#!/usr/bin/perl

# mbox-extract-patch -- extract a git patch series from an mbox
#
# Copyright (C) 2020 Sean Whitton
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

use 5.028;
use strict;
use warnings;

use Getopt::Long;
use Mail::Box::Mbox;
use File::Temp ();
use List::Util qw(max);

our $patch_tag_re = qr/\[(.*PATCH.*)\]/;
our $trailer_re   = qr/^[A-Z][a-z-]+: .+$/;
# ordering here is from Konstantin Ryabitsev's get-lore-mbox.py
our @trailer_order = (
    "fixes", "reported",   "suggested", "original",
    "co-",   "signed-off", "tested",    "reviewed",
    "acked", "cc",         "link",      "",
);

# empty STDIN into a temporary file
my $mbox = File::Temp->new;
binmode STDIN;
binmode $mbox;
my $BUFSIZ = 64 * (2**10);
while (read STDIN, my $buf, $BUFSIZ) {
    print $mbox $buf
      or die "couldn't write to " . $mbox->filename . ": $!";
}
$mbox->close;    # close filehandle for writing; keeps the file

# command line arguments
my $extract_trailers = 1;
my ($reroll_count, $cover_letter_trailers);
Getopt::Long::Configure("bundling");
GetOptions
  "reroll-count|v=i"       => \$reroll_count,
  "trailers!"              => \$extract_trailers,
  "cover-letter-trailers!" => \$cover_letter_trailers;

my $folder = Mail::Box::Mbox->new(folder => $mbox->filename, access => "rw");

# first pass: extract info from messages, and delete some known not to
# be wanted patches
my (@reroll_counts, %trailers, %covers);
foreach my $message ($folder->messages) {
    # we assume that the first text/plain part we find is the
    # patch/message, and if none, we give up on the message
    $message->delete, next unless defined $message->first_text_plain_part;

    my $subject = $message->study("subject");
    $subject =~ /$patch_tag_re/, my $subject_front = $` if defined $subject;
    my @lines = $message->first_text_plain_part->body->decoded->lines;

    # $is_cover is a bit simplistic right now
    my $is_patch = grep /^@@ [0-9 +,-]+ @@/, @lines;
    my $is_cover
      = defined $message->patch_count
      && $message->patch_count == 0
      && defined $subject_front
      && $subject_front !~ /Re: \z/i;

    if ($is_patch) {
        $message->delete, next
          if $reroll_count and $reroll_count != $message->reroll_count;
        # record reroll counts seen so we can determine, later,
        # whether there is more than one version of the patch series
        # in our input
        push @reroll_counts, $message->reroll_count;
    } elsif ($is_cover) {
        # all we need from covers is their msgids so we can look for
        # trailers sent in reply to those covers
        $covers{ $message->reroll_count } = $message->messageId;
        $message->delete;
    } else {
        my $in_replies_to = $message->get("In-Reply-To");
        if ($in_replies_to and my @ids = $in_replies_to =~ m/\<([^>]+)\>/g) {
            warn "In-Reply-To field with more than one Message-Id; using first"
              if @ids > 1;
            my $id = $ids[0];
            my @ts = grep /$trailer_re/, @lines;
            push $trailers{$id}->@*, @ts;
        }
        $message->delete;
    }
}
# expunge deleted messages
$folder->write or die "failed to update mbox!";

# second pass requires $reroll_count to be set, and we can now
# determine what it should be based on information gathered during the
# first pass
unless ($reroll_count) {
    if (@reroll_counts > 0) {
        # we saw one or more series, and user did not specify a reroll
        # count, so we extract the series with the highest version number
        $reroll_count = max @reroll_counts;
    } else {
        # we didn't see any reroll counts, so we mustn't have seen any
        # patches
        exit;
    }
}

# second pass: edits to patch messages, and delete remaining unwanted
# messages.  note that only patches remain in the mbox after first
# pass
foreach my $message ($folder->messages) {
    $message->delete, next
      unless $reroll_count == $message->reroll_count;

    my @ts;
    my $id  = $message->messageId;
    my $cid = $covers{ $message->reroll_count };
    @ts = $trailers{$id}->@* if $extract_trailers and $trailers{$id};
    push @ts, $trailers{$cid}->@*
      if $cover_letter_trailers and $trailers{$cid};
    $message->insert_trailers(@ts) if @ts;

    # if Subject: contains [PATCH nn/mm] then any text before that
    # should be stripped, as it should not form part of the commit
    # message.  (The debbugs system prepends 'Bug#nnnnnn: ')
    my $subject = $message->study("subject");
    $subject =~ /$patch_tag_re.*$/;
    $message->head->set(Subject => $&);
}

# save mbox and output
$folder->close or die "failed to update & close mbox!";
exit unless -e $mbox->filename;    # no patches to extract
open my $fh, "< :raw :bytes", $mbox->filename
  or die "couldn't open " . $mbox->filename . " for reading";
while (read $fh, my $buf, $BUFSIZ) {
    print $buf;
}

package Mail::Message {
    use Carp;
    use Mail::Message::Body;
    use List::MoreUtils qw(first_index);

    sub insert_trailers {
        my ($self, @ts) = @_;
        my $part = $self->first_text_plain_part;
        return unless defined $part;
        my @lines = $part->body->decoded->lines;
        my $i = my $j = first_index { /^---$/ } @lines;
        carp "couldn't find cut; not daring insert any trailers", return
          if $i == -1;
        $i-- while $i > 0 and $lines[$i - 1] =~ /$trailer_re/;
        unshift @ts, splice @lines, $i, $j - $i;

        # algorithm based on Konstantin Ryabitsev's in his get-lore-mbox.py
        my (@new_ts, %added);
        foreach my $pat (@trailer_order) {
            foreach my $t (@ts) {
                next if exists $added{$t};
                next unless $t =~ /^$pat(?:-by)?:/i;
                push @new_ts, $t;
                $added{$t} = undef;
            }
        }

        splice @lines, $i, 0, @new_ts;
        my $body = Mail::Message::Body->new(
            charset => "PERL",
            data    => \@lines
        );
        $body->encode;
        $part->body($body);
    }

    sub first_text_plain_part {
        my $self = shift;
        if ($self->isMultipart) {
            for ($self->parts("RECURSE")) {
                return $_ if $_->body->mimeType eq "text/plain";
            }
        } else {
            return $self if $self->body->mimeType eq "text/plain";
        }
        return;
    }

    sub reroll_count {
        for (shift->_subject_patch_components) {
            /\Av([0-9]+)\z/ and return $1;
        }
        return 1;
    }

    sub patch_count {
        for (shift->_subject_patch_components) {
            m#\A([0-9]+)/[0-9]+\z# and return $1;
        }
        return;
    }

    sub _subject_patch_components {
        my $subject = shift->study("subject");
        return unless defined $subject;
        $subject =~ /$patch_tag_re/;
        return unless defined $1;
        split " ", $1;
    }
}