fix corner case where #items-1 == #pages

[perl/list-index.git] / lib / List / Index.pm

diff --git a/lib/List/Index.pm b/lib/List/Index.pm
index 5b46313d7272168dea172ddf5135ce9ef480dae0..35f0549e288cd999cab4e5238cf6b8c142d7b17e 100644 (file)
--- a/lib/List/Index.pm
+++ b/lib/List/Index.pm
@@ -6,69 +6,92 @@ use warnings;
 
 use Exporter 'import';
 
-our $VERSION = '1.01';
+our $VERSION = '1.02';
 our @EXPORT_OK = qw(rangematch);
 
 sub new {
-       my ($class, $values) = @_;
-       bless [sort map { s/[^a-z]/./g; $_ } @$values], $class;
+       my ($class, $options) = @_;
+       $options ||= {};
+       bless $options, $class;
 }
 
 sub ranges {
        my $self = shift;
+       my @rows = sort map { s/[^a-z]/./g; $_ } @{ shift() };
        my $options = shift || {};
+       $options->{$_} //= $self->{$_} for keys %$self;
+
        my $pagesize = $options->{pagesize} || 50;
        my $context  = $options->{context } // 1 + ($pagesize >> 4);
        my $length   = $options->{length  } || 4;
-       my $pages    = $options->{pages   } || 1 + int $#$self / $pagesize;
+       my $pages    = $options->{pages   } || 1 + int($#rows / $pagesize);
+
+       $pagesize = $pages >= @rows ? 1 : @rows / $pages;
+       my $shrunk = 0;
+       my $enlarged = 0;
 
-       $pagesize = @$self / $pages;
-       my $offset = $pagesize + .5;
        my @links = ('');
-       while ($offset < @$self) {
-               my $link = substr $self->[$offset], 0, $length;
+       for (my $offset = $pagesize + .5; $offset < @rows; $offset += $pagesize) {
+               my $link = substr $rows[$offset], 0, $length;
                if ($context) {
-                       {
-                               # take a value slightly before the current offset
-                               my $before = $offset > $context ? $self->[$offset - $context] : '.';
+                       my $lookbehind = -$context + $shrunk;
+                       my $lookahead  =  $context - $enlarged;
+                       $shrunk = $enlarged = 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 //, $rows[$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 - 1) {
+                                               $rows[$_] =~ /^\Q$link/ or last;
+                                               $enlarged++;
+                                       }
+                               }
                        }
 
-                       if ($offset + $context < $#$self) {
-                               # take a value after the current offset
-                               my $after = $self->[$offset + $context];
+                       # take a value after the current offset
+                       if ((my $after = $offset + $lookahead) < $#rows) {
                                # see how much of it matches the current link
                                my $trim = 1;
-                               for my $match (split //, $after) {
+                               pos $link = 0;
+                               for my $match (split //, $rows[$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;
+                                       $enlarged = 0;
+                                       for ($offset + 1 .. $after) {
+                                               my $prefix = substr $rows[$_], 0, $trim;
+                                               # advance lookbehind offset on the next page
+                                               $shrunk++;
+                                               next if $link =~ /^\Q$prefix/;
+                                               $link = $prefix;
+                                               last;
+                                       }
                                }
                        }
                }
 
-               push @links, $link;
-               $offset += $pagesize;
+               push @links, $link unless $links[-1] eq $link;
        }
 
-       use List::MoreUtils 'uniq';
-       @links = uniq @links;
+       # add range end to each link
        for my $i (0 .. $#links - 1) {
-               my ($link, $lastchar) = $links[$i + 1] =~ /(.*)(.)/;
-               $link .= $lastchar le 'a' ? '.' : chr( ord($lastchar) - 1 );
-               next if $link eq $links[$i] and $i;
-               $links[$i] .= '-'.$link;
+               # end at start of next value with the last character decremented
+               my $next = $links[$i + 1];
+               $next =~ s{(.)$}{ $1 le 'a' ? '.' : chr( ord($1) - 1 ) }e;
+               # amend range if it's ahead
+               $links[$i] .= '-'.$next unless $next eq $links[$i];
        }
+       # final value takes the rest
        $links[-1] .= '-';
 
        return \@links;
@@ -169,8 +192,8 @@ 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});
+       my $index = List::Index->new({ pagesize => 50 });
+       my @pages = $index->ranges(\@values);
        say "<a href='?q=$_'>$_</a>" for @pages;
 
        use List::Index 'rangematch';