feat: finish FileFilters class in dialog helper.

- finish FileFilters class representing the file types area in popup dialog.

src/DialogHelper.hpp

@@ -4,6 +4,8 @@
 
 #include <string>
 #include <vector>
+#include <initializer_list>
+#include <memory>
 
 #include "WinImportPrefix.hpp"
 #include <Windows.h>
@@ -13,6 +15,57 @@
 
 namespace YYCC::DialogHelper {
 
+	/**
+	 * @brief The class represent the file types region in file dialog.
+	*/
+	class FileFilters {
+	public:
+		FileFilters() : 
+			m_Filters(),
+			m_WinFilters(), m_WinDataStruct(nullptr)
+		{}
+
+		/**
+		 * @brief Add a filter pair in file types list.
+		 * @param filter_name[in] The friendly name of the filter.
+		 * @param il[in] A C++ initialize list.
+		 * Every entries must be `const char*` represent a single filter pattern.
+		 * The list at least should have one valid pattern.
+		 * This function will not validate these filter patterns, so please write them carefully.
+		 * @return True if added success, otherwise false.
+		 * @remarks This function allow you register multiple filter patterns for single friendly name.
+		 * For example: `Add("Microsoft Word (*.doc; *.docx)", {"*.doc", "*.docx"})`
+		*/
+		bool Add(const char* filter_name, std::initializer_list<const char*> il);
+		/**
+		 * @brief Clear filter pairs for following re-use.
+		*/
+		void Clear();
+
+		/**
+		 * @brief Generate Windows dialog system used data struct.
+		 * @param filter_count[out] The count of generated filter data struct.
+		 * @param filter_specs[out] The pointer to generated filter data struct.
+		 * @remarks User should not call this function. This function is used by internal functions.
+		 * @return True if generation is success, otherwise false.
+		*/
+		bool Generate(UINT& filter_count, COMDLG_FILTERSPEC*& filter_specs);
+
+	protected:
+		using FilterModes = std::vector<std::string>;
+		using FilterName = std::string;
+		using FilterPair = std::pair<FilterName, FilterModes>;
+
+		std::vector<FilterPair> m_Filters;
+
+		using WinFilterModes = std::wstring;
+		using WinFilterName = std::wstring;
+		using WinFilterPair = std::pair<WinFilterName, WinFilterModes>;
+
+		std::vector<WinFilterPair> m_WinFilters;
+		std::unique_ptr<COMDLG_FILTERSPEC[]> m_WinDataStruct;
+	};
+
 	//struct FileDialogParameter {
 	//	FileDialogParameter() :
 	//		m_Owner(nullptr),