# -*- coding: utf-8 -*-
# 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.
  - GET /extract/<bucket>/path/to/archive?file=path/to/file
      Extract a file form a compressed/uncompressed TAR archive.
"""

from __future__ import print_function

import argparse
import functools
import os
import subprocess
import sys
import tempfile

from six.moves import http_client
from six.moves import urllib

import requests
import cherrypy  # pylint: disable=import-error

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

_WRITE_BUFFER_SIZE_BYTES = 1024 * 1024  # 1 MB

# When extract files from TAR (either compressed or uncompressed), we suppose
# the TAR exists, so we can call `download` RPC to get it. It's straightforward
# for uncompressed TAR. But for compressed TAR, we cannot `download` it from
# GS because it doesn't exist there at all. In this case, we call `decompress`
# RPC internally to download and decompress. In order to tell if invoke of
# `download` RPC is a real download, or download+decompress, we use below HTTP
# header as a flag. It can also tell use what's the extension name of the
# compressed tar, e.g. '.tar.gz', etc. We use this information to get the file
# name on GS.
_HTTP_HEADER_COMPRESSED_TAR_EXT = 'X-Compressed-Tar-Ext'

# 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 _log_filtered_headers(all_headers, filtered_headers, level=logging.DEBUG):
  """Log the filtered headers only."""
  _log('Filtered headers: %s', {k: all_headers.get(k) for k in
                                filtered_headers}, level=level)


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.')

  if not ext_names:
    return filename

  for ext_name in ext_names:
    if filename.endswith(ext_name):
      return filename

  raise ValueError("Extension name of '%s' isn't in %s" % (filename,
                                                           ext_names))


def _safe_get_param(all_params, param_name):
  """Check if |param_name| is in |all_params| and has non-empty value.

  Args:
    all_params: A dict of all parameters of the call.
    param_name: The parameter name to be checked.

  Returns:
    A set of all non-empty value.

  Raises:
    Raise HTTP 400 error if no valid parameter in |all_params|.
  """
  try:
    value = all_params[param_name]
  except KeyError:
    raise cherrypy.HTTPError(http_client.BAD_REQUEST,
                             'Parameter "%s" is required!' % param_name)

  return set(value) if isinstance(value, list) else {value}


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_client.BAD_REQUEST, err.message)  # pylint: disable=exception-message-attribute
  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 = urllib.parse.urlunsplit(
        self._url + ('%s/%s' % (action, path),
                     urllib.parse.urlencode(args or {}),
                     None))
    _log('Sending request to caching server: %s', url)
    # The header to control using or bypass cache.
    _log_filtered_headers(headers, ('Range', 'X-No-Cache',
                                    _HTTP_HEADER_COMPRESSED_TAR_EXT))
    rsp = requests.get(url, headers=headers, stream=True)
    _log('Caching server response %s: %s', rsp.status_code, url)
    _log_filtered_headers(rsp.headers, ('Content-Type', 'Content-Length',
                                        'Content-Range', 'X-Cache',
                                        'Cache-Control', 'Date'))
    rsp.raise_for_status()
    return rsp

  def _download_and_decompress_tar(self, path, ext_name, headers=None):
    """Helper function to download and decompress compressed TAR."""
    # The |path| we have is like foo.tar. Combine with |ext_name| we can get
    # the compressed file name on Google storage, e.g.
    # 'foo.tar' + '.gz' => foo.tar.gz
    # But it's special for '.tgz', i.e. 'foo.tar' + '.tgz' => 'foo.tgz'
    if ext_name == '.tgz':
      path, _ = os.path.splitext(path)

    path = '%s%s' % (path, ext_name)
    _log('Download and decompress %s', path)
    return self._call('decompress', path, headers=headers)

  def download(self, path, headers=None):
    """Download file |path| from the caching server."""
    # When the request comes with header _HTTP_HEADER_COMPRESSED_TAR_EXT, we
    # internally call `decompress` instead of `download` because Google storage
    # only has the compressed version of the file to be "downloaded".
    ext_name = headers.pop(_HTTP_HEADER_COMPRESSED_TAR_EXT, None)

    # RPC `decompress` validates ext_name, so doesn't do that here.
    if ext_name:
      return self._download_and_decompress_tar(path, ext_name, headers=headers)
    else:
      return self._call('download', path, headers=headers)


_SERVICE_ACCOUNT_BOTO_FILE = os.path.expanduser('~/.boto.service_account')


class _GSContext(object):
  """A wrapper class of gs.GSContext for service account migration purpose."""

  def __init__(self):
    self._ctx_default = gs.GSContext()
    if os.path.isfile(_SERVICE_ACCOUNT_BOTO_FILE):
      self._ctx_service_account = gs.GSContext(
          boto_file=_SERVICE_ACCOUNT_BOTO_FILE)
    else:
      self._ctx_service_account = None

  def fetch_file(self, path, want_content=True):
    """Fetch the file stat and/or content from GS bucket.

    Args:
      path: The GS path of the file to fetch.
      want_content: A boolean of whether fetch the content (as an iterator).

    Returns:
      A tuple of (stat, content) which is the GS file stat and content
      iterator (or None).
    """
    try:
      stat = self._ctx_default.Stat(path)
      ctx = self._ctx_default
    except gs.GSCommandError as err:
      if not self._ctx_service_account:
        raise
      if not err.stderr.startswith("You aren't authorized to read "):
        raise
      _log('Not authorized by default. Trying service account.')
      stat = self._ctx_service_account.Stat(path)
      ctx = self._ctx_service_account

    if want_content:
      _log('Downloading %s', path, level=logging.INFO)
      return stat, ctx.StreamingCat(path)

    return stat, None


class GsArchiveServerError(Exception):
  """Standard exception class for GsArchiveServer."""


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

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

  @cherrypy.expose
  @_to_cherrypy_error
  def list_dir(self, *args):
    """Lists contents of specified GS bucket/<board>/version."""
    path = 'gs://%s' % _check_file_extension('/'.join(args))
    gs_cmd = ['gsutil', 'ls', path]
    try:
      proc = subprocess.Popen(gs_cmd, stdout=subprocess.PIPE,
                              stderr=subprocess.PIPE)
      content, _ = proc.communicate()
    except subprocess.CalledProcessError as e:
      raise cherrypy.HTTPError(http_client.NOT_FOUND, e.output)
    return content


  @cherrypy.expose
  @cherrypy.config(**{'response.stream': True})
  @_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))
    try:
      want_content = cherrypy.request.method != 'HEAD'
      stat, content = self._gsutil.fetch_file(path, want_content)
    except gs.GSNoSuchKey as err:
      raise cherrypy.HTTPError(http_client.NOT_FOUND, err.message)  # pylint: disable=exception-message-attribute
    except gs.GSCommandError as err:
      if "You aren't authorized to read" in err.result.error:
        status = http_client.UNAUTHORIZED
      else:
        status = http_client.SERVICE_UNAVAILABLE
      raise cherrypy.HTTPError(status, '%s: %s' % (err.message,  # pylint: disable=exception-message-attribute
                                                   err.result.error))

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

    return content

  @cherrypy.expose
  @cherrypy.config(**{'response.stream': True})
  @_to_cherrypy_error
  def extract(self, *args, **kwargs):
    """Extract files from a compressed/uncompressed Tar archive.

    The RPC accepts query 'file=' which is either a file name or a glob pattern.

    It's optional to encode the file name or pattern in 'percent-encoding', i.e.
    '/' -> '%2F', '*' -> '%2A', etc.

    Examples:
      Extracting file 'path/to/file' from files.tgz:
      GET /extract/<bucket>/files.tgz?file=path%2Fto%2Ffile

    Args:
      *args: All parts of the GS path of the archive, without gs:// prefix.
      kwargs: file: The path or pattern of file to be extracted.

    Returns:
      Extracted file content (Binary data).
    """
    archive = _check_file_extension(
        '/'.join(args),
        ext_names=['.tar', '.tar.gz', '.tgz', '.tar.bz2', '.tar.xz'])
    files = _safe_get_param(kwargs, 'file')
    if len(files) != 1:
      raise GsArchiveServerError('Cannot extract more than one file at a time.')
    file_to_be_extracted = files.pop()
    _log('Extracting "%s" from "%s".', file_to_be_extracted, archive)
    archive_basename, archive_extname = os.path.splitext(archive)
    headers = cherrypy.request.headers.copy()
    if archive_extname == '.tar':
      decompressed_archive_name = archive
    else:
      # Compressed tar archives: we don't decompress them here. Instead, we
      # suppose they have been decompressed, and continue the routine to extract
      # from the supposed decompressed archive name.
      # The magic is, we set a special HTTP header, and pass it to caching
      # server. Eventually, caching server loops it back to `download` RPC.
      # In `download`, we check this header. If it exists, then call
      # `decompress` RPC other than a normal `download` RPC.
      headers[_HTTP_HEADER_COMPRESSED_TAR_EXT] = archive_extname
      # Get the name of decompressed archive, e.g. foo.tgz => foo.tar,
      # bar.tar.xz => bar.tar, etc.
      if archive_extname == '.tgz':
        decompressed_archive_name = '%s.tar' % archive_basename
      else:
        decompressed_archive_name = archive_basename

    return self._extract_file_from_tar(file_to_be_extracted,
                                       decompressed_archive_name, headers)

  def _extract_file_from_tar(self, target_file, archive, headers=None):
    """Extracts the target file from the given archive.

    Args:
      target_file: The file to be extracted.
      archive: The archive from which the file should be extracted.
      headers: headers for the request that will get the archive.

    Returns:
      Extracted file content (Binary data).
    """
    rsp = self._caching_server.download(archive, headers=headers)
    cmd = ['tar', '-O', '-x', target_file]

    with tempfile.SpooledTemporaryFile(max_size=_SPOOL_FILE_SIZE_BYTES) as df:
      proc = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=df)
      for chunk in rsp.iter_content(constants.READ_BUFFER_SIZE_BYTES):
        proc.stdin.write(chunk)
      proc.stdin.close()
      proc.wait()

      # Update the response's content type to support yielding binary data.
      cherrypy.response.headers['Content-Type'] = 'application/octet-stream'

      # Go to the beginning of the file.
      df.seek(0)

      # Read the SpooledFile in chunks and yield the data.
      while True:
        data = df.read(constants.READ_BUFFER_SIZE_BYTES)
        if not data:
          break
        yield data

  @cherrypy.expose
  @cherrypy.config(**{'response.stream': True})
  @_to_cherrypy_error
  def decompress(self, *args):
    """Decompress the compressed TAR archive.

    Args:
      *args: All parts of the GS path of the compressed archive, without gs://
          prefix.

    Returns:
      The content generator of decompressed TAR archive.
    """
    zarchive = _check_file_extension(
        '/'.join(args), ext_names=['.tar.gz', '.tar.bz2', '.tar.xz', '.tgz'])
    _log('Decompressing "%s"', zarchive)

    rsp = self._caching_server.download(zarchive,
                                        headers=cherrypy.request.headers)
    cherrypy.response.headers['Content-Type'] = 'application/x-tar'
    cherrypy.response.headers['Accept-Ranges'] = 'bytes'

    basename = os.path.basename(zarchive)
    _, extname = os.path.splitext(basename)

    # Command lines used to decompress file.
    commands = {
        '.gz': ['gzip', '-d', '-c'],
        '.tgz': ['gzip', '-d', '-c'],
        '.xz': ['xz', '-d', '-c'],
        '.bz2': ['bzip2', '-d', '-c'],
    }
    decompressed_file = tempfile.SpooledTemporaryFile(
        max_size=_SPOOL_FILE_SIZE_BYTES)
    proc = subprocess.Popen(commands[extname], stdin=subprocess.PIPE,
                            stdout=decompressed_file)
    _log('Decompress process id: %s.', proc.pid)
    for chunk in rsp.iter_content(constants.READ_BUFFER_SIZE_BYTES):
      proc.stdin.write(chunk)
    proc.stdin.close()
    _log('Decompression done.')
    proc.wait()

    # The header of Content-Length is necessary for supporting range request.
    # So we have to decompress the file locally to get the size. This may cause
    # connection timeout issue if the decompression take too long time (e.g. 90
    # seconds). As a reference, it takes about 10 seconds to decompress a 400MB
    # tgz file.
    decompressed_file.seek(0, os.SEEK_END)
    content_length = decompressed_file.tell()
    _log('Decompressed content length is %d bytes.', content_length)
    cherrypy.response.headers['Content-Length'] = str(content_length)
    decompressed_file.seek(0)

    def decompressed_content():
      _log('Streaming decompressed content of "%s" begin.', zarchive)
      while True:
        data = decompressed_file.read(constants.READ_BUFFER_SIZE_BYTES)
        if not data:
          break
        yield data
      decompressed_file.close()
      _log('Streaming of "%s" done.', zarchive)

    return decompressed_content()


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 = urllib.parse.urlsplit(input_string)
  if not split_result.scheme:
    input_string = 'http://%s' % input_string

  split_result = urllib.parse.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.')

  parser.add_argument(
      '-b', '--bind', default='127.0.0.1', type=str,
      help='Option to specify alternate bind address. By default, '
      'gs_archive_server starts on 127.0.0.1.')

  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(0o002)

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

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


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