#!/usr/bin/env python
#
# Copyright 2016 - The Android Open Source Project
#
# 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.

"""Common Utilities.

The following code is copied from chromite with modifications.
  - class TempDir: chromite/lib/osutils.py

"""

import base64
import binascii
import errno
import getpass
import logging
import os
import shutil
import struct
import subprocess
import sys
import tarfile
import tempfile
import time
import uuid

from acloud.public import errors


logger = logging.getLogger(__name__)


SSH_KEYGEN_CMD = ["ssh-keygen", "-t", "rsa", "-b", "4096"]


class TempDir(object):
    """Object that creates a temporary directory.

    This object can either be used as a context manager or just as a simple
    object. The temporary directory is stored as self.tempdir in the object, and
    is returned as a string by a 'with' statement.
    """

    def __init__(self, prefix='tmp', base_dir=None, delete=True):
        """Constructor. Creates the temporary directory.

        Args:
            prefix: See tempfile.mkdtemp documentation.
            base_dir: The directory to place the temporary directory.
                      If None, will choose from system default tmp dir.
            delete: Whether the temporary dir should be deleted as part of cleanup.
        """
        self.delete = delete
        self.tempdir = tempfile.mkdtemp(prefix=prefix, dir=base_dir)
        os.chmod(self.tempdir, 0o700)

    def Cleanup(self):
        """Clean up the temporary directory."""
        # Note that _TempDirSetup may have failed, resulting in these attributes
        # not being set; this is why we use getattr here (and must).
        tempdir = getattr(self, 'tempdir', None)
        if tempdir is not None and self.delete:
            try:
                shutil.rmtree(tempdir)
            except EnvironmentError as e:
                # Ignore error if directory or file does not exist.
                if e.errno != errno.ENOENT:
                    raise
            finally:
                self.tempdir = None

    def __enter__(self):
        """Return the temporary directory."""
        return self.tempdir

    def __exit__(self, exc_type, exc_value, exc_traceback):
        """Exit the context manager."""
        try:
            self.Cleanup()
        except Exception:  # pylint: disable=W0703
            if exc_type:
                # If an exception from inside the context was already in progress,
                # log our cleanup exception, then allow the original to resume.
                logger.error('While exiting %s:', self, exc_info=True)

                if self.tempdir:
                    # Log all files in tempdir at the time of the failure.
                    try:
                        logger.error('Directory contents were:')
                        for name in os.listdir(self.tempdir):
                            logger.error('  %s', name)
                    except OSError:
                        logger.error('  Directory did not exist.')
            else:
                # If there was not an exception from the context, raise ours.
                raise

    def __del__(self):
        """Delete the object."""
        self.Cleanup()

def RetryOnException(retry_checker, max_retries, sleep_multiplier=0,
                     retry_backoff_factor=1):
  """Decorater which retries the function call if |retry_checker| returns true.

  Args:
    retry_checker: A callback function which should take an exception instance
                   and return True if functor(*args, **kwargs) should be retried
                   when such exception is raised, and return False if it should
                   not be retried.
    max_retries: Maximum number of retries allowed.
    sleep_multiplier: Will sleep sleep_multiplier * attempt_count seconds if
                      retry_backoff_factor is 1.  Will sleep
                      sleep_multiplier * (
                          retry_backoff_factor ** (attempt_count -  1))
                      if retry_backoff_factor != 1.
    retry_backoff_factor: See explanation of sleep_multiplier.

  Returns:
    The function wrapper.
  """
  def _Wrapper(func):
    def _FunctionWrapper(*args, **kwargs):
      return Retry(retry_checker, max_retries, func, sleep_multiplier,
                   retry_backoff_factor,
                   *args, **kwargs)
    return _FunctionWrapper
  return _Wrapper


def Retry(retry_checker, max_retries, functor, sleep_multiplier=0,
          retry_backoff_factor=1, *args, **kwargs):
  """Conditionally retry a function.

  Args:
    retry_checker: A callback function which should take an exception instance
                   and return True if functor(*args, **kwargs) should be retried
                   when such exception is raised, and return False if it should
                   not be retried.
    max_retries: Maximum number of retries allowed.
    functor: The function to call, will call functor(*args, **kwargs).
    sleep_multiplier: Will sleep sleep_multiplier * attempt_count seconds if
                      retry_backoff_factor is 1.  Will sleep
                      sleep_multiplier * (
                          retry_backoff_factor ** (attempt_count -  1))
                      if retry_backoff_factor != 1.
    retry_backoff_factor: See explanation of sleep_multiplier.
    *args: Arguments to pass to the functor.
    **kwargs: Key-val based arguments to pass to the functor.

  Returns:
    The return value of the functor.

  Raises:
    Exception: The exception that functor(*args, **kwargs) throws.
  """
  attempt_count = 0
  while attempt_count <= max_retries:
    try:
      attempt_count += 1
      return_value = functor(*args, **kwargs)
      return return_value
    except Exception as e:  # pylint: disable=W0703
      if retry_checker(e) and attempt_count <= max_retries:
        if retry_backoff_factor != 1:
          sleep = sleep_multiplier * (
              retry_backoff_factor ** (attempt_count -  1))
        else:
          sleep = sleep_multiplier * attempt_count
        time.sleep(sleep)
      else:
        raise


def RetryExceptionType(exception_types, max_retries, functor, *args, **kwargs):
  """Retry exception if it is one of the given types.

  Args:
    exception_types: A tuple of exception types, e.g. (ValueError, KeyError)
    max_retries: Max number of retries allowed.
    functor: The function to call. Will be retried if exception is raised and
             the exception is one of the exception_types.
    *args: Arguments to pass to Retry function.
    **kwargs: Key-val based arguments to pass to Retry functions.

  Returns:
    The value returned by calling functor.
  """
  return Retry(lambda e: isinstance(e, exception_types), max_retries,
               functor, *args, **kwargs)


def PollAndWait(func, expected_return, timeout_exception, timeout_secs,
                sleep_interval_secs, *args, **kwargs):
    """Call a function until the function returns expected value or times out.

    Args:
        func: Function to call.
        expected_return: The expected return value.
        timeout_exception: Exception to raise when it hits timeout.
        timeout_secs: Timeout seconds.
                      If 0 or less than zero, the function will run once and
                      we will not wait on it.
        sleep_interval_secs: Time to sleep between two attemps.
        *args: list of args to pass to func.
        **kwargs: dictionary of keyword based args to pass to func.

    Raises:
        timeout_exception: if the run of function times out.
    """
    # TODO(fdeng): Currently this method does not kill
    # |func|, if |func| takes longer than |timeout_secs|.
    # We can use a more robust version from chromite.
    start = time.time()
    while True:
        return_value = func(*args, **kwargs)
        if return_value == expected_return:
            return
        elif time.time() - start > timeout_secs:
            raise timeout_exception
        else:
            if sleep_interval_secs > 0:
                time.sleep(sleep_interval_secs)


def GenerateUniqueName(prefix=None, suffix=None):
    """Generate a random unque name using uuid4.

    Args:
        prefix: String, desired prefix to prepend to the generated name.
        suffix: String, desired suffix to append to the generated name.

    Returns:
        String, a random name.
    """
    name = uuid.uuid4().hex
    if prefix:
        name = "-".join([prefix, name])
    if suffix:
        name = "-".join([name, suffix])
    return name


def MakeTarFile(src_dict, dest):
    """Archive files in tar.gz format to a file named as |dest|.

    Args:
        src_dict: A dictionary that maps a path to be archived
                  to the corresponding name that appears in the archive.
        dest: String, path to output file, e.g. /tmp/myfile.tar.gz
    """
    logger.info("Compressing %s into %s.", src_dict.keys(), dest)
    with tarfile.open(dest, "w:gz") as tar:
        for src, arcname in src_dict.iteritems():
            tar.add(src, arcname=arcname)


def CreateSshKeyPairIfNotExist(private_key_path, public_key_path):
    """Create the ssh key pair if they don't exist.

    Check if the public and private key pairs exist at
    the given places. If not, create them.

    Args:
        private_key_path: Path to the private key file.
                          e.g. ~/.ssh/acloud_rsa
        public_key_path: Path to the public key file.
                         e.g. ~/.ssh/acloud_rsa.pub
    Raises:
        error.DriverError: If failed to create the key pair.
    """
    public_key_path = os.path.expanduser(public_key_path)
    private_key_path = os.path.expanduser(private_key_path)
    create_key = (
            not os.path.exists(public_key_path) and
            not os.path.exists(private_key_path))
    if not create_key:
        logger.debug("The ssh private key (%s) or public key (%s) already exist,"
                     "will not automatically create the key pairs.",
                     private_key_path, public_key_path)
        return
    cmd = SSH_KEYGEN_CMD + ["-C", getpass.getuser(), "-f", private_key_path]
    logger.info("The ssh private key (%s) and public key (%s) do not exist, "
                "automatically creating key pair, calling: %s",
                private_key_path, public_key_path, " ".join(cmd))
    try:
        subprocess.check_call(cmd, stdout=sys.stderr, stderr=sys.stdout)
    except subprocess.CalledProcessError as e:
        raise errors.DriverError(
                "Failed to create ssh key pair: %s" % str(e))
    except OSError as e:
        raise errors.DriverError(
                "Failed to create ssh key pair, please make sure "
                "'ssh-keygen' is installed: %s" % str(e))

    # By default ssh-keygen will create a public key file
    # by append .pub to the private key file name. Rename it
    # to what's requested by public_key_path.
    default_pub_key_path = "%s.pub" % private_key_path
    try:
        if default_pub_key_path != public_key_path:
            os.rename(default_pub_key_path, public_key_path)
    except OSError as e:
        raise errors.DriverError(
                "Failed to rename %s to %s: %s" %
                (default_pub_key_path, public_key_path, str(e)))

    logger.info("Created ssh private key (%s) and public key (%s)",
                private_key_path, public_key_path)


def VerifyRsaPubKey(rsa):
    """Verify the format of rsa public key.

    Args:
        rsa: content of rsa public key. It should follow the format of
             ssh-rsa AAAAB3NzaC1yc2EA.... test@test.com

    Raises:
        DriverError if the format is not correct.
    """
    if not rsa or not all(ord(c) < 128 for c in rsa):
        raise errors.DriverError(
            "rsa key is empty or contains non-ascii character: %s" % rsa)

    elements = rsa.split()
    if len(elements) != 3:
        raise errors.DriverError("rsa key is invalid, wrong format: %s" % rsa)

    key_type, data, _ = elements
    try:
        binary_data = base64.decodestring(data)
        # number of bytes of int type
        int_length = 4
        # binary_data is like "7ssh-key..." in a binary format.
        # The first 4 bytes should represent 7, which should be
        # the length of the following string "ssh-key".
        # And the next 7 bytes should be string "ssh-key".
        # We will verify that the rsa conforms to this format.
        # ">I" in the following line means "big-endian unsigned integer".
        type_length = struct.unpack(">I", binary_data[:int_length])[0]
        if binary_data[int_length:int_length + type_length] != key_type:
            raise errors.DriverError("rsa key is invalid: %s" % rsa)
    except (struct.error, binascii.Error) as e:
        raise errors.DriverError("rsa key is invalid: %s, error: %s" %
                                 (rsa, str(e)))


class BatchHttpRequestExecutor(object):
    """A helper class that executes requests in batch with retry.

    This executor executes http requests in a batch and retry
    those that have failed. It iteratively updates the dictionary
    self._final_results with latest results, which can be retrieved
    via GetResults.
    """

    def __init__(self,
                 execute_once_functor,
                 requests,
                 retry_http_codes=None,
                 max_retry=None,
                 sleep=None,
                 backoff_factor=None,
                 other_retriable_errors=None):
        """Initializes the executor.

        Args:
            execute_once_functor: A function that execute requests in batch once.
                                  It should return a dictionary like
                                  {request_id: (response, exception)}
            requests: A dictionary where key is request id picked by caller,
                      and value is a apiclient.http.HttpRequest.
            retry_http_codes: A list of http codes to retry.
            max_retry: See utils.Retry.
            sleep: See utils.Retry.
            backoff_factor: See utils.Retry.
            other_retriable_errors: A tuple of error types that should be retried
                                    other than errors.HttpError.
        """
        self._execute_once_functor = execute_once_functor
        self._requests = requests
        # A dictionary that maps request id to pending request.
        self._pending_requests = {}
        # A dictionary that maps request id to a tuple (response, exception).
        self._final_results = {}
        self._retry_http_codes = retry_http_codes
        self._max_retry = max_retry
        self._sleep = sleep
        self._backoff_factor = backoff_factor
        self._other_retriable_errors = other_retriable_errors

    def _ShoudRetry(self, exception):
        """Check if an exception is retriable."""
        if isinstance(exception, self._other_retriable_errors):
            return True

        if (isinstance(exception, errors.HttpError) and
                exception.code in self._retry_http_codes):
            return True
        return False

    def _ExecuteOnce(self):
        """Executes pending requests and update it with failed, retriable ones.

        Raises:
            HasRetriableRequestsError: if some requests fail and are retriable.
        """
        results = self._execute_once_functor(self._pending_requests)
        # Update final_results with latest results.
        self._final_results.update(results)
        # Clear pending_requests
        self._pending_requests.clear()
        for request_id, result in results.iteritems():
            exception = result[1]
            if exception is not None and self._ShoudRetry(exception):
                # If this is a retriable exception, put it in pending_requests
                self._pending_requests[request_id] = self._requests[request_id]
        if self._pending_requests:
            # If there is still retriable requests pending, raise an error
            # so that Retry will retry this function with pending_requests.
            raise errors.HasRetriableRequestsError(
                "Retriable errors: %s" % [str(results[rid][1])
                                          for rid in self._pending_requests])

    def Execute(self):
        """Executes the requests and retry if necessary.

        Will populate self._final_results.
        """
        def _ShouldRetryHandler(exc):
            """Check if |exc| is a retriable exception.

            Args:
                exc: An exception.

            Returns:
                True if exception is of type HasRetriableRequestsError; False otherwise.
            """
            should_retry = isinstance(exc, errors.HasRetriableRequestsError)
            if should_retry:
                logger.info("Will retry failed requests.", exc_info=True)
                logger.info("%s", exc)
            return should_retry

        try:
            self._pending_requests = self._requests.copy()
            Retry(
                _ShouldRetryHandler, max_retries=self._max_retry,
                functor=self._ExecuteOnce,
                sleep_multiplier=self._sleep,
                retry_backoff_factor=self._backoff_factor)
        except errors.HasRetriableRequestsError:
            logger.debug("Some requests did not succeed after retry.")

    def GetResults(self):
        """Returns final results.

        Returns:
            results, a dictionary in the following format
            {request_id: (response, exception)}
            request_ids are those from requests; response
            is the http response for the request or None on error;
            exception is an instance of DriverError or None if no error.
        """
        return self._final_results