libcamera: Introduce YamlParser as a helper to parse yaml files

Introduce YamlParser as a helper to convert contents of a yaml file to
a tree based structure for easier reading, and to avoid writing parser
with raw yaml tokens. The class is based on libyaml, and only support
reading but not writing a yaml file.

The interface is inspired by Json::Value class from jsoncpp:
http://jsoncpp.sourceforge.net/class_json_1_1_value.html

Signed-off-by: Han-Lin Chen <hanlinchen@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/meson.build

@@ -42,4 +42,5 @@ libcamera_internal_headers = files([
     'v4l2_pixelformat.h',
     'v4l2_subdevice.h',
     'v4l2_videodevice.h',
+    'yaml_parser.h',
 ])

include/libcamera/internal/yaml_parser.h

@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022, Google Inc.
+ *
+ * yaml_parser.h - libcamera YAML parsing helper
+ */
+
+#pragma once
+
+#include <cstdio>
+#include <map>
+#include <string>
+#include <vector>
+
+#include <libcamera/base/class.h>
+
+#include <libcamera/geometry.h>
+
+namespace libcamera {
+
+class YamlParserContext;
+
+class YamlObject
+{
+public:
+	YamlObject();
+	~YamlObject();
+
+	bool isValue() const
+	{
+		return type_ == Value;
+	}
+	bool isList() const
+	{
+		return type_ == List;
+	}
+	bool isDictionary() const
+	{
+		return type_ == Dictionary;
+	}
+
+#ifndef __DOXYGEN__
+	template<typename T,
+		 typename std::enable_if_t<
+			 std::is_same<bool, T>::value ||
+			 std::is_same<double, T>::value ||
+			 std::is_same<int32_t, T>::value ||
+			 std::is_same<uint32_t, T>::value ||
+			 std::is_same<std::string, T>::value ||
+			 std::is_same<Size, T>::value> * = nullptr>
+#else
+	template<typename T>
+#endif
+	T get(const T &defaultValue, bool *ok = nullptr) const;
+
+	std::size_t size() const;
+	const YamlObject &operator[](std::size_t index) const;
+
+	bool contains(const std::string &key) const;
+	const YamlObject &operator[](const std::string &key) const;
+	std::vector<std::string> memberNames() const;
+
+private:
+	LIBCAMERA_DISABLE_COPY_AND_MOVE(YamlObject)
+
+	friend class YamlParserContext;
+
+	enum Type {
+		Dictionary,
+		List,
+		Value,
+	};
+
+	Type type_;
+
+	std::string value_;
+	std::vector<std::unique_ptr<YamlObject>> list_;
+	std::map<const std::string, std::unique_ptr<YamlObject>> dictionary_;
+};
+
+class YamlParser final
+{
+public:
+	static std::unique_ptr<YamlObject> parse(std::FILE *fh);
+};
+
+} /* namespace libcamera */