<?php
/*---------------------------------------------------------------------------*/

	define('FILTER_SEP_AND', '+');
	define('FILTER_SEP_OR', ',');
	define('FILTER_ESCAPE', '\\');

	function parse_filter($source) {
		$filter = array(array('')); $escape = false;
		$length = strlen($source); $index = 0;
		$group = 0; $sub_group = 0;

		while ($index++ < $length) {
			$char = $source[$index - 1];

			// Toggle escape status:
			if ($char == FILTER_ESCAPE) {
				$escape = !$escape;

				if ($escape) continue;

			// Handle unescaped:
			} else if (!$escape) {
				if ($char == FILTER_SEP_AND) {
					$filter[] = array('');
					$group++; $sub_group = 0;
					continue;

				} else if ($char == FILTER_SEP_OR) {
					$filter[$group][] = '';
					$sub_group++;
					continue;
				}

			} else {
				$escape = false;
			}

			$filter[$group][$sub_group] .= $char;
		}

		return $filter;
	}

	function build_query($filter) {
		$query = "(";

		foreach ($filter as $index => $group) {
			if ($index) $query .= "\n)\nAND (";

			foreach ($group as $sub_index => $sub_group) {
				$query .= "\n\t";

				if ($sub_index) $query .= "OR ";

				$query .= "value = " . trim($sub_group);
			}
		}

		$query .= "\n)";

		return $query;
	}

/*---------------------------------------------------------------------------*/

	header('content-type: text/plain');

	$source = 'one, two \\+ three, four + five, six\\, \\"seven\\" \\\\+ eight';
	$filter = parse_filter($source);
	$query = build_query($filter);

	echo "Turn this: {$source}\n\nInto this:\n";
	echo $query;

/*---------------------------------------------------------------------------*/
?>