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+# -*- perl -*-
+# Lintian::Processable::Installable::Relation -- interface to binary package data collection
+
+# Copyright (C) 2008, 2009 Russ Allbery
+# Copyright (C) 2008 Frank Lichtenheld
+# Copyright (C) 2012 Kees Cook
+# Copyright (C) 2020 Felix Lechner
+#
+# 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 2 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/>.
+
+package Lintian::Processable::Installable::Relation;
+
+use v5.20;
+use warnings;
+use utf8;
+
+use Carp qw(croak);
+use Unicode::UTF8 qw(encode_utf8);
+
+use Lintian::Relation;
+
+use Moo::Role;
+use namespace::clean;
+
+=head1 NAME
+
+Lintian::Processable::Installable::Relation - Lintian interface to binary package data collection
+
+=head1 SYNOPSIS
+
+    my ($name, $type, $dir) = ('foobar', 'binary', '/path/to/lab-entry');
+    my $collect = Lintian::Processable::Installable::Relation->new($name);
+
+=head1 DESCRIPTION
+
+Lintian::Processable::Installable::Relation provides an interface to package data for binary
+packages.  It implements data collection methods specific to binary
+packages.
+
+This module is in its infancy.  Most of Lintian still reads all data from
+files in the laboratory whenever that data is needed and generates that
+data via collect scripts.  The goal is to eventually access all data about
+binary packages via this module so that the module can cache data where
+appropriate and possibly retire collect scripts in favor of caching that
+data in memory.
+
+Native heuristics are only available in source packages.
+
+=head1 INSTANCE METHODS
+
+=over 4
+
+=item relation (FIELD)
+
+Returns a L<Lintian::Relation> object for the specified FIELD, which should
+be one of the possible relationship fields of a Debian package or one of
+the following special values:
+
+=over 4
+
+=item All
+
+The concatenation of Pre-Depends, Depends, Recommends, and Suggests.
+
+=item Strong
+
+The concatenation of Pre-Depends and Depends.
+
+=item Weak
+
+The concatenation of Recommends and Suggests.
+
+=back
+
+If FIELD isn't present in the package, the returned Lintian::Relation
+object will be empty (always present and satisfies nothing).
+
+=item saved_relations
+
+=cut
+
+has saved_relations => (
+    is => 'rw',
+    coerce => sub { my ($hashref) = @_; return ($hashref // {}); },
+    default => sub { {} }
+);
+
+my %alias = (
+    all    => [qw(Pre-Depends Depends Recommends Suggests)],
+    strong => [qw(Pre-Depends Depends)],
+    weak   => [qw(Recommends Suggests)]
+);
+
+my %known = map { $_ => 1 }
+  qw(pre-depends depends recommends suggests enhances breaks
+  conflicts provides replaces);
+
+sub relation {
+    my ($self, $name) = @_;
+
+    my $lowercase = lc $name;
+
+    my $relation = $self->saved_relations->{$lowercase};
+    unless (defined $relation) {
+
+        if (exists $alias{$lowercase}) {
+            $relation
+              = Lintian::Relation->new->logical_and(map { $self->relation($_) }
+                  @{ $alias{$lowercase} });
+        } else {
+            croak encode_utf8("unknown relation field $name")
+              unless $known{$lowercase};
+
+            my $value = $self->fields->value($name);
+            $relation = Lintian::Relation->new->load($value);
+        }
+
+        $self->saved_relations->{$lowercase} = $relation;
+    }
+
+    return $relation;
+}
+
+=back
+
+=head1 AUTHOR
+
+Originally written by Frank Lichtenheld <djpig@debian.org> for Lintian.
+Amended by Felix Lechner <felix.lechner@lease-up.com> for Lintian.
+
+=head1 SEE ALSO
+
+lintian(1)
+
+=cut
+
+1;
+
+# Local Variables:
+# indent-tabs-mode: nil
+# cperl-indent-level: 4
+# End:
+# vim: syntax=perl sw=4 sts=4 sr et