import json
import logging
import uuid

from abc import ABCMeta, abstractmethod, abstractproperty
from datetime import datetime
from six import add_metaclass

from alembic import op
from sqlalchemy import text

from util.abchelpers import nooper

logger = logging.getLogger(__name__)

def escape_table_name(table_name):
  if op.get_bind().engine.name == 'postgresql':
    # Needed for the `user` table.
    return '"%s"' % table_name

  return table_name


class DataTypes(object):
  @staticmethod
  def DateTime():
    return datetime.now()

  @staticmethod
  def Date():
    return datetime.now()

  @staticmethod
  def String():
    return 'somestringvalue'

  @staticmethod
  def Token():
    return '%s%s' % ('a' * 60, 'b' * 60)

  @staticmethod
  def UTF8Char():
    return 'some other value'

  @staticmethod
  def UUID():
    return str(uuid.uuid4())

  @staticmethod
  def JSON():
    return json.dumps(dict(foo='bar', baz='meh'))

  @staticmethod
  def Boolean():
    if op.get_bind().engine.name == 'postgresql':
      return True

    return 1

  @staticmethod
  def BigInteger():
    return 21474836470

  @staticmethod
  def Integer():
    return 42

  @staticmethod
  def Constant(value):
    def get_value():
      return value
    return get_value

  @staticmethod
  def Foreign(table_name):
    def get_index():
      result = op.get_bind().execute("SELECT id FROM %s LIMIT 1" % escape_table_name(table_name))
      try:
        return list(result)[0][0]
      except IndexError:
        raise Exception('Could not find row for table %s' % table_name)
      finally:
        result.close()

    return get_index


@add_metaclass(ABCMeta)
class MigrationTester(object):
  """ Implements an interface for adding testing capabilities to the
      data model migration system in Alembic.
  """
  TestDataType = DataTypes

  @abstractproperty
  def is_testing(self):
    """ Returns whether we are currently under a migration test. """

  @abstractmethod
  def populate_table(self, table_name, fields):
    """ Called to populate a table with the given fields filled in with testing data. """

  @abstractmethod
  def populate_column(self, table_name, col_name, field_type):
    """ Called to populate a column in a table to be filled in with testing data. """


@nooper
class NoopTester(MigrationTester):
  """ No-op version of the tester, designed for production workloads. """


class PopulateTestDataTester(MigrationTester):
  @property
  def is_testing(self):
    return True

  def populate_table(self, table_name, fields):
    columns = {field_name: field_type() for field_name, field_type in fields}
    field_name_vars = [':' + field_name for field_name, _ in fields]

    if op.get_bind().engine.name == 'postgresql':
      field_names = ["%s" % field_name for field_name, _ in fields]
    else:
      field_names = ["`%s`" % field_name for field_name, _ in fields]

    table_name = escape_table_name(table_name)
    query = text('INSERT INTO %s (%s) VALUES (%s)' % (table_name, ', '.join(field_names),
                                                      ', '.join(field_name_vars)))
    logger.info("Executing test query %s with values %s", query, columns.values())
    op.get_bind().execute(query, **columns)

  def populate_column(self, table_name, col_name, field_type):
    col_value = field_type()
    row_id = DataTypes.Foreign(table_name)()

    table_name = escape_table_name(table_name)
    update_text = text("UPDATE %s SET %s=:col_value where ID=:row_id" % (table_name, col_name))
    logger.info("Executing test query %s with value %s on row %s", update_text, col_value, row_id)
    op.get_bind().execute(update_text, col_value=col_value, row_id=row_id)