1 files changed, 50 insertions, 0 deletions
diff --git a/include/mbgl/style/expression/find_zoom_curve.hpp b/include/mbgl/style/expression/find_zoom_curve.hpp
new file mode 100644
index 0000000000..81a4951bf5
--- /dev/null
+++ b/include/mbgl/style/expression/find_zoom_curve.hpp
@@ -0,0 +1,50 @@
+#pragma once
+
+#include <mbgl/style/expression/step.hpp>
+#include <mbgl/style/expression/compound_expression.hpp>
+#include <mbgl/style/expression/let.hpp>
+#include <mbgl/style/expression/coalesce.hpp>
+
+#include <mbgl/util/variant.hpp>
+#include <mbgl/util/optional.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+template <typename T>
+optional<variant<Interpolate<T>*, Step*>> findZoomCurve(expression::Expression* e) {
+    if (auto curve = dynamic_cast<Interpolate<T>*>(e)) {
+        auto z = dynamic_cast<CompoundExpressionBase*>(curve->getInput().get());
+        if (z && z->getName() == "zoom") {
+            return {curve};
+        } else {
+            return optional<variant<Interpolate<T>*, Step*>>();
+        }
+    } else if (auto step = dynamic_cast<Step*>(e)) {
+        auto z = dynamic_cast<CompoundExpressionBase*>(step->getInput().get());
+        if (z && z->getName() == "zoom") {
+            return {step};
+        } else {
+            return optional<variant<Interpolate<T>*, Step*>>();
+        }
+    } else if (auto let = dynamic_cast<Let*>(e)) {
+        return findZoomCurve<T>(let->getResult());
+    } else if (auto coalesce = dynamic_cast<Coalesce*>(e)) {
+        std::size_t length = coalesce->getLength();
+        for (std::size_t i = 0; i < length; i++) {
+            optional<variant<Interpolate<T>*, Step*>> childInterpolate = findZoomCurve<T>(coalesce->getChild(i));
+            if (!childInterpolate) {
+                continue;
+            } else {
+                return childInterpolate;
+            }
+        }
+    }
+
+    return optional<variant<Interpolate<T>*, Step*>>();
+}
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl