#!/usr/bin/env python3
# Copyright 2020 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Extract all the licenses from the man page comments.

Each man page may be licensed under a unique license, so we have to walk each
one and extract the details.
"""

import argparse
import os
from pathlib import Path
import re
import sys


# Extract the license name & text from a section like:
# .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
# .\" ...text...
# .\" %%%LICENSE_END
EXTRACT_LICENSE = re.compile(
    r'^[^\n]*%%%LICENSE_START\(([^)]+)\)\n(.*)%%%LICENSE_END$',
    flags=re.MULTILINE | re.DOTALL)


# Licenses that require copyright attribution.
ATTRIBUTION_LICENSES = {
    'BSD_3_CLAUSE_UCB',
    'BSD_4_CLAUSE_UCB',
    'BSD_ONELINE_CDROM',
    'MISC',
    'MIT',
    'PERMISSIVE_MISC',
    'VERBATIM',
    'VERBATIM_ONE_PARA',
    'VERBATIM_PROF',
    'VERBATIM_TWO_PARA',
}

# All licenses we know about.  If a new one shows up, we'll throw an error so
# we're forced to evaluate it.
KNOWN_LICENSES = ATTRIBUTION_LICENSES | {
    'FREELY_REDISTRIBUTABLE',
    'GPL_NOVERSION_ONELINE',
    'GPLv2+',
    'GPLv2+_DOC_FULL',
    'GPLv2+_DOC_MISC',
    'GPLv2+_DOC_ONEPARA',
    'GPLv2_MISC',
    'GPLv2_ONELINE',
    'GPLv2+_SW_3_PARA',
    'GPLv2+_SW_ONEPARA',
    'LDPv1',
    'PUBLIC_DOMAIN',
}


def line_iscomment(line):
    """Whether |line| is a roff comment."""
    # A variety of possible formats here.  This should get cleaned up in newer
    # versions, but we have to deal with it in current releases.
    # \" ...
    # .\" ...
    # '\" ...
    return re.match(r'''^[.']?\\"''', line)


def extract_license(page):
    """Extract the license from |page|."""
    with open(page, encoding='utf-8') as fp:
        data = fp.read()

        # Ignore stub pointer files.
        if data.startswith('.so '):
            return

        # Find the name of the license to do high level checks.
        matches = list(EXTRACT_LICENSE.finditer(data))
        assert matches, f'{page}: unable to find licenses'
        for match in matches:
            name = match.group(1)
            assert name in KNOWN_LICENSES, (
                f'{page}: {name}: unknown license; please update script')

            # We'll yield the entire preceding header to the license.
            if name in ATTRIBUTION_LICENSES:
                # Walk backwards to collect copyrights until we:
                # (1) Hit the start of the file.
                # (2) Hit a non-comment line (as all copyrights are comments).
                # (3) Hit the previous license.
                header = data[0:match.start(0)]
                lines = []
                for line in reversed(header.splitlines()):
                    if not line_iscomment(line) or '%%%LICENSE_' in line:
                        break
                    lines.insert(0, line[3:].strip())
                assert len(lines) > 1, header
                # Trim a weird leading line pending upstream cleanup.
                if lines[0] == 't':
                    lines.pop(0)
                copyright_text = '\n'.join(lines).strip()

                # Format the license text.
                lines = [x[3:].strip()
                         for x in match.group(2).strip().splitlines()]
                license_text = '\n'.join(lines).strip()

                yield f'{page.name}\n{copyright_text}\n\n{license_text}\n'
                break


def find_licenses(srcdir):
    """Walk |srcdir| looking for man page licenses."""
    for page in srcdir.glob('man[0-9]/*.[0-9]'):
        yield from extract_license(page)


def get_parser():
    """Get CLI parser."""
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('-o', '--output', type=Path,
                        help='File to write combined license to.')
    parser.add_argument('-d', '--srcdir', type=Path,
                        default=os.environ.get('S'),
                        help='Source dir to walk (e.g. $S)')
    return parser


def main(argv):
    """The main entry point for scripts."""
    parser = get_parser()
    opts = parser.parse_args(argv)

    if not opts.srcdir:
        parser.error('--srcdir is required')
    if not opts.srcdir.is_dir():
        parser.error(f'{opts.srcdir}: --srcdir does not exist')

    licenses = find_licenses(opts.srcdir)
    data = '\n'.join(licenses)
    if opts.output:
        with open(opts.output, 'w', encoding='utf-8') as fp:
            fp.write(data)
    else:
        print(data, end='')


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))