#!/usr/bin/env python
#
# 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.
#
# Verify HEAD against origin/master to see if anything bad has been added to
# HEAD that we would not want to roll.  For example, if HEAD introduces any
# UNCHECKED_BITSTREAM_READERs, then we definitely want to fix that before
# including HEAD in Chromium.
#
# Usage: check_merge.py [new_branch]
# where |new_branch| is the branch that we'd like to compare to origin/master.

import os
import re
import sys
import subprocess

# The current good ffmpeg + config that we're diffing against.
EXISTING_COMMIT = "origin/master"

# If any of these regexes match, it indicates failure.  Generally, we want to
# catch any change in how these are defined.  These are checked against things
# that are added with respect to |EXISTING_COMMIT| by the commit we're checking.
#
# Remember that we're going to check ffmpeg files and Chromium files (e.g.,
# the build configs for each platform, ffmpeg_generated.gni, etc.).
# TODO(liberato): consider making these a dictionary, with the value as some
# descriptive text (e.g., the bug number) about why it's not allowed.
INSERTION_TRIPWIRES = [
    # In Chromium, all codecs should use the safe bitstream reader. Roller must
    # undo any new usage of the unchecked reader.
    "^.define.*UNCHECKED_BITSTREAM_READER.*1",

    # In Chromium, explicitly skipping some matroskadec code blocks for
    # the following CONFIG variables (which should remain defined as 0) is
    # necessary to remove code that may be a security risk. Discuss with cevans@
    # before removing these explicit skips or enabling these variables.
    "^.define.*CONFIG_LZO.*1",
    "^.define.*CONFIG_SIPR_DECODER.*1",
    "^.define.*CONFIG_RA_288_DECODER.*1",
    "^.define.*CONFIG_COOK_DECODER.*1",
    "^.define.*CONFIG_ATRAC3_DECODER.*1",

    # Miscellaneous tripwires.
    "^.define.*CONFIG_SPDIF_DEMUXER.*1",
    "^.define.*CONFIG_W64_DEMUXER.*1",
    "^.define.*[Vv]4[Ll]2.*1",
    "^.define.*CONFIG_PRORES_.*1",
]

# Filenames that will be excluded from the regex matching.
EXCLUDED_FILENAMES = [
    r"^configure$",
    r"^chromium/scripts/",
    r"^chromium/patches/",
]

def search_regexps(text, regexps):
  return [r for r in regexps if re.search(r, text)]

def main(argv):
  # What we're considering merging, and would like to check.  Normally, this
  # is HEAD, but you might want to verify some previous merge.
  if len(argv) > 1:
    new_commit = argv[1]
  else:
    new_commit = "HEAD"

  print(f"Comparing {new_commit} to baseline {EXISTING_COMMIT}...")

  diff = subprocess.Popen(["git", "diff", "-U0", EXISTING_COMMIT, new_commit],
          stdout=subprocess.PIPE).communicate()[0].decode(sys.stdout.encoding)
  filename=None
  skip = False
  files_encountered = 0
  files_skipped = 0
  failures = set()
  for line in diff.splitlines():
      if line.startswith("+++"):
        # +++ b/filename => filename
        filename = line.split("/",1)[1]
        skip = False
        files_encountered += 1
        if search_regexps(filename, EXCLUDED_FILENAMES):
          skip = True
          files_skipped += 1
      elif line.startswith("+") and not skip:
        # |line| is an insertion into |new_commit|.
        # Drop the leading "+" from the string being searched.
        tripwire = search_regexps(line[1:], INSERTION_TRIPWIRES)
        if tripwire:
          failures.add("Tripwire '%s' found in %s" % (tripwire, filename))

  # If we have failures, then print them and fail.
  if failures:
    for failure in failures:
      print(f"Failure: {failure}")
    sys.exit(2)

  checked = files_encountered - files_skipped
  print(f"No problems found! Checked {checked}, skipped {files_skipped}.")

if __name__ == '__main__':
  main(sys.argv)