# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Library to make common google storage operations more reliable.
"""

import logging
import os

from chromite.lib import cros_build_lib


# Default pathway; stored here rather than usual buildbot.constants since
# we don't want to import buildbot code from here.
# Note that this value is reset after GSContext via the GetDefaultGSUtilBin
# method; we set it initially here just for the sake of making clear it
# exists.
GSUTIL_BIN = None


class GSContextException(Exception):
  """Thrown when expected google storage preconditions are not met."""


class GSContextPreconditionFailed(GSContextException):
  """Thrown when google storage returns code=PreconditionFailed."""


class GSContext(object):
  """A class to wrap common google storage operations."""

  DEFAULT_BOTO_FILE = os.path.expanduser('~/.boto')
  # This is set for ease of testing.
  DEFAULT_GSUTIL_BIN = None
  DEFAULT_GSUTIL_BUILDER_BIN = '/b/build/third_party/gsutil/gsutil'
  # How many times to retry uploads.
  DEFAULT_RETRIES = 10

  # Multiplier for how long to sleep (in seconds) between retries; will delay
  # (1*sleep) the first time, then (2*sleep), continuing via attempt * sleep.
  DEFAULT_SLEEP_TIME = 60

  @classmethod
  def GetDefaultGSUtilBin(cls):
    if cls.DEFAULT_GSUTIL_BIN is None:
      gsutil_bin = cls.DEFAULT_GSUTIL_BUILDER_BIN
      if not os.path.exists(gsutil_bin):
        gsutil_bin = cros_build_lib.RunCommandCaptureOutput(
            ['which', 'gsutil']).output.strip()
      cls.DEFAULT_GSUTIL_BIN = gsutil_bin
    return cls.DEFAULT_GSUTIL_BIN

  def __init__(self, boto_file=None, acl_file=None,
               dry_run=False, gsutil_bin=None, retries=None, sleep=None):
    """Constructor.

    Args:
      boto_file: Fully qualified path to user's .boto credential file.
      acl_file: A permission file capable of setting different permissions
        for different sets of users.
      dry_run: Testing mode that prints commands that would be run.
      gsutil_bin: If given, the absolute path to the gsutil binary.  Else
        the default fallback will be used.
      retries: Number of times to retry a command before failing.
      sleep: Amount of time to sleep between failures.
    """
    if gsutil_bin is not None:
      self._CheckFile('gsutil not found', gsutil_bin)
    else:
      gsutil_bin = self.GetDefaultGSUtilBin()
    self.gsutil_bin = gsutil_bin

    # Prefer boto_file if specified, else prefer the env then the default.
    if boto_file is None:
      boto_file = os.environ.get('BOTO_CONFIG', self.DEFAULT_BOTO_FILE)
    self._CheckFile('Boto credentials not found', boto_file)
    self.boto_file = boto_file

    if acl_file is not None:
      self._CheckFile('Not a valid permissions file', acl_file)
    self.acl_file = acl_file

    self.dry_run = dry_run
    self._retries = self.DEFAULT_RETRIES if retries is None else int(retries)
    self._sleep_time = self.DEFAULT_SLEEP_TIME if sleep is None else int(sleep)

  def _CheckFile(self, errmsg, afile):
    """Pre-flight check for valid inputs.

    Args:
      errmsg: Error message to display.
      afile: Fully qualified path to test file existance.
    """
    if not os.path.isfile(afile):
      raise GSContextException('%s, %s is not a file' % (errmsg, afile))

  def CopyInto(self, local_path, remote_dir, filename=None, acl=None,
               version=None):
    """Upload a local file into a directory in google storage.

    Args:
      local_path: Local file path to copy.
      remote_dir: Full gs:// url of the directory to transfer the file into.
      filename: If given, the filename to place the content at; if not given,
        it's discerned from basename(local_path).
      acl: If given, a canned ACL.
      version: If given, the generation; essentially the timestamp of the last
        update.  Note this is not the same as sequence-number; it's
        monotonically increasing bucket wide rather than reset per file.
        The usage of this is if we intend to replace/update only if the version
        is what we expect.  This is useful for distributed reasons- for example,
        to ensure you don't overwrite someone else's creation, a version of
        0 states "only update if no version exists".
    """
    filename = filename if filename is not None else local_path
    # Basename it even if an explicit filename was given; we don't want
    # people using filename as a multi-directory path fragment.
    return self.Copy(local_path,
                      '%s/%s' % (remote_dir, os.path.basename(filename)),
                      acl=acl, version=version)

  def _DoCommand(self, gsutil_cmd, headers=()):
    """Run a gsutil command, suppressing output, and setting retry/sleep.

    Returns:
      A RunCommandResult object.
    """
    cmd = [self.gsutil_bin]
    for header in headers:
      cmd += ['-h', header]
    cmd.extend(gsutil_cmd)

    if self.dry_run:
      logging.debug("%s: would've ran %r", self.__class__.__name__, cmd)
    else:
      return cros_build_lib.RetryCommand(
          cros_build_lib.RunCommandCaptureOutput, self._retries, cmd,
          sleep=self._sleep_time, extra_env={'BOTO_CONFIG': self.boto_file})

  def Copy(self, src_path, dest_path, acl=None, version=None):
    """Copy to/from GS bucket.

    Canned ACL permissions can be specified on the gsutil cp command line.

    More info:
    https://developers.google.com/storage/docs/accesscontrol#applyacls

    Args:
      src_path: Fully qualified local path or full gs:// path of the src file.
      dest_path: Fully qualified local path or full gs:// path of the dest
                 file.
      acl: One of the google storage canned_acls to apply.
      version: If given, the generation; essentially the timestamp of the last
        update.  Note this is not the same as sequence-number; it's
        monotonically increasing bucket wide rather than reset per file.
        The usage of this is if we intend to replace/update only if the version
        is what we expect.  This is useful for distributed reasons- for example,
        to ensure you don't overwrite someone else's creation, a version of
        0 states "only update if no version exists".

    Raises:
      RunCommandError if the command failed despite retries.
    Returns:
      Return the CommandResult from the run.
    """
    cmd, headers = [], []

    if version is not None:
      headers = ['x-goog-if-generation-match:%d' % version]

    cmd.append('cp')

    acl = self.acl_file if acl is None else acl
    if acl is not None:
      cmd += ['-a', acl]

    cmd += ['--', src_path, dest_path]

    try:
      # For ease of testing, only pass headers if we got some.
      kwds = {'headers': headers} if headers else {}
      return self._DoCommand(cmd, **kwds)
    # gsutil uses the same exit code for any failure, so we are left to
    # parse the output as needed.
    except cros_build_lib.RunCommandError as e:
      if 'code=PreconditionFailed' in e.result.output:
        raise GSContextPreconditionFailed(e)
      raise

  def SetACL(self, upload_url, acl=None):
    """Set access on a file already in google storage.

    Args:
      upload_url: gs:// url that will have acl applied to it.
      acl: An ACL permissions file or canned ACL.
    """
    if acl is None:
      if not self.acl_file:
        raise GSContextException(
            "SetAcl invoked w/out a specified acl, nor a default acl.")
      acl = self.acl_file

    self._DoCommand(['setacl', acl, upload_url])

# Set GSUTIL_BIN now.
try:
  GSUTIL_BIN = GSContext.GetDefaultGSUtilBin()
except cros_build_lib.RunCommandError:
  # Ignore it; let consuming code go boom in this case.
  cros_build_lib.logger.warning("Didn't find a usable gsutil in default paths")