import boto.rds2
import logging

from auth.permissions import SuperUserPermission
from flask import session
from health.services import check_all_services

logger = logging.getLogger(__name__)


def get_healthchecker(app, config_provider, instance_keys):
  """ Returns a HealthCheck instance for the given app. """
  return HealthCheck.get_checker(app, config_provider, instance_keys)


class HealthCheck(object):
  def __init__(self, app, config_provider, instance_keys, instance_skips=None):
    self.app = app
    self.config_provider = config_provider
    self.instance_keys = instance_keys
    self.instance_skips = instance_skips or []

  def check_instance(self):
    """
    Conducts a check on this specific instance, returning a dict representing the HealthCheck
    output and a number indicating the health check response code.
    """
    service_statuses = check_all_services(self.app, self.instance_skips)
    return self.get_instance_health(service_statuses)

  def check_endtoend(self):
    """
    Conducts a check on all services, returning a dict representing the HealthCheck
    output and a number indicating the health check response code.
    """
    service_statuses = check_all_services(self.app, [])
    return self.calculate_overall_health(service_statuses)

  def get_instance_health(self, service_statuses):
    """
    For the given service statuses, returns a dict representing the HealthCheck
    output and a number indicating the health check response code. By default,
    this simply ensures that all services are reporting as healthy.
    """
    return self.calculate_overall_health(service_statuses)

  def calculate_overall_health(self, service_statuses, skip=None, notes=None):
    """ Returns true if and only if all the given service statuses report as healthy. """
    is_healthy = True
    notes = notes or []

    service_statuses_bools = {}
    service_status_expanded = {}

    for service_name in service_statuses:
      status, message = service_statuses[service_name]

      service_statuses_bools[service_name] = status
      service_status_expanded[service_name] = {
        'status': status,
      }

      if not status:
        service_status_expanded[service_name]['failure'] = message
      elif message:
        service_status_expanded[service_name]['message'] = message

      if skip and service_name in skip:
        notes.append('%s skipped in compute health' % service_name)
        continue

      is_healthy = is_healthy and status

    data = {
      'services': service_statuses_bools,
    }

    add_debug_information = SuperUserPermission().can() or session.get('health_debug', False)
    if add_debug_information:
      data.update({
        'services_expanded': service_status_expanded,
        'notes': notes,
        'is_testing': self.app.config['TESTING'],
        'config_provider': self.config_provider.provider_id,
        'local_service_key_id': self.instance_keys.local_key_id,
      })

    return (data, 200 if is_healthy else 503)

  @classmethod
  def get_checker(cls, app, config_provider, instance_keys):
    name = app.config['HEALTH_CHECKER'][0]
    parameters = app.config['HEALTH_CHECKER'][1] or {}

    for subc in cls.__subclasses__():
      if name in subc.check_names():
        return subc(app, config_provider, instance_keys, **parameters)

    raise Exception('Unknown health check with name %s' % name)


class LocalHealthCheck(HealthCheck):
  def __init__(self, app, config_provider, instance_keys):
    super(LocalHealthCheck, self).__init__(app, config_provider, instance_keys, [
      'redis', 'storage'])

  @classmethod
  def check_names(cls):
    return ['LocalHealthCheck']


class RDSAwareHealthCheck(HealthCheck):
  def __init__(self, app, config_provider, instance_keys, access_key, secret_key,
               db_instance='quay', region='us-east-1'):
    super(RDSAwareHealthCheck, self).__init__(app, config_provider, instance_keys, [
      'redis', 'storage'])

    self.access_key = access_key
    self.secret_key = secret_key
    self.db_instance = db_instance
    self.region = region

  @classmethod
  def check_names(cls):
    return ['RDSAwareHealthCheck', 'ProductionHealthCheck']

  def get_instance_health(self, service_statuses):
    # Note: We skip the redis check because if redis is down, we don't want ELB taking the
    # machines out of service. Redis is not considered a high avaliability-required service.
    skip = []
    notes = []

    # If the database is marked as unhealthy, check the status of RDS directly. If RDS is
    # reporting as available, then the problem is with this instance. Otherwise, the problem is
    # with RDS, and so we skip the DB status so we can keep this machine as 'healthy'.
    db_healthy = service_statuses['database']
    if not db_healthy:
      rds_status = self._get_rds_status()
      notes.append('DB reports unhealthy; RDS status: %s' % rds_status)

      # If the RDS is in any state but available, then we skip the DB check since it will
      # fail and bring down the instance.
      if rds_status != 'available':
        skip.append('database')

    return self.calculate_overall_health(service_statuses, skip=skip, notes=notes)

  def _get_rds_status(self):
    """ Returns the status of the RDS instance as reported by AWS. """
    try:
      region = boto.rds2.connect_to_region(self.region, aws_access_key_id=self.access_key,
                                           aws_secret_access_key=self.secret_key)

      response = region.describe_db_instances()['DescribeDBInstancesResponse']
      result = response['DescribeDBInstancesResult']
      instances = [
        i for i in result['DBInstances'] if i['DBInstanceIdentifier'] == self.db_instance]
      if not instances:
        return 'error'

      status = instances[0]['DBInstanceStatus']
      return status
    except:
      logger.exception("Exception while checking RDS status")
      return 'error'