From 530e6a27004910679481ad4a8e52f4beca643c32 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Mon, 1 Aug 2016 15:04:10 +0100
Subject: [PATCH] stv: wip, delay transfer

---
 stv | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 71 insertions(+), 10 deletions(-)

diff --git a/stv b/stv
index bd4a6b3..762da63 100755
--- a/stv
+++ b/stv
@@ -73,6 +73,18 @@ foreach my $vote (@allvotes) {
     $continuing{$_}=1 foreach @{ $vote->{Prefs} };
 }
 
+sub equalpiles ($@) {
+    my ($how, @sorted) = @_;
+    return () unless @sorted;
+    my $s = $sorted[0];
+    my $eqtotal = $s->{Total};
+    my $count = 0;
+    while ($count < @$sorted && $sorted[$count]{Total} == $eqtotal) {
+	printf "%7s %10s\n", $how, $sorted[$count]{Cand};
+	$count++;
+    }
+    
+
 for (;;) {
     $stage++;
 
@@ -92,7 +104,11 @@ for (;;) {
 	    $sorted{$firstpref}{Total} += $vote->{Weight};
 	}
     }
-    my @sorted = nsort_by { -$_->{Total} } values %sorted;
+    my @sorted;
+    my $sort_update = sub {
+	@sorted = nsort_by { -$_->{Total} } values %sorted;
+    };
+    $sort_update->();
 
     push @stagerecord, { map { ($_->{Cand}, $_->{Total}) } @sorted };
 
@@ -145,26 +161,71 @@ for (;;) {
 	    votelog $vote, "elected $s->{Cand}, derated $weightmult";
 	    $vote->{Weight} /= $derate;
 	}
-	shift @sorted;
 	push @surpluses, $s;
-	delete %sorted->{ $s->{Cand} };
+	delete %sorted{ $s->{Cand} };
 	delete $continuing{ $s->{Cand} };
 
+	$sort_update->();
 	$need_to_transfer_surplus = 0;
 	# before actually transferring a surplus, we will consider
 	# eliminating, and then reconsider with a lower quota
     }
 
+    my $deferredsurplus = sum map { $_->{Total} } @surpluses;
+    printf "%7s %10s %s\n", 'def.srp', 'total', pr $deferredsurplus;
+
     # Look for people to eliminate
     # We eliminate before trying to transfer surpluses
     # ERS 5.2.5
+    for (;;) {
+	last unless @sorted;
+
+	my @elim = equalpiles 'elim?', reverse @sorted;
+	my $elimvote = sum map { $_->{Total} } @elim;
+	my $elimvotetotal = $elimvote * scalar @elim;
+
+	if (@surpluses and $elimvotetotal > $deferredsurplus) {
+	    printf "no-elim, un-defer\n";
+	    last;
+	}
+
+	if ((scalar keys %continuing) - (scalar @elim) < $placesremain) {
+	    # eliminate only one then, and try again
+	    printf "elim-tie!\n";
+	    @elim = historically_prefer -1, @elim;
+	}
+
+	foreach my $s (@elim) {
+	    my $c = $s->{Cand};
+	    printf "%7s %10s\n", 'ELIM', $c;
+	    my $votes = $s->{Votes};
+	    votelog $_, "failed to stop $c elimination" foreach @$votes;
+	    delete %continuing{$c};
+	    delete %sorted{$c};
+	    push @unsorted, @$votes;
+	}
+	
+	$sort_update->();
+	$need_to_transfer_surplus = 0;
+    }
     
-    
-	# transfer the surplus
-	filterout $topfirst, "candidate was elected";
-    } else {
-	my $elim = $sorted{ $#sorted };
-	printf "%10s eliminated\n", $elim;
-	filterout $elim, "candidate was eliminated";
+    next unless $need_to_transfer_surplus;
+
+    @surpluses = nsort_by { $_->{Total} }, @surpluses;
+    my @surplusxfer = equalpiles 'xfer?', @surpluses;
+    die unless @surplusxfer;
+
+    if (@surplusxfer > 1) {
+	@surplusxfer = historically_prefer +1, @surplusxfer;
     }
+
+    my $s = $surplusxfer[0];
+    my $c = $s->{Cand};
+    printf "%7s %10s\n", 'xfer', $c;
+    my $votes = $s->{Votes};
+    votelog $_, "surplus transferred" foreach @$votes;
+    @surpluses = grep { $_->{Cand} ne $c } @surpluses;
+    push @unsorted, @$votes;
 }
+
+print "done.\n";
-- 
2.30.2