# Copyright 2016 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Takes care of manipulating the chrome's HTTP cache.
"""

from datetime import datetime
import json
import os
import re
import shutil
import subprocess
import sys
import tempfile
import zipfile

_SRC_DIR = os.path.abspath(os.path.join(
    os.path.dirname(__file__), '..', '..', '..'))

sys.path.append(os.path.join(_SRC_DIR, 'build', 'android'))
from pylib import constants

import device_setup
import options


OPTIONS = options.OPTIONS


# Cache back-end types supported by cachetool.
BACKEND_TYPES = ['simple']

# Default build output directory.
OUT_DIRECTORY = os.getenv('CR_OUT_FULL', os.path.join(
    os.path.dirname(__file__), '../../../out/Release'))

# Default cachetool binary location.
CACHETOOL_BIN_PATH = os.path.join(OUT_DIRECTORY, 'cachetool')

# Default content_decoder_tool binary location.
CONTENT_DECODER_TOOL_BIN_PATH = os.path.join(OUT_DIRECTORY,
                                             'content_decoder_tool')

# Regex used to parse HTTP headers line by line.
HEADER_PARSING_REGEX = re.compile(r'^(?P<header>\S+):(?P<value>.*)$')


def _EnsureCleanCacheDirectory(directory_dest_path):
  """Ensure that a cache directory is created and clean.

  Args:
    directory_dest_path: Path of the cache directory to ensure cleanliness.
  """
  if os.path.isdir(directory_dest_path):
    shutil.rmtree(directory_dest_path)
  elif not os.path.isdir(os.path.dirname(directory_dest_path)):
    os.makedirs(os.path.dirname(directory_dest_path))
  assert not os.path.exists(directory_dest_path)


def _RemoteCacheDirectory():
  """Returns the path of the cache directory's on the remote device."""
  return '/data/data/{}/cache/Cache'.format(
      constants.PACKAGE_INFO[OPTIONS.chrome_package_name].package)


def _AdbShell(adb, cmd):
  adb.Shell(subprocess.list2cmdline(cmd))


def PullBrowserCache(device):
  """Pulls the browser cache from the device and saves it locally.

  Cache is saved with the same file structure as on the device. Timestamps are
  important to preserve because indexing and eviction depends on them.

  Returns:
    Temporary directory containing all the browser cache.
  """
  _INDEX_DIRECTORY_NAME = 'index-dir'
  _REAL_INDEX_FILE_NAME = 'the-real-index'

  remote_cache_directory = _RemoteCacheDirectory()
  save_target = tempfile.mkdtemp(suffix='.cache')

  # Pull the cache recursively.
  device.adb.Pull(remote_cache_directory, save_target)

  # Update the modification time stamp on the local cache copy.
  def _UpdateTimestampFromAdbStat(filename, stat):
    assert os.path.exists(filename)
    os.utime(filename, (stat.st_time, stat.st_time))

  for filename, stat in device.adb.Ls(remote_cache_directory):
    if filename == '..':
      continue
    if filename == '.':
      cache_directory_stat = stat
      continue
    original_file = os.path.join(remote_cache_directory, filename)
    saved_file = os.path.join(save_target, filename)
    _UpdateTimestampFromAdbStat(saved_file, stat)
    if filename == _INDEX_DIRECTORY_NAME:
      # The directory containing the index was pulled recursively, update the
      # timestamps for known files. They are ignored by cache backend, but may
      # be useful for debugging.
      index_dir_stat = stat
      saved_index_dir = os.path.join(save_target, _INDEX_DIRECTORY_NAME)
      saved_index_file = os.path.join(saved_index_dir, _REAL_INDEX_FILE_NAME)
      for sub_file, sub_stat in device.adb.Ls(original_file):
        if sub_file == _REAL_INDEX_FILE_NAME:
          _UpdateTimestampFromAdbStat(saved_index_file, sub_stat)
          break
      _UpdateTimestampFromAdbStat(saved_index_dir, index_dir_stat)

  # Store the cache directory modification time. It is important to update it
  # after all files in it have been written. The timestamp is compared with
  # the contents of the index file when freshness is determined.
  _UpdateTimestampFromAdbStat(save_target, cache_directory_stat)
  return save_target


def PushBrowserCache(device, local_cache_path):
  """Pushes the browser cache saved locally to the device.

  Args:
    device: Android device.
    local_cache_path: The directory's path containing the cache locally.
  """
  remote_cache_directory = _RemoteCacheDirectory()

  # Clear previous cache.
  _AdbShell(device.adb, ['rm', '-rf', remote_cache_directory])
  _AdbShell(device.adb, ['mkdir', remote_cache_directory])

  # Push cache content.
  device.adb.Push(local_cache_path, remote_cache_directory)

  # Command queue to touch all files with correct timestamp.
  command_queue = []

  # Walk through the local cache to update mtime on the device.
  def MirrorMtime(local_path):
    cache_relative_path = os.path.relpath(local_path, start=local_cache_path)
    remote_path = os.path.join(remote_cache_directory, cache_relative_path)
    timestamp = os.stat(local_path).st_mtime
    touch_stamp = datetime.fromtimestamp(timestamp).strftime('%Y%m%d.%H%M%S')
    command_queue.append(['touch', '-t', touch_stamp, remote_path])

  for local_directory_path, dirnames, filenames in os.walk(
        local_cache_path, topdown=False):
    for filename in filenames:
      MirrorMtime(os.path.join(local_directory_path, filename))
    for dirname in dirnames:
      MirrorMtime(os.path.join(local_directory_path, dirname))
  MirrorMtime(local_cache_path)

  device_setup.DeviceSubmitShellCommandQueue(device, command_queue)


def ZipDirectoryContent(root_directory_path, archive_dest_path):
  """Zip a directory's content recursively with all the directories'
  timestamps preserved.

  Args:
    root_directory_path: The directory's path to archive.
    archive_dest_path: Archive destination's path.
  """
  with zipfile.ZipFile(archive_dest_path, 'w') as zip_output:
    timestamps = {}
    root_directory_stats = os.stat(root_directory_path)
    timestamps['.'] = {
        'atime': root_directory_stats.st_atime,
        'mtime': root_directory_stats.st_mtime}
    for directory_path, dirnames, filenames in os.walk(root_directory_path):
      for dirname in dirnames:
        subdirectory_path = os.path.join(directory_path, dirname)
        subdirectory_relative_path = os.path.relpath(subdirectory_path,
                                                     root_directory_path)
        subdirectory_stats = os.stat(subdirectory_path)
        timestamps[subdirectory_relative_path] = {
            'atime': subdirectory_stats.st_atime,
            'mtime': subdirectory_stats.st_mtime}
      for filename in filenames:
        file_path = os.path.join(directory_path, filename)
        file_archive_name = os.path.join('content',
            os.path.relpath(file_path, root_directory_path))
        file_stats = os.stat(file_path)
        timestamps[file_archive_name[8:]] = {
            'atime': file_stats.st_atime,
            'mtime': file_stats.st_mtime}
        zip_output.write(file_path, arcname=file_archive_name)
    zip_output.writestr('timestamps.json',
                        json.dumps(timestamps, indent=2))


def UnzipDirectoryContent(archive_path, directory_dest_path):
  """Unzip a directory's content recursively with all the directories'
  timestamps preserved.

  Args:
    archive_path: Archive's path to unzip.
    directory_dest_path: Directory destination path.
  """
  _EnsureCleanCacheDirectory(directory_dest_path)
  with zipfile.ZipFile(archive_path) as zip_input:
    timestamps = None
    for file_archive_name in zip_input.namelist():
      if file_archive_name == 'timestamps.json':
        timestamps = json.loads(zip_input.read(file_archive_name))
      elif file_archive_name.startswith('content/'):
        file_relative_path = file_archive_name[8:]
        file_output_path = os.path.join(directory_dest_path, file_relative_path)
        file_parent_directory_path = os.path.dirname(file_output_path)
        if not os.path.exists(file_parent_directory_path):
          os.makedirs(file_parent_directory_path)
        with open(file_output_path, 'w') as f:
          f.write(zip_input.read(file_archive_name))

    assert timestamps
    for relative_path, stats in timestamps.iteritems():
      output_path = os.path.join(directory_dest_path, relative_path)
      if not os.path.exists(output_path):
        os.makedirs(output_path)
      os.utime(output_path, (stats['atime'], stats['mtime']))


def CopyCacheDirectory(directory_src_path, directory_dest_path):
  """Copies a cache directory recursively with all the directories'
  timestamps preserved.

  Args:
    directory_src_path: Path of the cache directory source.
    directory_dest_path: Path of the cache directory destination.
  """
  assert os.path.isdir(directory_src_path)
  _EnsureCleanCacheDirectory(directory_dest_path)
  shutil.copytree(directory_src_path, directory_dest_path)


class CacheBackend(object):
  """Takes care of reading and deleting cached keys.
  """

  def __init__(self, cache_directory_path, cache_backend_type,
               cachetool_bin_path=CACHETOOL_BIN_PATH):
    """Chrome cache back-end constructor.

    Args:
      cache_directory_path: The directory path where the cache is locally
        stored.
      cache_backend_type: A cache back-end type in BACKEND_TYPES.
      cachetool_bin_path: Path of the cachetool binary.
    """
    assert os.path.isdir(cache_directory_path)
    assert cache_backend_type in BACKEND_TYPES
    assert os.path.isfile(cachetool_bin_path), 'invalid ' + cachetool_bin_path
    self._cache_directory_path = cache_directory_path
    self._cache_backend_type = cache_backend_type
    self._cachetool_bin_path = cachetool_bin_path
    # Make sure cache_directory_path is a valid cache.
    self._CachetoolCmd('validate')

  def ListKeys(self):
    """Lists cache's keys.

    Returns:
      A list of all keys stored in the cache.
    """
    return [k.strip() for k in self._CachetoolCmd('list_keys').split('\n')[:-1]]

  def GetStreamForKey(self, key, index):
    """Gets a key's stream.

    Args:
      key: The key to access the stream.
      index: The stream index:
          index=0 is the HTTP response header;
          index=1 is the transport encoded content;
          index=2 is the compiled content.

    Returns:
      String holding stream binary content.
    """
    return self._CachetoolCmd('get_stream', key, str(index))

  def DeleteKey(self, key):
    """Deletes a key from the cache.

    Args:
      key: The key delete.
    """
    self._CachetoolCmd('delete_key', key)

  def _CachetoolCmd(self, operation, *args):
    """Runs the cache editor tool and return the stdout.

    Args:
      operation: Cachetool operation.
      *args: Additional operation argument to append to the command line.

    Returns:
      Cachetool's stdout string.
    """
    editor_tool_cmd = [
        self._cachetool_bin_path,
        self._cache_directory_path,
        self._cache_backend_type,
        operation]
    editor_tool_cmd.extend(args)
    process = subprocess.Popen(editor_tool_cmd, stdout=subprocess.PIPE)
    stdout_data, _ = process.communicate()
    assert process.returncode == 0
    return stdout_data

  def GetDecodedContentForKey(self, key):
    """Gets a key's decoded content.

    HTTP cache is storing into key's index stream 1 the transport layer resource
    binary. However, the resources might be encoded using a compression
    algorithm specified in the Content-Encoding response header. This method
    takes care of returning decoded binary content of the resource.

    Args:
      key: The key to access the decoded content.

    Returns:
      String holding binary content.
    """
    response_headers = self.GetStreamForKey(key, 0)
    content_encoding = None
    for response_header_line in response_headers.split('\n'):
      match = HEADER_PARSING_REGEX.match(response_header_line)
      if not match:
        continue
      if match.group('header').lower() == 'content-encoding':
        content_encoding = match.group('value')
        break
    encoded_content = self.GetStreamForKey(key, 1)
    if content_encoding == None:
      return encoded_content

    cmd = [CONTENT_DECODER_TOOL_BIN_PATH]
    cmd.extend([s.strip() for s in content_encoding.split(',')])
    process = subprocess.Popen(cmd,
                               stdin=subprocess.PIPE,
                               stdout=subprocess.PIPE)
    decoded_content, _ = process.communicate(input=encoded_content)
    assert process.returncode == 0
    return decoded_content


def ApplyUrlWhitelistToCacheArchive(cache_archive_path,
                                    whitelisted_urls,
                                    output_cache_archive_path):
  """Generate a new cache archive containing only whitelisted urls.

  Args:
    cache_archive_path: Path of the cache archive to apply the white listing.
    whitelisted_urls: Set of url to keep in cache.
    output_cache_archive_path: Destination path of cache archive containing only
      white-listed urls.
  """
  cache_temp_directory = tempfile.mkdtemp(suffix='.cache')
  try:
    UnzipDirectoryContent(cache_archive_path, cache_temp_directory)
    backend = CacheBackend(cache_temp_directory, 'simple')
    cached_urls = backend.ListKeys()
    for cached_url in cached_urls:
      if cached_url not in whitelisted_urls:
        backend.DeleteKey(cached_url)
    for cached_url in backend.ListKeys():
      assert cached_url in whitelisted_urls
    ZipDirectoryContent(cache_temp_directory, output_cache_archive_path)
  finally:
    shutil.rmtree(cache_temp_directory)


def ManualTestMain():
  import argparse
  parser = argparse.ArgumentParser(description='Tests cache back-end.')
  parser.add_argument('cache_archive_path', type=str)
  parser.add_argument('backend_type', type=str, choices=BACKEND_TYPES)
  command_line_args = parser.parse_args()

  cache_path = tempfile.mkdtemp()
  UnzipDirectoryContent(command_line_args.cache_archive_path, cache_path)

  cache_backend = CacheBackend(
      cache_directory_path=cache_path,
      cache_backend_type=command_line_args.backend_type)
  keys = sorted(cache_backend.ListKeys())
  selected_key = None
  for key in keys:
    if key.endswith('.js'):
      selected_key = key
      break
  assert selected_key
  print '{}\'s HTTP response header:'.format(selected_key)
  print cache_backend.GetStreamForKey(selected_key, 0)
  print cache_backend.GetDecodedContentForKey(selected_key)
  cache_backend.DeleteKey(keys[1])
  assert keys[1] not in cache_backend.ListKeys()
  shutil.rmtree(cache_path)


if __name__ == '__main__':
  ManualTestMain()