package Dancer::Session::Abstract;
use strict;
use warnings;
use Carp;

use base 'Dancer::Engine';

use Dancer::Config 'setting';
use Dancer::Cookies;
use File::Spec;

__PACKAGE__->attributes('id');

# args: ($class, $id)
# receives a session id and should return a session object if found, or undef
# otherwise.
sub retrieve {
    confess "retrieve not implemented";
}

# args: ($class)
# create a new empty session, flush it and return it.
sub create {
    confess "create not implemented";
}

# args: ($self)
# write the (serialized) current session to the session storage
sub flush {
    confess "flush not implemented";
}

# args: ($self)
# remove the session from the session storage
sub destroy {
    confess "destroy not implemented";
}

# does nothing in most cases (exception is YAML)
sub reset {
    return;
}

# if subclass overrides to true, flush will not be called after write
# and subclass or application must call flush (perhaps in an after hook)
sub is_lazy { 0 };

# This is the default constructor for the session object, the only mandatory
# attribute is 'id'. The whole object should be serialized by the session
# engine.
# If you override this constructor, remember to call $self->SUPER::init() so
# that the session ID is still generated.
sub init {
    my ($self) = @_;
    $self->id(build_id());
}

# this method can be overwritten in any Dancer::Session::* module
sub session_name {
    setting('session_name') || 'dancer.session';
}


# Methods below this line should not be overloaded.

# we try to make the best random number
# with native Perl 5 code.
# to rebuild a session id, an attacker should know:
# - the running PID of the server
# - the current timestamp of the time it was built
# - the path of the installation directory
# - guess the correct number between 0 and 1000000000
# - should be able to reproduce that 3 times
sub build_id {
    my $session_id = "";
    foreach my $seed (rand(1000), rand(1000), rand(1000)) {
        my $c = 0;
        $c += ord($_) for (split //, File::Spec->rel2abs(File::Spec->curdir));
        my $current = int($seed * 1000000000) + time + $$ + $c;
        $session_id .= $current;
    }
    return $session_id;
}

sub read_session_id {
    my $name = session_name();
    my $c = Dancer::Cookies->cookies->{$name};
    return (defined $c) ? $c->value : undef;
}

sub write_session_id {
    my ($class, $id) = @_;

    my $name = session_name();
    my %cookie = (
        name   => $name,
        value  => $id,
        domain => setting('session_domain'),
        secure => setting('session_secure'),
        http_only => defined(setting("session_is_http_only")) ?
                     setting("session_is_http_only") : 1,
    );
    if (my $expires = setting('session_expires')) {
        # It's # of seconds from the current time
        # Otherwise just feed it through.
        $expires = Dancer::Cookie::_epoch_to_gmtstring(time + $expires) if $expires =~ /^\d+$/;
        $cookie{expires} = $expires;
    }

    my $c = Dancer::Cookie->new(%cookie);
    Dancer::Cookies->set_cookie_object($name => $c);
}

1;
__END__

=pod

=head1 NAME

Dancer::Session::Abstract - abstract class for session engine

=head1 SPEC

=over 4

=item B<role>

A Dancer::Session object represents a session engine and should provide anything
needed to manipulate a session, whatever its storing engine is.

=item B<id>

The session id will be written to a cookie, by default named C<dancer.session>, 
it is assumed that a client must accept cookies to be able to use a 
session-aware Dancer webapp. (The cookie name can be change using the
C<session_name> config setting.)

=item B<storage engine>

When the session engine is enabled, a I<before> filter takes care to initialize
the appropriate session engine (according to the setting C<session>).

Then, the filter looks for a cookie named C<dancer.session> (or whatever you've
set the C<session_name> setting to, if you've used it) in order to
I<retrieve> the current session object. If not found, a new session object is
I<created> and its id written to the cookie.

Whenever a session call is made within a route handler, the singleton
representing the current session object is modified.

A I<flush> is made to the session object after every modification unless
the session engine overrides the C<is_lazy> method to return true.

=back

=head1 DESCRIPTION

This virtual class describes how to build a session engine for Dancer. This is
done in order to allow multiple session storage backends with a common interface.

Any session engine must inherit from Dancer::Session::Abstract and implement
the following abstract methods.

=head2 Configuration

These settings control how a session acts.

=head3 session_name

The default session name is "dancer_session". This can be set in your config file:

    setting session_name: "mydancer_session"

=head3 session_domain

Allows you to set the domain property on the cookie, which will
override the default.  This is useful for setting the session cookie's
domain to something like C<.domain.com> so that the same cookie will
be applicable and usable across subdomains of a base domain.

=head3 session_secure

The user's session id is stored in a cookie.  If true, this cookie
will be made "secure" meaning it will only be served over https.

=head3 session_expires

When the session should expire.  The format is either the number of
seconds in the future, or the human readable offset from
L<Dancer::Cookie/expires>.

By default, there is no expiration.

=head3 session_is_http_only

This setting defaults to 1 and instructs the session cookie to be
created with the C<HttpOnly> option active, meaning that JavaScript
will not be able to access to its value.

=head2 Abstract Methods

=over 4

=item B<retrieve($id)>

Look for a session with the given id, return the session object if found, undef
if not.

=item B<create()>

Create a new session, return the session object.

=item B<flush()>

Write the session object to the storage engine.

=item B<destroy()>

Remove the current session object from the storage engine.

=item B<session_name> (optional)

Returns a string with the name of cookie used for storing the session ID.

You should probably not override this; the user can control the cookie name
using the C<session_name> setting.

=back

=head2 Inherited Methods

The following methods are not supposed to be overloaded, they are generic and
should be OK for each session engine.

=over 4

=item B<build_id>

Build a new uniq id.

=item B<read_session_id>

Reads the C<dancer.session> cookie.

=item B<write_session_id>

Write the current session id to the C<dancer.session> cookie.

=item B<is_lazy>

Default is false.  If true, session data will not be flushed after every
modification and the session engine (or application) will need to ensure
that a flush is called before the end of the request.

=back

=cut