Text preprocessor

function format(string $format, array $tokens): string
{
    $prev = '';

    $tag = '';
    $nextCond = [];
    $context = 'out'; // out, start, end, in

    $escapees = '{?}';
    $result = '';
    $escaped = $prevEscaped = false;

    //Lotta spaghetti... There's gotta be a way to simplify the conditions. Right?
    for ($i = 0; $i < strlen($format); $i++) {
        $ch = $format[$i];
        $prevEscaped = $escaped;
        if (strpos($escapees, $ch) !== false && $i>0 && $format[$i-1] === '\\') {
            $escaped = true;
        } else {
            $escaped = false;
            if ($ch === '\\' && strlen($format) > $i+1 && strpos($escapees, $format[$i+1]) !== false) continue;
        }

        if ($context === 'start') {
            if ($ch === '{') $result .= '{';
            else $context = 'in';
        }

        if ($format[$i] === '{' && !$escaped && $context === 'out') {
            $context = 'start';
            continue;
        } elseif ($format[$i] === '}' && !$escaped && ($context === 'in' || $context === 'inc')) {
            $context = 'end';
        }

        if ($context === 'end') {
            if ($format[$i-1] === '?' && !$prevEscaped) {
                $nextCond[] = $tag;
                $nextCond[] = '';
            } else {
                foreach ($nextCond as $item) {
                    if ($item[-1] === '?') {
                        if (array_key_exists($tag, $tokens) && !empty($tokens[$tag])) {
                            if ($item[0] === '?') {
                                if (array_key_exists($prev, $tokens) && !empty($tokens[$prev]))
                                    $result .= substr($item, 1, strlen($item)-1);
                            }
                            else $result .= substr($item, 0, strlen($item)-1);
                        }
                    }
                    else $result .= $item;
                }
                $nextCond = [];
            }
            if ($tag[0] !== '?' && $tag[-1] !== '?') {
                if (array_key_exists($tag, $tokens))
                    $result .= $tokens[$tag];
                $prev = $tag;
            } elseif ($tag[0] === '?' && ($tag[-1] !== '?' || $prevEscaped) && array_key_exists($prev, $tokens) && !empty($tokens[$prev])) {
                $result .= substr($tag, 1);
            }
            $context = 'out';
            $tag = '';
            continue;
        }

        if ($context === 'in') {
            $tag .= $format[$i];
        }

        if ($context === 'out') {
            if (!empty($nextCond))
                $nextCond[count($nextCond)-1] .= $ch;
            else $result .= $ch;
        }
    }
    return $result;
}