Smarty: Whitespace Control

prefilter.whitespace_control.php

<?php

$string = '{foreach $element->children as $c}
        {-if $c->max_count == 1}
    {-$c->getClassName()} {$c->getMemberVariableName()-};
        {-else-}
    {$c->getClassName()} {$c->getMemberVariableName()};
    std::vector<{$c->getClassName()}> {$c->getMemberVariableName()}s;
        {-/if-}
    {-/foreach}    hello
    
    {--sometag}

    {-+sometag}';

/*
    {-tag}  remove white space infront of tag up to the previous non-whitespace character or beginning of the line
            "text \n\n\t {-tag}" -> "text \n\n{tag}"
            "text \n\n\t text\t {-tag}" -> "text \n\n\t text{tag}"
    {--tag} remove white space infront of tag up to the previous non-whitespace character
            "text \n\n\t {--tag}" -> "text{tag}"
            "text \n\n\t text\t {--tag}" -> "text \n\n\t text{tag}"
    {+-tag}
    {-+tag} replace white space infront of tag up to the previous non-whitespace character by a single line-break
            "text \n\n\t {-+tag}" -> "text\n{tag}"
            "text \n\n\t text\t {-+tag}" -> "text \n\n\t text\n{tag}"
    
    {tag-}  remove white space after tag up to the next non-whitespace character or end of the line
            "{tag-} \n\n\t text" -> "{tag}\n\n\t text"
            "{tag-} text \n\n\t text" -> "{tag}text \n\n\t text"
    {tag--} remove white space after tag up to the next non-whitespace character
            "{tag--} \n\n\t text" -> "{tag}text"
            "{tag--} text \n\n\t text" -> "{tag}text \n\n\t text"
    {tag+-}
    {tag-+} replace white space after tag up to the next non-whitespace character by a single line-break
            "{tag-+} \n\n\t text" -> "{tag}\n\ntext"
            "{tag-+} text \n\n\t text" -> "{tag}\n\ntext \n\n\t text"
    
    {tag+}  replace white space after tag up to the end of the line with an additional line-break
            "{tag+} \n\t text" -> "{tag}\n\n\t text"
            "{tag+} text \n\n\t text" -> "{tag}\n\ntext \n\n\t text"
    
    Any combination of the above, say {--tag+} is possible. Any + modifiers are executed before - modifiers, so
        "{tag+-}{--tag}" will lead to "{tag}{tag}"
    
    NOTE: {tag+} and {tag-+} cause two trailing \n. This is done because PHP itself throws away the first \n. 
    So \n\n in the template will lead to \n in the output
*/

function smarty_prefilter_whitespace_control($string, $template) {
    // $ldelim = $template->smarty->left_delimiter;
    // $rdelim = $template->smarty->right_delimiter;
    $ldelim = '{';
    $rdelim = '}';
    $_ldelim = preg_quote($ldelim);
    $_rdelim = preg_quote($rdelim);


    // remove preceeding whitepsace preserving a single line-break
    $string =  preg_replace('#\s*'. $_ldelim .'(?:-\+|\+-)#', "\n" . $ldelim, $string);
    // remove trailing whitespace preserving s single line-break
    $string =  preg_replace('#(?:\+-|-\+)'. $_rdelim .'\s*#', $rdelim . "\n\n", $string);
    
    // remove preceeding whitepsace
    $string =  preg_replace('#\s*'. $_ldelim .'--|[^\S\r\n]*'. $_ldelim .'-#', $ldelim, $string);
    // remove trailing whitespace
    $string =  preg_replace('#--'. $_rdelim .'\s*|-'. $_rdelim .'[^\S\r\n]*#', $rdelim, $string);

    // force trailing line-break
    $string =  preg_replace('#\+'. $_rdelim .'(?:\s*[\r\n]|[^\S\r\n]*)#', $rdelim . "\n\n", $string);

    return $string;
}

echo smarty_prefilter_whitespace_control($string, null), "#end\n";

$tests = array(
    "text \n\n\t {-tag}" => "text \n\n{tag}",
    "text \n\n\t text\t {-tag}" => "text \n\n\t text{tag}",
    "text \n\n\t {--tag}" => "text{tag}",
    "text \n\n\t text\t {--tag}" => "text \n\n\t text{tag}",
    "text \n\n\t {-+tag}" => "text\n{tag}",
    "text \n\n\t text\t {-+tag}" => "text \n\n\t text\n{tag}",
    "{tag-} \n\n\t text" => "{tag}\n\n\t text",
    "{tag-} text \n\n\t text" => "{tag}text \n\n\t text",
    "{tag--} \n\n\t text" => "{tag}text",
    "{tag--} text \n\n\t text" => "{tag}text \n\n\t text",
    "{tag-+} \n\n\t text" => "{tag}\n\ntext",
    "{tag-+} text \n\n\t text" => "{tag}\n\ntext \n\n\t text",
    "{tag+} \n\t text" => "{tag}\n\n\t text",
    "{tag+} text \n\n\t text" => "{tag}\n\ntext \n\n\t text",
    "{tag+-}{--tag}" => "{tag}{tag}",
);

function nl($string) {
    $string = str_replace("\n", '\n', $string);
    $string = str_replace("\t", '\t', $string);
    return $string;
}

foreach ($tests as $in => $out) {
    $res = smarty_prefilter_whitespace_control($in, null);
    if ($res !== $out) {
        echo "failed '", nl($in), "' got '", nl($res), "' but expected '", nl($out), "'\n";
    }
}

echo "\n";