"""Collection of utility functions to work with git."""

from __future__ import absolute_import
import collections
import os
import re
import six

CHERRY_PICK_MSG = r'\(cherry picked from commit [0-9a-f]{5,40}\)'
SHA_PATTERN = r'[a-fA-F0-9]{40}'

# `git diff` uses /dev/null as a placeholder name for new/deleted files.
FILENAME_PLACEHOLDER = '/dev/null'


def check_history_depth(executor, directory):
  depth = executor.exec_subprocess(
      ['git', 'rev-list', '--count', 'HEAD'], cwd=directory, check_output=True)
  try:
    return int(depth)
  except ValueError:
    return 0


def changed_files(executor,
                  file_extensions=None,
                  directory=None,
                  file_exclusion_pattern=None,
                  depth=1):
  """Returns a list of names of changed files in newest |depth| commits.

  Args:
    executor: Executes the subprocess.
    file_extensions: Filter output to only files with matching extensions. (e.g.
      ['.cc', '.h'] for C++ files)
    directory: Directory to execute the subprocess in.
    file_exclusion_pattern: A regex pattern to filter files with. If the pattern
      matches a file that file will not be included in the changed file list.
    depth: The number of commits to find files from.

  Returns:
    List of names of changed files.
  """
  diff_output = executor.exec_subprocess([
      'git', 'diff', 'HEAD~{}'.format(depth), '--name-only', '--diff-filter=AMR'
  ],
                                         cwd=directory,
                                         check_output=True)

  if not diff_output:
    return []

  changed_filenames = diff_output.strip().split('\n')

  return filtered_files(
      changed_filenames,
      file_extensions=file_extensions,
      file_exclusion_pattern=file_exclusion_pattern)


def get_changed_files_in_all_patches(executor,
                                     patches,
                                     path_lookup,
                                     file_extensions=None,
                                     file_exclusion_pattern=None):
  """Returns every file that is changed as a result of applying |patches|.

  This method is useful when determining all files that have changed when a
  series of patches have been applied via the Depends-On tag. This method
  supports patches in multiple projects, as well as multiple patches in a
  single project.

  Args:
    executor: Executes the subprocess.
    patches: A list of all of the patches applied to the checkout. For more
      detail on the entries in this list, see scripts/slave/base_step.py.
    path_lookup: A dictionary mapping project name to path.
    file_extensions: Filter output to only files with matching extensions. (e.g.
      ['.cc', '.h'] for C++ files)
    file_exclusion_pattern: A regex pattern to filter files with. If the pattern
      matches a file that file will not be included in the changed file list.

  Returns:
    A list of file paths relative to the checkout root directory.
  """

  # |project_depth| is a dictionary mapping each project name to the number of
  # patches that have been applied on top of that project's HEAD. Here's an
  # example of what this might look like:
  # {
  #   "chromecast/internal": 1,
  #   "chromium/src": 2,
  #   "some_other_project": 1
  # }
  project_depths = collections.Counter(
      patch['project'] for patch in patches if patch['project'] in path_lookup)

  # |path_lookup| dictionary uses real paths relative to the root checkout
  # directory. However, some tools like gn expect paths to be symlinks, e.g.
  # chromium/src/chromecast/internal/receiver/app/dummy.cc instead of
  # cast/internal/receiver/app/dummy.cc. Create a dictionary here so that
  # symlinks can be returned for some projects.
  file_prefix_dict = {
      "chromecast/internal": "chromium/src/chromecast/internal"
  }
  file_prefix_dict = path_lookup.get_dict() | file_prefix_dict

  # For each project, calculate the list of changed files, concatenate each file
  # path with the project's path from checkout root, and append them to a list.
  files = []
  for project in project_depths.keys():
    depth = project_depths[project]
    if depth < check_history_depth(executor, path_lookup[project]):
      files.extend([
          os.path.join(file_prefix_dict[project], f)
          for f in changed_files(
              executor, file_extensions, path_lookup[project],
              file_exclusion_pattern, depth)
      ])
  return files


def filtered_files(filenames,
                   file_extensions=None,
                   file_exclusion_pattern=None):
  """Filters the list of files.

  Args:
    filenames: A list of filenames to filter.
    file_extensions: Filter output to only files with matching extensions. (e.g.
      ['.cc', '.h'] for C++ files)
    file_exclusion_pattern: A regex pattern to filter files with. If the pattern
      matches a file that file will not be included in the changed file list.

  Returns:
    List of files after applying the filters.
  """
  if file_extensions:
    filenames = [f for f in filenames if f.endswith(tuple(file_extensions))]
  if file_exclusion_pattern:
    filenames = [
        f for f in filenames if not re.search(file_exclusion_pattern, f)
    ]
  return filenames


def commit_message(executor, directory=None):
  """Returns the most recent git commit message.

  Note that this does not include the Author: or Date: fields,
  only the message body.

  Args:
    executor: Executes the subprocess.
    directory: Directory to execute the subprocess in (defaults to cwd)

  Returns:
    The most recent git commit message.
  """
  return executor.exec_subprocess(['git', 'log', '--format=%B', '-n', '1'],
                                  cwd=directory,
                                  check_output=True)


def is_cherry_pick(executor, directory=None):
  """Returns if the most recent commit is a cherry pick.

  Args:
    executor: Executes the subprocess.
    directory: Directory to execute the subproccess in (defaults to cwd)

  Returns:
    True iff the most recent commit is a cherry pick.
  """
  return bool(
      re.search(CHERRY_PICK_MSG, commit_message(executor, directory),
                re.MULTILINE))


def commit_author_email(executor, directory=None):
  """Returns the author email of the most recent git commit.

  Args:
    executor: Executes the subprocess.
    directory: Directory to execute the subprocess in (defaults to cwd)

  Returns:
    The email of the author of the most recent git commit.
  """
  author = executor.exec_subprocess(['git', 'log', '--format=%ae', '-n', '1'],
                                    cwd=directory,
                                    check_output=True).strip()
  # We have to first convert to a unicode str, then decode removing unicode
  # chars.
  return six.text_type(author.decode('utf-8')).encode('ascii', errors='ignore')


def is_sha(revision):
  """Returns True if revision looks like a SHA."""
  return re.match(SHA_PATTERN, revision)


def get_head_sha(executor, directory):
  """Returns the SHA of the HEAD revision for the given directory,

  or None if the directory specified is not a git repository
  """

  cmd_get_sha = ['git', 'rev-parse', 'HEAD']
  returncode, stdout, _ = executor.exec_subprocess(cmd_get_sha, cwd=directory)
  return stdout.strip() if returncode == 0 else None