# -*- coding: utf-8 -*- #
# Copyright 2016 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.

"""Methods for looking up completions from the static CLI tree."""


import os
import shlex
import sys
from googlecloudsdk.core.util import encoding
from googlecloudsdk.core.util import platforms
import six


LINE_ENV_VAR = 'COMP_LINE'
POINT_ENV_VAR = 'COMP_POINT'
IFS_ENV_VAR = '_ARGCOMPLETE_IFS'
IFS_ENV_DEFAULT = '\013'
COMPLETIONS_OUTPUT_FD = 8

FLAG_PREFIX = '--'

FLAG_BOOLEAN = 'bool'
FLAG_DYNAMIC = 'dynamic'
FLAG_VALUE = 'value'
ENV_VAR = 'env_var'

LOOKUP_COMMANDS = 'commands'
LOOKUP_FLAGS = 'flags'

_EMPTY_STRING = ''
_VALUE_SEP = '='
_SPACE = ' '


class CannotHandleCompletionError(Exception):
  """Error for when completions cannot be handled."""
  pass


def _GetCmdLineFromEnv():
  """Gets the command line from the environment.

  Returns:
    str, Command line.
  """
  cmd_line = encoding.GetEncodedValue(os.environ, LINE_ENV_VAR)
  completion_point = int(encoding.GetEncodedValue(os.environ, POINT_ENV_VAR))
  cmd_line = cmd_line[:completion_point]
  return cmd_line


def _GetCmdWordQueue(cmd_line):
  """Converts the given cmd_line to a queue of command line words.

  Args:
    cmd_line: str, full command line before parsing.

  Returns:
    [str], Queue of command line words.
  """
  cmd_words = shlex.split(cmd_line)[1:]  # First word should always be 'gcloud'

  # We need to know if last word was empty. Shlex removes trailing whitespaces.
  if cmd_line[-1] == _SPACE:
    cmd_words.append(_EMPTY_STRING)

  # Reverse so we can use as a queue
  cmd_words.reverse()
  return cmd_words


def GetEnvVarPrefix():
  # TODO(b/207384119) support powershell environment variables
  return '%' if platforms.OperatingSystem.IsWindows() else '$'


def MatchEnvVars(word, env_vars):
  """Returns environment variables beginning with `word`.

  Args:
    word: The word that is being compared to environment variables.
    env_vars: The list of environment variables.

  Returns:
    []: No completions.
    [completions]: List, all possible sorted completions.
  """
  completions = []
  prefix = word[1:]  # exclude '$' or '%' and only use the variable name
  for child in env_vars:
    if child.startswith(prefix):
      if platforms.OperatingSystem.IsWindows():
        completions.append('%' + child + '%')
      else:
        completions.append('$' + child)
  return completions


def _FindCompletions(root, cmd_line):
  """Try to perform a completion based on the static CLI tree.

  Args:
    root: The root of the tree that will be traversed to find completions.
    cmd_line: [str], original command line.

  Raises:
    CannotHandleCompletionError: If FindCompletions cannot handle completion.

  Returns:
    []: No completions.
    [completions]: List, all possible sorted completions.
  """
  words = _GetCmdWordQueue(cmd_line)
  node = root

  global_flags = node[LOOKUP_FLAGS]

  completions = []
  flag_mode = FLAG_BOOLEAN

  env_var_prefix = GetEnvVarPrefix()
  env_vars = os.environ
  while words:
    word = words.pop()

    if word.startswith(FLAG_PREFIX):
      is_flag_word = True
      child_nodes = node.get(LOOKUP_FLAGS, {})
      child_nodes.update(global_flags)
      # Add the value part back to the queue if it exists
      if _VALUE_SEP in word:
        word, flag_value = word.split(_VALUE_SEP, 1)
        # This predates the env var completion but is necessary for completing
        # environment variables that are flag values.
        words.append(flag_value)
    elif word.startswith(env_var_prefix):
      is_flag_word = False
      child_nodes = env_vars
      flag_mode = ENV_VAR
    else:
      is_flag_word = False
      child_nodes = node.get(LOOKUP_COMMANDS, {})

    # Consume word
    if words:
      if word in child_nodes:
        if is_flag_word:
          flag_mode = child_nodes[word]
        else:
          flag_mode = FLAG_BOOLEAN
          node = child_nodes[word]  # Progress to next command node
      elif flag_mode == ENV_VAR:
        continue
      elif flag_mode != FLAG_BOOLEAN:
        flag_mode = FLAG_BOOLEAN
        continue  # Just consume if we are expecting a flag value
      elif not is_flag_word and not node.get(LOOKUP_COMMANDS):
        # If we're at a leaf command node, this could be a positional arg, so
        # consume it and move on.
        flag_mode = FLAG_BOOLEAN
        continue
      else:
        return []  # Non-existing command/flag, so nothing to do

    # Complete word
    else:
      if flag_mode == FLAG_DYNAMIC:
        raise CannotHandleCompletionError(
            'Dynamic completions are not handled by this module')
      elif flag_mode == FLAG_VALUE:
        return []  # Cannot complete, so nothing to do
      elif flag_mode == ENV_VAR:
        completions += MatchEnvVars(word, child_nodes)
      elif flag_mode != FLAG_BOOLEAN:  # Must be list of choices
        for value in flag_mode:
          if value.startswith(word):
            completions.append(value)
      elif not child_nodes:
        raise CannotHandleCompletionError(
            'Positional completions are not handled by this module')
      else:  # Command/flag completion
        for child, value in six.iteritems(child_nodes):
          if not child.startswith(word):
            continue
          if is_flag_word and value != FLAG_BOOLEAN:
            child += _VALUE_SEP
          completions.append(child)
  return sorted(completions)


def _GetInstallationRootDir():
  """Returns the SDK installation root dir."""
  # Intentionally ignoring config path abstraction imports.
  return os.path.sep.join(__file__.split(os.path.sep)[:-5])


def _GetCompletionCliTreeDir():
  """Returns the SDK static completion CLI tree dir."""
  # Intentionally ignoring config path abstraction imports.
  return os.path.join(_GetInstallationRootDir(), 'data', 'cli')


def CompletionCliTreePath(directory=None):
  """Returns the SDK static completion CLI tree path."""
  # Intentionally ignoring config path abstraction imports.
  return os.path.join(
      directory or _GetCompletionCliTreeDir(), 'gcloud_completions.py')


def LoadCompletionCliTree():
  """Loads and returns the static completion CLI tree."""
  try:
    sys_path = sys.path[:]
    sys.path.append(_GetCompletionCliTreeDir())
    import gcloud_completions  # pylint: disable=g-import-not-at-top
    tree = gcloud_completions.STATIC_COMPLETION_CLI_TREE
  except ImportError:
    raise CannotHandleCompletionError(
        'Cannot find static completion CLI tree module.')
  finally:
    sys.path = sys_path
  return tree


def _OpenCompletionsOutputStream():
  """Returns the completions output stream."""
  return os.fdopen(COMPLETIONS_OUTPUT_FD, 'wb')


def _GetCompletions():
  """Returns the static completions, None if there are none."""
  root = LoadCompletionCliTree()
  cmd_line = _GetCmdLineFromEnv()
  return _FindCompletions(root, cmd_line)


def Complete():
  """Attempts completions and writes them to the completion stream."""
  completions = _GetCompletions()
  if completions:
    # The bash/zsh completion scripts set IFS_ENV_VAR to one character.
    ifs = encoding.GetEncodedValue(os.environ, IFS_ENV_VAR, IFS_ENV_DEFAULT)
    # Write completions to stream
    f = None
    try:
      f = _OpenCompletionsOutputStream()
      # the other side also uses the console encoding
      f.write(ifs.join(completions).encode())
    finally:
      if f:
        f.close()