#!/usr/bin/perl
# Copyright (C) 2015 The Qt Company Ltd.
# Contact: http://www.qt.io/licensing/
#
# You may use this file under the terms of the 3-clause BSD license.
# See the file LICENSE from this package for details.
#

use strict;
use warnings;

use Getopt::Long;

sub usage {
    print STDERR
q{Usage: git rewrite-author --from <from> --to <to> [ -f | --force ]
    [--] [<rev-list options>...]

  Replace author and committer field in some commits.


EXAMPLE:

  You've accidentally made some commits like this:

    Author: bjones <bjones@localhost.localdomain>

  ... where it should have been:

    Author: Bob Jones <bob.jones@example.com>

  The first bad commit is a1b2c3d4...

  Fix it up by:

   $ git rewrite-author --from "bjones <bjones@localhost.localdomain>" \
      --to "Bob Jones <bob.jones@example.com>" a1b2c3d4^..HEAD

  If you omit a range of commits, this command will scan _all_ commits
  leading up to HEAD, which will take a long time for repositories with
  a large history.

  WARNING: this script will change the SHA1 of every commit including
  and following the first rewritten commit. You can't do this for commits
  you've already pushed unless you really know what you're doing!
};
}

sub parse_author
{
    my $author = shift;
    if ($author =~ /^(.*?) <([^>]+)>$/) {
        return ($1, $2);
    }
    else {
        die "Could not parse `$author'; expected something like \"Some Name <some.address\@example.com>\"";
    }
}


# Return a string single-quoted for use in shell
sub sh_squote
{
    my $out = shift;
    $out =~ s/'/'"'"'/g;
    return "'$out'";
}

# Return fragment of shell code to rewrite a specific env var
sub rewrite_env
{
    my %opts = @_;
    my $env = $opts{env};
    my $from = sh_squote($opts{from});
    my $to = sh_squote($opts{to});

    my $cmd = <<EOF
if [ "\$$env" = $from ]; then
    $env=$to;
    export $env;
    if [ \$REWROTE = 0 ]; then
        echo;
        echo Hit for \$GIT_COMMIT:;
        REWROTE=1;
    fi;
    echo "   $env:" $from '->' $to;
fi
EOF
    ;

    $cmd =~ s/\n */ /sg;

    return $cmd;
}

my $from;
my $to;
my $force;
if (!GetOptions(
    "from=s"        => \$from,
    "to=s"          => \$to,
    "f|force"       => \$force,
)) {
    usage;
    exit 2;
}

if (!$from || !$to) {
    print STDERR "Need `--from' and `--to' arguments\n";
    usage;
    exit 2;
}

my ($from_name, $from_address) = parse_author($from);
my ($to_name, $to_address)     = parse_author($to);

my $env_filter_command = "REWROTE=0; ".
    rewrite_env(
        env     =>  'GIT_AUTHOR_NAME',
        from    =>  $from_name,
        to      =>  $to_name,
    )
    . "; " .
    rewrite_env(
        env     =>  'GIT_COMMITTER_NAME',
        from    =>  $from_name,
        to      =>  $to_name,
    )
    . "; " .
    rewrite_env(
        env     =>  'GIT_AUTHOR_EMAIL',
        from    =>  $from_address,
        to      =>  $to_address,
    )
    . "; " .
    rewrite_env(
        env     =>  'GIT_COMMITTER_EMAIL',
        from    =>  $from_address,
        to      =>  $to_address,
    )
;

my @git_filter_branch = ("git", "filter-branch", "--env-filter", $env_filter_command);
if ($force) {
    push @git_filter_branch, "--force";
}
push @git_filter_branch, @ARGV;

exec @git_filter_branch;