package HTTP::Headers;

use strict;
use Carp ();

use vars qw($VERSION $TRANSLATE_UNDERSCORE);
$VERSION = "5.818";

# The $TRANSLATE_UNDERSCORE variable controls whether '_' can be used
# as a replacement for '-' in header field names.
$TRANSLATE_UNDERSCORE = 1 unless defined $TRANSLATE_UNDERSCORE;

# "Good Practice" order of HTTP message headers:
#    - General-Headers
#    - Request-Headers
#    - Response-Headers
#    - Entity-Headers

my @general_headers = qw(
    Cache-Control Connection Date Pragma Trailer Transfer-Encoding Upgrade
    Via Warning
);

my @request_headers = qw(
    Accept Accept-Charset Accept-Encoding Accept-Language
    Authorization Expect From Host
    If-Match If-Modified-Since If-None-Match If-Range If-Unmodified-Since
    Max-Forwards Proxy-Authorization Range Referer TE User-Agent
);

my @response_headers = qw(
    Accept-Ranges Age ETag Location Proxy-Authenticate Retry-After Server
    Vary WWW-Authenticate
);

my @entity_headers = qw(
    Allow Content-Encoding Content-Language Content-Length Content-Location
    Content-MD5 Content-Range Content-Type Expires Last-Modified
);

my %entity_header = map { lc($_) => 1 } @entity_headers;

my @header_order = (
    @general_headers,
    @request_headers,
    @response_headers,
    @entity_headers,
);

# Make alternative representations of @header_order.  This is used
# for sorting and case matching.
my %header_order;
my %standard_case;

{
    my $i = 0;
    for (@header_order) {
	my $lc = lc $_;
	$header_order{$lc} = ++$i;
	$standard_case{$lc} = $_;
    }
}



sub new
{
    my($class) = shift;
    my $self = bless {}, $class;
    $self->header(@_) if @_; # set up initial headers
    $self;
}


sub header
{
    my $self = shift;
    Carp::croak('Usage: $h->header($field, ...)') unless @_;
    my(@old);
    my %seen;
    while (@_) {
	my $field = shift;
        my $op = @_ ? ($seen{lc($field)}++ ? 'PUSH' : 'SET') : 'GET';
	@old = $self->_header($field, shift, $op);
    }
    return @old if wantarray;
    return $old[0] if @old <= 1;
    join(", ", @old);
}

sub clear
{
    my $self = shift;
    %$self = ();
}


sub push_header
{
    my $self = shift;