#! /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.
# Documentation & bugtracker: https://github.com/moy/Git-Mediawiki/

use strict;
use MediaWiki::API;
use Git;
use Git::Mediawiki qw(clean_filename smudge_filename connect_maybe
                                        EMPTY HTTP_CODE_OK);
use DateTime::Format::ISO8601;
use warnings;

# By default, use UTF-8 to communicate with Git and the user
binmode STDERR, ':encoding(UTF-8)';
binmode STDOUT, ':encoding(UTF-8)';

use URI::Escape;

# It's not always possible to delete pages (may require some
# privileges). 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';

# Used on Git's side to reflect empty edit messages on the wiki
use constant EMPTY_MESSAGE => '*Empty MediaWiki Message*';

# Number of pages taken into account at once in submodule get_mw_page_list
use constant SLICE_SIZE => 50;

# Number of linked mediafile to get at once in get_linked_mediafiles
# The query is split in small batches because of the MW API limit of
# the number of links to be returned (500 links max).
use constant BATCH_SIZE => 10;

if (@ARGV != 2) {
        exit_error_usage();
}

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);

# Import media files on pull
my $import_media = run_git("config --get --bool remote.${remotename}.mediaimport");
chomp($import_media);
$import_media = ($import_media eq 'true');

# Export media files on push
my $export_media = run_git("config --get --bool remote.${remotename}.mediaexport");
chomp($export_media);
$export_media = !($export_media eq 'false');

my $wiki_login = run_git("config --get remote.${remotename}.mwLogin");
# Note: mwPassword is discourraged. Use the credential system instead.
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');

# Fetch (clone and pull) by revisions instead of by pages. This behavior
# is more efficient when we have a wiki with lots of pages and we fetch
# the revisions quite often so that they concern only few pages.
# Possible values:
# - by_rev: perform one query per new revision on the remote wiki
# - by_page: query each tracked page for new revision
my $fetch_strategy = run_git("config --get remote.${remotename}.fetchStrategy");
if (!$fetch_strategy) {
        $fetch_strategy = run_git('config --get mediawiki.fetchStrategy');
}
chomp($fetch_strategy);
if (!$fetch_strategy) {
        $fetch_strategy = 'by_page';
}

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

# 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");
if (!$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
while (<STDIN>) {
        chomp;

        if (!parse_command($_)) {
                last;
        }

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

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

## error handling
sub exit_error_usage {
        die "ERROR: git-remote-mediawiki module was not called with a correct number of\n" .
            "parameters\n" .
            "You may obtain this error because you attempted to run the git-remote-mediawiki\n" .
            "module directly.\n" .
            "This module can be used the following way:\n" .
            "\tgit clone mediawiki://<address of a mediawiki>\n" .
            "Then, use git commit, push and pull as with every normal git repository.\n";
}

sub parse_command {
        my ($line) = @_;
        my @cmd = split(/ /, $line);
        if (!defined $cmd[0]) {
                return 0;
        }
        if ($cmd[0] eq 'capabilities') {
                die("Too many arguments for capabilities\n")
                    if (defined($cmd[1]));
                mw_capabilities();
        } elsif ($cmd[0] eq 'list') {
                die("Too many arguments for list\n") if (defined($cmd[2]));
                mw_list($cmd[1]);
        } elsif ($cmd[0] eq 'import') {
                die("Invalid argument for import\n")
                    if ($cmd[1] eq EMPTY);
                die("Too many arguments for import\n")
                    if (defined($cmd[2]));
                mw_import($cmd[1]);
        } elsif ($cmd[0] eq 'option') {
                die("Invalid arguments for option\n")
                    if ($cmd[1] eq EMPTY || $cmd[2] eq EMPTY);
                die("Too many arguments for option\n")
                    if (defined($cmd[3]));
                mw_option($cmd[1],$cmd[2]);
        } elsif ($cmd[0] eq 'push') {
                mw_push($cmd[1]);
        } else {
                print {*STDERR} "Unknown command. Aborting...\n";
                return 0;
        }
        return 1;
}

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

sub fatal_mw_error {
        my $action = shift;
        print STDERR "fatal: could not $action.\n";
        print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
        if ($url =~ /^https/) {
                print STDERR "fatal: make sure '$url/api.php' is a valid page\n";
                print STDERR "fatal: and the SSL certificate is correct.\n";
        } else {
                print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
        }
        print STDERR "fatal: (error " .
            $mediawiki->{error}->{code} . ': ' .
            $mediawiki->{error}->{details} . ")\n";
        exit 1;
}

## Functions for listing pages on the remote wiki
sub get_mw_tracked_pages {
        my $pages = shift;
        get_mw_page_list(\@tracked_pages, $pages);
        return;
}

sub get_mw_page_list {
        my $page_list = shift;
        my $pages = shift;
        my @some_pages = @{$page_list};
        while (@some_pages) {
                my $last_page = SLICE_SIZE;
                if ($#some_pages < $last_page) {
                        $last_page = $#some_pages;
                }
                my @slice = @some_pages[0..$last_page];
                get_mw_first_pages(\@slice, $pages);
                @some_pages = @some_pages[(SLICE_SIZE + 1)..$#some_pages];
        }
        return;
}

sub get_mw_tracked_categories {
        my $pages = shift;
        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} . "\n";
                foreach my $page (@{$mw_pages}) {
                        $pages->{$page->{title}} = $page;
                }
        }
        return;
}

sub get_mw_all_pages {
        my $pages = shift;
        # No user-provided list, get the list of pages from the API.
        my $mw_pages = $mediawiki->list({
                action => 'query',
                list => 'allpages',
                aplimit => 'max'
        });
        if (!defined($mw_pages)) {
                fatal_mw_error("get the list of wiki pages");
        }
        foreach my $page (@{$mw_pages}) {
                $pages->{$page->{title}} = $page;
        }
        return;
}

# queries the wiki for a set of pages. Meant to be used within a loop
# querying the wiki for slices of page list.
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)) {
                fatal_mw_error("query the list of wiki pages");
        }
        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;
                }
        }
        return;
}

# Get the list of pages to be fetched according to configuration.
sub get_mw_pages {
        $mediawiki = connect_maybe($mediawiki, $remotename, $url);

        print {*STDERR} "Listing pages on remote wiki...\n";

        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.
                get_mw_tracked_pages(\%pages);
        }
        if (@tracked_categories) {
                $user_defined = 1;
                get_mw_tracked_categories(\%pages);
        }
        if (!$user_defined) {
                get_mw_all_pages(\%pages);
        }
        if ($import_media) {
                print {*STDERR} "Getting media files for selected pages...\n";
                if ($user_defined) {
                        get_linked_mediafiles(\%pages);
                } else {
                        get_all_mediafiles(\%pages);
                }
        }
        print {*STDERR} (scalar keys %pages) . " pages found.\n";
        return %pages;
}

# usage: $out = run_git("command args");
#        $out = run_git("command args", "raw"); # don't interpret output as UTF-8.
sub run_git {
        my $args = shift;
        my $encoding = (shift || 'encoding(UTF-8)');
        open(my $git, "-|:${encoding}", "git ${args}")
            or die "Unable to fork: $!\n";
        my $res = do {
                local $/ = undef;
                <$git>
        };
        close($git);

        return $res;
}


sub get_all_mediafiles {
        my $pages = shift;
        # Attach list of all pages for media files from the API,
        # they are in a different namespace, only one namespace
        # can be queried at the same moment
        my $mw_pages = $mediawiki->list({
                action => 'query',
                list => 'allpages',
                apnamespace => get_mw_namespace_id('File'),
                aplimit => 'max'
        });
        if (!defined($mw_pages)) {
                print {*STDERR} "fatal: could not get the list of pages for media files.\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;
}

sub get_linked_mediafiles {
        my $pages = shift;
        my @titles = map { $_->{title} } values(%{$pages});

        my $batch = BATCH_SIZE;
        while (@titles) {
                if ($#titles < $batch) {
                        $batch = $#titles;
                }
                my @slice = @titles[0..$batch];

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

                # Media files could be included or linked from
                # a page, get all related
                my $query = {
                        action => 'query',
                        prop => 'links|images',
                        titles => $mw_titles,
                        plnamespace => get_mw_namespace_id('File'),
                        pllimit => 'max'
                };
                my $result = $mediawiki->api($query);

                while (my ($id, $page) = each(%{$result->{query}->{pages}})) {
                        my @media_titles;
                        if (defined($page->{links})) {
                                my @link_titles
                                    = map { $_->{title} } @{$page->{links}};
                                push(@media_titles, @link_titles);
                        }
                        if (defined($page->{images})) {
                                my @image_titles
                                    = map { $_->{title} } @{$page->{images}};
                                push(@media_titles, @image_titles);
                        }
                        if (@media_titles) {
                                get_mw_page_list(\@media_titles, $pages);
                        }
                }

                @titles = @titles[($batch+1)..$#titles];
        }
        return;
}

sub get_mw_mediafile_for_page_revision {
        # Name of the file on Wiki, with the prefix.
        my $filename = shift;
        my $timestamp = shift;
        my %mediafile;

        # Search if on a media file with given timestamp exists on
        # MediaWiki. In that case download the file.
        my $query = {
                action => 'query',
                prop => 'imageinfo',
                titles => "File:${filename}",
                iistart => $timestamp,
                iiend => $timestamp,
                iiprop => 'timestamp|archivename|url',
                iilimit => 1
        };
        my $result = $mediawiki->api($query);

        my ($fileid, $file) = each( %{$result->{query}->{pages}} );
        # If not defined it means there is no revision of the file for
        # given timestamp.
        if (defined($file->{imageinfo})) {
                $mediafile{title} = $filename;

                my $fileinfo = pop(@{$file->{imageinfo}});
                $mediafile{timestamp} = $fileinfo->{timestamp};
                # Mediawiki::API's download function doesn't support https URLs
                # and can't download old versions of files.
                print {*STDERR} "\tDownloading file $mediafile{title}, version $mediafile{timestamp}\n";
                $mediafile{content} = download_mw_mediafile($fileinfo->{url});
        }
        return %mediafile;
}

sub download_mw_mediafile {
        my $download_url = shift;

        my $response = $mediawiki->{ua}->get($download_url);
        if ($response->code == HTTP_CODE_OK) {
                return $response->decoded_content;
        } else {
                print {*STDERR} "Error downloading mediafile from :\n";
                print {*STDERR} "URL: ${download_url}\n";
                print {*STDERR} 'Server response: ' . $response->code . q{ } . $response->message . "\n";
                exit 1;
        }
}

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;
}

# Get the last remote revision without taking in account which pages are
# tracked or not. This function makes a single request to the wiki thus
# avoid a loop onto all tracked pages. This is useful for the fetch-by-rev
# option.
sub get_last_global_remote_rev {
        $mediawiki = connect_maybe($mediawiki, $remotename, $url);

        my $query = {
                action => 'query',
                list => 'recentchanges',
                prop => 'revisions',
                rclimit => '1',
                rcdir => 'older',
        };
        my $result = $mediawiki->api($query);
        return $result->{query}->{recentchanges}[0]->{revid};
}

# Get the last remote revision concerning the tracked pages and the tracked
# categories.
sub get_last_remote_revision {
        $mediawiki = connect_maybe($mediawiki, $remotename, $url);

        my %pages_hash = get_mw_pages();
        my @pages = values(%pages_hash);

        my $max_rev_num = 0;

        print {*STDERR} "Getting last revision id on tracked pages...\n";

        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 EMPTY && $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) {
                $string = EMPTY;
        }
        # This \n is important. This is due to mediawiki's way to handle end of files.
        return "${string}\n";
}

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

sub literal_data_raw {
        # Output possibly binary content.
        my ($content) = @_;
        # Avoid confusion between size in bytes and in characters
        utf8::downgrade($content);
        binmode STDOUT, ':raw';
        print {*STDOUT} 'data ', bytes::length($content), "\n", $content;
        binmode STDOUT, ':encoding(UTF-8)';
        return;
}

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/${remotename}/*\n";
        print {*STDOUT} "import\n";
        print {*STDOUT} "list\n";
        print {*STDOUT} "push\n";
        if ($dumb_push) {
                print {*STDOUT} "no-private-update\n";
        }
        print {*STDOUT} "\n";
        return;
}

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";
        return;
}

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

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);
                        $revnum++;
                }
                last if (!$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 fe_escape_path {
    my $path = shift;
    $path =~ s/\\/\\\\/g;
    $path =~ s/"/\\"/g;
    $path =~ s/\n/\\n/g;
    return qq("${path}");
}

sub import_file_revision {
        my $commit = shift;
        my %commit = %{$commit};
        my $full_import = shift;
        my $n = shift;
        my $mediafile = shift;
        my %mediafile;
        if ($mediafile) {
                %mediafile = %{$mediafile};
        }

        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 ($content ne DELETED_CONTENT) {
                print {*STDOUT} 'M 644 inline ' .
                    fe_escape_path("${title}.mw") . "\n";
                literal_data($content);
                if (%mediafile) {
                        print {*STDOUT} 'M 644 inline '
                            . fe_escape_path($mediafile{title}) . "\n";
                        literal_data_raw($mediafile{content});
                }
                print {*STDOUT} "\n\n";
        } else {
                print {*STDOUT} 'D ' . fe_escape_path("${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";
        return;
}

# 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 =~ /^$cmd (.*)$/) {
                        push(@refs, $1);
                } elsif ($line eq "\n") {
                        return @refs;
                } else {
                        die("Invalid command in a '$cmd' batch: $_\n");
                }
        }
        return;
}

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";
        return;
}

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;
        }

        $mediawiki = connect_maybe($mediawiki, $remotename, $url);

        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 $n = 0;
        if ($fetch_strategy eq 'by_rev') {
                print {*STDERR} "Fetching & writing export data by revs...\n";
                $n = mw_import_ref_by_revs($fetch_from);
        } elsif ($fetch_strategy eq 'by_page') {
                print {*STDERR} "Fetching & writing export data by pages...\n";
                $n = mw_import_ref_by_pages($fetch_from);
        } else {
                print {*STDERR} qq(fatal: invalid fetch strategy "${fetch_strategy}".\n);
                print {*STDERR} "Check your configuration variables remote.${remotename}.fetchStrategy and mediawiki.fetchStrategy\n";
                exit 1;
        }

        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 referring to unknown object 0000000000000000000
                # and the clone fails.
        }
        return;
}

sub mw_import_ref_by_pages {

        my $fetch_from = shift;
        my %pages_hash = get_mw_pages();
        my @pages = values(%pages_hash);

        my ($n, @revisions) = fetch_mw_revisions(\@pages, $fetch_from);

        @revisions = sort {$a->{revid} <=> $b->{revid}} @revisions;
        my @revision_ids = map { $_->{revid} } @revisions;

        return mw_import_revids($fetch_from, \@revision_ids, \%pages_hash);
}

sub mw_import_ref_by_revs {

        my $fetch_from = shift;
        my %pages_hash = get_mw_pages();

        my $last_remote = get_last_global_remote_rev();
        my @revision_ids = $fetch_from..$last_remote;
        return mw_import_revids($fetch_from, \@revision_ids, \%pages_hash);
}

# Import revisions given in second argument (array of integers).
# Only pages appearing in the third argument (hash indexed by page titles)
# will be imported.
sub mw_import_revids {
        my $fetch_from = shift;
        my $revision_ids = shift;
        my $pages = shift;

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

        foreach my $pagerevid (@{$revision_ids}) {
                # Count page even if we skip it, since we display
                # $n/$total and $total includes skipped pages.
                $n++;

                # fetch the content of the pages
                my $query = {
                        action => 'query',
                        prop => 'revisions',
                        rvprop => 'content|timestamp|comment|user|ids',
                        revids => $pagerevid,
                };

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

                if (!$result) {
                        die "Failed to retrieve modified page for revision $pagerevid\n";
                }

                if (defined($result->{query}->{badrevids}->{$pagerevid})) {
                        # The revision id does not exist on the remote wiki.
                        next;
                }

                if (!defined($result->{query}->{pages})) {
                        die "Invalid revision ${pagerevid}.\n";
                }

                my @result_pages = values(%{$result->{query}->{pages}});
                my $result_page = $result_pages[0];
                my $rev = $result_pages[0]->{revisions}->[0];

                my $page_title = $result_page->{title};

                if (!exists($pages->{$page_title})) {
                        print {*STDERR} "${n}/", scalar(@{$revision_ids}),
                                ": Skipping revision #$rev->{revid} of ${page_title}\n";
                        next;
                }

                $n_actual++;

                my %commit;
                $commit{author} = $rev->{user} || 'Anonymous';
                $commit{comment} = $rev->{comment} || EMPTY_MESSAGE;
                $commit{title} = smudge_filename($page_title);
                $commit{mw_revision} = $rev->{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);

                # Differentiates classic pages and media files.
                my ($namespace, $filename) = $page_title =~ /^([^:]*):(.*)$/;
                my %mediafile;
                if ($namespace) {
                        my $id = get_mw_namespace_id($namespace);
                        if ($id && $id == get_mw_namespace_id('File')) {
                                %mediafile = get_mw_mediafile_for_page_revision($filename, $rev->{timestamp});
                        }
                }
                # If this is a revision of the media page for new version
                # of a file do one common commit for both file and media page.
                # Else do commit only for that page.
                print {*STDERR} "${n}/", scalar(@{$revision_ids}), ": Revision #$rev->{revid} of $commit{title}\n";
                import_file_revision(\%commit, ($fetch_from == 1), $n_actual, \%mediafile);
        }

        return $n_actual;
}

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} qq(error $_[0] "non-fast-forward"\n);
        return 0;
}

sub mw_upload_file {
        my $complete_file_name = shift;
        my $new_sha1 = shift;
        my $extension = shift;
        my $file_deleted = shift;
        my $summary = shift;
        my $newrevid;
        my $path = "File:${complete_file_name}";
        my %hashFiles = get_allowed_file_extensions();
        if (!exists($hashFiles{$extension})) {
                print {*STDERR} "${complete_file_name} is not a permitted file on this wiki.\n";
                print {*STDERR} "Check the configuration of file uploads in your mediawiki.\n";
                return $newrevid;
        }
        # Deleting and uploading a file requires a priviledged user
        if ($file_deleted) {
                $mediawiki = connect_maybe($mediawiki, $remotename, $url);
                my $query = {
                        action => 'delete',
                        title => $path,
                        reason => $summary
                };
                if (!$mediawiki->edit($query)) {
                        print {*STDERR} "Failed to delete file on remote wiki\n";
                        print {*STDERR} "Check your permissions on the remote site. Error code:\n";
                        print {*STDERR} $mediawiki->{error}->{code} . ':' . $mediawiki->{error}->{details};
                        exit 1;
                }
        } else {
                # Don't let perl try to interpret file content as UTF-8 => use "raw"
                my $content = run_git("cat-file blob ${new_sha1}", 'raw');
                if ($content ne EMPTY) {
                        $mediawiki = connect_maybe($mediawiki, $remotename, $url);
                        $mediawiki->{config}->{upload_url} =
                                "${url}/index.php/Special:Upload";
                        $mediawiki->edit({
                                action => 'upload',
                                filename => $complete_file_name,
                                comment => $summary,
                                file => [undef,
                                         $complete_file_name,
                                         Content => $content],
                                ignorewarnings => 1,
                        }, {
                                skip_encoding => 1
                        } ) || die $mediawiki->{error}->{code} . ':'
                                 . $mediawiki->{error}->{details} . "\n";
                        my $last_file_page = $mediawiki->get_page({title => $path});
                        $newrevid = $last_file_page->{revid};
                        print {*STDERR} "Pushed file: ${new_sha1} - ${complete_file_name}.\n";
                } else {
                        print {*STDERR} "Empty file ${complete_file_name} not pushed.\n";
                }
        }
        return $newrevid;
}

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 $oldrevid = shift;
        my $newrevid;

        if ($summary eq EMPTY_MESSAGE) {
                $summary = EMPTY;
        }

        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);
        $complete_file_name = clean_filename($complete_file_name);

        my ($title, $extension) = $complete_file_name =~ /^(.*)\.([^\.]*)$/;
        if (!defined($extension)) {
                $extension = EMPTY;
        }
        if ($extension eq 'mw') {
                my $ns = get_mw_namespace_id_for_page($complete_file_name);
                if ($ns && $ns == get_mw_namespace_id('File') && (!$export_media)) {
                        print {*STDERR} "Ignoring media file related page: ${complete_file_name}\n";
                        return ($oldrevid, 'ok');
                }
                my $file_content;
                if ($page_deleted) {
                        # Deleting a page usually requires
                        # special privileges. 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}");
                }

                $mediawiki = connect_maybe($mediawiki, $remotename, $url);

                my $result = $mediawiki->edit( {
                        action => 'edit',
                        summary => $summary,
                        title => $title,
                        basetimestamp => $basetimestamps{$oldrevid},
                        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 mediawiki: ' . $mediawiki->{error}->{details} .
                                    ".\n";
                                return ($oldrevid, 'non-fast-forward');
                        } else {
                                # Other errors. Shouldn't happen => just die()
                                die 'Fatal: Error ' .
                                    $mediawiki->{error}->{code} .
                                    ' from mediawiki: ' . $mediawiki->{error}->{details} . "\n";
                        }
                }
                $newrevid = $result->{edit}->{newrevid};
                print {*STDERR} "Pushed file: ${new_sha1} - ${title}\n";
        } elsif ($export_media) {
                $newrevid = mw_upload_file($complete_file_name, $new_sha1,
                                           $extension, $page_deleted,
                                           $summary);
        } else {
                print {*STDERR} "Ignoring media file ${title}\n";
        }
        $newrevid = ($newrevid or $oldrevid);
        return ($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>\n");
                if ($force) {
                        print {*STDERR} "Warning: forced push not allowed on a MediaWiki.\n";
                }
                if ($local eq EMPTY) {
                        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";
        }
        return;
}

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
                print {*STDERR} "Computing path from local to remote ...\n";
                my @local_ancestry = split(/\n/, run_git("rev-list --boundary --parents ${local} ^${parsed_sha1}"));
                my %local_ancestry;
                foreach my $line (@local_ancestry) {
                        if (my ($child, $parents) = $line =~ /^-?([a-f0-9]+) ([a-f0-9 ]+)/) {
                                foreach my $parent (split(/ /, $parents)) {
                                        $local_ancestry{$parent} = $child;
                                }
                        } elsif (!$line =~ /^([a-f0-9]+)/) {
                                die "Unexpected output from git rev-list: ${line}\n";
                        }
                }
                while ($parsed_sha1 ne $HEAD_sha1) {
                        my $child = $local_ancestry{$parsed_sha1};
                        if (!$child) {
                                print {*STDERR} "Cannot find a path in history from remote commit to last commit\n";
                                return error_non_fast_forward($remote);
                        }
                        push(@commit_pairs, [$parsed_sha1, $child]);
                        $parsed_sha1 = $child;
                }
        } 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 subject line of the commit message as mediawiki comment for the revision
                my $commit_msg = run_git(qq(log --no-walk --format="%s" ${sha1_commit}));
                chomp($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()\n");
                        }
                }
                if (!$dumb_push) {
                        run_git(qq(notes --ref=${remotename}/mediawiki add -f -m "mediawiki_revision: ${mw_revision}" ${sha1_commit}));
                }
        }

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

sub get_allowed_file_extensions {
        $mediawiki = connect_maybe($mediawiki, $remotename, $url);

        my $query = {
                action => 'query',
                meta => 'siteinfo',
                siprop => 'fileextensions'
                };
        my $result = $mediawiki->api($query);
        my @file_extensions = map { $_->{ext}} @{$result->{query}->{fileextensions}};
        my %hashFile = map { $_ => 1 } @file_extensions;

        return %hashFile;
}

# In memory cache for MediaWiki namespace ids.
my %namespace_id;

# Namespaces whose id is cached in the configuration file
# (to avoid duplicates)
my %cached_mw_namespace_id;

# Return MediaWiki id for a canonical namespace name.
# Ex.: "File", "Project".
sub get_mw_namespace_id {
        $mediawiki = connect_maybe($mediawiki, $remotename, $url);
        my $name = shift;

        if (!exists $namespace_id{$name}) {
                # Look at configuration file, if the record for that namespace is
                # already cached. Namespaces are stored in form:
                # "Name_of_namespace:Id_namespace", ex.: "File:6".
                my @temp = split(/\n/,
                                 run_git("config --get-all remote.${remotename}.namespaceCache"));
                chomp(@temp);
                foreach my $ns (@temp) {
                        my ($n, $id) = split(/:/, $ns);
                        if ($id eq 'notANameSpace') {
                                $namespace_id{$n} = {is_namespace => 0};
                        } else {
                                $namespace_id{$n} = {is_namespace => 1, id => $id};
                        }
                        $cached_mw_namespace_id{$n} = 1;
                }
        }

        if (!exists $namespace_id{$name}) {
                print {*STDERR} "Namespace ${name} not found in cache, querying the wiki ...\n";
                # NS not found => get namespace id from MW and store it in
                # configuration file.
                my $query = {
                        action => 'query',
                        meta => 'siteinfo',
                        siprop => 'namespaces'
                };
                my $result = $mediawiki->api($query);

                while (my ($id, $ns) = each(%{$result->{query}->{namespaces}})) {
                        if (defined($ns->{id}) && defined($ns->{canonical})) {
                                $namespace_id{$ns->{canonical}} = {is_namespace => 1, id => $ns->{id}};
                                if ($ns->{'*'}) {
                                        # alias (e.g. french Fichier: as alias for canonical File:)
                                        $namespace_id{$ns->{'*'}} = {is_namespace => 1, id => $ns->{id}};
                                }
                        }
                }
        }

        my $ns = $namespace_id{$name};
        my $id;

        if (!defined $ns) {
                print {*STDERR} "No such namespace ${name} on MediaWiki.\n";
                $ns = {is_namespace => 0};
                $namespace_id{$name} = $ns;
        }

        if ($ns->{is_namespace}) {
                $id = $ns->{id};
        }

        # Store "notANameSpace" as special value for inexisting namespaces
        my $store_id = ($id || 'notANameSpace');

        # Store explicitely requested namespaces on disk
        if (!exists $cached_mw_namespace_id{$name}) {
                run_git(qq(config --add remote.${remotename}.namespaceCache "${name}:${store_id}"));
                $cached_mw_namespace_id{$name} = 1;
        }
        return $id;
}

sub get_mw_namespace_id_for_page {
        my $namespace = shift;
        if ($namespace =~ /^([^:]*):/) {
                return get_mw_namespace_id($namespace);
        } else {
                return;
        }
}