Extended Storage::Disk::Disk to permit write-back of modified tracks, exposed some interface via Storage::Disk::Drive.

Storage/Disk/Disk.cpp

@@ -10,9 +10,23 @@
 
 using namespace Storage::Disk;
 
+int Disk::get_id_for_track_at_position(unsigned int head, unsigned int position)
+{
+	return (int)(position * get_head_count() + head);
+}
+
+void Disk::set_track_at_position(unsigned int head, unsigned int position, const std::shared_ptr<Track> &track)
+{
+	if(!get_is_read_only()) return;
+
+	int address = get_id_for_track_at_position(head, position);
+	cached_tracks_[address] = track;
+	modified_tracks_.insert(address);
+}
+
 std::shared_ptr<Track> Disk::get_track_at_position(unsigned int head, unsigned int position)
 {
-	int address = (int)(position * get_head_count() + head);
+	int address = get_id_for_track_at_position(head, position);
 	std::map<int, std::shared_ptr<Track>>::iterator cached_track = cached_tracks_.find(address);
 	if(cached_track != cached_tracks_.end()) return cached_track->second;
 
@@ -20,3 +34,17 @@ std::shared_ptr<Track> Disk::get_track_at_position(unsigned int head, unsigned i
 	cached_tracks_[address] = track;
 	return track;
 }
+
+std::shared_ptr<Track> Disk::get_modified_track_at_position(unsigned int head, unsigned int position)
+{
+	int address = get_id_for_track_at_position(head, position);
+	if(modified_tracks_.find(address) == modified_tracks_.end()) return nullptr;
+	std::map<int, std::shared_ptr<Track>>::iterator cached_track = cached_tracks_.find(address);
+	if(cached_track == cached_tracks_.end()) return nullptr;
+	return cached_track->second;
+}
+
+bool Disk::get_is_modified()
+{
+	return !modified_tracks_.empty();
+}

Storage/Disk/Disk.hpp

@@ -11,6 +11,7 @@
 
 #include <memory>
 #include <map>
+#include <set>
 #include "../Storage.hpp"
 
 namespace Storage {
@@ -85,6 +86,18 @@ class Disk {
 		*/
 		std::shared_ptr<Track> get_track_at_position(unsigned int head, unsigned int position);
 
+		/*!
+			Replaces the Track at position @c position underneath @c head with @c track. Ignored if this disk is read-only.
+			Subclasses that are not read-only should use the protected methods @c get_is_modified and, optionally,
+			@c get_modified_track_at_position to query for changes when closing.
+		*/
+		void set_track_at_position(unsigned int head, unsigned int position, const std::shared_ptr<Track> &track);
+
+		/*!
+			@returns whether the disk image is read only. Defaults to @c true if not overridden.
+		*/
+		virtual bool get_is_read_only() { return true; }
+
 	protected:
 		/*!
 			Subclasses should implement this to return the @c Track at @c position underneath @c head. Returned tracks
@@ -93,8 +106,20 @@ class Disk {
 		*/
 		virtual std::shared_ptr<Track> get_uncached_track_at_position(unsigned int head, unsigned int position) = 0;
 
+		/*!
+			@returns @c true if any calls to set_track_at_position occurred; @c false otherwise.
+		*/
+		bool get_is_modified();
+
+		/*!
+			@returns the @c Track at @c position underneath @c head if a modification was written there.
+		*/
+		std::shared_ptr<Track> get_modified_track_at_position(unsigned int head, unsigned int position);
+
 	private:
 		std::map<int, std::shared_ptr<Track>> cached_tracks_;
+		std::set<int> modified_tracks_;
+		int get_id_for_track_at_position(unsigned int head, unsigned int position);
 };
 
 }

Storage/Disk/Drive.cpp

@@ -39,8 +39,19 @@ void Drive::set_head(unsigned int head)
 	head_ = head;
 }
 
+bool Drive::get_is_read_only()
+{
+	if(disk_) return disk_->get_is_read_only();
+	return false;
+}
+
 std::shared_ptr<Track> Drive::get_track()
 {
 	if(disk_) return disk_->get_track_at_position(head_, (unsigned int)head_position_);
 	return nullptr;
 }
+
+void Drive::set_track(const std::shared_ptr<Track> &track)
+{
+	if(disk_) disk_->set_track_at_position(head_, (unsigned int)head_position_, track);
+}

Storage/Disk/Drive.hpp

@@ -44,7 +44,10 @@ class Drive {
 		*/
 		void set_head(unsigned int head);
 
+		bool get_is_read_only();
+
 		std::shared_ptr<Track> get_track();
+		void set_track(const std::shared_ptr<Track> &track);
 
 	private:
 		std::shared_ptr<Disk> disk_;