package Git::Packet;
use 5.008;
use strict;
use warnings;
BEGIN {
        require Exporter;
        if ($] < 5.008003) {
                *import = \&Exporter::import;
        } else {
                # Exporter 5.57 which supports this invocation was
                # released with perl 5.8.3
                Exporter->import('import');
        }
}

our @EXPORT = qw(
                        packet_compare_lists
                        packet_bin_read
                        packet_txt_read
                        packet_key_val_read
                        packet_bin_write
                        packet_txt_write
                        packet_flush
                        packet_initialize
                        packet_read_capabilities
                        packet_read_and_check_capabilities
                        packet_check_and_write_capabilities
                );
our @EXPORT_OK = @EXPORT;

sub packet_compare_lists {
        my ($expect, @result) = @_;
        my $ix;
        if (scalar @$expect != scalar @result) {
                return undef;
        }
        for ($ix = 0; $ix < $#result; $ix++) {
                if ($expect->[$ix] ne $result[$ix]) {
                        return undef;
                }
        }
        return 1;
}

sub packet_bin_read {
        my $buffer;
        my $bytes_read = read STDIN, $buffer, 4;
        if ( $bytes_read == 0 ) {
                # EOF - Git stopped talking to us!
                return ( -1, "" );
        } elsif ( $bytes_read != 4 ) {
                die "invalid packet: '$buffer'";
        }
        my $pkt_size = hex($buffer);
        if ( $pkt_size == 0 ) {
                return ( 1, "" );
        } elsif ( $pkt_size > 4 ) {
                my $content_size = $pkt_size - 4;
                $bytes_read = read STDIN, $buffer, $content_size;
                if ( $bytes_read != $content_size ) {
                        die "invalid packet ($content_size bytes expected; $bytes_read bytes read)";
                }
                return ( 0, $buffer );
        } else {
                die "invalid packet size: $pkt_size";
        }
}

sub remove_final_lf_or_die {
        my $buf = shift;
        unless ( $buf =~ s/\n$// ) {
                die "A non-binary line MUST be terminated by an LF.\n"
                    . "Received: '$buf'";
        }
        return $buf;
}

sub packet_txt_read {
        my ( $res, $buf ) = packet_bin_read();
        unless ( $res == -1 or $buf eq '' ) {
                $buf = remove_final_lf_or_die($buf);
        }
        return ( $res, $buf );
}

# Read a text packet, expecting that it is in the form "key=value" for
# the given $key.  An EOF does not trigger any error and is reported
# back to the caller (like packet_txt_read() does).  Die if the "key"
# part of "key=value" does not match the given $key, or the value part
# is empty.
sub packet_key_val_read {
        my ( $key ) = @_;
        my ( $res, $buf ) = packet_txt_read();
        unless ( $res == -1 or ( $buf =~ s/^$key=// and $buf ne '' ) ) {
                die "bad $key: '$buf'";
        }
        return ( $res, $buf );
}

sub packet_bin_write {
        my $buf = shift;
        print STDOUT sprintf( "%04x", length($buf) + 4 );
        print STDOUT $buf;
        STDOUT->flush();
}

sub packet_txt_write {
        packet_bin_write( $_[0] . "\n" );
}

sub packet_flush {
        print STDOUT sprintf( "%04x", 0 );
        STDOUT->flush();
}

sub packet_initialize {
        my ($name, $version) = @_;

        packet_compare_lists([0, $name . "-client"], packet_txt_read()) ||
                die "bad initialize";
        packet_compare_lists([0, "version=" . $version], packet_txt_read()) ||
                die "bad version";
        packet_compare_lists([1, ""], packet_bin_read()) ||
                die "bad version end";

        packet_txt_write( $name . "-server" );
        packet_txt_write( "version=" . $version );
        packet_flush();
}

sub packet_read_capabilities {
        my @cap;
        while (1) {
                my ( $res, $buf ) = packet_bin_read();
                if ( $res == -1 ) {
                        die "unexpected EOF when reading capabilities";
                }
                return ( $res, @cap ) if ( $res != 0 );
                $buf = remove_final_lf_or_die($buf);
                unless ( $buf =~ s/capability=// ) {
                        die "bad capability buf: '$buf'";
                }
                push @cap, $buf;
        }
}

# Read remote capabilities and check them against capabilities we require
sub packet_read_and_check_capabilities {
        my @required_caps = @_;
        my ($res, @remote_caps) = packet_read_capabilities();
        my %remote_caps = map { $_ => 1 } @remote_caps;
        foreach (@required_caps) {
                unless (exists($remote_caps{$_})) {
                        die "required '$_' capability not available from remote" ;
                }
        }
        return %remote_caps;
}

# Check our capabilities we want to advertise against the remote ones
# and then advertise our capabilities
sub packet_check_and_write_capabilities {
        my ($remote_caps, @our_caps) = @_;
        foreach (@our_caps) {
                unless (exists($remote_caps->{$_})) {
                        die "our capability '$_' is not available from remote"
                }
                packet_txt_write( "capability=" . $_ );
        }
        packet_flush();
}

1;