From 5c36d0a5946b41e5372f8a12d4cd6945643d7d1b Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Mon, 14 Jan 2019 15:51:47 +0000
Subject: [PATCH] wip break out edge_id_to_other_id

---
 parse-input-graph | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/parse-input-graph b/parse-input-graph
index 69dc87e..e65df41 100755
--- a/parse-input-graph
+++ b/parse-input-graph
@@ -146,6 +146,20 @@ sub adjacencies () {
   print STDERR "total $ndikes dikes\n";
 }
 
+sub edge_id_to_other_id ($$) {
+  my ($ra, $adjia) = @_;
+  my $adjsa = $region{$ra}{Adj};
+  my $adja = $adjsa->[$adjia];
+  my $rb = $adja->{Name};
+  my $adjsb = $region{$rb}{Adj};
+  foreach my $adjib (0..$#$adjsb) {
+    my $adjb = $adjsb->[$adjib];
+    next unless $adjb->{Name} eq $ra;
+    return ($rb, $adjib);
+  }
+  confess "$ra $adjia ?";
+}
+
 sub dual () {
   # We want to turn the graph from a graph on the regions, to
   # one where the nodes are the vertices of region boundaries.
@@ -165,27 +179,23 @@ sub dual () {
   foreach my $ra (sort keys %region) {
     my $adjsa = $region{$ra}{Adj};
     foreach my $adjia (0..$#$adjsa) {
+      my ($rb, $adjib) = edge_id_to_other_id($ra, $adjia);
       my $adja = $adjsa->[$adjia];
       my $va = "$ra # $adjia";
       # $va is the vertex at the anticlockwise end
       # of edge no.$adjia of region $ra
-      my $rb = $adja->{Name};
       next if ($rb eq 'L' or $rb eq 'NZ') and
 	      ($ra eq 'L' or $ra eq 'NZ');
       # $rb is the region on the other side of that edge
       my $adjsb = $region{$rb}{Adj};
-      foreach my $adjib (0..$#$adjsb) {
-	my $adjb = $adjsb->[$adjib];
-	next unless $adjb->{Name} eq $ra;
-	# $adjb is the same edge seen from the other side
-	my $adjibc = ($adjib + 1) % @$adjsb;
-	my $vb = "$rb # $adjibc";
-	# $vb is the vertex at the *clockwise* end
-	# of that same edge, which is edge no $adjib of region $rb
-	print STDERR "vertex $va = $vb\n";
-	$g->add_edge($va,$vb);
-	last;
-      }
+      # $adjb is the same edge seen from the other side
+      my $adjibc = ($adjib + 1) % @$adjsb;
+      my $vb = "$rb # $adjibc";
+      # $vb is the vertex at the *clockwise* end
+      # of that same edge, which is edge no $adjib of region $rb
+      print STDERR "vertex $va = $vb\n";
+      $g->add_edge($va,$vb);
+      last;
     }
   }
   my %edgeid2vi;
-- 
2.30.2