# Copyright 2006 Google LLC. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Container of APIProxy stubs for more convenient unittesting.

Classes/variables/functions defined here:
  APIProxyStubMap: container of APIProxy stubs.
  apiproxy: global instance of an APIProxyStubMap.
  MakeSyncCall: APIProxy entry point.
  UserRPC: User-visible class wrapping asynchronous RPCs.
"""


# WARNING: This file is externally viewable by our users.  All comments from
# this file will be stripped.  The docstrings will NOT.  Do not put sensitive
# information in docstrings.  If you must communicate internal information in
# this source file, please use comments.


from __future__ import absolute_import

import inspect
import sys
import threading

from googlecloudsdk.appengine.api import apiproxy_rpc
from googlecloudsdk.appengine.runtime import apiproxy_errors


def CreateRPC(service, stubmap=None):
  """Creates a RPC instance for the given service.

  The instance is suitable for talking to remote services.
  Each RPC instance can be used only once, and should not be reused.

  Args:
    service: string representing which service to call.
    stubmap: optional APIProxyStubMap instance, for dependency injection.

  Returns:
    the rpc object.

  Raises:
    AssertionError or RuntimeError if the stub for service doesn't supply a
    CreateRPC method.
  """
  if stubmap is None:
    stubmap = apiproxy
  stub = stubmap.GetStub(service)
  assert stub, 'No api proxy found for service "%s"' % service
  assert hasattr(stub, 'CreateRPC'), (('The service "%s" doesn\'t have ' +
                                       'a CreateRPC method.') % service)
  return stub.CreateRPC()


def MakeSyncCall(service, call, request, response, stubmap=None):
  """The APIProxy entry point for a synchronous API call.

  Args:
    service: string representing which service to call
    call: string representing which function to call
    request: protocol buffer for the request
    response: protocol buffer for the response
    stubmap: optional APIProxyStubMap instance, for dependency injection.

  Returns:
    Response protocol buffer or None. Some implementations may return
    a response protocol buffer instead of modifying 'response'.
    Caller must use returned value in such cases. If 'response' is modified
    then returns None.

  Raises:
    apiproxy_errors.Error or a subclass.
  """
  if stubmap is None:
    stubmap = apiproxy
  return stubmap.MakeSyncCall(service, call, request, response)


class ListOfHooks(object):
  """An ordered collection of hooks for a particular API call.

  A hook is a function that has exactly the same signature as
  a service stub. It will be called before or after an api hook is
  executed, depending on whether this list is for precall of postcall hooks.
  Hooks can be used for debugging purposes (check certain
  pre- or postconditions on api calls) or to apply patches to protocol
  buffers before/after a call gets submitted.
  """

  def __init__(self):
    """Constructor."""

    # a list of (key, function, service, num_args) tuples
    self.__content = []

    # a set of (key, module) tuples, used for existence checks
    self.__unique_keys = set()

  def __len__(self):
    """Returns the amount of elements in the collection."""
    return self.__content.__len__()

  def __Insert(self, index, key, function, service=None):
    """Appends a hook at a certain position in the list.

    Args:
      index: the index of where to insert the function
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    unique_key = (key, inspect.getmodule(function))
    if unique_key in self.__unique_keys:
      return False
    num_args = len(inspect.getargspec(function)[0])
    if (inspect.ismethod(function)):
      num_args -= 1
    self.__content.insert(index, (key, function, service, num_args))
    self.__unique_keys.add(unique_key)
    return True

  def Append(self, key, function, service=None):
    """Appends a hook at the end of the list.

    Args:
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    return self.__Insert(len(self), key, function, service)

  def Push(self, key, function, service=None):
    """Inserts a hook at the beginning of the list.

    Args:
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    return self.__Insert(0, key, function, service)

  def Clear(self):
    """Removes all hooks from the list (useful for unit tests)."""
    self.__content = []
    self.__unique_keys = set()

  def Call(self, service, call, request, response, rpc=None, error=None):
    """Invokes all hooks in this collection.

    NOTE: For backwards compatibility, if error is not None, hooks
    with 4 or 5 arguments are *not* called.  This situation
    (error=None) only occurs when the RPC request raised an exception;
    in the past no hooks would be called at all in that case.

    Args:
      service: string representing which service to call
      call: string representing which function to call
      request: protocol buffer for the request
      response: protocol buffer for the response
      rpc: optional RPC used to make this call
      error: optional Exception instance to be passed as 6th argument
    """
    for key, function, srv, num_args in self.__content:
      if srv is None or srv == service:
        if num_args == 6:
          function(service, call, request, response, rpc, error)
        elif error is not None:
          # For backward compatibility, if an error object is given,
          # we do not call the hook if it has fewer than 6 arguments.
          pass
        elif num_args == 5:
          function(service, call, request, response, rpc)
        else:
          function(service, call, request, response)


class APIProxyStubMap(object):
  """Container of APIProxy stubs for more convenient unittesting.

  Stubs may be either trivial implementations of APIProxy services (e.g.
  DatastoreFileStub, UserServiceStub) or "real" implementations.

  For unittests, we may want to mix and match real and trivial implementations
  of services in order to better focus testing on individual service
  implementations. To achieve this, we allow the client to attach stubs to
  service names, as well as define a default stub to be used if no specific
  matching stub is identified.
  """

  # For more information about "real" APIProxy, see
  # apphosting/runtime/apiproxy.h

  def __init__(self, default_stub=None):
    """Constructor.

    Args:
      default_stub: optional stub

    'default_stub' will be used whenever no specific matching stub is found.
    """
    self.__stub_map = {}
    self.__default_stub = default_stub
    self.__precall_hooks = ListOfHooks()
    self.__postcall_hooks = ListOfHooks()

  def GetPreCallHooks(self):
    """Gets a collection for all precall hooks."""
    return self.__precall_hooks

  def GetPostCallHooks(self):
    """Gets a collection for all precall hooks."""
    return self.__postcall_hooks

  def ReplaceStub(self, service, stub):
    """Replace the existing stub for the specified service with a new one.

    NOTE: This is a risky operation; external callers should use this with
    caution.

    Args:
      service: string
      stub: stub
    """
    self.__stub_map[service] = stub

    # corp/conference_manager/conference_entity_test.py,
    # recruiting/codejam/tests/test_common.py,
    # experimental/users/powera/prom_test/quizzer_test.py, and
    # experimental/users/abednego/sphinx/indexed_table_unittest.py.
    if service == 'datastore':
      self.RegisterStub('datastore_v3', stub)

  def RegisterStub(self, service, stub):
    """Register the provided stub for the specified service.

    Args:
      service: string
      stub: stub
    """
    assert service not in self.__stub_map, repr(service)
    self.ReplaceStub(service, stub)

  def GetStub(self, service):
    """Retrieve the stub registered for the specified service.

    Args:
      service: string

    Returns:
      stub

    Returns the stub registered for 'service', and returns the default stub
    if no such stub is found.
    """
    return self.__stub_map.get(service, self.__default_stub)

  def _CopyStubMap(self):
    """Get a copy of the stub map. For testing only.

    Returns:
      Get a shallow copy of the stub map.
    """
    return dict(self.__stub_map)

  def MakeSyncCall(self, service, call, request, response):
    """The APIProxy entry point.

    Args:
      service: string representing which service to call
      call: string representing which function to call
      request: protocol buffer for the request
      response: protocol buffer for the response

    Returns:
      Response protocol buffer or None. Some implementations may return
      a response protocol buffer instead of modifying 'response'.
      Caller must use returned value in such cases. If 'response' is modified
      then returns None.

    Raises:
      apiproxy_errors.Error or a subclass.
    """
    # See apphosting/runtime/apiproxy_errors.py for details on the different
    # subclasses, including ApplicationError.
    stub = self.GetStub(service)
    assert stub, 'No api proxy found for service "%s"' % service
    if hasattr(stub, 'CreateRPC'):
      rpc = stub.CreateRPC()
      self.__precall_hooks.Call(service, call, request, response, rpc)
      try:
        rpc.MakeCall(service, call, request, response)
        rpc.Wait()
        rpc.CheckSuccess()
      except Exception as err:
        self.__postcall_hooks.Call(service, call, request, response, rpc, err)
        raise
      else:
        self.__postcall_hooks.Call(service, call, request, response, rpc)
    else:
      self.__precall_hooks.Call(service, call, request, response)
      try:
        returned_response = stub.MakeSyncCall(service, call, request, response)
      except Exception as err:
        self.__postcall_hooks.Call(service, call, request, response, None, err)
        raise
      else:
        self.__postcall_hooks.Call(service, call, request,
                                   returned_response or response)
        return returned_response

  def CancelApiCalls(self):
    if self.__default_stub:
      self.__default_stub.CancelApiCalls()


class UserRPC(object):
  """Wrapper class for asynchronous RPC.

  Simplest low-level usage pattern:

    rpc = UserRPC('service', [deadline], [callback])
    rpc.make_call('method', request, response)
    .
    .
    .
    rpc.wait()
    rpc.check_success()

  However, a service module normally provides a wrapper so that the
  typical usage pattern becomes more like this:

    from google.appengine.api import service
    rpc = service.create_rpc([deadline], [callback])
    service.make_method_call(rpc, [service-specific-args])
    .
    .
    .
    rpc.wait()
    result = rpc.get_result()

  The service.make_method_call() function sets a service- and method-
  specific hook function that is called by rpc.get_result() with the
  rpc object as its first argument, and service-specific value as its
  second argument.  The hook function should call rpc.check_success()
  and then extract the user-level result from the rpc.result
  protobuffer.  Additional arguments may be passed from
  make_method_call() to the get_result hook via the second argument.

  Also note wait_any() and wait_all(), which wait for multiple RPCs.
  """

  __method = None
  __get_result_hook = None
  __user_data = None
  __postcall_hooks_called = False
  __must_call_user_callback = False

  class MyLocal(threading.local):
    """Class to hold per-thread class level attributes."""

    may_interrupt_wait = False

  __local = MyLocal()  # Per thread class variable.

  def __init__(self, service, deadline=None, callback=None, stubmap=None):
    """Constructor.

    Args:
      service: The service name.
      deadline: Optional deadline.  Default depends on the implementation.
      callback: Optional argument-less callback function.
      stubmap: optional APIProxyStubMap instance, for dependency injection.
    """
    if stubmap is None:
      stubmap = apiproxy
    self.__stubmap = stubmap
    self.__service = service
    self.__rpc = CreateRPC(service, stubmap)
    self.__rpc.deadline = deadline
    self.__rpc.callback = self.__internal_callback
    self.callback = callback  # This is a plain user-settable variable.

    # As a precaution, reset may_interrupt_wait.  This variable
    # defaults to False, and it is supposed to be False everywhere
    # except in a tiny section of wait_any(), which resets it using a
    # 'finally' clause.  Yet, there is the remote possibility that an
    # uncatchable DeadlineExceededError would prevent the latter from
    # running, leaving the variable True into the start of the next
    # request.  So here we reset it.  Note that no user code should
    # ever run while the variable is True, so there is no chance of
    # resetting it causing trouble.  Also, if the variable is False
    # when it should be True, the worst that can happen is that
    # wait_any() is a little slower than it could be.  But if it is
    # True when it should be False, nasty tracebacks will happen.
    self.__class__.__local.may_interrupt_wait = False

  def __internal_callback(self):
    """This is the callback set on the low-level RPC object.

    It sets a flag on the current object indicating that the high-level
    callback should now be called.  If interrupts are enabled, it also
    interrupts the current wait_any() call by raising an exception.
    """
    self.__must_call_user_callback = True
    self.__rpc.callback = None  # Break refcount cycle (b/3272101).
    if self.__class__.__local.may_interrupt_wait and not self.__rpc.exception:
      # Raise InterruptedError, so that we may catch it.  (The
      # production runtime always turns exceptions raised by callbacks
      # into InterruptedError, but the dev_appserver doesn't -- the
      # latter just passes through the actual exception raised.  I
      # only want to catch one exception so I'm raising
      # InterruptedError.)  However, if an exception is already
      # pending, don't do this, as it would override the original
      # exception.
      raise apiproxy_errors.InterruptedError(None, self.__rpc)

  @property
  def service(self):
    """Return the service name."""
    return self.__service

  @property
  def method(self):
    """Return the method name."""
    return self.__method

  @property
  def deadline(self):
    """Return the deadline, if set explicitly (otherwise None)."""
    return self.__rpc.deadline

  @property
  def request(self):
    """Return the request protocol buffer object."""
    return self.__rpc.request

  @property
  def response(self):
    """Return the response protocol buffer object."""
    return self.__rpc.response

  @property
  def state(self):
    """Return the RPC state.

    Possible values are attributes of apiproxy_rpc.RPC: IDLE, RUNNING,
    FINISHING.
    """
    return self.__rpc.state

  @property
  def get_result_hook(self):
    """Return the get-result hook function."""
    return self.__get_result_hook

  @property
  def user_data(self):
    """Return the user data for the hook function."""
    return self.__user_data

  def make_call(self, method, request, response,
                get_result_hook=None, user_data=None):
    """Initiate a call.

    Args:
      method: The method name.
      request: The request protocol buffer.
      response: The response protocol buffer.
      get_result_hook: Optional get-result hook function.  If not None,
        this must be a function with exactly one argument, the RPC
        object (self).  Its return value is returned from get_result().
      user_data: Optional additional arbitrary data for the get-result
        hook function.  This can be accessed as rpc.user_data.  The
        type of this value is up to the service module.

    This function may only be called once per RPC object.  It sends
    the request to the remote server, but does not wait for a
    response.  This allows concurrent execution of the remote call and
    further local processing (e.g., making additional remote calls).

    Before the call is initiated, the precall hooks are called.
    """
    # Check for virginal RPC object.
    assert self.__rpc.state == apiproxy_rpc.RPC.IDLE, repr(self.state)
    # Save the method name.
    self.__method = method
    # Save the get-result hook function and its user_data.
    self.__get_result_hook = get_result_hook
    self.__user_data = user_data
    # Call the precall hooks.
    self.__stubmap.GetPreCallHooks().Call(
        self.__service, method, request, response, self.__rpc)
    # Set self.__rpc.request and .response and initiate the call.
    self.__rpc.MakeCall(self.__service, method, request, response)

  def wait(self):
    """Wait for the call to complete, and call callback if needed.

    This and wait_any()/wait_all() are the only time callback
    functions may be called.  (However, note that check_success() and
    get_result() call wait().)  Waiting for one RPC will not cause
    callbacks for other RPCs to be called.  Callback functions may
    call check_success() and get_result().

    Callbacks are called without arguments; if a callback needs access
    to the RPC object a Python nested function (a.k.a. closure) or a
    bound may be used.  To facilitate this, the callback may be
    assigned after the RPC object is created (but before make_call()
    is called).

    Note: don't confuse callbacks with get-result hooks or precall
    and postcall hooks.
    """
    # Check that make_call has been called.
    assert self.__rpc.state != apiproxy_rpc.RPC.IDLE, repr(self.state)
    # Only call Wait() once.
    if self.__rpc.state == apiproxy_rpc.RPC.RUNNING:
      self.__rpc.Wait()
    # Now the RPC should be done.
    assert self.__rpc.state == apiproxy_rpc.RPC.FINISHING, repr(self.state)
    self.__call_user_callback()

  def __call_user_callback(self):
    """Call the high-level callback, if requested."""
    if self.__must_call_user_callback:
      self.__must_call_user_callback = False
      if self.callback is not None:
        self.callback()

  def check_success(self):
    """Check for success of the RPC, possibly raising an exception.

    This function should be called at least once per RPC.  If wait()
    hasn't been called yet, it is called first.  If the RPC caused
    an exceptional condition, an exception will be raised here.
    The first time check_success() is called, the postcall hooks
    are called.
    """
    # Always call wait() and CheckSuccess(); they're idempotent.  This
    # means that any exceptions they raise won't be ignored.
    self.wait()
    try:
      self.__rpc.CheckSuccess()
    except Exception as err:
      # Call the postcall hooks, but only once.
      if not self.__postcall_hooks_called:
        self.__postcall_hooks_called = True
        self.__stubmap.GetPostCallHooks().Call(self.__service, self.__method,
                                               self.request, self.response,
                                               self.__rpc, err)
      raise
    else:
      # Call the postcall hooks, but only once.
      if not self.__postcall_hooks_called:
        self.__postcall_hooks_called = True
        self.__stubmap.GetPostCallHooks().Call(self.__service, self.__method,
                                               self.request, self.response,
                                               self.__rpc)

  def get_result(self):
    """Get the result of the RPC, or possibly raise an exception.

    This implies a call to check_success().  If a get-result hook was
    passed to make_call(), that hook is responsible for calling
    check_success(), and the return value of the hook is returned.
    Otherwise, check_success() is called directly and None is
    returned.
    """
    # Call the service's get-result hook function.  The hook is
    # responsible for calling check_success(), and for accessing the
    # response attribute.  It can also access user_data.  If no hook
    # is specified, we call check_success() directly.
    if self.__get_result_hook is None:
      self.check_success()
      return None
    else:
      return self.__get_result_hook(self)

  @classmethod
  def __check_one(cls, rpcs):
    """Check the list of RPCs for one that is finished, or one that is running.

    Args:
      rpcs: Iterable collection of UserRPC instances.

    Returns:
      A pair (finished, running), as follows:
      (UserRPC, None) indicating the first RPC found that is finished;
      (None, UserRPC) indicating the first RPC found that is running;
      (None, None) indicating no RPCs are finished or running.
    """
    rpc = None  # In case rpcs is empty.
    for rpc in rpcs:
      assert isinstance(rpc, cls), repr(rpc)
      state = rpc.__rpc.state
      if state == apiproxy_rpc.RPC.FINISHING:
        rpc.__call_user_callback()
        return rpc, None
      assert state != apiproxy_rpc.RPC.IDLE, repr(rpc)
    return None, rpc

  @classmethod
  def wait_any(cls, rpcs):
    """Wait until an RPC is finished.

    Args:
      rpcs: Iterable collection of UserRPC instances.

    Returns:
      A UserRPC instance, indicating the first RPC among the given
      RPCs that finished; or None, indicating that either an RPC not
      among the given RPCs finished in the mean time, or the iterable
      is empty.

    NOTES:

    (1) Repeatedly calling wait_any() with the same arguments will not
        make progress; it will keep returning the same RPC (the one
        that finished first).  The callback, however, will only be
        called the first time the RPC finishes (which may be here or
        in the wait() method).

    (2) It may return before any of the given RPCs finishes, if
        another pending RPC exists that is not included in the rpcs
        argument.  In this case the other RPC's callback will *not*
        be called.  The motivation for this feature is that wait_any()
        may be used as a low-level building block for a variety of
        high-level constructs, some of which prefer to block for the
        minimal amount of time without busy-waiting.
    """
    assert iter(rpcs) is not rpcs, 'rpcs must be a collection, not an iterator'
    finished, running = cls.__check_one(rpcs)
    if finished is not None:
      return finished
    if running is None:
      return None  # Nothing to do.
    try:
      cls.__local.may_interrupt_wait = True
      try:
        running.__rpc.Wait()
      except apiproxy_errors.InterruptedError as err:
        # We don't care what happened, we just want to break out of
        # the Wait().  It's always __internal_callback() anyway.
        # Clear the exception on the RPC that raised it (not
        # necessarily the one we just Wait()ed on!), otherwise
        # check_success() will re-raise it.
        err.rpc._exception = None
        err.rpc._traceback = None
    finally:
      cls.__local.may_interrupt_wait = False
    finished, running = cls.__check_one(rpcs)
    return finished

  @classmethod
  def wait_all(cls, rpcs):
    """Wait until all given RPCs are finished.

    This is a thin wrapper around wait_any() that loops until all
    given RPCs have finished.

    Args:
      rpcs: Iterable collection of UserRPC instances.

    Returns:
      None.
    """
    rpcs = set(rpcs)
    while rpcs:
      finished = cls.wait_any(rpcs)
      if finished is not None:
        rpcs.remove(finished)


# APIProxy if available as the default stub.
def GetDefaultAPIProxy():
  try:
    # preemptively, looking for "from ... import ..." statements, and tries to
    # resolve them. grr!
    #
    # separate the module and package so that __import__ returns the imported
    # module, not the top-level module.
    runtime = __import__('googlecloudsdk.appengine.runtime', globals(), locals(),
                         ['apiproxy'])
    return APIProxyStubMap(runtime.apiproxy)
  except (AttributeError, ImportError):
    return APIProxyStubMap()


# Global APIProxyStubMap instance. This instance may be reinitialized
# by a client of apiproxy_stub_map.py.
apiproxy = GetDefaultAPIProxy()
