#!/usr/bin/env python3

# Copyright (C) 2020  Agilent Technologies, Inc.
# Author: Chris Laplante <chris.laplante@agilent.com>

# This sendemail-validate hook injects 'From: ' header lines into outgoing
# emails sent via 'git send-email', to ensure that accurate commit authorship
# information is present. It was created because some email servers
# (notably Microsoft Exchange / Office 360) seem to butcher outgoing patches,
# resulting in incorrect authorship.

# Current limitations:
#   1. Assumes one per patch per email
#   2. Minimal error checking
#
# Installation:
#   1. Copy to .git/hooks/sendemail-validate
#   2. chmod +x .git/hooks/sendemail-validate


import enum
import re
import subprocess
import sys


class Subject(enum.IntEnum):
    NOT_SEEN = 0
    CONSUMING = 1
    SEEN = 2


def make_from_line():
    cmd = ["git", "var", "GIT_COMMITTER_IDENT"]
    proc = subprocess.run(cmd, check=True, stdout=subprocess.PIPE, universal_newlines=True)
    regex = re.compile(r"^(.*>).*$")
    match = regex.match(proc.stdout)
    assert match is not None
    return "From: {0}".format(match.group(1))


def main():
    email = sys.argv[1]

    with open(email, "r") as f:
        email_lines = f.read().split("\n")

    subject_seen = Subject.NOT_SEEN
    first_body_line = None
    for i, line in enumerate(email_lines):
        if (subject_seen == Subject.NOT_SEEN) and line.startswith("Subject: "):
            subject_seen = Subject.CONSUMING
            continue
        if subject_seen == Subject.CONSUMING:
            if not line.strip():
                subject_seen = Subject.SEEN
                continue
        if subject_seen == Subject.SEEN:
            first_body_line = i
            break

    assert subject_seen == Subject.SEEN
    assert first_body_line is not None

    from_line = make_from_line()
    # Only add FROM line if it is not already there
    if email_lines[first_body_line] != from_line:
        email_lines.insert(first_body_line, from_line)
        email_lines.insert(first_body_line + 1, "")
        with open(email, "w") as f:
            f.write("\n".join(email_lines))

    return 0


if __name__ == "__main__":
    sys.exit(main())