Writing tags (mikekazakov#153)

* Implementing routines to write the Finder Tags

* Expanded the WritePListObject function to support long strings and unicode strings

* Added routines to write tags into actual files

* Added a function that gathers all tags on the filesystem via Spotlight

* Added comments

Source/Utility/include/Utility/Tags.h

@@ -5,14 +5,15 @@
 #include <vector>
 #include <string>
 #include <filesystem>
+#include <optional>
+#include <utility>
 
 namespace nc::utility {
 
 class Tags
 {
 public:
-    enum class Color : unsigned char
-    {
+    enum class Color : unsigned char {
         None = 0,
         Gray = 1,
         Green = 2,
@@ -32,18 +33,37 @@ class Tags
     // Parses the "com.apple.FinderInfo" xattr and extracts a tag color if any is present.
     // Returns an empty vector as an error mechanism.
     static std::vector<Tag> ParseFinderInfo(std::span<const std::byte> _bytes) noexcept;
-        
+
     // Loads the contents an the xattrs and processes it with ParseMDItemUserTags
     static std::vector<Tag> ReadMDItemUserTags(int _fd) noexcept;
-    
+
     // Loads the contents an the xattrs and processes it with ParseFinderInfo
     static std::vector<Tag> ReadFinderInfo(int _fd) noexcept;
 
     // Loads tags from MDItemUserTags (1st priority) or from FinderInfo(2nd priority), works with file handles
     static std::vector<Tag> ReadTags(int _fd) noexcept;
-    
+
     // Loads tags from MDItemUserTags (1st priority) or from FinderInfo(2nd priority), works with file paths
     static std::vector<Tag> ReadTags(const std::filesystem::path &_path) noexcept;
+
+    // Composes a binary blob representing the contents of the "com.apple.metadata:_kMDItemUserTags" xattr corresponding
+    // to the specified list of tags. Empty blob is returned if no tags were provided.
+    static std::vector<std::byte> BuildMDItemUserTags(std::span<const Tag> _tags) noexcept;
+
+    // Writes the "com.apple.metadata:_kMDItemUserTags" and "com.apple.FinderInfo" xattrs to the specified file
+    // according to the provided set of tags.
+    static bool WriteTags(int _fd, std::span<const Tag> _tags) noexcept;
+
+    // Writes the "com.apple.metadata:_kMDItemUserTags" and "com.apple.FinderInfo" xattrs to the specified file
+    // according to the provided set of tags.
+    static bool WriteTags(const std::filesystem::path &_path, std::span<const Tag> _tags) noexcept;
+
+    // Executes a "kMDItemUserTags=*" query by Spotlight to gather all indexed items on the filesystem that contain any
+    // tags.
+    static std::vector<std::filesystem::path> GatherAllItemsWithTags() noexcept;
+
+    // Gather a current set of tags used by the items on the filesystem.
+    static std::vector<Tag> GatherAllItemsTags() noexcept;
 };
 
 // Non-owning class that represent a text label and a color of a tag.
@@ -62,3 +82,17 @@ class Tags::Tag
 };
 
 } // namespace nc::utility
+
+namespace std {
+
+template <>
+class hash<nc::utility::Tags::Tag>
+{
+public:
+    size_t operator()(const nc::utility::Tags::Tag &_tag) const noexcept
+    {
+        return std::hash<std::string>{}(_tag.Label()) + std::to_underlying(_tag.Color());
+    }
+};
+
+} // namespace std