# Copyright (c) 2013 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.

import os
import threading

import build_artifact
import common_util
import log_util


class Downloader(log_util.Loggable):
  """Downloader of images to the devsever.

  Given a URL to a build on the archive server:
    - Caches that build and the given artifacts onto the devserver.
    - May also initiate caching of related artifacts in the background.

  Private class members:
    archive_url: a URL where to download build artifacts from.
    static_dir: local filesystem directory to store all artifacts.
    build_dir: the local filesystem directory to store artifacts for the given
      build defined by the archive_url.
  """

  # This filename must be kept in sync with clean_staged_images.py
  _TIMESTAMP_FILENAME = 'staged.timestamp'

  def __init__(self, static_dir, archive_url):
    super(Downloader, self).__init__()
    self._archive_url = archive_url
    self._static_dir = static_dir
    self._build_dir = Downloader.GetBuildDir(static_dir, archive_url)

  @staticmethod
  def ParseUrl(archive_url):
    """Parses archive_url into rel_path and build.

    Parses archive_url into rel_path and build e.g.
    gs://chromeos-image-archive/{rel_path}/{build}.

    Args:
      archive_url: a URL at which build artifacts are archived.

    Returns:
      A tuple of (build relative path, short build name)
    """
    # The archive_url is of the form gs://server/[some_path/target]/...]/build
    # This function discards 'gs://server/' and extracts the [some_path/target]
    # as rel_path and the build as build.
    sub_url = archive_url.partition('://')[2]
    split_sub_url = sub_url.split('/')
    rel_path = '/'.join(split_sub_url[1:-1])
    build = split_sub_url[-1]
    return rel_path, build

  @staticmethod
  def GetBuildDir(static_dir, archive_url):
    """Returns the path to where the artifacts will be staged.

    Args:
      static_dir: The base static dir that will be used.
      archive_url: The gs path to the archive url.
    """
    # Parse archive_url into rel_path (contains the build target) and
    # build e.g. gs://chromeos-image-archive/{rel_path}/{build}.
    rel_path, build = Downloader.ParseUrl(archive_url)
    return os.path.join(static_dir, rel_path, build)

  @staticmethod
  def _TouchTimestampForStaged(directory_path):
    file_name = os.path.join(directory_path, Downloader._TIMESTAMP_FILENAME)
    # Easiest python version of |touch file_name|
    with file(file_name, 'a'):
      os.utime(file_name, None)

  def Download(self, artifacts):
    """Downloads and caches the |artifacts|.

    Downloads and caches the |artifacts|. Returns once these
    are present on the devserver. A call to this will attempt to cache
    non-specified artifacts in the background following the principle of
    spatial locality.

    Args:
      artifacts: a list of artifact names that correspond to artifacts to stage.
    """
    common_util.MkDirP(self._build_dir)

    # We are doing some work on this build -- let's touch it to indicate that
    # we shouldn't be cleaning it up anytime soon.
    Downloader._TouchTimestampForStaged(self._build_dir)

    # Create factory to create build_artifacts from artifact names.
    build = self.ParseUrl(self._archive_url)[1]
    factory = build_artifact.ArtifactFactory(self._build_dir, self._archive_url,
                                             artifacts, build)
    background_artifacts = factory.OptionalArtifacts()
    if background_artifacts:
      self._DownloadArtifactsInBackground(background_artifacts)

    required_artifacts = factory.RequiredArtifacts()
    str_repr = [str(a) for a in required_artifacts]
    self._Log('Downloading artifacts %s.', ' '.join(str_repr))
    self._DownloadArtifactsSerially(required_artifacts, no_wait=True)

  def _DownloadArtifactsSerially(self, artifacts, no_wait):
    """Simple function to download all the given artifacts serially.

    Args:
      artifacts: List of build_artifact.BuildArtifact instances to download.
      no_wait: If True, don't block waiting for artifact to exist if we fail to
               immediately find it.
    """
    for artifact in artifacts:
      artifact.Process(no_wait)

  def _DownloadArtifactsInBackground(self, artifacts):
    """Downloads |artifacts| in the background.

    Downloads |artifacts| in the background. As these are backgrounded
    artifacts, they are done best effort and may not exist.

    Args:
      artifacts: List of build_artifact.BuildArtifact instances to download.
    """
    self._Log('Invoking background download of artifacts for %r', artifacts)
    thread = threading.Thread(target=self._DownloadArtifactsSerially,
                              args=(artifacts, False))
    thread.start()