from django.core.exceptions import ImproperlyConfigured
from django.core.management.base import BaseCommand, CommandError
from django.core import serializers
from django.db import connections, DEFAULT_DB_ALIAS
from django.utils.datastructures import SortedDict

from optparse import make_option

class Command(BaseCommand):
    option_list = BaseCommand.option_list + (
        make_option('--format', default='json', dest='format',
            help='Specifies the output serialization format for fixtures.'),
        make_option('--indent', default=None, dest='indent', type='int',
            help='Specifies the indent level to use when pretty-printing output'),
        make_option('--database', action='store', dest='database',
            default=DEFAULT_DB_ALIAS, help='Nominates a specific database to load '
                'fixtures into. Defaults to the "default" database.'),
        make_option('-e', '--exclude', dest='exclude',action='append', default=[],
            help='App to exclude (use multiple --exclude to exclude multiple apps).'),
        make_option('-n', '--natural', action='store_true', dest='use_natural_keys', default=False,
            help='Use natural keys if they are available.'),
    )
    help = 'Output the contents of the database as a fixture of the given format.'
    args = '[appname ...]'

    def handle(self, *app_labels, **options):
        from django.db.models import get_app, get_apps, get_models, get_model

        format = options.get('format','json')
        indent = options.get('indent',None)
        using = options.get('database', DEFAULT_DB_ALIAS)
        connection = connections[using]
        exclude = options.get('exclude',[])
        show_traceback = options.get('traceback', False)
        use_natural_keys = options.get('use_natural_keys', False)

        excluded_apps = set(get_app(app_label) for app_label in exclude)

        if len(app_labels) == 0:
            app_list = SortedDict((app, None) for app in get_apps() if app not in excluded_apps)
        else:
            app_list = SortedDict()
            for label in app_labels:
                try:
                    app_label, model_label = label.split('.')
                    try:
                        app = get_app(app_label)
                    except ImproperlyConfigured:
                        raise CommandError("Unknown application: %s" % app_label)

                    model = get_model(app_label, model_label)
                    if model is None:
                        raise CommandError("Unknown model: %s.%s" % (app_label, model_label))

                    if app in app_list.keys():
                        if app_list[app] and model not in app_list[app]:
                            app_list[app].append(model)
                    else:
                        app_list[app] = [model]
                except ValueError:
                    # This is just an app - no model qualifier
                    app_label = label
                    try:
                        app = get_app(app_label)
                    except ImproperlyConfigured:
                        raise CommandError("Unknown application: %s" % app_label)
                    app_list[app] = None

        # Check that the serialization format exists; this is a shortcut to
        # avoid collating all the objects and _then_ failing.
        if format not in serializers.get_public_serializer_formats():
            raise CommandError("Unknown serialization format: %s" % format)

        try:
            serializers.get_serializer(format)
        except KeyError:
            raise CommandError("Unknown serialization format: %s" % format)

        # Now collate the objects to be serialized.
        objects = []
        for model in sort_dependencies(app_list.items()):
            if not model._meta.proxy:
                objects.extend(model._default_manager.using(using).all())

        try:
            return serializers.serialize(format, objects, indent=indent,
                        use_natural_keys=use_natural_keys)
        except Exception, e:
            if show_traceback:
                raise
            raise CommandError("Unable to serialize database: %s" % e)

def sort_dependencies(app_list):
    """Sort a list of app,modellist pairs into a single list of models.

    The single list of models is sorted so that any model with a natural key
    is serialized before a normal model, and any model with a natural key
    dependency has it's dependencies serialized first.
    """
    from django.db.models import get_model, get_models
    # Process the list of models, and get the list of dependencies
    model_dependencies = []
    models = set()
    for app, model_list in app_list:
        if model_list is None:
            model_list = get_models(app)

        for model in model_list:
            models.add(model)
            # Add any explicitly defined dependencies
            if hasattr(model, 'natural_key'):
                deps = getattr(model.natural_key, 'dependencies', [])
                if deps:
                    deps = [get_model(*d.split('.')) for d in deps]
            else:
                deps = []

            # Now add a dependency for any FK or M2M relation with
            # a model that defines a natural key
            for field in model._meta.fields:
                if hasattr(field.rel, 'to'):
                    rel_model = field.rel.to
                    if hasattr(rel_model, 'natural_key'):
                        deps.append(rel_model)
            for field in model._meta.many_to_many:
                rel_model = field.rel.to
                if hasattr(rel_model, 'natural_key'):
                    deps.append(rel_model)
            model_dependencies.append((model, deps))

    model_dependencies.reverse()
    # Now sort the models to ensure that dependencies are met. This
    # is done by repeatedly iterating over the input list of models.
    # If all the dependencies of a given model are in the final list,
    # that model is promoted to the end of the final list. This process
    # continues until the input list is empty, or we do a full iteration
    # over the input models without promoting a model to the final list.
    # If we do a full iteration without a promotion, that means there are
    # circular dependencies in the list.
    model_list = []
    while model_dependencies:
        skipped = []
        changed = False
        while model_dependencies:
            model, deps = model_dependencies.pop()

            # If all of the models in the dependency list are either already
            # on the final model list, or not on the original serialization list,
            # then we've found another model with all it's dependencies satisfied.
            found = True
            for candidate in ((d not in models or d in model_list) for d in deps):
                if not candidate:
                    found = False
            if found:
                model_list.append(model)
                changed = True
            else:
                skipped.append((model, deps))
        if not changed:
            raise CommandError("Can't resolve dependencies for %s in serialized app list." %
                ', '.join('%s.%s' % (model._meta.app_label, model._meta.object_name)
                for model, deps in sorted(skipped, key=lambda obj: obj[0].__name__))
            )
        model_dependencies = skipped

    return model_list