<?php

class Klein {  
    private $code;

    function compile($html) {
        $pattern = array_map(function ($grammar) {
            list(, $result) = $grammar;
            $body = strtr($grammar[0], [" " => "\s*", "+" => "\s+", ":var" => "(\w+(\s*\.\s*\w+)*)", ":id" => "(\w+)"]);
            return ["/$body/",
                function ($x) use ($result) {
                    return "<?php " . preg_replace_callback("/#([\d\w]+)/", function ($s) use($x) {
                        return preg_replace("/\.\s*(\w+)/", "['$1']", $x[$s[1]]);
                    }, $result) . " ?>";
                }];
        }, [
            ["{% for+:id+in+:var %}", "foreach(\$#2 as \$index => \$#1): \$loop = Klein::loop(\$index, \$#2);"],
            ["{% for+:id , :id+in+:var %}", "foreach(\$#3 as \$#1 => \$#2):"],
            ["{% endfor %}", "endforeach;"],
            ["{% if+:var %}", "if(isset(\$#1) && \$#1 ):"],
            ["{% endif %}", "endif;"],
            ["{{ :var }}", "echo \$#1;"],
            ["{{ :var\|:id }}", "echo #3(\$#1);"]
        ]);
  
        $result = file_get_contents($html);
        foreach($pattern as $arg) {
            $result = preg_replace_callback($arg[0], $arg[1], $result);
        }

        $this->code = $result;
    }

    static function loop($idx, &$array) {
        $is_even =  $idx % 2;
        return ['first' => $idx == 0
                , 'last' => $idx == count($array) - 1
                , 'odd' => !$is_even
                , 'even' => $is_even];
    }        

    function render($vars) {
        extract($vars);
        ob_start();
        eval(" ?>".$this->code."<?php ");
        return ob_get_clean();
    }
}