CLK/Storage/Disk/DiskImage/DiskImage.hpp

//
//  DiskImage.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 21/09/2017.
//  Copyright 2017 Thomas Harte. All rights reserved.
//

#pragma once

#include <map>
#include <memory>

#include "../Disk.hpp"
#include "../Track/Track.hpp"
#include "../../TargetPlatforms.hpp"

namespace Storage::Disk {

enum class Error {
	InvalidFormat = -2,
	UnknownVersion = -3
};

/*!
	Models a disk image as a collection of tracks, plus a range of possible track positions.

	The intention is not that tracks necessarily be evenly spaced; a head_position_count of 3 wih track
	A appearing in positions 0 and 1, and track B appearing in position 2 is an appropriate use of this API
	if it matches the media.
*/
class DiskImage {
	public:
		virtual ~DiskImage() = default;

		/*!
			@returns the distance at which there stops being any further content.

			This is not necessarily a track count. There is no implicit guarantee that every position will
			return a distinct track, or, e.g. if the media is holeless, will return any track at all.
		*/
		virtual HeadPosition get_maximum_head_position() = 0;

		/*!
			@returns the number of heads (and, therefore, impliedly surfaces) available on this disk.
		*/
		virtual int get_head_count() { return 1; }

		/*!
			@returns the @c Track at @c position underneath @c head if there are any detectable events there;
			returns @c nullptr otherwise.
		*/
		virtual std::shared_ptr<Track> get_track_at_position(Track::Address address) = 0;

		/*!
			Replaces the Tracks indicated by the map, that maps from physical address to track content.
		*/
		virtual void set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &) {}

		/*!
			Communicates that it is likely to be a while before any more tracks are written.
		*/
		virtual void flush_tracks() {}

		/*!
			@returns whether the disk image is read only. Defaults to @c true if not overridden.
		*/
		virtual bool get_is_read_only() { return true; }

		/*!
			@returns @c true if the tracks at the two addresses are different. @c false if they are the same track.
				This can avoid some degree of work when disk images offer sub-head-position precision.
		*/
		virtual bool tracks_differ(Track::Address lhs, Track::Address rhs) { return lhs != rhs; }
};

class DiskImageHolderBase: public Disk {
	protected:
		std::set<Track::Address> unwritten_tracks_;
		std::map<Track::Address, std::shared_ptr<Track>> cached_tracks_;
		std::unique_ptr<Concurrency::AsyncTaskQueue<true>> update_queue_;
};

/*!
	Provides a wrapper that wraps a DiskImage to make it into a Disk, providing caching and,
	thereby, an intermediate store for modified tracks so that mutable disk images can either
	update on the fly or perform a block update on closure, as appropriate.

	Implements TargetPlatform::TypeDistinguisher to return either no information whatsoever, if
	the underlying image doesn't implement TypeDistinguisher, or else to pass the call along.
*/
template <typename T> class DiskImageHolder: public DiskImageHolderBase, public TargetPlatform::TypeDistinguisher {
	public:
		template <typename... Ts> DiskImageHolder(Ts&&... args) :
			disk_image_(args...) {}
		~DiskImageHolder();

		HeadPosition get_maximum_head_position();
		int get_head_count();
		std::shared_ptr<Track> get_track_at_position(Track::Address address);
		void set_track_at_position(Track::Address address, const std::shared_ptr<Track> &track);
		void flush_tracks();
		bool get_is_read_only();
		bool tracks_differ(Track::Address lhs, Track::Address rhs);

	private:
		T disk_image_;

		TargetPlatform::Type target_platform_type() final {
			if constexpr (std::is_base_of<TargetPlatform::TypeDistinguisher, T>::value) {
				return static_cast<TargetPlatform::TypeDistinguisher *>(&disk_image_)->target_platform_type();
			} else {
				return TargetPlatform::Type(~0);
			}
		}
};

#include "DiskImageImplementation.hpp"

}