#!/usr/bin/perl
# Copyright (C) 2018 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 v5.14;
use strict;
use warnings;
no warnings qw(io);

our ($script, $script_path);
BEGIN {
    use Cwd qw(abs_path);
    if ($^O eq "msys") {
        $0 =~ s,\\,/,g;
        $0 =~ s,^(.):/,/$1/,g;
    }
    $script_path = $script = abs_path($0);
    $script_path =~ s,/[^/]+$,,;
    unshift @INC, $script_path;
}
use git_gpush;

use JSON;

sub usage()
{
    print << "EOM";
Usage:
    git ggc [options]

    This program cleans up state from git-gpush that became stale due
    to local Changes disappearing (most likely being upstreamed).

    You should use git-gpull instead of 'git pull --rebase', to make
    sure that git-ggc is called at regular intervals (default 30 days,
    configurable with gpush.gcInterval).

    The only recognized options are --help (-h, -?), --dry-run (-n),
    --verbose (-v), --quiet (-q), and --debug with the usual meanings
    (see git-gpush help).

Copyright:
    Copyright (C) 2018 The Qt Company Ltd.
    Contact: http://www.qt.io/licensing/

License:
    You may use this file under the terms of the 3-clause BSD license.
EOM
}

sub parse_arguments(@)
{
    while (scalar @_) {
        my $arg = shift @_;
        if ($arg eq "-v" || $arg eq "--verbose") {
            $verbose = 1;
        } elsif ($arg eq "-q" || $arg eq "--quiet") {
            $quiet = 1;
        } elsif ($arg eq "--debug") {
            $debug = 1;
            $verbose = 1;
        } elsif ($arg eq "-n" || $arg eq "--dry-run") {
            $dry_run = 1;
        } elsif ($arg eq "-?" || $arg eq "--?" || $arg eq "-h" || $arg eq "--help") {
            usage();
            exit;
        } else {
            fail("Unrecognized command line argument '$arg'.\n");
        }
    }
    fail("--quiet and --verbose/--debug are mutually exclusive.\n")
        if ($quiet && $verbose);
}

my %upstream_remotes;

sub get_gerrit_config()
{
    $remote = git_config('gpush.remote');
    # If a remote is specified, use exactly that one.
    if (!$remote) {
        # Otherwise try 'gerrit', and fall back to the origin.
        $remote = 'gerrit';
        if (!git_config('remote.'.$remote.'.url')) {
            my @remotes = keys %upstream_remotes;
            if (@remotes == 1) {
                $remote = shift @remotes;
            } else {
                $remote = git_config('gpush.upstream', 'origin');
                werr("Notice: Upstream remote is ambiguous; defaulting to '$remote'.\n")
                    if (!$quiet);
            }
        }
    }
    set_gerrit_config($remote);
}

sub visit_revs_pull(@)
{
    my %changeids;
    my $log = open_cmd_pipe(USE_STDIN, 'git', 'log', '-z', '--pretty=%H%x00%B', '--stdin',
                                       @upstream_excludes);
    write_process($log, map { "$_\n" } @_);
    while (read_fields($log, my ($id, $message))) {
        $message =~ /^(.*)$/m;
        my $subject = $1;

        # Gerrit uses the last Change-Id if multiple are present.
        my @cids = ($message =~ /^Change-Id: (.+)$/mg);
        next if (!@cids);
        my $changeid = $cids[-1];

        print "-- $id: $subject\n" if ($debug);

        $changeids{$changeid} = 1;
    }
    close_process($log);
    return \%changeids;
}

# The garbage-collecting workhorse.
# Note that we entirely ignore branches. A Change is assumed to be still
# relevant if it exists on any local branch or exists in a non-terminal
# state on Gerrit for any branch.
sub perform_gc()
{
    print "Loading refs ...\n" if ($debug);
    my %pushed;  # { sequence-number => sha1 }
    my %zaps;  # { sequence-number => [ state-ref, ... ] }
    my %fzaps;  # { gerrit-number => [ patchset-number => fetched-ref, ... ] }
    my @fsha1s;  # [ fetched-sha1, ... ]
    my @local_refs;  # These define which Changes are still active.
    my %remote_refs;  # Used for quickly validating upstreams.
    my $branches = open_cmd_pipe(0, "git", "for-each-ref", "--format=%(objectname) %(refname)",
                                    "refs/heads/", "refs/remotes/", "refs/gpush/");
    while (read_process($branches)) {
        if (s,^.{40} refs/remotes/,,) {
            $remote_refs{$_} = 1;
        } elsif (s,^.{40} refs/heads/,,) {
            push @local_refs, $_;
        } elsif (s,^(.{40}) refs/gpush/,,) {
            my $sha1 = $1;
            if (m,^i(\d+)_(.*)$,) {
                push @{$zaps{$1}}, $_;
                $pushed{$1} = $sha1 if ($2 eq "pushed");
            } elsif (m,^g(\d+)_(\d+)$,) {
                $fzaps{$1}[$2] = $_;
                push @fsha1s, $sha1;
            } elsif (!m,^state(-new)?$,) {
                print "Keeping unrecognized '$_'.\n" if ($debug);
            }
        }
    }
    close_process($branches);

    my %upstream_refs;
    foreach my $ref (@local_refs) {
        my ($uprm, $upbr) = (git_config("branch.$ref.remote"), git_config("branch.$ref.merge"));
        # Local WIP branches typically have no upstream.
        next if (!$uprm || !$upbr);
        $upbr =~ s,^refs/heads/,,;
        my $upref = $uprm.'/'.$upbr;
        # The upstream branch may have been pruned. Don't error out when this happens.
        next if (!defined($remote_refs{$upref}));
        # Note that multiple branches may have the same upstream.
        $upstream_refs{$upref} = 1;
        # Record which remotes are used as upstreams.
        $upstream_remotes{$uprm} = 1;
    }
    @upstream_excludes = map { '^refs/remotes/'.$_ } keys %upstream_refs;

    # Changes which are on local branches are excluded from pruning. Obviously.
    print "Visiting local branches ...\n" if ($debug);
    my $local_changes = visit_revs_pull('HEAD', (map { 'refs/heads/'.$_ } @local_refs));

    print "Collecting locally present Changes ...\n" if ($debug);
    my %zap_ids;  # { change-id => 1 }
    foreach my $key (sort keys %change_by_key) {
        my $change = $change_by_key{$key};
        my $changeid = $$change{id};
        if (defined($$local_changes{$changeid})) {
            print "Keeping $key ($changeid): exists locally.\n"
                if ($verbose);
            delete $zaps{$key};
        } else {
            $zap_ids{$changeid} = 1;
        }
    }

    my %change2active;
    if (%zap_ids || %fzaps) {
        print "Querying Gerrit for prunable Changes ...\n" if ($debug);
        get_gerrit_config();
        my $ginfos = query_gerrit_only([ map { "change:".$_ } (keys %zap_ids, keys %fzaps) ]);
        foreach my $ginfo (@$ginfos) {
            my ($key, $changeid, $status, $branch) =
                    ($$ginfo{key}, $$ginfo{id}, $$ginfo{status}, $$ginfo{branch});
            my $active = (($status ne 'MERGED') && ($status ne 'ABANDONED'));
            print "$changeid is ".($active ? "" : "NOT ")."active on $branch.\n" if ($debug);
            $change2active{$changeid} ||= $active;
        }
    }

    print "Pruning stale Changes ...\n" if ($debug);
    foreach my $key (sort keys %change_by_key) {
        my $change = $change_by_key{$key};
        # Even Changes which are absent from the local branch are pruned
        # only if they are in a terminal state. Otherwise, there is reason
        # to believe that they might be used again at a later point.
        my $changeid = $$change{id};
        if (!defined($zap_ids{$changeid})) {
            # Exists locally; already handled above.
        } elsif ($change2active{$changeid}) {
            print "Keeping $key ($changeid): active on Gerrit.\n"
                if ($verbose);
            $$local_changes{$changeid} = 1;
            delete $zaps{$key};
        } else {
            print "Pruning $key ($changeid).\n" if ($verbose);
            $$change{garbage} = 1;
        }
    }
    if ($verbose) {
        foreach my $key (sort keys %zaps) {
            # This is unlikely to ever trigger, as the regular load_refs()
            # cleans up anyway.
            print "Pruning $key (unrecognized Change).\n"
                if (!$change_by_key{$key});
        }
    }

    print "Visiting fetched PatchSets ...\n" if ($debug);
    visit_local_commits(\@fsha1s);

    # Keep fetched PatchSets that correspond with kept Changes, but only the ones
    # that are not older than the pushed revision of the Change. Older PatchSets
    # are accessed only when explicitly picking an old state of the series, which
    # is very rare, so it is not worth keeping these refs cached.
    my (@visit_sha1s, %seen_sha1s, %chop_gs);
    foreach my $key (sort keys %fzaps) {
        my $ginfo = $gerrit_info_by_key{$key};
        if (!defined($ginfo)) {
            $chop_gs{$key} = -1;
            next;
        }

        my $changeid = $$ginfo{id};
        if (!defined($$local_changes{$changeid})) {
            # Might be still referenced recursively.
            print "Might prune fetched $key ($changeid): corresponds with no kept Change.\n"
                if ($debug);
            next;
        }

        my $chgs = $changes_by_id{$changeid};
        if (!$chgs) {
            # Corresponding commits exist locally, but we never assigned them to Changes.
            print "Might prune fetched $key ($changeid): corresponds with no tracked Change.\n"
                if ($debug);
            next;
        }

        my $revs = $$ginfo{revs};
        my $mps = $$revs[-1]{ps};
        # Subsequent sync-up attempts will fetch the current (and previous,
        # for MERGED Changes) PatchSet, so keep that in every case.
        my $kps = ($mps > 1 && ($$ginfo{status} eq "MERGED")) ? $mps - 1 : $mps;
        foreach my $change (@$chgs) {
            next if ($$change{garbage});

            my $sha1 = $pushed{$$change{key}};
            # This Change was not gpushed/gpicked, and a possible sync-up failed.
            next if (!defined($sha1));

            my $rev = $$ginfo{rev_by_id}{$sha1};
            # A Change on a different branch owns this commit.
            next if (!$rev);

            my $ps = $$rev{ps};
            $kps = $ps if ($ps < $kps);
        }

        # Note that this may include SHA1s that were not fetched.
        push @visit_sha1s, map { $$_{id} } grep { $$_{ps} >= $kps } @$revs;
        $chop_gs{$key} = $kps;
    }
    # Keep all fetched PatchSets that are ancestors of other kept
    # PatchSets, recursively.
    while (my $sha1 = shift @visit_sha1s) {
        while (!defined($seen_sha1s{$sha1})) {
            $seen_sha1s{$sha1} = 1;

            my $commit = $commit_by_id{$sha1};
            last if (!$commit);  # Hit bottom of series, or initial commit was not fetched.

            # If the Change disappeared, then its fetched refs will be nuked anyway,
            # and ancestors which are not in the initial set won't be accessed anymore.
            my $ginfo = $gerrit_info_by_sha1{$sha1};
            last if (!$ginfo);

            # Ancestry traversal may lead us to older PatchSets than those in the
            # initial set, but assemble_series()' callbacks would upgrade from these
            # anyway, so we can just stop here.
            last if (defined($$local_changes{$$ginfo{id}}));

            my $ps = $$ginfo{rev_by_id}{$sha1};
            last if (!defined($ps));  # Shouldn't happen.

            push @visit_sha1s, map { $$_{id} } grep { $$_{ps} >= $ps } @{$$ginfo{revs}};
            my $key = $$ginfo{key};
            my $ops = $chop_gs{$key};
            $chop_gs{$key} = $ps if (!defined($ops) || $ops > $ps);

            $sha1 = get_1st_parent($commit);
        }
    }
    foreach my $key (sort keys %fzaps) {
        my $fzap = $fzaps{$key};
        my $kps = $chop_gs{$key};
        if (!defined($kps)) {
            print "Pruning fetched $key (unused).\n" if ($verbose);
        } elsif ($kps < 0) {
            print "Pruning fetched $key (disappeared from Gerrit).\n" if ($verbose);
        } else {
            my $mps = $#$fzap;
            print "Keeping fetched $key starting at $kps/$mps.\n" if ($verbose);
            splice @$fzap, $kps;
        }
        $fzaps{$key} = [ grep { defined($_) } @$fzap ];
    }

    # We completely bypass the regular state handling when it comes
    # to refs, as we want to also prune refs in our namespace that
    # don't correspond with known state keys.
    update_refs(DRY_RUN, [
        map { "delete refs/gpush/$_\n" } map { @$_ } (values %zaps, values %fzaps)
    ]);
}

parse_arguments(@ARGV);
goto_gitdir();
load_config();
load_state_file();  # No load_state(), and thus no load_refs().
perform_gc();
$last_gc = time();
save_state($dry_run);