#! /usr/bin/perl

# Copyright (C) 2011
#     Jérémie Nikaes <jeremie.nikaes@ensimag.imag.fr>
#     Arnaud Lacurie <arnaud.lacurie@ensimag.imag.fr>
#     Claire Fousse <claire.fousse@ensimag.imag.fr>
#     David Amouyal <david.amouyal@ensimag.imag.fr>
#     Matthieu Moy <matthieu.moy@grenoble-inp.fr>
# License: GPL v2 or later

# Gateway between Git and MediaWiki.
#   https://github.com/Bibzball/Git-Mediawiki/wiki
#
# Known limitations:
#
# - Only wiki pages are managed, no support for [[File:...]]
#   attachments.
#
# - Poor performance in the best case: it takes forever to check
#   whether we're up-to-date (on fetch or push) or to fetch a few
#   revisions from a large wiki, because we use exclusively a
#   page-based synchronization. We could switch to a wiki-wide
#   synchronization when the synchronization involves few revisions
#   but the wiki is large.
#
# - Git renames could be turned into MediaWiki renames (see TODO
#   below)
#
# - login/password support requires the user to write the password
#   cleartext in a file (see TODO below).
#
# - No way to import "one page, and all pages included in it"
#
# - Multiple remote MediaWikis have not been very well tested.

use strict;
use MediaWiki::API;
use DateTime::Format::ISO8601;
use encoding 'utf8';

# use encoding 'utf8' doesn't change STDERROR
# but we're going to output UTF-8 filenames to STDERR
binmode STDERR, ":utf8";

use URI::Escape;
use warnings;

# Mediawiki filenames can contain forward slashes. This variable decides by which pattern they should be replaced
use constant SLASH_REPLACEMENT => "%2F";

# It's not always possible to delete pages (may require some
# priviledges). Deleted pages are replaced with this content.
use constant DELETED_CONTENT => "[[Category:Deleted]]\n";

# It's not possible to create empty pages. New empty files in Git are
# sent with this content instead.
use constant EMPTY_CONTENT => "<!-- empty page -->\n";

# used to reflect file creation or deletion in diff.
use constant NULL_SHA1 => "0000000000000000000000000000000000000000";

my $remotename = $ARGV[0];
my $url = $ARGV[1];

# Accept both space-separated and multiple keys in config file.
# Spaces should be written as _ anyway because we'll use chomp.
my @tracked_pages = split(/[ \n]/, run_git("config --get-all remote.". $remotename .".pages"));
chomp(@tracked_pages);

# Just like @tracked_pages, but for MediaWiki categories.
my @tracked_categories = split(/[ \n]/, run_git("config --get-all remote.". $remotename .".categories"));
chomp(@tracked_categories);

my $wiki_login = run_git("config --get remote.". $remotename .".mwLogin");
# TODO: ideally, this should be able to read from keyboard, but we're
# inside a remote helper, so our stdin is connect to git, not to a
# terminal.
my $wiki_passwd = run_git("config --get remote.". $remotename .".mwPassword");
my $wiki_domain = run_git("config --get remote.". $remotename .".mwDomain");
chomp($wiki_login);
chomp($wiki_passwd);
chomp($wiki_domain);

# Import only last revisions (both for clone and fetch)
my $shallow_import = run_git("config --get --bool remote.". $remotename .".shallow");
chomp($shallow_import);
$shallow_import = ($shallow_import eq "true");

# Dumb push: don't update notes and mediawiki ref to reflect the last push.
#
# Configurable with mediawiki.dumbPush, or per-remote with
# remote.<remotename>.dumbPush.
#
# This means the user will have to re-import the just-pushed
# revisions. On the other hand, this means that the Git revisions
# corresponding to MediaWiki revisions are all imported from the wiki,
# regardless of whether they were initially created in Git or from the
# web interface, hence all users will get the same history (i.e. if
# the push from Git to MediaWiki loses some information, everybody
# will get the history with information lost). If the import is
# deterministic, this means everybody gets the same sha1 for each
# MediaWiki revision.
my $dumb_push = run_git("config --get --bool remote.$remotename.dumbPush");
unless ($dumb_push) {
        $dumb_push = run_git("config --get --bool mediawiki.dumbPush");
}
chomp($dumb_push);
$dumb_push = ($dumb_push eq "true");

my $wiki_name = $url;
$wiki_name =~ s/[^\/]*:\/\///;
# If URL is like http://user:password@example.com/, we clearly don't
# want the password in $wiki_name. While we're there, also remove user
# and '@' sign, to avoid author like MWUser@HTTPUser@host.com
$wiki_name =~ s/^.*@//;

# Commands parser
my $entry;
my @cmd;
while (<STDIN>) {
        chomp;
        @cmd = split(/ /);
        if (defined($cmd[0])) {
                # Line not blank
                if ($cmd[0] eq "capabilities") {
                        die("Too many arguments for capabilities") unless (!defined($cmd[1]));
                        mw_capabilities();
                } elsif ($cmd[0] eq "list") {
                        die("Too many arguments for list") unless (!defined($cmd[2]));
                        mw_list($cmd[1]);
                } elsif ($cmd[0] eq "import") {
                        die("Invalid arguments for import") unless ($cmd[1] ne "" && !defined($cmd[2]));
                        mw_import($cmd[1]);
                } elsif ($cmd[0] eq "option") {
                        die("Too many arguments for option") unless ($cmd[1] ne "" && $cmd[2] ne "" && !defined($cmd[3]));
                        mw_option($cmd[1],$cmd[2]);
                } elsif ($cmd[0] eq "push") {
                        mw_push($cmd[1]);
                } else {
                        print STDERR "Unknown command. Aborting...\n";
                        last;
                }
        } else {
                # blank line: we should terminate
                last;
        }

        BEGIN { $| = 1 } # flush STDOUT, to make sure the previous
                         # command is fully processed.
}

########################## Functions ##############################

# MediaWiki API instance, created lazily.
my $mediawiki;

sub mw_connect_maybe {
        if ($mediawiki) {
            return;
        }
        $mediawiki = MediaWiki::API->new;
        $mediawiki->{config}->{api_url} = "$url/api.php";
        if ($wiki_login) {
                if (!$mediawiki->login({
                        lgname => $wiki_login,
                        lgpassword => $wiki_passwd,
                        lgdomain => $wiki_domain,
                })) {
                        print STDERR "Failed to log in mediawiki user \"$wiki_login\" on $url\n";
                        print STDERR "(error " .
                            $mediawiki->{error}->{code} . ': ' .
                            $mediawiki->{error}->{details} . ")\n";
                        exit 1;
                } else {
                        print STDERR "Logged in with user \"$wiki_login\".\n";
                }
        }
}

sub get_mw_first_pages {
        my $some_pages = shift;
        my @some_pages = @{$some_pages};

        my $pages = shift;

        # pattern 'page1|page2|...' required by the API
        my $titles = join('|', @some_pages);

        my $mw_pages = $mediawiki->api({
                action => 'query',
                titles => $titles,
        });
        if (!defined($mw_pages)) {
                print STDERR "fatal: could not query the list of wiki pages.\n";
                print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
                print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
                exit 1;
        }
        while (my ($id, $page) = each(%{$mw_pages->{query}->{pages}})) {
                if ($id < 0) {
                        print STDERR "Warning: page $page->{title} not found on wiki\n";
                } else {
                        $pages->{$page->{title}} = $page;
                }
        }
}

sub get_mw_pages {
        mw_connect_maybe();

        my %pages; # hash on page titles to avoid duplicates
        my $user_defined;
        if (@tracked_pages) {
                $user_defined = 1;
                # The user provided a list of pages titles, but we
                # still need to query the API to get the page IDs.

                my @some_pages = @tracked_pages;
                while (@some_pages) {
                        my $last = 50;
                        if ($#some_pages < $last) {
                                $last = $#some_pages;
                        }
                        my @slice = @some_pages[0..$last];
                        get_mw_first_pages(\@slice, \%pages);
                        @some_pages = @some_pages[51..$#some_pages];
                }
        }
        if (@tracked_categories) {
                $user_defined = 1;
                foreach my $category (@tracked_categories) {
                        if (index($category, ':') < 0) {
                                # Mediawiki requires the Category
                                # prefix, but let's not force the user
                                # to specify it.
                                $category = "Category:" . $category;
                        }
                        my $mw_pages = $mediawiki->list( {
                                action => 'query',
                                list => 'categorymembers',
                                cmtitle => $category,
                                cmlimit => 'max' } )
                            || die $mediawiki->{error}->{code} . ': ' . $mediawiki->{error}->{details};
                        foreach my $page (@{$mw_pages}) {
                                $pages{$page->{title}} = $page;
                        }
                }
        }
        if (!$user_defined) {
                # No user-provided list, get the list of pages from
                # the API.
                my $mw_pages = $mediawiki->list({
                        action => 'query',
                        list => 'allpages',
                        aplimit => 500,
                });
                if (!defined($mw_pages)) {
                        print STDERR "fatal: could not get the list of wiki pages.\n";
                        print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
                        print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
                        exit 1;
                }
                foreach my $page (@{$mw_pages}) {
                        $pages{$page->{title}} = $page;
                }
        }
        return values(%pages);
}

sub run_git {
        open(my $git, "-|:encoding(UTF-8)", "git " . $_[0]);
        my $res = do { local $/; <$git> };
        close($git);

        return $res;
}


sub get_last_local_revision {
        # Get note regarding last mediawiki revision
        my $note = run_git("notes --ref=$remotename/mediawiki show refs/mediawiki/$remotename/master 2>/dev/null");
        my @note_info = split(/ /, $note);

        my $lastrevision_number;
        if (!(defined($note_info[0]) && $note_info[0] eq "mediawiki_revision:")) {
                print STDERR "No previous mediawiki revision found";
                $lastrevision_number = 0;
        } else {
                # Notes are formatted : mediawiki_revision: #number
                $lastrevision_number = $note_info[1];
                chomp($lastrevision_number);
                print STDERR "Last local mediawiki revision found is $lastrevision_number";
        }
        return $lastrevision_number;
}

# Remember the timestamp corresponding to a revision id.
my %basetimestamps;

sub get_last_remote_revision {
        mw_connect_maybe();

        my @pages = get_mw_pages();

        my $max_rev_num = 0;

        foreach my $page (@pages) {
                my $id = $page->{pageid};

                my $query = {
                        action => 'query',
                        prop => 'revisions',
                        rvprop => 'ids|timestamp',
                        pageids => $id,
                };

                my $result = $mediawiki->api($query);

                my $lastrev = pop(@{$result->{query}->{pages}->{$id}->{revisions}});

                $basetimestamps{$lastrev->{revid}} = $lastrev->{timestamp};

                $max_rev_num = ($lastrev->{revid} > $max_rev_num ? $lastrev->{revid} : $max_rev_num);
        }

        print STDERR "Last remote revision found is $max_rev_num.\n";
        return $max_rev_num;
}

# Clean content before sending it to MediaWiki
sub mediawiki_clean {
        my $string = shift;
        my $page_created = shift;
        # Mediawiki does not allow blank space at the end of a page and ends with a single \n.
        # This function right trims a string and adds a \n at the end to follow this rule
        $string =~ s/\s+$//;
        if ($string eq "" && $page_created) {
                # Creating empty pages is forbidden.
                $string = EMPTY_CONTENT;
        }
        return $string."\n";
}

# Filter applied on MediaWiki data before adding them to Git
sub mediawiki_smudge {
        my $string = shift;
        if ($string eq EMPTY_CONTENT) {
                $string = "";
        }
        # This \n is important. This is due to mediawiki's way to handle end of files.
        return $string."\n";
}

sub mediawiki_clean_filename {
        my $filename = shift;
        $filename =~ s/@{[SLASH_REPLACEMENT]}/\//g;
        # [, ], |, {, and } are forbidden by MediaWiki, even URL-encoded.
        # Do a variant of URL-encoding, i.e. looks like URL-encoding,
        # but with _ added to prevent MediaWiki from thinking this is
        # an actual special character.
        $filename =~ s/[\[\]\{\}\|]/sprintf("_%%_%x", ord($&))/ge;
        # If we use the uri escape before
        # we should unescape here, before anything

        return $filename;
}

sub mediawiki_smudge_filename {
        my $filename = shift;
        $filename =~ s/\//@{[SLASH_REPLACEMENT]}/g;
        $filename =~ s/ /_/g;
        # Decode forbidden characters encoded in mediawiki_clean_filename
        $filename =~ s/_%_([0-9a-fA-F][0-9a-fA-F])/sprintf("%c", hex($1))/ge;
        return $filename;
}

sub literal_data {
        my ($content) = @_;
        print STDOUT "data ", bytes::length($content), "\n", $content;
}

sub mw_capabilities {
        # Revisions are imported to the private namespace
        # refs/mediawiki/$remotename/ by the helper and fetched into
        # refs/remotes/$remotename later by fetch.
        print STDOUT "refspec refs/heads/*:refs/mediawiki/$remotename/*\n";
        print STDOUT "import\n";
        print STDOUT "list\n";
        print STDOUT "push\n";
        print STDOUT "\n";
}

sub mw_list {
        # MediaWiki do not have branches, we consider one branch arbitrarily
        # called master, and HEAD pointing to it.
        print STDOUT "? refs/heads/master\n";
        print STDOUT "\@refs/heads/master HEAD\n";
        print STDOUT "\n";
}

sub mw_option {
        print STDERR "remote-helper command 'option $_[0]' not yet implemented\n";
        print STDOUT "unsupported\n";
}

sub fetch_mw_revisions_for_page {
        my $page = shift;
        my $id = shift;
        my $fetch_from = shift;
        my @page_revs = ();
        my $query = {
                action => 'query',
                prop => 'revisions',
                rvprop => 'ids',
                rvdir => 'newer',
                rvstartid => $fetch_from,
                rvlimit => 500,
                pageids => $id,
        };

        my $revnum = 0;
        # Get 500 revisions at a time due to the mediawiki api limit
        while (1) {
                my $result = $mediawiki->api($query);

                # Parse each of those 500 revisions
                foreach my $revision (@{$result->{query}->{pages}->{$id}->{revisions}}) {
                        my $page_rev_ids;
                        $page_rev_ids->{pageid} = $page->{pageid};
                        $page_rev_ids->{revid} = $revision->{revid};
                        push(@page_revs, $page_rev_ids);
                        $revnum++;
                }
                last unless $result->{'query-continue'};
                $query->{rvstartid} = $result->{'query-continue'}->{revisions}->{rvstartid};
        }
        if ($shallow_import && @page_revs) {
                print STDERR "  Found 1 revision (shallow import).\n";
                @page_revs = sort {$b->{revid} <=> $a->{revid}} (@page_revs);
                return $page_revs[0];
        }
        print STDERR "  Found ", $revnum, " revision(s).\n";
        return @page_revs;
}

sub fetch_mw_revisions {
        my $pages = shift; my @pages = @{$pages};
        my $fetch_from = shift;

        my @revisions = ();
        my $n = 1;
        foreach my $page (@pages) {
                my $id = $page->{pageid};

                print STDERR "page $n/", scalar(@pages), ": ". $page->{title} ."\n";
                $n++;
                my @page_revs = fetch_mw_revisions_for_page($page, $id, $fetch_from);
                @revisions = (@page_revs, @revisions);
        }

        return ($n, @revisions);
}

sub import_file_revision {
        my $commit = shift;
        my %commit = %{$commit};
        my $full_import = shift;
        my $n = shift;

        my $title = $commit{title};
        my $comment = $commit{comment};
        my $content = $commit{content};
        my $author = $commit{author};
        my $date = $commit{date};

        print STDOUT "commit refs/mediawiki/$remotename/master\n";
        print STDOUT "mark :$n\n";
        print STDOUT "committer $author <$author\@$wiki_name> ", $date->epoch, " +0000\n";
        literal_data($comment);

        # If it's not a clone, we need to know where to start from
        if (!$full_import && $n == 1) {
                print STDOUT "from refs/mediawiki/$remotename/master^0\n";
        }
        if ($content ne DELETED_CONTENT) {
                print STDOUT "M 644 inline $title.mw\n";
                literal_data($content);
                print STDOUT "\n\n";
        } else {
                print STDOUT "D $title.mw\n";
        }

        # mediawiki revision number in the git note
        if ($full_import && $n == 1) {
                print STDOUT "reset refs/notes/$remotename/mediawiki\n";
        }
        print STDOUT "commit refs/notes/$remotename/mediawiki\n";
        print STDOUT "committer $author <$author\@$wiki_name> ", $date->epoch, " +0000\n";
        literal_data("Note added by git-mediawiki during import");
        if (!$full_import && $n == 1) {
                print STDOUT "from refs/notes/$remotename/mediawiki^0\n";
        }
        print STDOUT "N inline :$n\n";
        literal_data("mediawiki_revision: " . $commit{mw_revision});
        print STDOUT "\n\n";
}

# parse a sequence of
# <cmd> <arg1>
# <cmd> <arg2>
# \n
# (like batch sequence of import and sequence of push statements)
sub get_more_refs {
        my $cmd = shift;
        my @refs;
        while (1) {
                my $line = <STDIN>;
                if ($line =~ m/^$cmd (.*)$/) {
                        push(@refs, $1);
                } elsif ($line eq "\n") {
                        return @refs;
                } else {
                        die("Invalid command in a '$cmd' batch: ". $_);
                }
        }
}

sub mw_import {
        # multiple import commands can follow each other.
        my @refs = (shift, get_more_refs("import"));
        foreach my $ref (@refs) {
                mw_import_ref($ref);
        }
        print STDOUT "done\n";
}

sub mw_import_ref {
        my $ref = shift;
        # The remote helper will call "import HEAD" and
        # "import refs/heads/master".
        # Since HEAD is a symbolic ref to master (by convention,
        # followed by the output of the command "list" that we gave),
        # we don't need to do anything in this case.
        if ($ref eq "HEAD") {
                return;
        }

        mw_connect_maybe();

        my @pages = get_mw_pages();

        print STDERR "Searching revisions...\n";
        my $last_local = get_last_local_revision();
        my $fetch_from = $last_local + 1;
        if ($fetch_from == 1) {
                print STDERR ", fetching from beginning.\n";
        } else {
                print STDERR ", fetching from here.\n";
        }
        my ($n, @revisions) = fetch_mw_revisions(\@pages, $fetch_from);

        # Creation of the fast-import stream
        print STDERR "Fetching & writing export data...\n";

        $n = 0;
        my $last_timestamp = 0; # Placeholer in case $rev->timestamp is undefined

        foreach my $pagerevid (sort {$a->{revid} <=> $b->{revid}} @revisions) {
                # fetch the content of the pages
                my $query = {
                        action => 'query',
                        prop => 'revisions',
                        rvprop => 'content|timestamp|comment|user|ids',
                        revids => $pagerevid->{revid},
                };

                my $result = $mediawiki->api($query);

                my $rev = pop(@{$result->{query}->{pages}->{$pagerevid->{pageid}}->{revisions}});

                $n++;

                my %commit;
                $commit{author} = $rev->{user} || 'Anonymous';
                $commit{comment} = $rev->{comment} || '*Empty MediaWiki Message*';
                $commit{title} = mediawiki_smudge_filename(
                        $result->{query}->{pages}->{$pagerevid->{pageid}}->{title}
                    );
                $commit{mw_revision} = $pagerevid->{revid};
                $commit{content} = mediawiki_smudge($rev->{'*'});

                if (!defined($rev->{timestamp})) {
                        $last_timestamp++;
                } else {
                        $last_timestamp = $rev->{timestamp};
                }
                $commit{date} = DateTime::Format::ISO8601->parse_datetime($last_timestamp);

                print STDERR "$n/", scalar(@revisions), ": Revision #$pagerevid->{revid} of $commit{title}\n";

                import_file_revision(\%commit, ($fetch_from == 1), $n);
        }

        if ($fetch_from == 1 && $n == 0) {
                print STDERR "You appear to have cloned an empty MediaWiki.\n";
                # Something has to be done remote-helper side. If nothing is done, an error is
                # thrown saying that HEAD is refering to unknown object 0000000000000000000
                # and the clone fails.
        }
}

sub error_non_fast_forward {
        my $advice = run_git("config --bool advice.pushNonFastForward");
        chomp($advice);
        if ($advice ne "false") {
                # Native git-push would show this after the summary.
                # We can't ask it to display it cleanly, so print it
                # ourselves before.
                print STDERR "To prevent you from losing history, non-fast-forward updates were rejected\n";
                print STDERR "Merge the remote changes (e.g. 'git pull') before pushing again. See the\n";
                print STDERR "'Note about fast-forwards' section of 'git push --help' for details.\n";
        }
        print STDOUT "error $_[0] \"non-fast-forward\"\n";
        return 0;
}

sub mw_push_file {
        my $diff_info = shift;
        # $diff_info contains a string in this format:
        # 100644 100644 <sha1_of_blob_before_commit> <sha1_of_blob_now> <status>
        my @diff_info_split = split(/[ \t]/, $diff_info);

        # Filename, including .mw extension
        my $complete_file_name = shift;
        # Commit message
        my $summary = shift;
        # MediaWiki revision number. Keep the previous one by default,
        # in case there's no edit to perform.
        my $newrevid = shift;

        my $new_sha1 = $diff_info_split[3];
        my $old_sha1 = $diff_info_split[2];
        my $page_created = ($old_sha1 eq NULL_SHA1);
        my $page_deleted = ($new_sha1 eq NULL_SHA1);
        $complete_file_name = mediawiki_clean_filename($complete_file_name);

        if (substr($complete_file_name,-3) eq ".mw") {
                my $title = substr($complete_file_name,0,-3);

                my $file_content;
                if ($page_deleted) {
                        # Deleting a page usually requires
                        # special priviledges. A common
                        # convention is to replace the page
                        # with this content instead:
                        $file_content = DELETED_CONTENT;
                } else {
                        $file_content = run_git("cat-file blob $new_sha1");
                }

                mw_connect_maybe();

                my $result = $mediawiki->edit( {
                        action => 'edit',
                        summary => $summary,
                        title => $title,
                        basetimestamp => $basetimestamps{$newrevid},
                        text => mediawiki_clean($file_content, $page_created),
                                  }, {
                                          skip_encoding => 1 # Helps with names with accentuated characters
                                  });
                if (!$result) {
                        if ($mediawiki->{error}->{code} == 3) {
                                # edit conflicts, considered as non-fast-forward
                                print STDERR 'Warning: Error ' .
                                    $mediawiki->{error}->{code} .
                                    ' from mediwiki: ' . $mediawiki->{error}->{details} .
                                    ".\n";
                                return ($newrevid, "non-fast-forward");
                        } else {
                                # Other errors. Shouldn't happen => just die()
                                die 'Fatal: Error ' .
                                    $mediawiki->{error}->{code} .
                                    ' from mediwiki: ' . $mediawiki->{error}->{details};
                        }
                }
                $newrevid = $result->{edit}->{newrevid};
                print STDERR "Pushed file: $new_sha1 - $title\n";
        } else {
                print STDERR "$complete_file_name not a mediawiki file (Not pushable on this version of git-remote-mediawiki).\n"
        }
        return ($newrevid, "ok");
}

sub mw_push {
        # multiple push statements can follow each other
        my @refsspecs = (shift, get_more_refs("push"));
        my $pushed;
        for my $refspec (@refsspecs) {
                my ($force, $local, $remote) = $refspec =~ /^(\+)?([^:]*):([^:]*)$/
                    or die("Invalid refspec for push. Expected <src>:<dst> or +<src>:<dst>");
                if ($force) {
                        print STDERR "Warning: forced push not allowed on a MediaWiki.\n";
                }
                if ($local eq "") {
                        print STDERR "Cannot delete remote branch on a MediaWiki\n";
                        print STDOUT "error $remote cannot delete\n";
                        next;
                }
                if ($remote ne "refs/heads/master") {
                        print STDERR "Only push to the branch 'master' is supported on a MediaWiki\n";
                        print STDOUT "error $remote only master allowed\n";
                        next;
                }
                if (mw_push_revision($local, $remote)) {
                        $pushed = 1;
                }
        }

        # Notify Git that the push is done
        print STDOUT "\n";

        if ($pushed && $dumb_push) {
                print STDERR "Just pushed some revisions to MediaWiki.\n";
                print STDERR "The pushed revisions now have to be re-imported, and your current branch\n";
                print STDERR "needs to be updated with these re-imported commits. You can do this with\n";
                print STDERR "\n";
                print STDERR "  git pull --rebase\n";
                print STDERR "\n";
        }
}

sub mw_push_revision {
        my $local = shift;
        my $remote = shift; # actually, this has to be "refs/heads/master" at this point.
        my $last_local_revid = get_last_local_revision();
        print STDERR ".\n"; # Finish sentence started by get_last_local_revision()
        my $last_remote_revid = get_last_remote_revision();
        my $mw_revision = $last_remote_revid;

        # Get sha1 of commit pointed by local HEAD
        my $HEAD_sha1 = run_git("rev-parse $local 2>/dev/null"); chomp($HEAD_sha1);
        # Get sha1 of commit pointed by remotes/$remotename/master
        my $remoteorigin_sha1 = run_git("rev-parse refs/remotes/$remotename/master 2>/dev/null");
        chomp($remoteorigin_sha1);

        if ($last_local_revid > 0 &&
            $last_local_revid < $last_remote_revid) {
                return error_non_fast_forward($remote);
        }

        if ($HEAD_sha1 eq $remoteorigin_sha1) {
                # nothing to push
                return 0;
        }

        # Get every commit in between HEAD and refs/remotes/origin/master,
        # including HEAD and refs/remotes/origin/master
        my @commit_pairs = ();
        if ($last_local_revid > 0) {
                my $parsed_sha1 = $remoteorigin_sha1;
                # Find a path from last MediaWiki commit to pushed commit
                while ($parsed_sha1 ne $HEAD_sha1) {
                        my @commit_info =  grep(/^$parsed_sha1/, split(/\n/, run_git("rev-list --children $local")));
                        if (!@commit_info) {
                                return error_non_fast_forward($remote);
                        }
                        my @commit_info_split = split(/ |\n/, $commit_info[0]);
                        # $commit_info_split[1] is the sha1 of the commit to export
                        # $commit_info_split[0] is the sha1 of its direct child
                        push(@commit_pairs, \@commit_info_split);
                        $parsed_sha1 = $commit_info_split[1];
                }
        } else {
                # No remote mediawiki revision. Export the whole
                # history (linearized with --first-parent)
                print STDERR "Warning: no common ancestor, pushing complete history\n";
                my $history = run_git("rev-list --first-parent --children $local");
                my @history = split('\n', $history);
                @history = @history[1..$#history];
                foreach my $line (reverse @history) {
                        my @commit_info_split = split(/ |\n/, $line);
                        push(@commit_pairs, \@commit_info_split);
                }
        }

        foreach my $commit_info_split (@commit_pairs) {
                my $sha1_child = @{$commit_info_split}[0];
                my $sha1_commit = @{$commit_info_split}[1];
                my $diff_infos = run_git("diff-tree -r --raw -z $sha1_child $sha1_commit");
                # TODO: we could detect rename, and encode them with a #redirect on the wiki.
                # TODO: for now, it's just a delete+add
                my @diff_info_list = split(/\0/, $diff_infos);
                # Keep the first line of the commit message as mediawiki comment for the revision
                my $commit_msg = (split(/\n/, run_git("show --pretty=format:\"%s\" $sha1_commit")))[0];
                chomp($commit_msg);
                # Push every blob
                while (@diff_info_list) {
                        my $status;
                        # git diff-tree -z gives an output like
                        # <metadata>\0<filename1>\0
                        # <metadata>\0<filename2>\0
                        # and we've split on \0.
                        my $info = shift(@diff_info_list);
                        my $file = shift(@diff_info_list);
                        ($mw_revision, $status) = mw_push_file($info, $file, $commit_msg, $mw_revision);
                        if ($status eq "non-fast-forward") {
                                # we may already have sent part of the
                                # commit to MediaWiki, but it's too
                                # late to cancel it. Stop the push in
                                # the middle, but still give an
                                # accurate error message.
                                return error_non_fast_forward($remote);
                        }
                        if ($status ne "ok") {
                                die("Unknown error from mw_push_file()");
                        }
                }
                unless ($dumb_push) {
                        run_git("notes --ref=$remotename/mediawiki add -m \"mediawiki_revision: $mw_revision\" $sha1_commit");
                        run_git("update-ref -m \"Git-MediaWiki push\" refs/mediawiki/$remotename/master $sha1_commit $sha1_child");
                }
        }

        print STDOUT "ok $remote\n";
        return 1;
}