#!/usr/bin/perl

use strict;
use warnings;
use IO::Handle;

our %flag;
our (@order, @order_final_maybe);
our $verbose=0;
our $propsmode=0;
our $marker=5;

# we don't use Getopt::Long because we want to be quick to start up
# and we're not really a very user-facing utility

while (@ARGV && $ARGV[0] =~ m/^\-/) {
    $_ = shift @ARGV;
    if (s/^-U//) {
	$flag{$_}{ForceResult} = 1;
	$flag{$_}{Result} = undef;
	push @order_final_maybe, $_;
    } elsif (s/^-D//) {
	$flag{$_}{ForceResult} = 1;
	$flag{$_}{Result} = '';
	push @order_final_maybe, $_;
    } elsif (m/^-v$/) {
	$verbose = 1;
    } elsif (m/^-P$/) {
	$propsmode = 1;
    } elsif (m/^-M(\d+)$/) {
	$marker = $1;
    } elsif (m/^--$/) {
	last;
    } else {
	die "$0: bad option\n";
    }
}

@ARGV==3 or die "$0: bad usage\n";

foreach my $ix (qw(0 1 2)) {
    open F, '<', $ARGV[$ix] or die "$ix $!";
    while (<F>) {
	chomp or die;
	($propsmode && m/ /) or m/$/;
	$flag{$`}{Input}[$ix] = $'; #';
	push @order, $` unless $flag{$`}{InOrder}++;
    }
    F->error and die $!;
    close F or die $!;
}

foreach $_ (@order_final_maybe) {
    push @order, $_ unless $flag{$_}{InOrder}++;
}

my $current = $ARGV[0];

open O, '>', "$current.tmp" or die "$current.tmp $!";

sub prmark ($) { 
    print O $_[0] x $marker, "\n" or die $!;
 }
sub prval ($) {
    my $v = @_;
    print O $v,"\n" or die $! if defined $v;
}

our $f;

if ($verbose) {
    sub verb ($) { print STDERR "MERGE_LISTS $f @_\n" or die $!; }
} else {
    sub verb { }
}

our $conflicts = 0;

foreach $f (@order) {
    my $ff = $flag{$f};
    verb("BEGIN");
    if (defined $ff->{ForceResult}) {
	verb("FORCE");
    } else {
	my @in = @{ $ff->{Input} };
	verb(defined ? "DEF $_": "U") foreach @in;
	if (iseq($in[0], $in[2])) {
	    verb("SAME");
	    $ff->{Result} = [0];
	} elsif (iseq($in[0], $in[1])) {
	    verb("THEIRS");
	    $ff->{Result} = $in[2];
	} elsif (iseq($in[2], $in[1])) {
	    verb("OURS");
	    $ff->{Result} = $in[0];
	} else {
	    $conflicts++;
	    verb("CONFLICT");
	    prmark('<');
	    prval($in[0]);
	    prmark('=');
	    prval($in[2]);
	    prmark('>');
	    next;
	}
    }
    prval($ff->{Result});
}

close O or die $!;
rename "$current.tmp", "$current" or die "$current $!";
exit $conficts ? 1 :0;