<?php
/**
 * Kleiner, sicherer Formel-Interpreter (kein eval).
 * Unterstützt: Zahlen, Variablen, + - * /, Klammern, unäres Minus,
 * Vergleiche (>= <= > < == !=), Ternär (a ? b : c) und die Funktionen
 * sqrt, pow, abs, min, max, round, floor, ceil.
 *
 * Damit rechnet das Plugin mit GENAU DER Formel, die in Directus hinterlegt
 * ist – Änderungen an der Formel wirken automatisch mit.
 */

if (!defined('ABSPATH')) exit;

/** Zerlegt den Ausdruck in Tokens. */
function skrift_formel_tokens($ausdruck) {
    $s = (string) $ausdruck;
    $s = str_replace('Math.', '', $s);        // Math.sqrt(...) → sqrt(...)
    $s = preg_replace('/%(\w+)%/', '$1', $s); // %qty% → qty
    $tokens = array();
    $pos = 0; $len = strlen($s);
    while ($pos < $len) {
        $c = $s[$pos];
        if (ctype_space($c)) { $pos++; continue; }
        if (ctype_digit($c) || ($c === '.' && $pos + 1 < $len && ctype_digit($s[$pos + 1]))) {
            $start = $pos;
            while ($pos < $len && (ctype_digit($s[$pos]) || $s[$pos] === '.')) $pos++;
            $tokens[] = array('num', (float) substr($s, $start, $pos - $start));
            continue;
        }
        if (ctype_alpha($c) || $c === '_') {
            $start = $pos;
            while ($pos < $len && (ctype_alnum($s[$pos]) || $s[$pos] === '_')) $pos++;
            $tokens[] = array('id', substr($s, $start, $pos - $start));
            continue;
        }
        $zwei = substr($s, $pos, 2);
        if (in_array($zwei, array('>=', '<=', '==', '!='), true)) { $tokens[] = array('op', $zwei); $pos += 2; continue; }
        $tokens[] = array('op', $c); $pos++;
    }
    return $tokens;
}

function skrift_formel_ist($t, $i, $wert) {
    return $i < count($t) && $t[$i][0] === 'op' && $t[$i][1] === $wert;
}

function skrift_formel_fn($name, $args) {
    $a0 = isset($args[0]) ? (float) $args[0] : 0.0;
    switch ($name) {
        case 'sqrt':  return $a0 < 0 ? 0.0 : sqrt($a0);
        case 'pow':   return pow($a0, isset($args[1]) ? (float) $args[1] : 0.0);
        case 'abs':   return abs($a0);
        case 'min':   return empty($args) ? 0.0 : min($args);
        case 'max':   return empty($args) ? 0.0 : max($args);
        case 'round': return round($a0);
        case 'floor': return floor($a0);
        case 'ceil':  return ceil($a0);
    }
    return 0.0;
}

function skrift_formel_primary(&$i, $t, $v) {
    if ($i >= count($t)) return 0.0;
    $tk = $t[$i];
    if ($tk[0] === 'num') { $i++; return $tk[1]; }
    if ($tk[0] === 'id') {
        $name = $tk[1]; $i++;
        if (skrift_formel_ist($t, $i, '(')) {
            $i++; $args = array();
            if (!skrift_formel_ist($t, $i, ')')) {
                $args[] = skrift_formel_ternary($i, $t, $v);
                while (skrift_formel_ist($t, $i, ',')) { $i++; $args[] = skrift_formel_ternary($i, $t, $v); }
            }
            if (skrift_formel_ist($t, $i, ')')) $i++;
            return skrift_formel_fn($name, $args);
        }
        return isset($v[$name]) ? (float) $v[$name] : 0.0;
    }
    if ($tk[0] === 'op' && $tk[1] === '(') {
        $i++; $r = skrift_formel_ternary($i, $t, $v);
        if (skrift_formel_ist($t, $i, ')')) $i++;
        return $r;
    }
    $i++; return 0.0;
}

function skrift_formel_unary(&$i, $t, $v) {
    if (skrift_formel_ist($t, $i, '-')) { $i++; return -skrift_formel_unary($i, $t, $v); }
    if (skrift_formel_ist($t, $i, '+')) { $i++; return skrift_formel_unary($i, $t, $v); }
    return skrift_formel_primary($i, $t, $v);
}

function skrift_formel_mul(&$i, $t, $v) {
    $l = skrift_formel_unary($i, $t, $v);
    while (skrift_formel_ist($t, $i, '*') || skrift_formel_ist($t, $i, '/')) {
        $op = $t[$i][1]; $i++;
        $r = skrift_formel_unary($i, $t, $v);
        $l = $op === '*' ? $l * $r : ($r == 0 ? 0.0 : $l / $r);
    }
    return $l;
}

function skrift_formel_add(&$i, $t, $v) {
    $l = skrift_formel_mul($i, $t, $v);
    while (skrift_formel_ist($t, $i, '+') || skrift_formel_ist($t, $i, '-')) {
        $op = $t[$i][1]; $i++;
        $r = skrift_formel_mul($i, $t, $v);
        $l = $op === '+' ? $l + $r : $l - $r;
    }
    return $l;
}

function skrift_formel_compare(&$i, $t, $v) {
    $l = skrift_formel_add($i, $t, $v);
    while ($i < count($t) && $t[$i][0] === 'op'
        && in_array($t[$i][1], array('>=', '<=', '==', '!=', '>', '<'), true)) {
        $op = $t[$i][1]; $i++;
        $r = skrift_formel_add($i, $t, $v);
        switch ($op) {
            case '>=': $l = $l >= $r; break;
            case '<=': $l = $l <= $r; break;
            case '>':  $l = $l >  $r; break;
            case '<':  $l = $l <  $r; break;
            case '==': $l = $l == $r; break;
            case '!=': $l = $l != $r; break;
        }
    }
    return $l;
}

function skrift_formel_ternary(&$i, $t, $v) {
    $c = skrift_formel_compare($i, $t, $v);
    if (skrift_formel_ist($t, $i, '?')) {
        $i++;
        $a = skrift_formel_ternary($i, $t, $v);
        if (skrift_formel_ist($t, $i, ':')) $i++;
        $b = skrift_formel_ternary($i, $t, $v);
        return $c ? $a : $b;
    }
    return $c;
}

/** Wertet den Ausdruck aus. Bei Problemen wird $fallback zurückgegeben. */
function skrift_formel_eval($ausdruck, $vars, $fallback = 1.0) {
    if (!is_string($ausdruck) || trim($ausdruck) === '') return $fallback;
    try {
        $t = skrift_formel_tokens($ausdruck);
        $i = 0;
        $r = (float) skrift_formel_ternary($i, $t, $vars);
        if (!is_finite($r)) return $fallback;
        return $r;
    } catch (Throwable $e) {
        return $fallback;
    }
}