1 files changed, 233 insertions, 0 deletions
diff --git a/library/Icinga/Less/Visitor.php b/library/Icinga/Less/Visitor.php
new file mode 100644
index 0000000..c04a0eb
--- /dev/null
+++ b/library/Icinga/Less/Visitor.php
@@ -0,0 +1,233 @@
+<?php
+/* Icinga Web 2 | (c) 2022 Icinga GmbH | GPLv2+ */
+
+namespace Icinga\Less;
+
+use Less_Parser;
+use Less_Tree_Expression;
+use Less_Tree_Rule;
+use Less_Tree_Value;
+use Less_Tree_Variable;
+use Less_VisitorReplacing;
+use LogicException;
+use ReflectionProperty;
+
+/**
+ * Replace compiled Less colors with CSS var() function calls and inject light mode calls
+ *
+ * Color replacing basically works by replacing every visited Less variable with {@link ColorPropOrVariable},
+ * which is later compiled to {@link ColorProp} if it is a color.
+ *
+ * Light mode calls are generated from light mode definitions.
+ */
+class Visitor extends Less_VisitorReplacing
+{
+    const LIGHT_MODE_CSS = <<<'CSS'
+@media (min-height: @prefer-light-color-scheme), print,
+(prefers-color-scheme: light) and (min-height: @enable-color-preference) {
+    %s
+}
+CSS;
+
+    const LIGHT_MODE_NAME = 'light-mode';
+
+    public $isPreEvalVisitor = true;
+
+    /**
+     * Whether calling var() CSS function
+     *
+     * If that's the case, don't try to replace compiled Less colors with CSS var() function calls.
+     *
+     * @var bool|string
+     */
+    protected $callingVar = false;
+
+    /**
+     * Whether defining a variable
+     *
+     * If that's the case, don't try to replace compiled Less colors with CSS var() function calls.
+     *
+     * @var false|string
+     */
+    protected $definingVariable = false;
+
+    /** @var Less_Tree_Rule If defining a variable, determines the origin rule of the variable */
+    protected $variableOrigin;
+
+    /** @var LightMode Light mode registry */
+    protected $lightMode;
+
+    /** @var false|string Whether parsing module Less */
+    protected $moduleScope = false;
+
+    /** @var null|string CSS module selector if any */
+    protected $moduleSelector;
+
+    public function visitCall($c)
+    {
+        if ($c->name !== 'var') {
+            // We need to use our own tree call class , so that we can precompile the arguments before making
+            // the actual LESS function calls. Otherwise, it will produce lots of invalid argument exceptions!
+            $c = Call::fromCall($c);
+        }
+
+        return $c;
+    }
+
+    public function visitDetachedRuleset($drs)
+    {
+        if ($this->variableOrigin->name === '@' . static::LIGHT_MODE_NAME) {
+            $this->variableOrigin->name .= '-' . substr(sha1(uniqid(mt_rand(), true)), 0, 7);
+
+            $this->lightMode->add($this->variableOrigin->name);
+
+            if ($this->moduleSelector !== false) {
+                $this->lightMode->setSelector($this->variableOrigin->name, $this->moduleSelector);
+            }
+
+            $drs = LightModeDefinition::fromDetachedRuleset($drs)
+                ->setLightMode($this->lightMode)
+                ->setName($this->variableOrigin->name);
+        }
+
+        // Since a detached ruleset is a variable definition in the first place,
+        // just reset that we define a variable.
+        $this->definingVariable = false;
+
+        return $drs;
+    }
+
+    public function visitMixinCall($c)
+    {
+        // Less_Tree_Mixin_Call::accept() does not visit arguments, but we have to replace them if necessary.
+        foreach ($c->arguments as $a) {
+            $a['value'] = $this->visitObj($a['value']);
+        }
+
+        return $c;
+    }
+
+    public function visitMixinDefinition($m)
+    {
+        // Less_Tree_Mixin_Definition::accept() does not visit params, but we have to replace them if necessary.
+        foreach ($m->params as $p) {
+            if (! isset($p['value'])) {
+                continue;
+            }
+
+            $p['value'] = $this->visitObj($p['value']);
+        }
+
+        return $m;
+    }
+
+    public function visitRule($r)
+    {
+        if ($r->name[0] === '@' && $r->variable) {
+            if ($this->definingVariable !== false) {
+                throw new LogicException('Already defining a variable');
+            }
+
+            $this->definingVariable = spl_object_hash($r);
+            $this->variableOrigin = $r;
+
+            if ($r->value instanceof Less_Tree_Value) {
+                if ($r->value->value[0] instanceof Less_Tree_Expression) {
+                    if ($r->value->value[0]->value[0] instanceof Less_Tree_Variable) {
+                        // Transform the variable definition rule into our own class
+                        $r->value->value[0]->value[0] = new DeferredColorProp($r->name, $r->value->value[0]->value[0]);
+                    }
+                }
+            }
+        }
+
+        return $r;
+    }
+
+    public function visitRuleOut($r)
+    {
+        if ($this->definingVariable !== false && $this->definingVariable === spl_object_hash($r)) {
+            $this->definingVariable = false;
+            $this->variableOrigin = null;
+        }
+    }
+
+    public function visitRuleset($rs)
+    {
+        // Method is required, otherwise visitRulesetOut will not be called.
+        return $rs;
+    }
+
+    public function visitRulesetOut($rs)
+    {
+        if ($this->moduleScope !== false
+            && isset($rs->selectors)
+            && spl_object_hash($rs->selectors[0]) === $this->moduleScope
+        ) {
+            $this->moduleSelector = null;
+            $this->moduleScope = false;
+        }
+    }
+
+    public function visitSelector($s)
+    {
+        if ($s->_oelements_len === 2 && $s->_oelements[0] === '.icinga-module') {
+            $this->moduleSelector = implode('', $s->_oelements);
+            $this->moduleScope = spl_object_hash($s);
+        }
+
+        return $s;
+    }
+
+    public function visitVariable($v)
+    {
+        if ($this->definingVariable !== false) {
+            return $v;
+        }
+
+        return (new ColorPropOrVariable())
+            ->setVariable($v);
+    }
+
+    public function run($node)
+    {
+        $this->lightMode = new LightMode();
+
+        $evald = $this->visitObj($node);
+
+        // The visitor has registered all light modes in visitDetachedRuleset, but has not called them yet.
+        // Now the light mode calls are prepared with the appropriate CSS selectors.
+        $calls = [];
+        foreach ($this->lightMode as $mode) {
+            if ($this->lightMode->hasSelector($mode)) {
+                $calls[] = "{$this->lightMode->getSelector($mode)} {\n$mode();\n}";
+            } else {
+                $calls[] = "$mode();";
+            }
+        }
+
+        if (! empty($calls)) {
+            // Place and parse light mode calls into a new anonymous file,
+            // leaving the original Less in which the light modes were defined untouched.
+            $parser = (new Less_Parser())
+                ->parse(sprintf(static::LIGHT_MODE_CSS, implode("\n", $calls)));
+
+            // Because Less variables are block scoped,
+            // we can't just access the light mode definitions in the calls above.
+            // The LightModeVisitor ensures that all calls have access to the environment in which the mode was defined.
+            // Finally, the rules are merged so that the light mode calls are also rendered to CSS.
+            $rules = new ReflectionProperty(get_class($parser), 'rules');
+            $rules->setAccessible(true);
+            $evald->rules = array_merge(
+                $evald->rules,
+                (new LightModeVisitor())
+                    ->setLightMode($this->lightMode)
+                    ->visitArray($rules->getValue($parser))
+            );
+            // The LightModeVisitor is used explicitly here instead of using it as a plugin
+            // since we only need to process the newly created rules for the light mode calls.
+        }
+
+        return $evald;
+    }
+}