libcamera: value_node: Add functions to erase child nodes

There will be a need to erase child nodes when implementing support for
overriding configuration options. Add two erase() functions to the
ValueNode class, mimicking the add() API.

More erase() overloads could be added, for instance taking iterators as
parameters, to improve efficiency. This should be considered later, when
usage of the ValueNode class will expand, based on the actual usage
patterns.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>

include/libcamera/internal/value_node.h

@@ -244,6 +244,9 @@ public:
 	ValueNode *add(std::initializer_list<std::string_view> path,
 		       std::unique_ptr<ValueNode> &&child);
 
+	void erase(std::string_view key);
+	void erase(std::initializer_list<std::string_view> path);
+
 private:
 	LIBCAMERA_DISABLE_COPY_AND_MOVE(ValueNode)
 

src/libcamera/value_node.cpp

@@ -622,4 +622,58 @@ ValueNode *ValueNode::add(std::initializer_list<std::string_view> path,
 	return node;
 }
 
+/**
+ * \brief Erase a child node in a dictionary
+ * \param[in] key The dictionary key
+ *
+ * Erase the child node referenced by \a key in a dictionary node. If the \a
+ * key does not exist, or if this node is not a dictionary, the function
+ * returns without performing any operation.
+ */
+void ValueNode::erase(std::string_view key)
+{
+	auto node = dictionary_.find(key);
+	if (node == dictionary_.end())
+		return;
+
+	/* \todo Not an ideal algorithm */
+	for (auto iter = list_.begin(); iter != list_.end(); ++iter) {
+		if (iter->value.get() != node->second)
+			continue;
+
+		list_.erase(iter);
+		break;
+	}
+
+	dictionary_.erase(node);
+}
+
+/**
+ * \brief Erase the child node at the given path
+ * \param[in] path The path
+ *
+ * Erase the child node at the given \a path. If no child node exists for the
+ * path, the function returns without performing any operation.
+ */
+void ValueNode::erase(std::initializer_list<std::string_view> path)
+{
+	if (!path.size())
+		return;
+
+	ValueNode *node = this;
+
+	for (const auto [i, name] : utils::enumerate(path)) {
+		if (i == path.size() - 1) {
+			node->erase(name);
+			return;
+		}
+
+		auto iter = node->dictionary_.find(name);
+		if (iter == node->dictionary_.end())
+			return;
+
+		node = iter->second;
+	}
+}
+
 } /* namespace libcamera */