/*
This Source Code Form is subject to the
terms of the Mozilla Public License, v.
2.0. If a copy of the MPL was not
distributed with this file, You can
obtain one at
http://mozilla.org/MPL/2.0/.
*/

#pragma once

#include <cstdint>
#include <string>

namespace network
{

// layout of the snapshot container. a reader refuses a blob it does not understand
constexpr uint32_t SNAPSHOT_VERSION = 2;

// the sections a snapshot is built from. a reader skips over any id it does not know,
// which is what makes the format extensible: a peer built before a section existed can
// still read a newer snapshot and simply ignores what it has no use for
enum snapshot_chunk : uint16_t
{
	// tick, clock, weather and (in a full snapshot) the state of the random engine
	SNAPSHOT_SESSION = 1,
	// where every vehicle is, what its controls and appliances are set to, and what its
	// brakes are doing
	SNAPSHOT_VEHICLES = 2,
	// who is working which vehicle
	SNAPSHOT_CREWS = 3,
	// contents of the memory cells - this is what signalling reads
	SNAPSHOT_MEMCELLS = 4,
	// which way the switches are thrown
	SNAPSHOT_SWITCHES = 5
};

// what a peer is meant to do with the blob it received
enum class snapshot_mode
{
	// the peer is coming in cold and takes the world as it is given
	join,
	// routine correction on top of a simulation that is already running
	correction
};

struct snapshot_result
{
	bool ok{false};
	// how far the worst vehicle was from where the authority says it is
	double worst_position_error{0.0};
	uint32_t vehicles{0};
	uint32_t repositioned{0};
};

// packs the state of the world. only ever called on the authority.
// a full snapshot carries everything and is what a joining peer gets; otherwise only what
// has changed since the last one goes out, which is what keeps the routine correction
// stream small
std::string take_snapshot(bool Full);

// restores state handed to us by the authority
snapshot_result apply_snapshot(std::string const &Blob, snapshot_mode Mode);

// forgets what was last sent, so that the next delta comes out complete
void reset_snapshot_history();

} // namespace network