# Copyright 2018 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.

"""The backend service of Google Storage Cache Server.

Run `./bin/gs_archive_server` to start the server. After started, it listens on
a TCP port and/or an Unix domain socket. The latter performs better when work
with a local hosted reverse proxy server, e.g. Nginx.

The server accepts below requests:
  - GET /download/<bucket>/path/to/file: download the file from google storage
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import argparse
import contextlib
import functools
import os
import StringIO
import subprocess
import sys
import tempfile
import urllib
import urlparse

import cherrypy
import requests

import tarfile_utils
from chromite.lib import cros_logging as logging
from chromite.lib import gs

# some http status codes
_HTTP_BAD_REQUEST = 400
_HTTP_UNAUTHORIZED = 401
_HTTP_NOT_FOUND = 404
_HTTP_SERVICE_UNAVAILABLE = 503

_READ_BUFFER_SIZE_BYTES = 1024 * 1024  # 1 MB
_WRITE_BUFFER_SIZE_BYTES = 1024 * 1024  # 1 MB

# The max size of temporary spool file in memory.
_SPOOL_FILE_SIZE_BYTES = 100 * 1024 * 1024  # 100 MB

_logger = logging.getLogger(__file__)


def _log(*args, **kwargs):
  """A wrapper function of logging.debug/info, etc."""
  level = kwargs.pop('level', logging.DEBUG)
  _logger.log(level, extra=cherrypy.request.headers, *args, **kwargs)


def _check_file_extension(filename, ext_names=None):
  """Check the file name and, optionally, the ext name.

  Args:
    filename: The file name to be checked.
    ext_names: The valid extension of |filename| should have.

  Returns:
    The filename if the check is good.

  Raises:
    ValueError: Raised if the checking failed.
  """
  if not filename:
    raise ValueError('File name is required.')

  for ext_name in ext_names or []:
    if filename.endswith(ext_name):
      break
    else:
      raise ValueError("Extension name of '%s' isn't in %s" % (filename,
                                                               ext_names))
  return filename


def _to_cherrypy_error(func):
  """A decorator to convert Exceptions raised to proper cherrypy.HTTPError."""
  @functools.wraps(func)
  def func_wrapper(*args, **kwargs):
    try:
      return func(*args, **kwargs)
    except requests.HTTPError as err:
      # cherrypy.HTTPError wraps the error messages with HTML tags. But
      # requests.HTTPError also do same work. So return the error message
      # directly.
      cherrypy.response.status = err.response.status_code
      return err.response.content
    except ValueError as err:
      # The exception message is just a plain text, so wrap it with
      # cherrypy.HTTPError to have necessary HTML tags
      raise cherrypy.HTTPError(_HTTP_BAD_REQUEST, err.message)
  return func_wrapper


class _CachingServer(object):
  r"""The interface of caching server for GsArchiveServer.

  This class provides an interface to work with the caching server (usually a
  reversed http proxy server) which caches all intermediate results, e.g.
  downloaded files, etc. and serves to GsArchiveServer.

  The relationship of this class and other components is:
    /-------------(python function call)-----------------------\
    |                                                          |
    v                                                          |
  _CachingServer --(http/socket)--> NGINX --(http/socket)--> GsArchiveServer
                                      ^                        |
                                      |                     (https)
  End user, DUTs ---(http)------------/                        |
                                                               V
                                                         GoogleStorage
  """

  def __init__(self, url):
    """Constructor

    Args:
      url: A tuple of URL scheme and netloc.

    Raises:
      ValueError: Raised when input URL in wrong format.
    """
    self._url = url

  def _call(self, action, path, args=None, headers=None):
    """Helper function to generate all RPC calls to the proxy server."""
    url = urlparse.urlunsplit(self._url + ('%s/%s' % (action, path),
                                           urllib.urlencode(args or {}), None))
    _log('Sending request to proxy: %s', url)
    rsp = requests.get(url, headers=headers, stream=True)
    _log('Proxy response %s', rsp.status_code)
    rsp.raise_for_status()
    return rsp

  def download(self, path, headers=None):
    """Call download RPC."""
    return self._call('download', path, headers=headers)


class GsArchiveServer(object):
  """The backend of Google Storage Cache server."""

  def __init__(self, caching_server):
    self._gsutil = gs.GSContext()
    self._caching_server = caching_server

  @cherrypy.expose
  @_to_cherrypy_error
  def list_member(self, *args):
    """Get file list of an tar archive in CSV format.

    An example, GET /list_member/bucket/path/to/file.tar
    The output is in format of:
      <file name>,<data1>,<data2>,...<data6>
      <file name>,<data1>,<data2>,...<data6>
      ...

    Details:
      <file name>: The file name of the member, in URL percent encoding, e.g.
        path/to/file,name  -> path/to/file%2Cname.
      <data1>: File record start offset, in bytes.
      <data2>: File record size, in bytes.
      <data3>: File record end offset, in bytes.
      <data4>: File content start offset, in bytes.
      <data5>: File content size, in bytes.
      <data6>: File content end offset, in bytes.

    This is an internal RPC and shouldn't be called by end user!

    Args:
      *args: All parts of tar file name (must end with '.tar').

    Returns:
      The generator of CSV stream.
    """
    # TODO(guocb): new parameter to filter the list

    archive = _check_file_extension('/'.join(args), ext_names=['.tar'])
    rsp = self._caching_server.download(archive, cherrypy.request.headers)
    cherrypy.response.headers['Content-Type'] = 'text/csv'

    # We run tar command to get member list of a tar file (python tarfile module
    # is too slow). Option '--block-number/-R' of tar prints out the starting
    # block number for each file record.
    _log('list member of the tar %s', archive)
    tar_tv = tempfile.SpooledTemporaryFile(max_size=_SPOOL_FILE_SIZE_BYTES)
    tar = subprocess.Popen(['tar', 'tv', '--block-number'],
                           stdin=subprocess.PIPE, stdout=tar_tv)
    for chunk in rsp.iter_content(_READ_BUFFER_SIZE_BYTES):
      tar.stdin.write(chunk)

    tar.wait()

    def _tar_member_list():
      with tar_tv, contextlib.closing(StringIO.StringIO()) as stream:
        tar_tv.seek(0)
        for info in tarfile_utils.list_tar_members(tar_tv):
          # some pre-computation for easier use of clients
          content_end = info.content_start + info.size - 1
          record_end = info.record_start + info.record_size - 1

          # encode file name using URL percent encoding, so ',' => '%2C'
          stream.write('%s,%d,%d,%d,%d,%d,%d\n' % (
              urllib.quote(info.filename), info.record_start, info.record_size,
              record_end, info.content_start, info.size, content_end))

          if stream.tell() > _WRITE_BUFFER_SIZE_BYTES:
            yield stream.getvalue()
            stream.seek(0)

        if stream.tell():
          yield stream.getvalue()

      _log('list_member done')

    return _tar_member_list()

  @cherrypy.expose
  @_to_cherrypy_error
  def download(self, *args):
    """Download a file from Google Storage.

    For example: GET /download/bucket/path/to/file. This downloads the file
    gs://bucket/path/to/file.

    Args:
      *args: All parts of the GS file path without gs:// prefix.

    Returns:
      The stream of downloaded file.
    """
    path = 'gs://%s' % _check_file_extension('/'.join(args))

    _log('Downloading %s', path, level=logging.INFO)
    try:
      stat = self._gsutil.Stat(path)
      content = self._gsutil.StreamingCat(path)
    except gs.GSNoSuchKey as err:
      raise cherrypy.HTTPError(_HTTP_NOT_FOUND, err.message)
    except gs.GSCommandError as err:
      if "You aren't authorized to read" in err.result.error:
        status = _HTTP_UNAUTHORIZED
      else:
        status = _HTTP_SERVICE_UNAVAILABLE
      raise cherrypy.HTTPError(status, '%s: %s' % (err.message,
                                                   err.result.error))

    cherrypy.response.headers.update({
        'Content-Type': stat.content_type,
        'Accept-Ranges': 'bytes',
        'Content-Length': stat.content_length,
    })
    _log('Download complete.')

    return content

  # pylint:disable=protected-access
  download._cp_config = {'response.stream': True}
  list_member._cp_config = {'response.stream': True}


def _url_type(input_string):
  """Ensure |input_string| is a valid URL and convert to target type.

  The target type is a tuple of (scheme, netloc).
  """
  split_result = urlparse.urlsplit(input_string)
  if not split_result.scheme:
    input_string = 'http://%s' % input_string

  split_result = urlparse.urlsplit(input_string)
  if not split_result.scheme or not split_result.netloc:
    raise argparse.ArgumentTypeError('Wrong URL format: %s' % input_string)

  return split_result.scheme, split_result.netloc


def parse_args(argv):
  """Parse arguments."""
  parser = argparse.ArgumentParser(
      formatter_class=argparse.RawDescriptionHelpFormatter,
      description=__doc__)

  # The service can either bind to a socket or listen to a port, but doesn't do
  # both.
  socket_or_port = parser.add_mutually_exclusive_group(required=True)
  socket_or_port.add_argument('-s', '--socket',
                              help='Unix domain socket to bind')
  socket_or_port.add_argument('-p', '--port', type=int,
                              help='Port number to listen.')

  # TODO(guocb): support Unix domain socket
  parser.add_argument(
      '-c', '--caching-server', required=True, type=_url_type,
      help='URL of the proxy server. Valid format is '
      '[http://]{<hostname>|<IP>}[:<port_number>]. When skipped, the default '
      'scheme is http and port number is 80. Any other components in URL are '
      'ignored.')
  return parser.parse_args(argv)


def setup_logger():
  """Setup logger."""
  formatter = logging.Formatter(
      '%(module)s:%(asctime)-15s [%(Remote-Addr)s:%(thread)d] %(levelname)s:'
      ' %(message)s')
  handler = logging.StreamHandler(sys.stdout)
  handler.setFormatter(formatter)
  _logger.setLevel(logging.DEBUG)
  _logger.addHandler(handler)


def main(argv):
  """Main function."""
  args = parse_args(argv)
  setup_logger()

  if args.socket:
    # in order to allow group user writing to domain socket, the directory
    # should have GID bit set, i.e. g+s
    os.umask(0002)

  cherrypy.server.socket_port = args.port
  cherrypy.server.socket_file = args.socket

  cherrypy.quickstart(GsArchiveServer(_CachingServer(args.caching_server)))


if __name__ == '__main__':
  sys.exit(main(sys.argv[1:]))