=encoding utf8

=head1 NAME

std/math/range - Format integer lists as compact display ranges.

=head1 SYNOPSIS

  from std/math/range import abbreviate;

  let values := [ 3, 4, 9, 10, 11, 12, 15 ];
  let compact := abbreviate( values );
  # [ "3", "4", "9-12", "15" ]

=head1 IMPLEMENTATION SUPPORT

This module is supported by all implementations of ZuzuScript.

=head1 DESCRIPTION

This module exports C<abbreviate>, which converts a list of test
numbers into compact range labels.

Only runs of three or more consecutive integers are collapsed into a
range token like C<9-12>. Single values and two-item runs are emitted
as individual tokens.

=head1 EXPORTS

=head2 Functions

=over

=item * C<< abbreviate(Array values) >>

Parameters: C<values> is an array of numbers. Returns: C<Array>. Returns
compact string labels for the provided numbers.

The input may be unsorted and may contain duplicates; values are
normalized before abbreviation.

=back

=cut

function _sorted_unique ( Array values ) {
	let sorted := values.sort( function ( a, b ) {
		return a <=> b;
	} );
	let out := [];
	let prev := null;
	for ( let n in sorted ) {
		if ( prev != null and n = prev ) {
			next;
		}
		out.push( n );
		prev := n;
	}
	return out;
}

function _push_run ( Array out, Number start, Number end ) {
	let size := end - start + 1;
	if ( size >= 3 ) {
		out.push( `${start}-${end}` );
		return;
	}
	if ( size = 2 ) {
		out.push( `${start}` );
		out.push( `${end}` );
		return;
	}
	out.push( `${start}` );
}

function abbreviate ( Array values ) {
	if ( values.length() = 0 ) {
		return [];
	}

	let normalized := _sorted_unique( values );
	if ( normalized.length() = 0 ) {
		return [];
	}

	let out := [];
	let start := normalized[0];
	let prev := normalized[0];
	let i := 1;

	while ( i < normalized.length() ) {
		let n := normalized[i];
		if ( n = prev + 1 ) {
			prev := n;
			i++;
			next;
		}
		_push_run( out, start, prev );
		start := n;
		prev := n;
		i++;
	}

	_push_run( out, start, prev );
	return out;
}

=head1 COPYRIGHT AND LICENCE

B<< std/math/range >> is copyright Toby Inkster.

It is free software; you may redistribute it and/or modify it under
the terms of either the Artistic License 1.0 or the GNU General Public
License version 2.

=cut
