#!/usr/bin/env python3
#
# Copyright 2018 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Verify HEAD against upstream to see if anything bad has been added.

Verify HEAD against upstream 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_READER`s, 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 upstream.
"""

import re
import sys
import subprocess

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

# 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(crbug.com/450394703): 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.
# Note: chromium/scripts can be removed once the scripts move out of ffmpeg.
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)