<?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 ($result) {
                    return "<?php " . preg_replace_callback("/#(\d+)(s?)/", function ($s) use($x) {
                        $pref = $s[2] == 's' ? '$' : '';
                        return implode(", ", array_map(function ($s) use($pref) { return $pref.preg_replace("/\.\s*(\w+)/", "['$1']", $s); }, preg_split("/\s*,\s*/", $x[$s[1]])));
                    }, $result) . " ?>";
                }];
        }, [
            ["{% for+:id+in+:var %}", "foreach(#2s as \$index => #1s): \$loop = Klein::loop(\$index, #2s);"],
            ["{% for+:id , :id+in+:var %}", "foreach(#3s as #1s => #2s):"],
            ["{% endfor %}", "endforeach;"],
            ["{% if+:var %}", "if(isset(#1s) && #1s):"],
            ["{% else %}", "else:"],
            ["{% endif %}", "endif;"],
            ["{{ :var }}", "echo #1s;"],
            ["{{ :id\(( :var (, :var )*)?\) }}", "echo macro_#1(#2s);"],
            ["{{ :var\|:id }}", "echo #3(#1s);"],
            ["{% macro+:id\(( :id (, :id )*)?\) %}", "function macro_#1(#2s) {"],
            ["{% endmacro %}", "}"]
        ]);
  
        $result = file_get_contents($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();
    }
}