index.js

var postcss = require('postcss');

module.exports = postcss.plugin('postcss-simple-grid', function (opts) {
	opts = opts || {
		separator: '--'
	};

	function unitParse(str) {
		var returnValue = {};
		var match = str.match(/\d./);

		if(str.length) {
			var value = match[0];
			var unit = (str.replace(value, '')).trim();
			returnValue.unit = unit;
			returnValue.value = parseInt(value, 10);
		}

		return returnValue;
	}

	return function(css, result) {

		css.walkDecls(function (decl) {
			if(decl.prop === 'create-row') {
				var selectorName = decl.parent.selector;
				var rowValue = decl.value;

				decl.parent.append({
					prop: 'margin', value: '0 auto'
				});
				decl.parent.append({
					prop: 'max-width', value: rowValue
				});
				decl.parent.append({
					prop: 'position', value: 'relative'
				});

				css.insertAfter(decl.parent ,(selectorName + ':before,' + selectorName + ':after { content: " "; display: table; }' + selectorName + ':after { clear: both; }'));

				decl.remove();
			}

			if(decl.prop === 'create-column') {
				var selectorName = decl.parent.selector;
				var colGut = unitParse(decl.value);

				decl.parent.append({
					prop: 'float', value: 'left'
				});
				decl.parent.append({
					prop: 'padding', value: '0 ' + (colGut.value/2) + colGut.unit
				});
				decl.parent.append({
					prop: 'position', value: 'relative'
				});
				decl.parent.append({
					prop: 'width', value: '100%'
				});

				decl.remove();
			}

			if(decl.prop === 'create-grid') {
				var totalColumns = decl.value;
				var selectorName = decl.parent.selector + opts.separator;

				for (i = 1; i <= totalColumns; i++) {
					var width = ((i / totalColumns) * 100).toFixed(5) * 1;
					decl.parent.parent.append(selectorName + i + '{ width: '+ width + '%; }');
				}

				decl.parent.remove();
			}

			if(decl.prop === 'create-offset') {
				var totalColumns = decl.value;
				var offsetColumns = totalColumns - 1;
				var selectorName = decl.parent.selector + opts.separator;

				for (i = 0; i <= offsetColumns; i++) {
					var offsetWidth = ((i / totalColumns) * 100).toFixed(5) * 1;
					decl.parent.parent.append(selectorName + i + '{ margin-left: ' + offsetWidth + '%; }');
				}

				decl.parent.remove();
			}

			if(decl.prop === 'create-push') {
				var totalColumns = decl.value;
				var pushColumns = totalColumns - 1;
				var selectorName = decl.parent.selector + opts.separator;

				for (i = 0; i <= pushColumns; i++) {
					var pushWidth = ((i / totalColumns) * 100).toFixed(5) * 1;
					decl.parent.parent.append(selectorName + i + '{ left: ' + pushWidth + '%; right: auto; }');
				}

				decl.parent.remove();
			}

			if(decl.prop === 'create-pull') {
				var totalColumns = decl.value;
				var pullColumns = totalColumns - 1;
				var selectorName = decl.parent.selector + opts.separator;

				for (i = 0; i <= pullColumns; i++) {
					var pullWidth = ((i / totalColumns) * 100).toFixed(5) * 1;
					decl.parent.parent.append(selectorName + i + '{ left: auto; right: ' + pullWidth + '%; }');
				}

				decl.parent.remove();
			}
		});

	};
});