replace proposition sequence in-place rather than re-running from scratch

diff --git a/lib/DX/QueryState.pm b/lib/DX/QueryState.pm
index cd54b82..aa5fede 100644 (file)
--- a/lib/DX/QueryState.pm
+++ b/lib/DX/QueryState.pm
@@ -45,15 +45,52 @@ sub new_search_process_for {
 }
 
 sub with_additional_proposition {
-  my ($self, $prop) = @_;
-  my $prop_seq = $self->proposition_sequence
-                      ->with_additional_proposition($prop);
-  my $sol_ss = $self->new_search_process_for($prop_seq)
+  my ($self, $new_prop) = @_;
+  my $old_prop_seq = $self->proposition_sequence;
+  my $new_prop_seq = $old_prop_seq->with_additional_proposition($new_prop);
+  my $old_ss = $self->search_process->current_search_state;
+  my %seen;
+  my $_munge; $_munge = sub {
+    my ($ss) = @_;
+    return $seen{$ss} ||= do {
+      my %but = (
+        decisions_taken => [
+          map [ $_->[0], $_->[1]->$_munge ], @{$ss->decisions_taken}
+        ]
+      );
+      if ($ss->propositions eq $old_prop_seq) {
+        $but{propositions} = $new_prop_seq;
+      }
+      foreach my $type (qw(on_solution_step on_exhaustion_step)) {
+        my $step = $ss->$type;
+        if ($step and $step->can('resume_search_state')) {
+          $but{$type}
+            = $seen{$step}
+            ||= $step->but(
+                  resume_search_state => $step->resume_search_state->$_munge
+                );
+        }
+      }
+      $ss->but(%but);
+    };
+  };
+  my $munged_ss = $old_ss->$_munge;
+  undef($_munge);
+
+  my $new_ss = $munged_ss->but(
+    is_solution_state => 0,
+    next_step => DX::Step::ConsiderProposition->new(
+                   proposition => $new_prop
+                 ),
+  );
+
+  my $sol_sp = $self->search_process
+                    ->but(current_search_state => $new_ss)
                     ->find_solution;
-  die "No solution\n" unless $sol_ss;
+  die "No solution\n" unless $sol_sp;
   $self->but(
-    proposition_sequence => $prop_seq,
-    search_process => $sol_ss,
+    proposition_sequence => $new_prop_seq,
+    search_process => $sol_sp,
   );
 }