#!/usr/bin/perl -w
# git-debrebase
# Script helping make fast-forwarding histories while still rebasing
# upstream deltas when working on Debian packaging
#
# Copyright (C)2017 Ian Jackson
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

use strict;

use Memoize;
use Data::Dumper;

use Debian::Dgit;

sub cfg ($) {
    my ($k) = @_;
    $/ = "\0";
    my @cmd = qw(git config -z);
    push @cmd, qw(--get-all) if wantarray;
    push @cmd, $k;
    my $out = cmdoutput @cmd;
    return split /\0/, $out;
}

memoize('cfg');

# usage
#  git debrebase launder

sub get_commit ($) {
    my ($objid) = @_;
    my ($type,$data) = git_cat_file $objid;
    die unless $type eq 'commit';
    $data =~ m/(?<=\n)\n/;
    return ($`,$');
}

sub D_DEB ()     { return 0x1; }
sub D_UPS ()     { return 0x2; }
sub D_PAT_ADD () { return 0x4; }
sub D_PAT_OTH () { return 0x8; }

sub commit_pr_info ($) {
    my ($r) = @_;
    return Data::Dumper->dump([$r], [qw(commit)]);
}

sub classify ($) {
    my ($objid) = @_;

    my ($h,$m) = get_commit $objid;

    my ($t) = $h =~ m/^tree (\w+)$/m or die $cur;
    my (@ph) = $h =~ m/^parent (\w+)$/m;
    my @p;

    my $r = {
	CommitId => $objid,
	Hdr => $hdr,
	Msg => $m,
        Tree => $t,
	Parents => \@p,
    };

    foreach my $ph (@ph) {
	push @p, {
            Ix => $#p,
            CommitId => $ph,
            Differs => (get_differs $t, $ph),
        };
    }

    my $classify = sub {
	my ($type, @rest) = @_;
	$r = { %r, Type => $type, @rest };
	return $r;
    };
    my $unknown = sub {
	my ($why) = @_;
	$r = { %r, Type => Unknown };
	return $r;
    }

    if (@p == 1) {
	my $d = $r->{Parents}[0]{Differs};
	if ($d == D_DPAT_ADD) {
	    return $classify->(qw(AddPatches));
	} elsif ($d & (D_DPAT_ADD|D_DPAT_OTH)) {
	    return $unknown->("edits debian/patches");
	} elsif ($d == D_DEB) {
	    return $classify->(qw(Packaging));
	} elsif ($d == D_UPS) {
	    return $classify->(qw(Upstream));
	} elsif ($d == D_DEB|D_UPS) {
	    return $classify->(qw(Mixed));
	} elsif ($d == 0) {
	    return $unknown->("no changes");
	} else {
	    confess "internal error $objid ?";
	}
    }
    if (!@p) {
	return $unknown->("origin commit");
    }

    my @identical = grep { !$_->{Differs} } @p;
    if (@p == 2 && @identical == 1) {
	my @overwritten = grep { $_->{Differs} } @p;
	confess "internal error $objid ?" unless @overwritten==1;
	return $classify->(qw(Pseudomerge),
			   Overwritten => $overwritten[0],
			   Contributor => $identical[0]);
    }
    if (@p == 2 && @identical == 2) {
	my @bytime = nsort_by {
	    my ($ph,$pm) = get_commit $_->{CommitId};
	    $ph =~ m/^committer .* (\d+) [-+]\d+$/m or die "$_->{CommitId} ?";
	    $1;
	} @p;
	return $classify->(qw(Pseudomerge),
			   SubType => qw(Ambiguous),
			   Overwritten => $bytime[0],
			   Contributor => $bytime[1]);
    }!
    foreach my $p (@p) {
	my ($p_h, $p_m) = get_commit $p;
	$p->{IsOrigin} = $p_h !~ m/^parent \w+$/m;
	$p->{IsDgitImport} = $p_m =~ m/^\[dgit import .*\]$/m;
	$p->{IsDgitImportOrig} = $p_m =~ m/^\[dgit import orig .*\]$/m;
    }
    my $m2 = $m;
    if (!grep { !($_->{IsOrigin} && $_->{isDgitImport}) } @p and
	$m2 =~ s{^\[(dgit import unpatched .*)\]$}{[was: $1]}m) {

 xxx check exactly one IsDgitImport that is tarball
	$r->{NewMsg} = $m2;
	return $classify->(qw(DgitImportUnpatched));
    }

    my ($stype, $series) = git_cat_file "$t:debian/patches/series";
    my $haspatches = $stype ne 'missing' && $series =~ m/^\s*[^#\n\t ]/m;

    # how to decide about l/r ordering of breakwater merges
    # git --topo-order prefers to expand 2nd parent first
    # easy rune to look for debian/ history so that should
    # be 1st parent.
    if (@p == 2 &&
	!$haspatches &&
	!$p[0]{IsOrigin} && # breakwater merge never starts with an origin
	!($p[0]{Differs} & ~D_DEB) &&
	!($p[1]{Differs} & ~D_UPS)) {
	return $classify->(qw(BreakwaterUpstreamMerge),
			   Upstream => $p[1]);
    }

    return $unknown->("complex merge");
}

sub launder ($) {
    my ($cur) = @_;
    # go through commits backwards
    # we generate two lists of commits to apply
    my (@phases, @deb_cl, @ups_cl);
    my %found;
    my @psuedomerges;
    for (;;) {
	my $cl = classify $cur;
	my $ty = $cl->{Type};
	my $st = $cl->{SubType};
	$found{$ty. ( defined($st) ? "-$st" : '' )}++;
	my $p0 = $cl->{Parents}[0]{CommitId};
	if ($ty eq 'AddPatches') {
	    $cur = $p0;
	    next;
	} elsif ($ty eq 'Packaging') {
	    push @deb_cl, $cur;
	    $cur = $p0;
	    next;
	} elsif ($ty eq 'Upstream') {
	    push @ups_cl, $cur;
	    $cur = $p0;
	    next;
	} elsif ($ty eq 'Mixed') {
	    my $queue = sub {
		my ($q, $wh) = @_;
		my $ms = $cl->{Msg};
		chomp $ms;
		$ms .= "\n[git-debrebase split mixed commit: $wh part]\n";
		my $cls = { $cl, Msg => $ms };
		push @$q, $cls;
	    };
	    $queue->(\@deb_cl, "debian");
	    $queue->(\@ups_cl, "upstream");
	    next;
	} elsif ($ty eq 'Pseudomerge') {
	    push @pseudomerges, $cl;
	    $cur = $ty->{Contributor};
	    next;
	} elsif ($ty eq 'DgitImportUnpatched' &&
		 @pseudomerges == 1) {
	    # This import has a tree which is just like a breakwater
	    # tree, but it has the wrong history.  Its ought to have
	    # the previous breakwater (which dgit ought to have
	    # generated a pseudomerge to overwrite) as an ancestor.
	    # That will make the history of the debian/ files correct.
	    # As for the upstream version: either it's the same upstream
	    # as the previous breakwater, in which case that history is
	    # precisely right.  Otherwise, it was a non-gitish upload
	    # of a new upstream version.  We can tell these apart
	    # by looking at the tree of the supposed upstream.
	    my $previous_breakwater = launder $pseudomerges[0]{Overwritten};
	    my $differs = get_differs $previous_breakwater, $cl->{Tree};
	    if ($differs & D_UPS) {
		$r->{FixupUpstreamMerge} = $

		push @deb_cl, {
                    $cl,
                    Type => NonGitNewUpstreamDgitImport,
                    PreviousBreakwaterMerge => 
		

	    push @phases, [ @deb_cl, @ups_cl ];
	    
	    if (@pseudomerges != 1) {
}   

if ($ARGV[0] eq 'launder') {
    launder();
}

use Data::Dumper;
print Dumper(cfg('wombat.foo.bar'));


	((git_cat_file "$t:debian/patches/series"
	
    
    my @
			   
	

	    return $r;
	    $r->{Type} = '
	    $r->{Type} = '
	    return 
	    # changes on debian/patches, discard it
	    
	    $cur = $p[0];
	    next;
	}
	if ($d & DPAT) {
	    

    ($r->{Tree},) = 
    
		    




 when starting must record original start (for ff)
 and new rebase basis