TiddlyWiki5/core/modules/filters/range.js

/*\
title: $:/core/modules/filters/range.js
type: application/javascript
module-type: filteroperator

Filter operator for generating a numeric range.

\*/
(function(){

/*jslint node: true, browser: true */
/*global $tw: false */
"use strict";

/*
Export our filter function
*/
exports.range = function(source,operator,options) {
	var results = [];

	// Split the operand into numbers delimited by these symbols
	var parts = operator.operand.split(/[,:;]/g), beg, end, inc, i, fixed = 0;

	for (i = 0; i < parts.length; ++i) {
		// Validate real number
		if (!/^\s*[+-]?((\d+(\.\d*)?)|(\.\d+))\s*$/.test(parts[i]))
			return ["range: bad number \""+parts[i]+"\""];

		// Count digits; the most precise number determines decimal places in output.
		var frac = /\.\d+/.exec(parts[i]);
		if (frac) fixed = Math.max(fixed, frac[0].length-1);
		
		parts[i] = parseFloat(parts[i]);
	}

	switch (parts.length) {
		case 1:
			beg = 0;
			end = parts[0];
			inc = 1;
			break;
		case 2:
			beg = parts[0];
			end = parts[1];
			inc = 1;
			break;
		case 3:
			beg = parts[0];
			end = parts[1];
			inc = Math.abs(parts[2]);
			break;
	}

	if (inc === 0) return ["range: increment 0 causes infinite loop"];

	// May need to count backwards
	var direction = ((end<beg) ? -1 : 1);
	inc *= direction;

	// Estimate number of resulting elements
	if ((end-beg)/inc > 10000) return ["range: too many steps (over 10K)"];

	// Avoid rounding error on last step
	end += direction * 0.5 * Math.pow(0.1, fixed);

	var safety = 10010;

	// Enumerate the range
	if (end<beg) {for (i = beg; i > end; i += inc) {results.push(i.toFixed(fixed)); if (--safety<0) break;}}
	else         {for (i = beg; i < end; i += inc) {results.push(i.toFixed(fixed)); if (--safety<0) break;}}

	if (safety<0) return ["range: unexpectedly large output"];

	// Reverse?
	if (operator.prefix === "!") results.reverse();

	return results;
};

})();