first go at a dispatcher to dynamically recolor SVGs

The script accepts the following parameters:

svg - the SVG to load. Either an image in the img directory next to the
      script or a media file id. ACLs are checked
f   - wanted fill color
s   - wanted stroke color
fh  - wanted fill color on hover
sh  - wanted stroke color on hover

Colors are to be given in hex in the following formats:

RGB
RRGGBB
RRGGBBAA

What's missing:

* being able to define what is styled, currently hardcoded to 'path'
  elements only
* caching - no need to do all the processing every time
* background setting - that would require wrapping an additional <g>
  or <rect> element around all content and style. I'm not sure how to do
  that best.
* unit tests

svg.php

@@ -0,0 +1,165 @@
+<?php
+
+namespace dokuwiki\template\sprintdoc;
+
+if(!defined('DOKU_INC')) define('DOKU_INC', dirname(__FILE__) . '/../../../');
+require_once(DOKU_INC . 'inc/init.php');
+
+/**
+ * Custom XML node that allows prepending
+ */
+class SvgNode extends \SimpleXMLElement {
+    /**
+     * @param string $name Name of the new node
+     * @param null|string $value
+     * @return SvgNode
+     */
+    public function prependChild($name, $value = null) {
+        $dom = dom_import_simplexml($this);
+
+        $new = $dom->insertBefore(
+            $dom->ownerDocument->createElement($name, $value),
+            $dom->firstChild
+        );
+
+        return simplexml_import_dom($new, get_class($this));
+    }
+}
+
+/**
+ * Manage SVG recoloring
+ */
+class SVG {
+
+    const IMGDIR = __DIR__ . '/img/';
+
+    /** @var SvgNode */
+    protected $xml;
+
+    /**
+     * SVG constructor
+     */
+    public function __construct() {
+        global $INPUT;
+
+        $svg = cleanID($INPUT->str('svg'));
+        if(blank($svg)) $this->abort(404);
+
+        // try local file first
+        $file = self::IMGDIR . $svg;
+        if(!file_exists($file)) {
+            // media files are ACL protected
+            if(auth_quickaclcheck($svg)) $this->abort(403);
+            $file = mediaFN($svg);
+        }
+        // check if media exists
+        if(!file_exists($file)) $this->abort(404);
+
+        $this->xml = simplexml_load_file($file, SvgNode::class);
+    }
+
+    /**
+     * Generate and output
+     */
+    public function out() {
+        $this->setStyle();
+        header('image/svg+xml');
+        echo $this->xml->asXML();
+    }
+
+    /**
+     * Generate a style setting from the input variables
+     *
+     * @return string
+     */
+    protected function makeStyle() {
+        global $INPUT;
+
+        $element = 'path'; // FIXME configurable?
+
+        $colors = array(
+            's' => $this->fixColor($INPUT->str('s')),
+            'f' => $this->fixColor($INPUT->str('f')),
+            'sh' => $this->fixColor($INPUT->str('sh')),
+            'fh' => $this->fixColor($INPUT->str('fh')),
+        );
+
+        $style = '';
+        if($colors['s'] || $colors['f']) {
+            $style .= $element . '{';
+            if($colors['s']) $style .= 'stroke:' . $colors['s'] . ';';
+            if($colors['f']) $style .= 'fill:' . $colors['f'] . ';';
+            $style .= '}';
+        }
+
+        if($colors['sh'] || $colors['fh']) {
+            $style .= $element . ':hover{';
+            if($colors['sh']) $style .= 'stroke:' . $colors['sh'] . ';';
+            if($colors['fh']) $style .= 'fill:' . $colors['fh'] . ';';
+            $style .= '}';
+        }
+
+        return $style;
+    }
+
+    /**
+     * Takes a hexadecimal color string in the following forms:
+     *
+     * RGB
+     * RRGGBB
+     * RRGGBBAA
+     *
+     * Converts it to rgba() form
+     *
+     * @param string $color
+     * @return string
+     */
+    protected function fixColor($color) {
+        if(preg_match('/^([0-9a-f])([0-9a-f])([0-9a-f])$/i', $color, $m)) {
+            $r = hexdec($m[1] . $m[1]);
+            $g = hexdec($m[2] . $m[2]);
+            $b = hexdec($m[3] . $m[3]);
+            $a = hexdec('ff');
+        } elseif(preg_match('/^([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})?$/i', $color, $m)) {
+            $r = hexdec($m[1]);
+            $g = hexdec($m[2]);
+            $b = hexdec($m[3]);
+            if(isset($m[4])) {
+                $a = hexdec($m[4]);
+            } else {
+                $a = hexdec('ff');
+            }
+        } else {
+            return '';
+        }
+
+        return "rgba($r,$g,$b,$a)";
+    }
+
+    /**
+     * Apply the style to the SVG
+     */
+    protected function setStyle() {
+        $defs = $this->xml->defs;
+        if(!$defs) {
+            $defs = $this->xml->prependChild('defs');
+        }
+        $defs->addChild('style', $this->makeStyle());
+    }
+
+    /**
+     * Abort processing with given status code
+     *
+     * @param int $status
+     */
+    protected function abort($status) {
+        http_status($status);
+        exit;
+    }
+
+}
+
+// main
+$svg = new SVG();
+$svg->out();
+