from django.contrib.postgres.signals import (
    get_citext_oids, get_hstore_oids, register_type_handlers,
)
from django.db import NotSupportedError, router
from django.db.migrations import AddIndex, RemoveIndex
from django.db.migrations.operations.base import Operation


class CreateExtension(Operation):
    reversible = True

    def __init__(self, name):
        self.name = name

    def state_forwards(self, app_label, state):
        pass

    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        if (
            schema_editor.connection.vendor != 'postgresql' or
            not router.allow_migrate(schema_editor.connection.alias, app_label)
        ):
            return
        if not self.extension_exists(schema_editor, self.name):
            schema_editor.execute(
                'CREATE EXTENSION IF NOT EXISTS %s' % schema_editor.quote_name(self.name)
            )
        # Clear cached, stale oids.
        get_hstore_oids.cache_clear()
        get_citext_oids.cache_clear()
        # Registering new type handlers cannot be done before the extension is
        # installed, otherwise a subsequent data migration would use the same
        # connection.
        register_type_handlers(schema_editor.connection)

    def database_backwards(self, app_label, schema_editor, from_state, to_state):
        if not router.allow_migrate(schema_editor.connection.alias, app_label):
            return
        if self.extension_exists(schema_editor, self.name):
            schema_editor.execute(
                'DROP EXTENSION IF EXISTS %s' % schema_editor.quote_name(self.name)
            )
        # Clear cached, stale oids.
        get_hstore_oids.cache_clear()
        get_citext_oids.cache_clear()

    def extension_exists(self, schema_editor, extension):
        with schema_editor.connection.cursor() as cursor:
            cursor.execute(
                'SELECT 1 FROM pg_extension WHERE extname = %s',
                [extension],
            )
            return bool(cursor.fetchone())

    def describe(self):
        return "Creates extension %s" % self.name

    @property
    def migration_name_fragment(self):
        return 'create_extension_%s' % self.name


class BloomExtension(CreateExtension):

    def __init__(self):
        self.name = 'bloom'


class BtreeGinExtension(CreateExtension):

    def __init__(self):
        self.name = 'btree_gin'


class BtreeGistExtension(CreateExtension):

    def __init__(self):
        self.name = 'btree_gist'


class CITextExtension(CreateExtension):

    def __init__(self):
        self.name = 'citext'


class CryptoExtension(CreateExtension):

    def __init__(self):
        self.name = 'pgcrypto'


class HStoreExtension(CreateExtension):

    def __init__(self):
        self.name = 'hstore'


class TrigramExtension(CreateExtension):

    def __init__(self):
        self.name = 'pg_trgm'


class UnaccentExtension(CreateExtension):

    def __init__(self):
        self.name = 'unaccent'


class NotInTransactionMixin:
    def _ensure_not_in_transaction(self, schema_editor):
        if schema_editor.connection.in_atomic_block:
            raise NotSupportedError(
                'The %s operation cannot be executed inside a transaction '
                '(set atomic = False on the migration).'
                % self.__class__.__name__
            )


class AddIndexConcurrently(NotInTransactionMixin, AddIndex):
    """Create an index using PostgreSQL's CREATE INDEX CONCURRENTLY syntax."""
    atomic = False

    def describe(self):
        return 'Concurrently create index %s on field(s) %s of model %s' % (
            self.index.name,
            ', '.join(self.index.fields),
            self.model_name,
        )

    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        self._ensure_not_in_transaction(schema_editor)
        model = to_state.apps.get_model(app_label, self.model_name)
        if self.allow_migrate_model(schema_editor.connection.alias, model):
            schema_editor.add_index(model, self.index, concurrently=True)

    def database_backwards(self, app_label, schema_editor, from_state, to_state):
        self._ensure_not_in_transaction(schema_editor)
        model = from_state.apps.get_model(app_label, self.model_name)
        if self.allow_migrate_model(schema_editor.connection.alias, model):
            schema_editor.remove_index(model, self.index, concurrently=True)


class RemoveIndexConcurrently(NotInTransactionMixin, RemoveIndex):
    """Remove an index using PostgreSQL's DROP INDEX CONCURRENTLY syntax."""
    atomic = False

    def describe(self):
        return 'Concurrently remove index %s from %s' % (self.name, self.model_name)

    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        self._ensure_not_in_transaction(schema_editor)
        model = from_state.apps.get_model(app_label, self.model_name)
        if self.allow_migrate_model(schema_editor.connection.alias, model):
            from_model_state = from_state.models[app_label, self.model_name_lower]
            index = from_model_state.get_index_by_name(self.name)
            schema_editor.remove_index(model, index, concurrently=True)

    def database_backwards(self, app_label, schema_editor, from_state, to_state):
        self._ensure_not_in_transaction(schema_editor)
        model = to_state.apps.get_model(app_label, self.model_name)
        if self.allow_migrate_model(schema_editor.connection.alias, model):
            to_model_state = to_state.models[app_label, self.model_name_lower]
            index = to_model_state.get_index_by_name(self.name)
            schema_editor.add_index(model, index, concurrently=True)