#!/usr/bin/env python
"""Cron management classes."""


import logging
import random
import threading
import time

from grr import config
from grr.lib import rdfvalue
from grr.lib import registry
from grr.lib import stats
from grr.lib import utils
from grr.lib.rdfvalues import cronjobs as rdf_cronjobs
from grr.lib.rdfvalues import flows as rdf_flows
from grr.lib.rdfvalues import protodict as rdf_protodict
from grr.lib.rdfvalues import structs as rdf_structs
from grr.proto import flows_pb2

from grr.server import access_control
from grr.server import aff4
from grr.server import flow
from grr.server import master

from grr.server import queue_manager


class Error(Exception):
  pass


class CreateCronJobFlowArgs(rdf_structs.RDFProtoStruct):
  protobuf = flows_pb2.CreateCronJobFlowArgs
  rdf_deps = [
      rdfvalue.Duration,
      rdf_flows.FlowRunnerArgs,
      rdfvalue.RDFDatetime,
  ]

  def GetFlowArgsClass(self):
    if self.flow_runner_args.flow_name:
      flow_cls = flow.GRRFlow.classes.get(self.flow_runner_args.flow_name)
      if flow_cls is None:
        raise ValueError("Flow '%s' not known by this implementation." %
                         self.flow_runner_args.flow_name)

      # The required protobuf for this class is in args_type.
      return flow_cls.args_type


class CronManager(object):
  """CronManager is used to schedule/terminate cron jobs."""

  CRON_JOBS_PATH = rdfvalue.RDFURN("aff4:/cron")

  def ScheduleFlow(self,
                   cron_args=None,
                   job_name=None,
                   token=None,
                   disabled=False):
    """Creates a cron job that runs given flow with a given frequency.

    Args:
      cron_args: A protobuf of type CreateCronJobFlowArgs.

      job_name: Use this job_name instead of an autogenerated unique name (used
                for system cron jobs - we want them to have well-defined
                persistent name).

      token: Security token used for data store access.

      disabled: If True, the job object will be created, but will be disabled.

    Returns:
      URN of the cron job created.
    """
    if not job_name:
      uid = utils.PRNG.GetUShort()
      job_name = "%s_%s" % (cron_args.flow_runner_args.flow_name, uid)

    cron_job_urn = self.CRON_JOBS_PATH.Add(job_name)
    with aff4.FACTORY.Create(
        cron_job_urn,
        aff4_type=CronJob,
        mode="rw",
        token=token,
        force_new_version=False) as cron_job:

      # If the cronjob was already present we don't want to overwrite the
      # original start_time.
      existing_cron_args = cron_job.Get(cron_job.Schema.CRON_ARGS)
      if existing_cron_args and existing_cron_args.start_time:
        cron_args.start_time = existing_cron_args.start_time

      if cron_args != existing_cron_args:
        cron_job.Set(cron_job.Schema.CRON_ARGS(cron_args))

      if disabled != cron_job.Get(cron_job.Schema.DISABLED):
        cron_job.Set(cron_job.Schema.DISABLED(disabled))

    return cron_job_urn

  def ListJobs(self, token=None):
    """Returns a generator of URNs of all currently running cron jobs."""
    return aff4.FACTORY.Open(self.CRON_JOBS_PATH, token=token).ListChildren()

  def EnableJob(self, job_urn, token=None):
    """Enable cron job with the given URN."""
    cron_job = aff4.FACTORY.Open(
        job_urn, mode="rw", aff4_type=CronJob, token=token)
    cron_job.Set(cron_job.Schema.DISABLED(0))
    cron_job.Close()

  def DisableJob(self, job_urn, token=None):
    """Disable cron job with the given URN."""
    cron_job = aff4.FACTORY.Open(
        job_urn, mode="rw", aff4_type=CronJob, token=token)
    cron_job.Set(cron_job.Schema.DISABLED(1))
    cron_job.Close()

  def DeleteJob(self, job_urn, token=None):
    """Deletes cron job with the given URN."""
    aff4.FACTORY.Delete(job_urn, token=token)

  def RunOnce(self, token=None, force=False, urns=None):
    """Tries to lock and run cron jobs.

    Args:
      token: security token
      force: If True, force a run
      urns: List of URNs to run.  If unset, run them all
    """
    urns = urns or self.ListJobs(token=token)
    for cron_job_urn in urns:
      try:

        with aff4.FACTORY.OpenWithLock(
            cron_job_urn, blocking=False, token=token,
            lease_time=600) as cron_job:
          try:
            logging.info("Running cron job: %s", cron_job.urn)
            cron_job.Run(force=force)
          except Exception as e:  # pylint: disable=broad-except
            logging.exception("Error processing cron job %s: %s", cron_job.urn,
                              e)
            stats.STATS.IncrementCounter("cron_internal_error")

      except aff4.LockError:
        pass


CRON_MANAGER = CronManager()


class SystemCronFlow(flow.GRRFlow):
  """SystemCronFlows are scheduled automatically on workers startup."""

  frequency = rdfvalue.Duration("1d")
  lifetime = rdfvalue.Duration("20h")
  allow_overruns = False

  # By default we randomize the start time of system cron flows between 0 and
  # 'frequency' seconds after it is first created. This only affects the very
  # first run, after which they will run at 'frequency' intervals. Disable this
  # behaviour by setting start_time_randomization = False.
  start_time_randomization = True

  # Jobs that are broken, or are under development can be disabled using
  # the "disabled" attribute. These jobs won't get scheduled automatically,
  # and will get paused if they were scheduled before.
  disabled = False

  __abstract = True  # pylint: disable=g-bad-name

  def _ValidateState(self):
    # For normal flows it's a bug to write an empty state, here it's ok.
    pass


class StateReadError(Error):
  pass


class StateWriteError(Error):
  pass


class StatefulSystemCronFlow(SystemCronFlow):
  """SystemCronFlow that keeps a permanent state between iterations."""

  __abstract = True

  @property
  def cron_job_urn(self):
    return CRON_MANAGER.CRON_JOBS_PATH.Add(self.__class__.__name__)

  def ReadCronState(self):
    try:
      cron_job = aff4.FACTORY.Open(
          self.cron_job_urn, aff4_type=CronJob, token=self.token)
      res = cron_job.Get(cron_job.Schema.STATE_DICT)
      if res:
        return flow.AttributedDict(res.ToDict())
      return flow.AttributedDict()
    except aff4.InstantiationError as e:
      raise StateReadError(e)

  def WriteCronState(self, state):
    try:
      with aff4.FACTORY.OpenWithLock(
          self.cron_job_urn, aff4_type=CronJob, token=self.token) as cron_job:
        cron_job.Set(cron_job.Schema.STATE_DICT(state))
    except aff4.InstantiationError as e:
      raise StateWriteError(e)


def GetStartTime(cron_cls):
  """Get start time for a SystemCronFlow class.

  If start_time_randomization is True in the class, randomise the start
  time to be between now and (now + frequency)

  Args:
    cron_cls: SystemCronFlow class
  Returns:
    rdfvalue.RDFDatetime
  """
  if not cron_cls.start_time_randomization:
    return rdfvalue.RDFDatetime.Now()

  now = rdfvalue.RDFDatetime.Now()
  window_ms = cron_cls.frequency.microseconds

  start_time_ms = random.randint(now.AsMicroSecondsFromEpoch(),
                                 now.AsMicroSecondsFromEpoch() + window_ms)
  return rdfvalue.RDFDatetime(start_time_ms)


def ScheduleSystemCronFlows(names=None, token=None):
  """Schedule all the SystemCronFlows found."""

  for name in config.CONFIG["Cron.disabled_system_jobs"]:
    try:
      cls = flow.GRRFlow.classes[name]
    except KeyError:
      raise KeyError("No such flow: %s." % name)

    if not aff4.issubclass(cls, SystemCronFlow):
      raise ValueError("Disabled system cron job name doesn't correspond to "
                       "a flow inherited from SystemCronFlow: %s" % name)

  if names is None:
    names = flow.GRRFlow.classes.keys()

  for name in names:
    cls = flow.GRRFlow.classes[name]

    if aff4.issubclass(cls, SystemCronFlow):
      cron_args = CreateCronJobFlowArgs(periodicity=cls.frequency)
      cron_args.flow_runner_args.flow_name = name
      cron_args.lifetime = cls.lifetime
      cron_args.allow_overruns = cls.allow_overruns
      cron_args.start_time = GetStartTime(cls)

      if cls.disabled:
        disabled = True
      else:
        disabled = name in config.CONFIG["Cron.disabled_system_jobs"]

      CRON_MANAGER.ScheduleFlow(
          cron_args=cron_args, job_name=name, token=token, disabled=disabled)


class CronWorker(object):
  """CronWorker runs a thread that periodically executes cron jobs."""

  def __init__(self, thread_name="grr_cron", sleep=60 * 5):
    self.thread_name = thread_name
    self.sleep = sleep

    # SetUID is required to write cronjobs under aff4:/cron/
    self.token = access_control.ACLToken(
        username="GRRCron", reason="Implied.").SetUID()

  def _RunLoop(self):
    ScheduleSystemCronFlows(token=self.token)

    while True:
      if not master.MASTER_WATCHER.IsMaster():
        time.sleep(self.sleep)
        continue
      try:
        CRON_MANAGER.RunOnce(token=self.token)
      except Exception as e:  # pylint: disable=broad-except
        logging.error("CronWorker uncaught exception: %s", e)

      time.sleep(self.sleep)

  def Run(self):
    """Runs a working thread and waits for it to finish."""
    self.RunAsync().join()

  def RunAsync(self):
    """Runs a working thread and returns immediately."""
    self.running_thread = threading.Thread(
        name=self.thread_name, target=self._RunLoop)
    self.running_thread.daemon = True
    self.running_thread.start()
    return self.running_thread


class CronJob(aff4.AFF4Volume):
  """AFF4 object corresponding to cron jobs."""

  class SchemaCls(aff4.AFF4Volume.SchemaCls):
    """Schema for CronJob AFF4 object."""
    CRON_ARGS = aff4.Attribute("aff4:cron/args", CreateCronJobFlowArgs,
                               "This cron jobs' arguments.")

    DISABLED = aff4.Attribute(
        "aff4:cron/disabled",
        rdfvalue.RDFBool,
        "If True, don't run this job.",
        versioned=False)

    CURRENT_FLOW_URN = aff4.Attribute(
        "aff4:cron/current_flow_urn",
        rdfvalue.RDFURN,
        "URN of the currently running flow corresponding to this cron job.",
        versioned=False,
        lock_protected=True)

    LAST_RUN_TIME = aff4.Attribute(
        "aff4:cron/last_run",
        rdfvalue.RDFDatetime,
        "The last time this cron job ran.",
        "last_run",
        versioned=False,
        lock_protected=True)

    LAST_RUN_STATUS = aff4.Attribute(
        "aff4:cron/last_run_status",
        rdf_cronjobs.CronJobRunStatus,
        "Result of the last flow",
        lock_protected=True,
        creates_new_object_version=False)

    STATE_DICT = aff4.Attribute(
        "aff4:cron/state_dict",
        rdf_protodict.AttributedDict,
        "Cron flow state that is kept between iterations",
        lock_protected=True,
        versioned=False)

  def DeleteJobFlows(self, age=None):
    """Deletes flows initiated by the job that are older than specified."""
    if age is None:
      raise ValueError("age can't be None")

    child_flows = list(self.ListChildren(age=age))
    with queue_manager.QueueManager(token=self.token) as queuemanager:
      queuemanager.MultiDestroyFlowStates(child_flows)

    aff4.FACTORY.MultiDelete(child_flows, token=self.token)

  def IsRunning(self):
    """Returns True if there's a currently running iteration of this job."""
    current_urn = self.Get(self.Schema.CURRENT_FLOW_URN)
    if current_urn:
      try:
        current_flow = aff4.FACTORY.Open(
            urn=current_urn, aff4_type=flow.GRRFlow, token=self.token, mode="r")
      except aff4.InstantiationError:
        # This isn't a flow, something went really wrong, clear it out.
        self.DeleteAttribute(self.Schema.CURRENT_FLOW_URN)
        self.Flush()
        return False

      runner = current_flow.GetRunner()
      return runner.context.state == rdf_flows.FlowContext.State.RUNNING
    return False

  def DueToRun(self):
    """Called periodically by the cron daemon, if True Run() will be called.

    Returns:
        True if it is time to run based on the specified frequency.
    """
    if self.Get(self.Schema.DISABLED):
      return False

    cron_args = self.Get(self.Schema.CRON_ARGS)
    last_run_time = self.Get(self.Schema.LAST_RUN_TIME)
    now = rdfvalue.RDFDatetime.Now()

    # Its time to run.
    if (last_run_time is None or
        now > cron_args.periodicity.Expiry(last_run_time)):

      # Not due to start yet.
      if now < cron_args.start_time:
        return False

      # Do we allow overruns?
      if cron_args.allow_overruns:
        return True

      # No currently executing job - lets go.
      if self.Get(self.Schema.CURRENT_FLOW_URN) is None:
        return True

    return False

  def StopCurrentRun(self, reason="Cron lifetime exceeded.", force=True):
    current_flow_urn = self.Get(self.Schema.CURRENT_FLOW_URN)
    if current_flow_urn:
      flow.GRRFlow.TerminateFlow(
          current_flow_urn, reason=reason, force=force, token=self.token)
      self.Set(
          self.Schema.LAST_RUN_STATUS,
          rdf_cronjobs.CronJobRunStatus(
              status=rdf_cronjobs.CronJobRunStatus.Status.TIMEOUT))
      self.DeleteAttribute(self.Schema.CURRENT_FLOW_URN)
      self.Flush()

  def KillOldFlows(self):
    """Disable cron flow if it has exceeded CRON_ARGS.lifetime.

    Returns:
      bool: True if the flow is was killed, False if it is still alive
    """
    if self.IsRunning():
      start_time = self.Get(self.Schema.LAST_RUN_TIME)
      lifetime = self.Get(self.Schema.CRON_ARGS).lifetime
      elapsed = time.time() - start_time.AsSecondsFromEpoch()

      if lifetime and elapsed > lifetime.seconds:
        self.StopCurrentRun()
        stats.STATS.IncrementCounter(
            "cron_job_timeout", fields=[self.urn.Basename()])
        stats.STATS.RecordEvent(
            "cron_job_latency", elapsed, fields=[self.urn.Basename()])
        return True

    return False

  def Run(self, force=False):
    """Do the actual work of the Cron. Will first check if DueToRun is True.

    CronJob object must be locked (i.e. opened via OpenWithLock) for Run() to be
    called.

    Args:
      force: If True, the job will run no matter what (i.e. even if DueToRun()
             returns False).

    Raises:
      LockError: if the object is not locked.
    """
    if not self.locked:
      raise aff4.LockError("CronJob must be locked for Run() to be called.")

    self.KillOldFlows()

    # If currently running flow has finished, update our state.
    current_flow_urn = self.Get(self.Schema.CURRENT_FLOW_URN)
    if current_flow_urn:
      current_flow = aff4.FACTORY.Open(current_flow_urn, token=self.token)
      runner = current_flow.GetRunner()
      if not runner.IsRunning():
        if runner.context.state == rdf_flows.FlowContext.State.ERROR:
          self.Set(
              self.Schema.LAST_RUN_STATUS,
              rdf_cronjobs.CronJobRunStatus(
                  status=rdf_cronjobs.CronJobRunStatus.Status.ERROR))
          stats.STATS.IncrementCounter(
              "cron_job_failure", fields=[self.urn.Basename()])
        else:
          self.Set(
              self.Schema.LAST_RUN_STATUS,
              rdf_cronjobs.CronJobRunStatus(
                  status=rdf_cronjobs.CronJobRunStatus.Status.OK))

          start_time = self.Get(self.Schema.LAST_RUN_TIME)
          elapsed = time.time() - start_time.AsSecondsFromEpoch()
          stats.STATS.RecordEvent(
              "cron_job_latency", elapsed, fields=[self.urn.Basename()])

        self.DeleteAttribute(self.Schema.CURRENT_FLOW_URN)
        self.Flush()

    if not force and not self.DueToRun():
      return

    # Make sure the flow is created with cron job as a parent folder.
    cron_args = self.Get(self.Schema.CRON_ARGS)
    cron_args.flow_runner_args.base_session_id = self.urn

    flow_urn = flow.GRRFlow.StartFlow(
        runner_args=cron_args.flow_runner_args,
        args=cron_args.flow_args,
        token=self.token,
        sync=False)

    self.Set(self.Schema.CURRENT_FLOW_URN, flow_urn)
    self.Set(self.Schema.LAST_RUN_TIME, rdfvalue.RDFDatetime.Now())
    self.Flush()


class CronHook(registry.InitHook):

  pre = [aff4.AFF4InitHook, master.MasterInit]

  def RunOnce(self):
    """Main CronHook method."""
    stats.STATS.RegisterCounterMetric("cron_internal_error")
    stats.STATS.RegisterCounterMetric(
        "cron_job_failure", fields=[("cron_job_name", str)])
    stats.STATS.RegisterCounterMetric(
        "cron_job_timeout", fields=[("cron_job_name", str)])
    stats.STATS.RegisterEventMetric(
        "cron_job_latency", fields=[("cron_job_name", str)])

    # Start the cron thread if configured to.
    if config.CONFIG["Cron.active"]:

      self.cron_worker = CronWorker()
      self.cron_worker.RunAsync()
