#!/usr/bin/env python
#
# Copyright 2007 Google Inc.
#
# 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.
#




"""
A library for working with BackendInfoExternal records, describing backends
configured for an application. Supports loading the records from backend.yaml.
"""







import yaml
from yaml import representer

from google.appengine.api import validation
from google.appengine.api import yaml_builder
from google.appengine.api import yaml_listener
from google.appengine.api import yaml_object

NAME_REGEX = r'(?!-)[a-z\d\-]{1,100}'
FILE_REGEX = r'(?!\^).*(?!\$).{1,256}'
CLASS_REGEX =  r'^[bB](1|2|4|8)$'
OPTIONS_REGEX = r'^[a-z, ]*$'
STATE_REGEX = r'^(START|STOP|DISABLED)$'


BACKENDS = 'backends'


NAME = 'name'
CLASS = 'class'
INSTANCES = 'instances'
OPTIONS = 'options'
PUBLIC = 'public'
DYNAMIC = 'dynamic'
FAILFAST = 'failfast'
MAX_CONCURRENT_REQUESTS = 'max_concurrent_requests'
START = 'start'

VALID_OPTIONS = frozenset([PUBLIC, DYNAMIC, FAILFAST])


STATE = 'state'

class BadConfig(Exception):
  """An invalid configuration was provided."""

class ListWithoutSort(list):
  def sort(self):
    pass

class SortedDict(dict):
  def __init__(self, keys, data):
    super(SortedDict, self).__init__()
    self.keys = keys
    self.update(data)

  def items(self):
    result = ListWithoutSort()
    for key in self.keys:
      if type(self.get(key)) != type(None):
        result.append((key, self.get(key)))
    return result

representer.SafeRepresenter.add_representer(
    SortedDict, representer.SafeRepresenter.represent_dict)

class BackendEntry(validation.Validated):
  """A backend entry describes a single backend."""
  ATTRIBUTES = {
      NAME: NAME_REGEX,
      CLASS: validation.Optional(CLASS_REGEX),
      INSTANCES: validation.Optional(validation.TYPE_INT),
      MAX_CONCURRENT_REQUESTS: validation.Optional(validation.TYPE_INT),


      OPTIONS: validation.Optional(OPTIONS_REGEX),
      PUBLIC: validation.Optional(validation.TYPE_BOOL),
      DYNAMIC: validation.Optional(validation.TYPE_BOOL),
      FAILFAST: validation.Optional(validation.TYPE_BOOL),
      START: validation.Optional(FILE_REGEX),


      STATE: validation.Optional(STATE_REGEX),
  }

  def __init__(self, *args, **kwargs):
    super(BackendEntry, self).__init__(*args, **kwargs)
    self.Init()

  def Init(self):
    if self.public:
      raise BadConfig("Illegal field: 'public'")
    if self.dynamic:
      raise BadConfig("Illegal field: 'dynamic'")
    if self.failfast:
      raise BadConfig("Illegal field: 'failfast'")
    self.ParseOptions()
    return self

  def set_class(self, Class):
    """Setter for 'class', since an attribute reference is an error."""
    self.Set(CLASS, Class)

  def get_class(self):
    """Accessor for 'class', since an attribute reference is an error."""
    return self.Get(CLASS)

  def ToDict(self):
    """Returns a sorted dictionary representing the backend entry."""
    self.ParseOptions().WriteOptions()
    result = super(BackendEntry, self).ToDict()
    return SortedDict([NAME,
                       CLASS,
                       INSTANCES,
                       START,
                       OPTIONS,
                       MAX_CONCURRENT_REQUESTS,
                       STATE],
                      result)

  def ParseOptions(self):
    """Parses the 'options' field and sets appropriate fields."""
    if self.options:
      options = [option.strip() for option in self.options.split(',')]
    else:
      options = []

    for option in options:
      if option not in VALID_OPTIONS:
        raise BadConfig('Unrecognized option: %s', option)

    self.public = PUBLIC in options
    self.dynamic = DYNAMIC in options
    self.failfast = FAILFAST in options
    return self

  def WriteOptions(self):
    """Writes the 'options' field based on other settings."""
    options = []
    if self.public:
      options.append('public')
    if self.dynamic:
      options.append('dynamic')
    if self.failfast:
      options.append('failfast')
    if options:
      self.options = ', '.join(options)
    else:
      self.options = None
    return self


def LoadBackendEntry(backend_entry):
  """Parses a BackendEntry object from a string.

  Args:
    backend_entry: a backend entry, as a string

  Returns:
    A BackendEntry object.
  """
  builder = yaml_object.ObjectBuilder(BackendEntry)
  handler = yaml_builder.BuilderHandler(builder)
  listener = yaml_listener.EventListener(handler)
  listener.Parse(backend_entry)

  entries = handler.GetResults()
  if len(entries) < 1:
    raise BadConfig('Empty backend configuration.')
  if len(entries) > 1:
    raise BadConfig('Multiple backend entries were found in configuration.')

  return entries[0].Init()


class BackendInfoExternal(validation.Validated):
  """BackendInfoExternal describes all backend entries for an application."""
  ATTRIBUTES = {
      BACKENDS: validation.Optional(validation.Repeated(BackendEntry)),
  }


def LoadBackendInfo(backend_info):
  """Parses a BackendInfoExternal object from a string.

  Args:
    backend_info: a backends stanza (list of backends) as a string

  Returns:
    A BackendInfoExternal object.
  """
  builder = yaml_object.ObjectBuilder(BackendInfoExternal)
  handler = yaml_builder.BuilderHandler(builder)
  listener = yaml_listener.EventListener(handler)
  listener.Parse(backend_info)

  backend_info = handler.GetResults()
  if len(backend_info) < 1:
    return BackendInfoExternal(backends=[])
  if len(backend_info) > 1:
    raise BadConfig("Only one 'backends' clause is allowed.")

  info = backend_info[0]
  for backend in info.backends:
    backend.Init()
  return info
