Foreign keys
    reference a model created in the file, 'self', or a frozen stub of
    the target table. Anything else needing a definition is flagged
    with a TODO comment.
    """
    todos, imports = [], set()

    # Ensure all FK reference targets exist, either as classes or stubs.
    fks = []
    for model in diff.create_tables:
        fks.extend(f for f in model._meta.sorted_fields
                   if isinstance(f, ForeignKeyField) and
                   f.rel_model is not model)
    fks.extend(f for f in diff.add_columns
               if isinstance(f, ForeignKeyField))

    created = set(diff.create_tables)
    stubs = {}  # Existing fk target -> referenced fields, by name.
    for field in fks:
        rel = field.rel_model
        if rel in created:
            continue
        if rel not in stubs:
            stubs[rel] = {}  # A stub renders even when only its name is used.
        if not _is_implicit_id(field.rel_field):
            stubs[rel][field.rel_field.name] = field.rel_field
    targets = {model: model.__name__ for model in created | set(stubs)}

    # Build any stub models needed for FKs to resolve properly.
    plan = []
    for model in sorted(stubs, key=lambda m: m.__name__):
        fields = sorted(stubs[model].values(), key=lambda f: f._sort_key)
        up = _build_stub(model, fields, imports)
        up.append('')
        plan.append((up, []))

    # Create tables for models.
    for model in diff.create_tables:
        up = _build_model(model, imports, todos, targets)
        up.extend(['db.create_tables([%s])' % model.__name__, ''])

        meta = model._meta
        down = 'migrator.migrate(migrator.drop_table(%r%s))' % (
            meta.table_name,
            ', schema=%r' % meta.schema if meta.schema else '')
        plan.append((up, [down]))

    # Index drops here to avoid issues dropping indexed columns w/sqlite.
    dropped = set(diff.drop_columns)
    for idx in diff.drop_indexes:
        up = ['migrator.migrate(migrator.drop_index(%r, %r))' %
              (idx.table, idx.name)]
        down = []
        if idx.columns is None:
            todos.append('%s: dropped index %s (partial/expression) cannot '
                         'be restored by down()' % (idx.table, idx.name))
        elif any((idx.table, column) in dropped for column in idx.columns):
            todos.append('%s: dropped index %s cannot be restored by '
                         'down() (column dropped)' % (idx.table, idx.name))
        else:
            down.append(_build_add_index(idx))
        plan.append((up, down))

    for field in diff.add_columns:
        meta = field.model._meta
        source = _build_field(field, imports, todos, targets, unbound=True)
        if not field.null and field.default is None:
            todos.append('%s.%s: not-null column needs a default or '
                         'allow_not_null backfill' %
                         (meta.table_name, field.column_name))
        plan.append((
            ['migrator.migrate(migrator.add_column(%r, %r, %s))' %
             (meta.table_name, field.column_name, source)],
            ['migrator.migrate(migrator.drop_column(%r, %r))' %
             (meta.table_name, field.column_name)]))

    # add_column() creates the index for an index=True/unique=True field
    # itself, while `down()` drops the index before the column.
    auto_indexed = set((f.model._meta.table_name, (f.column_name,),
                        bool(f.unique))
                       for f in diff.add_columns if f.index or f.unique)
    for idx in diff.add_indexes:
        if idx.columns is None:
            todos.append('%s: create index %s (partial/expression, details '
                         'not detected)' % (idx.table, idx.name))
            continue
        up = []
        if (idx.table, idx.columns, idx.unique) not in auto_indexed:
            up.append(_build_add_index(idx))
        down = ['migrator.migrate(migrator.drop_index(%r, %r))' %
                (idx.table, make_index_name(idx.table, idx.columns))]
        plan.append((up, down))

    for table, name in diff.drop_columns:
        plan.append((['migrator.migrate(migrator.drop_column(%r, %r))' %
                      (table, name)], []))
        todos.append('%s.%s: dropped column cannot be restored by down()' %
                     (table, name))

    qualified = set(f.model._meta.table_name
                    for f in diff.add_columns if f.model._meta.schema)
    if qualified:
        todos.append('schema-qualified tables (%s): column/index '
                     'operations are emitted unqualified. Qualify by hand' %
                     ', '.join(sorted(qualified)))

    up, down = [], []
    for u, _ in plan:
        up.extend(u)
    for _, d in reversed(plan):
        down.extend(d)

    ts = datetime.datetime.now().strftime('%Y-%m-%d %H:%M')
    out = ['# Generated from a schema diff on %s.' % ts,
           'from peewee import *']

    out.extend(sorted(imports))
    out.append('')
    out.extend('# TODO: %s' % todo for todo in todos)
    if todos:
        out.append('')
    out.append(_block('up', up))
    out.append('')
    out.append('')
    out.append(_block('down', down))
    return '\n'.join(out) + '\n'


def _cwd_import(path):
    if os.getcwd() not in sys.path:
        sys.path.insert(0, os.getcwd())
    return importlib.import_module(path)


def _resolve_models(spec):
    attr = None
    if ':' in spec:
        spec, attr = spec.split(':', 1)
    module = _cwd_import(spec)
    if attr:
        obj = getattr(module, attr, None)
        if obj is None:
            raise MigrationError('"%s" not found in module "%s".'
                                 % (attr, spec))
        if is_model(obj):
            return [obj], []
        try:
            models = list(obj)
        except TypeError:
            raise MigrationError('"%s:%s" must name a Model or a list '
                                 'of Models.' % (spec, attr))
        for model in models:
            if not is_model(model):
                raise MigrationError('"%s:%s" must name a Model or a list '
                                     'of Models.' % (spec, attr))
        return models, []
    models, skipped = [], []
    for value in vars(module).values():
        if is_model(value) and value is not Model and \
           value.__module__ == module.__name__:
            fields = value._meta.sorted_fields
            if len(fields) == 1 and _is_implicit_id(fields[0]) and \
               not value._meta.indexes:
                skipped.append(value.__name__)
            else:
                models.append(value)
    if not models:
        raise MigrationError('no models found in module "%s".' % spec)
    return models, skipped


def _resolve_database(spec):
    if '://' in spec:
        from playhouse.db_url import connect
        try:
            database = connect(spec)
        except (RuntimeError, ValueError) as exc:  # Malformed url.
            raise MigrationError(str(exc))
        try:
            database.connect()
            database.close()
        except Exception as exc:
            raise MigrationError('cannot connect to "%s": %s' % (spec, exc))
        return database
    if os.path.isfile(spec):
        return SqliteDatabase(spec)
    if '.' not in spec:
        raise MigrationError('database must be given as a db url, a sqlite '
                             'filename, or a dotted path to a Database '
                             'instance.')
    module_path, attr = spec.rsplit('.', 1)
    try:
        module = _cwd_import(module_path)
    except ModuleNotFoundError as exc:
        raise MigrationError('cannot import "%s": %s' % (module_path, exc))
    obj = getattr(module, attr, None)
    if obj is None:
        raise MigrationError('"%s" not found in "%s".' % (attr, module_path))
    if isinstance(obj, Proxy):
        if obj.obj is None:
            raise MigrationError('"%s" proxy is uninitialized.' % spec)
        obj = obj.obj
    if not isinstance(obj, Database):
        raise MigrationError('"%s" did not resolve to a Database.' % spec)
    if not obj.database:
        raise MigrationError('"%s" is a deferred database. Initialize it, '
                             'or point at one that is.' % spec)
    return obj


def _resolve_diff(database, spec):
    from playhouse.schema_diff import SchemaDiff, diff_models
    models, skipped = _resolve_models(spec)
    for name in skipped:
        sys.stderr.write('skipped: %s (no fields)\n' % name)
    if database is None:  # initial: assume an empty database.
        # Virtual tables are out of scope, matching diff_models.
        accum = []
        for model in models:
            if getattr(model._meta, 'extension_module', None):
                sys.stderr.write('skipped: %s (virtual table)\n'
                                 % model.__name__)
            else:
                accum.append(model)
        return SchemaDiff(sort_models(accum), [], [], [], [])
    try:
        return diff_models(database, models)
    except ValueError as exc:
        raise MigrationError(str(exc))


def _report(verb, names):
    for name in names:
        print('%s: %s' % (verb, name))
    if not names:
        print('nothing to do.')


def _cmd_status(runner, args):
    rows = runner.status()
    for m in rows:
        if not m.applied:
            marker = ' '
        elif m.path is not None:
            marker = 'x'
        else:
            marker = '?'
        line = '[%s] %s' % (marker, m.name)
        if m.applied:
            line += '  ' + m.applied.strftime('%Y-%m-%d %H:%M:%S')
        print(line)
    # Exit 1 when pending, so status can gate a deploy.
    if any(not m.applied for m in rows):
        return 1


def _cmd_up(runner, args):
    _report('applied', runner.up(args.target))


def _cmd_down(runner, args):
    _report('reverted', runner.down(args.target))


def _cmd_fake(runner, args):
    _report('faked', runner.fake(args.target))


def _cmd_initial(runner, args):
    if not args.models:
        raise MigrationError('initial requires a models module.')
    if runner.migrations():
        raise MigrationError('migrations already exist in "%s".'
                             % args.directory)
    diff = _resolve_diff(None, args.models)
    print(runner.create('initial', body=template(diff)))


def _cmd_create(runner, args):
    print(runner.create(args.name))


def _cmd_generate(runner, args):
    if not args.models:
        raise MigrationError('generate requires a models module.')
    diff = _resolve_diff(runner.database, args.models)
    if not diff:
        print('schema matches models. Nothing to generate.')
        return
    print(runner.create(args.name, body=template(diff)))


def _cmd_diff(runner, args):
    if not args.models:
        raise MigrationError('diff requires a models module.')
    diff = _resolve_diff(runner.database, args.models)
    print(diff if diff else 'schema matches models.')


# Mirrored by the subparser declarations in _parser().
_COMMANDS = ('status', 'up', 'down', 'initial', 'create', 'generate',
             'fake', 'diff')


def _read_config(path):
    # The default dotfile is optional. A file named with -c must exist
    # (the caller checks).
    if path is None:
        path = '.pwmigrate'
        if not os.path.exists(path):
            return {}
    config = {}
    with open(path) as fh:
        for line in fh:
            line = line.strip()
            if not line or line.startswith('#'):
                continue
            key, _, value = line.partition('=')
            config[key.strip()] = value.strip()
    for key in sorted(set(config) - {'database', 'directory', 'models',
                                     'table'}):
        sys.stderr.write('warning: unknown key "%s" in %s\n' % (key, path))
    return config


def _parser(config):
    prog = os.path.basename(sys.argv[0] or '')
    if not prog.startswith('pwmigrate'):
        prog = 'python -m playhouse.migrations'
    parser = argparse.ArgumentParser(
        prog=prog, description='peewee migration runner')
    parser.add_argument('database', help='dotted path to a Database '
                        'instance (e.g. myapp.settings.db), db url (e.g. '
                        'postgres:///app), or path to a sqlite file')
    parser.add_argument('-c', '--config', metavar='FILE',
                        help='config file supplying argument defaults '
                        '(default: .pwmigrate)')

    common = argparse.ArgumentParser(add_help=False)
    common.add_argument('-d', '--directory',
                        default=config.get('directory', 'migrations'),
                        help='migrations directory (default: migrations)')
    common.add_argument('-t', '--table',
                        default=config.get('table', 'schema_migration'),
                        help='history table name')
    common.add_argument('-v', '--verbose', action='store_true',
                        help='echo SQL as it executes')

    sub = parser.add_subparsers(dest='command', metavar='command',
                                required=True)
    p = sub.add_parser('status', parents=[common],
                       help='list migrations and applied timestamps')
    p.set_defaults(func=_cmd_status)

    p = sub.add_parser('up', parents=[common],
                       help='apply pending migrations in order')
    p.add_argument('target', nargs='?', help='stop after this migration')
    p.set_defaults(func=_cmd_up)

    p = sub.add_parser('down', parents=[common],
                       help='revert the most recent migration')
    p.add_argument('target', nargs='?',
                   help='revert back through this migration')
    p.set_defaults(func=_cmd_down)

    p = sub.add_parser('initial', parents=[common],
                       help='generate the first migration, assuming an '
                       'empty database')
    p.add_argument('models', nargs='?', default=config.get('models'),
                   help='models module ("app.models" or '
                   '"app.models:MODELS")')
    p.set_defaults(func=_cmd_initial)

    p = sub.add_parser('create', parents=[common],
                       help='write a skeleton migration file')
    p.add_argument('name', help='migration name')
    p.set_defaults(func=_cmd_create)

    p = sub.add_parser('generate', parents=[common],
                       help='generate a migration from the schema diff')
    p.add_argument('name', help='migration name')
    p.add_argument('models', nargs='?', default=config.get('models'),
                   help='models module ("app.models" or '
                   '"app.models:MODELS")')
    p.set_defaults(func=_cmd_generate)

    p = sub.add_parser('fake', parents=[common],
                       help='record pending migrations without running them')
    p.add_argument('target', nargs='?', help='record through this migration')
    p.set_defaults(func=_cmd_fake)

    p = sub.add_parser('diff', parents=[common],
                       help='print schema drift against the models')
    p.add_argument('models', nargs='?', default=config.get('models'),
                   help='models module ("app.models" or '
                   '"app.models:MODELS")')
    p.set_defaults(func=_cmd_diff)
    return parser


def main(argv=None):
    if argv is None:
        argv = sys.argv[1:]
    # -c must be known before the parser is built: the config file
    # supplies argument defaults.
    pre = argparse.ArgumentParser(add_help=False)
    pre.add_argument('-c', '--config')
    known, argv = pre.parse_known_args(argv)
    if known.config and not os.path.exists(known.config):
        sys.stderr.write('error: config file "%s" not found.\n'
                         % known.config)
        return 2
    config = _read_config(known.config)

    if argv and argv[0] in _COMMANDS and not config.get('database'):
        sys.stderr.write('error: no database given and no .pwmigrate '
                         'config found.\n')
        return 2
    if config.get('database') and (not argv or argv[0] in _COMMANDS):
        argv = [config['database']] + argv

    args = _parser(config).parse_args(argv)
    if args.verbose:
        peewee_logger = logging.getLogger('peewee')
        peewee_logger.addHandler(logging.StreamHandler())
        peewee_logger.setLevel(logging.DEBUG)

    database = None
    try:
        database = _resolve_database(args.database)
        runner = Runner(database, args.directory, args.table)
        return args.func(runner, args) or 0
    except (MigrationError, DatabaseError, InterfaceError,
            ImproperlyConfigured) as exc:
        if args.verbose:
            traceback.print_exc()
        sys.stderr.write('error: %s\n' % exc)
        return 2
    finally:
        if database is not None:
            database.close()


if __name__ == '__main__':
    sys.exit(main())