X-Git-Url: http://git.shiar.net/perl/list-index.git/blobdiff_plain/f467842b8e311a78d9900c4626583fc08a8ce31b..36f8fe8df9e85055f0feb31985fe1d07a1f74a33:/lib/List/Index.pm

diff --git a/lib/List/Index.pm b/lib/List/Index.pm
index 483d1eb..b11b5f8 100644
--- a/lib/List/Index.pm
+++ b/lib/List/Index.pm
@@ -24,37 +24,54 @@ sub ranges {
 
 	$pagesize = @$self / $pages;
 	my $offset = $pagesize + .5;
+	my $lookbehind = -$context;
+	my $lookahead  =  $context;
 	my @links = ('');
 	while ($offset < @$self) {
 		my $link = substr $self->[$offset], 0, $length;
 		if ($context) {
-			{
-				# take a value slightly before the current offset
-				my $before = $offset > $context ? $self->[$offset - $context] : '.';
+			my $penalty = 0;
+			# take a value slightly before the current offset
+			if ((my $before = $offset + $lookbehind) > 0) {
 				# see how much of it matches the current link
 				my $trim = 1;
-				for my $match (split //, $before) {
+				for my $match (split //, $self->[$before - 1]) {
 					scalar $link =~ /\G\Q$match/g or last;
 					$trim++;
 				}
 				# truncate link upto where the earlier value starts to differ
-				substr($link, $trim) = '' unless $trim > length $link;
+				if ($trim < length $link) {
+					substr($link, $trim) = '';
+					for (reverse $before .. $offset) {
+						$self->[$offset - $penalty] =~ /^\Q$link/ or last;
+						$penalty++;
+					}
+				}
 			}
 
-			if ($offset + $context < $#$self) {
-				# take a value after the current offset
-				my $after = $self->[$offset + $context];
+			$lookbehind = -$context;
+
+			# take a value after the current offset
+			if ((my $after = $offset + $lookahead) < $#$self) {
 				# see how much of it matches the current link
 				my $trim = 1;
-				for my $match (split //, $after) {
+				for my $match (split //, $self->[$after]) {
 					scalar $link =~ /\G\Q$match/g or last;
 					$trim++;
 				}
 				# use this link if it's shorter
 				if ($trim < length $link) {
-					$link = substr $after, 0, $trim;
+					$link = substr $self->[$after], 0, $trim;
+					# advance lookbehind offset on the next page
+					$penalty = 0;
+					for ($offset .. $after) {
+						last if $self->[$_] =~ /^\Q$link/;
+						$lookbehind++;
+					}
 				}
 			}
+
+			$lookahead = $context - $penalty;
 		}
 
 		push @links, $link;
@@ -164,18 +181,18 @@ __END__
 
 =head1 NAME
 
-List::Index - Paginate alphabetic entries by finding minimal prefixes
+List::Index - Find and apply prefix ranges to paginate keywords
 
 =head1 SYNOPSIS
 
 	use List::Index;
 	my $index = List::Index->new(\@values);
 	my @pages = $index->ranges({pagesize => 50});
-	printf '<a href="?q=%s-%s">%1$s</a> ', @$_ for @pages;
+	say "<a href='?q=$_'>$_</a>" for @pages;
 
 	use List::Index 'rangematch';
-	my $limit = rangematch('b-bmq');  # matches prefix like 'baa'..'bmq'
-	@results = grep { $limit } @results;
+	my $limit = rangematch('b-bmq');  # ge 'b' && le 'bmq'
+	@request = grep { $limit } @values;
 
 =head1 DESCRIPTION