Implement lazy-loading audio tracks

libs/audio/include/psemek/audio/track.hpp

@@ -6,6 +6,7 @@
 
 #include <optional>
 #include <vector>
+#include <filesystem>
 
 namespace psemek::audio
 {
@@ -31,4 +32,6 @@ namespace psemek::audio
 	track_ptr load_mp3(util::blob data);
 	track_ptr load_mp3(std::vector<char> data);
 
+	track_ptr load_lazy(std::filesystem::path const & path);
+
 }

libs/audio/source/track_lazy.cpp

@@ -0,0 +1,59 @@
+#include <psemek/audio/track.hpp>
+#include <psemek/util/exception.hpp>
+#include <psemek/io/file_stream.hpp>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct lazy_track_impl
+			: track
+		{
+			lazy_track_impl(std::filesystem::path const & path)
+				: path_(path)
+			{}
+
+			stream_ptr stream() const override
+			{
+				load_proxy();
+				return proxy_->stream();
+			}
+
+			std::optional<std::size_t> length() const override
+			{
+				load_proxy();
+				return proxy_->length();
+			}
+
+		private:
+			std::filesystem::path path_;
+			mutable track_ptr proxy_;
+
+			void load_proxy() const
+			{
+				if (proxy_)
+					return;
+
+				auto data = io::read_full(io::file_istream(path_));
+				auto const extension = path_.extension();
+				if (extension == ".mp3")
+					proxy_ = load_mp3(std::move(data));
+				else if (extension == ".wav")
+					proxy_ = load_wav(std::move(data));
+				else if (extension == ".raw")
+					proxy_ = load_raw(std::move(data));
+				else
+					throw util::exception("Unknown audio format: " + extension.string());
+			}
+		};
+
+	}
+
+	track_ptr load_lazy(std::filesystem::path const & path)
+	{
+		return std::make_shared<lazy_track_impl>(path);
+	}
+
+}