#!/usr/bin/env python3
#
# Copyright 2018 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.
"""Generate owners (.owners file) by looking at commit author for
libfuzzer test.

Invoked by GN from fuzzer_test.gni.
"""

import argparse
import os
import re
import subprocess
import sys

AUTHOR_REGEX = re.compile('author-mail <(.+)>')
CHROMIUM_SRC_DIR = os.path.dirname(
    os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
OWNERS_FILENAME = 'OWNERS'
THIRD_PARTY = 'third_party'
THIRD_PARTY_SEARCH_STRING = THIRD_PARTY + os.path.sep


def GetAuthorFromGitBlame(blame_output):
  """Return author from git blame output."""
  for line in blame_output.decode('utf-8').splitlines():
    m = AUTHOR_REGEX.match(line)
    if m:
      return m.group(1)

  return None


def GetGitCommand():
  """Returns a git command that does not need to be executed using shell=True.
  On non-Windows platforms: 'git'. On Windows: 'git.bat'.
  """
  return 'git.bat' if sys.platform == 'win32' else 'git'


def GetOwnersIfThirdParty(source):
  """Return owners using the closest OWNERS file if in third_party."""
  match_index = source.find(THIRD_PARTY_SEARCH_STRING)
  if match_index == -1:
    # Not in third_party, skip.
    return None

  path_prefix = source[:match_index + len(THIRD_PARTY_SEARCH_STRING)]
  path_after_third_party = source[len(path_prefix):].split(os.path.sep)

  # Test all the paths after third_party/<libname>, making sure that we don't
  # test third_party/OWNERS itself, otherwise we'd default to CCing them for
  # all fuzzer issues without OWNERS, which wouldn't be nice.
  while path_after_third_party:
    owners_file_path = path_prefix + \
        os.path.join(*(path_after_third_party + [OWNERS_FILENAME]))

    if os.path.exists(owners_file_path):
      return open(owners_file_path).read()

    path_after_third_party.pop()

  return None

# pylint: disable=inconsistent-return-statements
def GetOwnersForFuzzer(sources):
  """Return owners given a list of sources as input."""
  if not sources:
    return

  for source in sources:
    full_source_path = os.path.join(CHROMIUM_SRC_DIR, source)
    if not os.path.exists(full_source_path):
      continue

    with open(full_source_path, 'r') as source_file_handle:
      source_content = source_file_handle.read()

    if SubStringExistsIn(
        ['FuzzOneInput', 'LLVMFuzzerTestOneInput', 'PROTO_FUZZER'],
        source_content):
      # Found the fuzzer source (and not dependency of fuzzer).

      git_dir = os.path.join(CHROMIUM_SRC_DIR, '.git')
      git_command = GetGitCommand()
      is_git_file = bool(subprocess.check_output(
          [git_command, '--git-dir', git_dir, 'ls-files', source],
          cwd=CHROMIUM_SRC_DIR))
      if not is_git_file:
        # File is not in working tree. Return owners for third_party.
        return GetOwnersIfThirdParty(full_source_path)

      # git log --follow and --reverse don't work together and using just
      # --follow is too slow. Make a best estimate with an assumption that
      # the original author has authored line 1 which is usually the
      # copyright line and does not change even with file rename / move.
      blame_output = subprocess.check_output(
          [git_command, '--git-dir', git_dir, 'blame', '--porcelain', '-L1,1',
           source], cwd=CHROMIUM_SRC_DIR)
      return GetAuthorFromGitBlame(blame_output)

  return None
# pylint: enable=inconsistent-return-statements

def FindGroupsAndDepsInDeps(deps_list, build_dir):
  """Return list of groups, as well as their deps, from a list of deps."""
  groups = []
  deps_for_groups = {}
  for deps in deps_list:
    output = subprocess.check_output(
        [GNPath(), 'desc', '--fail-on-unused-args', build_dir, deps]).decode(
                'utf8')
    needle = 'Type: '
    for line in output.splitlines():
      if needle and not line.startswith(needle):
        continue
      if needle == 'Type: ':
        if line != 'Type: group':
          break
        groups.append(deps)
        assert deps not in deps_for_groups
        deps_for_groups[deps] = []
        needle = 'Direct dependencies'
      elif needle == 'Direct dependencies':
        needle = ''
      else:
        assert needle == ''
        if needle == line:
          break
        deps_for_groups[deps].append(line.strip())

  return groups, deps_for_groups


def TraverseGroups(deps_list, build_dir):
  """Filter out groups from a deps list. Add groups' direct dependencies."""
  full_deps_set = set(deps_list)
  deps_to_check = full_deps_set.copy()

  # Keep track of groups to break circular dependendies, if any.
  seen_groups = set()

  while deps_to_check:
    # Look for groups from the deps set.
    groups, deps_for_groups = FindGroupsAndDepsInDeps(deps_to_check, build_dir)
    groups = set(groups).difference(seen_groups)
    if not groups:
      break

    # Update sets. Filter out groups from the full deps set.
    full_deps_set.difference_update(groups)
    deps_to_check.clear()
    seen_groups.update(groups)

    # Get the direct dependencies, and filter out known groups there too.
    for group in groups:
      deps_to_check.update(deps_for_groups[group])
    deps_to_check.difference_update(seen_groups)
    full_deps_set.update(deps_to_check)
  return list(full_deps_set)


def GetSourcesFromDeps(deps_list, build_dir):
  """Return list of sources from parsing deps."""
  if not deps_list:
    return None

  full_deps_list = TraverseGroups(deps_list, build_dir)
  all_sources = []
  for deps in full_deps_list:
    output = subprocess.check_output(
        [GNPath(), 'desc', '--fail-on-unused-args', build_dir, deps, 'sources'])
    for source in bytes(output).decode('utf8').splitlines():
      if source.startswith('//'):
        source = source[2:]
      all_sources.append(source)

  return all_sources


def GNPath():
  if sys.platform.startswith('linux'):
    subdir, exe = 'linux64', 'gn'
  elif sys.platform == 'darwin':
    subdir, exe = 'mac', 'gn'
  else:
    subdir, exe = 'win', 'gn.exe'

  return os.path.join(CHROMIUM_SRC_DIR, 'buildtools', subdir, exe)


def SubStringExistsIn(substring_list, string):
  """Return true if one of the substring in the list is found in |string|."""
  return any(substring in string for substring in substring_list)


def main():
  parser = argparse.ArgumentParser(description='Generate fuzzer owners file.')
  parser.add_argument('--owners', required=True)
  parser.add_argument('--build-dir')
  parser.add_argument('--deps', nargs='+')
  parser.add_argument('--sources', nargs='+')
  args = parser.parse_args()

  # Generate owners file.
  with open(args.owners, 'w') as owners_file:
    # If we found an owner, then write it to file.
    # Otherwise, leave empty file to keep ninja happy.
    owners = GetOwnersForFuzzer(args.sources)
    if owners:
      owners_file.write(owners)
      return

    # Could not determine owners from |args.sources|.
    # So, try parsing sources from |args.deps|.
    deps_sources = GetSourcesFromDeps(args.deps, args.build_dir)
    owners = GetOwnersForFuzzer(deps_sources)
    if owners:
      owners_file.write(owners)


if __name__ == '__main__':
  main()