/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @file saveload.cpp
 * All actions handling saving and loading goes on in this file. The general actions
 * are as follows for saving a game (loading is analogous):
 * <ol>
 * <li>initialize the writer by creating a temporary memory-buffer for it
 * <li>go through all to-be saved elements, each 'chunk' (#ChunkHandler) prefixed by a label
 * <li>use their description array (#SaveLoad) to know what elements to save and in what version
 *    of the game it was active (used when loading)
 * <li>write all data byte-by-byte to the temporary buffer so it is endian-safe
 * <li>when the buffer is full; flush it to the output (eg save to file) (_sl.buf, _sl.bufp, _sl.bufe)
 * <li>repeat this until everything is done, and flush any remaining output to file
 * </ol>
 */

#include "../stdafx.h"

#include "saveload.h"
#include "../debug.h"
#include "../string_func.h"
#include "../string_func_extra.h"
#include "../strings_func.h"
#include "../core/bitmath_func.hpp"
#include "../vehicle_base.h"
#include "../station_base.h"
#include "../linkgraph/linkgraph.h"
#include "../linkgraph/linkgraphjob.h"
#include "../town.h"
#include "../roadstop_base.h"
#include "../autoreplace_base.h"
#include "../core/ring_buffer.hpp"

#include <atomic>
#include <vector>
#include <string>
#include <map>
#include <list>

#include "../safeguards.h"

StringID RemapOldStringID(StringID s);
std::string CopyFromOldName(StringID id);

extern uint8_t SlSaveToTempBufferSetup();
extern std::span<byte> SlSaveToTempBufferRestore(uint8_t state);
extern void SlCopyBytesRead(void *ptr, size_t length);
extern void SlCopyBytesWrite(void *ptr, size_t length);

namespace upstream_sl {

/** What are we currently doing? */
enum SaveLoadAction {
	SLA_LOAD,        ///< loading
	SLA_SAVE,        ///< saving
	SLA_PTRS,        ///< fixing pointers
	SLA_NULL,        ///< null all pointers (on loading error)
	SLA_LOAD_CHECK,  ///< partial loading into #_load_check_data
};

enum NeedLength {
	NL_NONE = 0,       ///< not working in NeedLength mode
	NL_WANTLENGTH = 1, ///< writing length and data
	NL_CALCLENGTH = 2, ///< need to calculate the length
};

/** The saveload struct, containing reader-writer functions, buffer, version, etc. */
struct SaveLoadParams {
	SaveLoadAction action;               ///< are we doing a save or a load atm.
	NeedLength need_length;              ///< working in NeedLength (Autolength) mode?
	byte block_mode;                     ///< ???

	size_t obj_len;                      ///< the length of the current object we are busy with
	int array_index, last_array_index;   ///< in the case of an array, the current and last positions
	bool expect_table_header;            ///< In the case of a table, if the header is saved/loaded.
};

static SaveLoadParams _sl; ///< Parameters used for/at saveload.

static const std::vector<ChunkHandlerRef> &ChunkHandlers()
{
	/* These define the chunks */
	extern const ChunkHandlerTable _gamelog_chunk_handlers;
	extern const ChunkHandlerTable _map_chunk_handlers;
	extern const ChunkHandlerTable _misc_chunk_handlers;
	//extern const ChunkHandlerTable _name_chunk_handlers;
	extern const ChunkHandlerTable _cheat_chunk_handlers;
	extern const ChunkHandlerTable _setting_chunk_handlers;
	extern const ChunkHandlerTable _company_chunk_handlers;
	extern const ChunkHandlerTable _engine_chunk_handlers;
	extern const ChunkHandlerTable _veh_chunk_handlers;
	//extern const ChunkHandlerTable _waypoint_chunk_handlers;
	extern const ChunkHandlerTable _depot_chunk_handlers;
	extern const ChunkHandlerTable _order_chunk_handlers;
	extern const ChunkHandlerTable _town_chunk_handlers;
	extern const ChunkHandlerTable _sign_chunk_handlers;
	extern const ChunkHandlerTable _station_chunk_handlers;
	extern const ChunkHandlerTable _industry_chunk_handlers;
	extern const ChunkHandlerTable _economy_chunk_handlers;
	extern const ChunkHandlerTable _subsidy_chunk_handlers;
	extern const ChunkHandlerTable _cargomonitor_chunk_handlers;
	extern const ChunkHandlerTable _goal_chunk_handlers;
	extern const ChunkHandlerTable _story_page_chunk_handlers;
	extern const ChunkHandlerTable _league_chunk_handlers;
	extern const ChunkHandlerTable _ai_chunk_handlers;
	extern const ChunkHandlerTable _game_chunk_handlers;
	extern const ChunkHandlerTable _animated_tile_chunk_handlers;
	extern const ChunkHandlerTable _newgrf_chunk_handlers;
	extern const ChunkHandlerTable _group_chunk_handlers;
	extern const ChunkHandlerTable _cargopacket_chunk_handlers;
	extern const ChunkHandlerTable _autoreplace_chunk_handlers;
	extern const ChunkHandlerTable _labelmaps_chunk_handlers;
	extern const ChunkHandlerTable _linkgraph_chunk_handlers;
	extern const ChunkHandlerTable _airport_chunk_handlers;
	extern const ChunkHandlerTable _object_chunk_handlers;
	extern const ChunkHandlerTable _persistent_storage_chunk_handlers;
	extern const ChunkHandlerTable _water_region_chunk_handlers;
	extern const ChunkHandlerTable _randomizer_chunk_handlers;

	/** List of all chunks in a savegame. */
	static const ChunkHandlerTable _chunk_handler_tables[] = {
		_gamelog_chunk_handlers,
		_map_chunk_handlers,
		_misc_chunk_handlers,
		//_name_chunk_handlers,
		_cheat_chunk_handlers,
		_setting_chunk_handlers,
		_veh_chunk_handlers,
		//_waypoint_chunk_handlers,
		_depot_chunk_handlers,
		_order_chunk_handlers,
		_industry_chunk_handlers,
		_economy_chunk_handlers,
		_subsidy_chunk_handlers,
		_cargomonitor_chunk_handlers,
		_goal_chunk_handlers,
		_story_page_chunk_handlers,
		_league_chunk_handlers,
		_engine_chunk_handlers,
		_town_chunk_handlers,
		_sign_chunk_handlers,
		_station_chunk_handlers,
		_company_chunk_handlers,
		_ai_chunk_handlers,
		_game_chunk_handlers,
		_animated_tile_chunk_handlers,
		_newgrf_chunk_handlers,
		_group_chunk_handlers,
		_cargopacket_chunk_handlers,
		_autoreplace_chunk_handlers,
		_labelmaps_chunk_handlers,
		_linkgraph_chunk_handlers,
		_airport_chunk_handlers,
		_object_chunk_handlers,
		_persistent_storage_chunk_handlers,
		_water_region_chunk_handlers,
		_randomizer_chunk_handlers,
	};

	static std::vector<ChunkHandlerRef> _chunk_handlers;

	if (_chunk_handlers.empty()) {
		for (auto &chunk_handler_table : _chunk_handler_tables) {
			for (auto &chunk_handler : chunk_handler_table) {
				_chunk_handlers.push_back(chunk_handler);
			}
		}
	}

	return _chunk_handlers;
}

/** Null all pointers (convert index -> nullptr) */
void SlNullPointers()
{
	_sl.action = SLA_NULL;

	/* We don't want any savegame conversion code to run
	 * during NULLing; especially those that try to get
	 * pointers from other pools. */
	_sl_version = SAVEGAME_VERSION;

	for (const ChunkHandler &ch : ChunkHandlers()) {
		DEBUG(sl, 3, "Nulling pointers for %c%c%c%c", ch.id >> 24, ch.id >> 16, ch.id >> 8, ch.id);
		ch.FixPointers();
	}

	assert(_sl.action == SLA_NULL);
}

/**
 * Read in the header descriptor of an object or an array.
 * If the highest bit is set (7), then the index is bigger than 127
 * elements, so use the next byte to read in the real value.
 * The actual value is then both bytes added with the first shifted
 * 8 bits to the left, and dropping the highest bit (which only indicated a big index).
 * x = ((x & 0x7F) << 8) + SlReadByte();
 * @return Return the value of the index
 */
static uint SlReadSimpleGamma()
{
	uint i = SlReadByte();
	if (HasBit(i, 7)) {
		i &= ~0x80;
		if (HasBit(i, 6)) {
			i &= ~0x40;
			if (HasBit(i, 5)) {
				i &= ~0x20;
				if (HasBit(i, 4)) {
					i &= ~0x10;
					if (HasBit(i, 3)) {
						SlErrorCorrupt("Unsupported gamma");
					}
					i = SlReadByte(); // 32 bits only.
				}
				i = (i << 8) | SlReadByte();
			}
			i = (i << 8) | SlReadByte();
		}
		i = (i << 8) | SlReadByte();
	}
	return i;
}

/**
 * Write the header descriptor of an object or an array.
 * If the element is bigger than 127, use 2 bytes for saving
 * and use the highest byte of the first written one as a notice
 * that the length consists of 2 bytes, etc.. like this:
 * 0xxxxxxx
 * 10xxxxxx xxxxxxxx
 * 110xxxxx xxxxxxxx xxxxxxxx
 * 1110xxxx xxxxxxxx xxxxxxxx xxxxxxxx
 * 11110--- xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx
 * We could extend the scheme ad infinum to support arbitrarily
 * large chunks, but as sizeof(size_t) == 4 is still very common
 * we don't support anything above 32 bits. That's why in the last
 * case the 3 most significant bits are unused.
 * @param i Index being written
 */

static void SlWriteSimpleGamma(size_t i)
{
	if (i >= (1 << 7)) {
		if (i >= (1 << 14)) {
			if (i >= (1 << 21)) {
				if (i >= (1 << 28)) {
					assert(i <= UINT32_MAX); // We can only support 32 bits for now.
					SlWriteByte((byte)(0xF0));
					SlWriteByte((byte)(i >> 24));
				} else {
					SlWriteByte((byte)(0xE0 | (i >> 24)));
				}
				SlWriteByte((byte)(i >> 16));
			} else {
				SlWriteByte((byte)(0xC0 | (i >> 16)));
			}
			SlWriteByte((byte)(i >> 8));
		} else {
			SlWriteByte((byte)(0x80 | (i >> 8)));
		}
	}
	SlWriteByte((byte)i);
}

/** Return how many bytes used to encode a gamma value */
static inline uint SlGetGammaLength(size_t i)
{
	return 1 + (i >= (1 << 7)) + (i >= (1 << 14)) + (i >= (1 << 21)) + (i >= (1 << 28));
}

static inline uint SlReadSparseIndex()
{
	return SlReadSimpleGamma();
}

static inline void SlWriteSparseIndex(uint index)
{
	SlWriteSimpleGamma(index);
}

static inline uint SlReadArrayLength()
{
	return SlReadSimpleGamma();
}

static inline void SlWriteArrayLength(size_t length)
{
	SlWriteSimpleGamma(length);
}

static inline uint SlGetArrayLength(size_t length)
{
	return SlGetGammaLength(length);
}

/**
 * Return the type as saved/loaded inside the savegame.
 */
static uint8_t GetSavegameFileType(const SaveLoad &sld)
{
	switch (sld.cmd) {
		case SL_VAR:
			return GetVarFileType(sld.conv); break;

		case SL_STR:
		case SL_STDSTR:
		case SL_ARR:
		case SL_VECTOR:
		case SL_RING:
			return GetVarFileType(sld.conv) | SLE_FILE_HAS_LENGTH_FIELD; break;

		case SL_REF:
			return IsSavegameVersionBefore(SLV_69) ? SLE_FILE_U16 : SLE_FILE_U32;

		case SL_REFLIST:
		case SL_REFRING:
		case SL_REFVEC:
			return (IsSavegameVersionBefore(SLV_69) ? SLE_FILE_U16 : SLE_FILE_U32) | SLE_FILE_HAS_LENGTH_FIELD;

		case SL_SAVEBYTE:
			return SLE_FILE_U8;

		case SL_STRUCT:
		case SL_STRUCTLIST:
			return SLE_FILE_STRUCT | SLE_FILE_HAS_LENGTH_FIELD;

		default: NOT_REACHED();
	}
}

/**
 * Return the size in bytes of a certain type of normal/atomic variable
 * as it appears in memory. See VarTypes
 * @param conv VarType type of variable that is used for calculating the size
 * @return Return the size of this type in bytes
 */
static inline uint SlCalcConvMemLen(VarType conv)
{
	static const byte conv_mem_size[] = {1, 1, 1, 2, 2, 4, 4, 8, 8, 0};

	switch (GetVarMemType(conv)) {
		case SLE_VAR_STRB:
		case SLE_VAR_STR:
		case SLE_VAR_STRQ:
			return SlReadArrayLength();

		default:
			uint8_t type = GetVarMemType(conv) >> 4;
			assert(type < lengthof(conv_mem_size));
			return conv_mem_size[type];
	}
}

/**
 * Return the size in bytes of a certain type of normal/atomic variable
 * as it appears in a saved game. See VarTypes
 * @param conv VarType type of variable that is used for calculating the size
 * @return Return the size of this type in bytes
 */
static inline byte SlCalcConvFileLen(VarType conv)
{
	static const byte conv_file_size[] = {0, 1, 1, 2, 2, 4, 4, 8, 8, 2};

	uint8_t type = GetVarFileType(conv);
	assert(type < lengthof(conv_file_size));
	return conv_file_size[type];
}

/** Return the size in bytes of a reference (pointer) */
static inline size_t SlCalcRefLen()
{
	return IsSavegameVersionBefore(SLV_69) ? 2 : 4;
}

void SlSetArrayIndex(uint index)
{
	_sl.need_length = NL_WANTLENGTH;
	_sl.array_index = index;
}

static size_t _next_offs;

/**
 * Iterate through the elements of an array and read the whole thing
 * @return The index of the object, or -1 if we have reached the end of current block
 */
int SlIterateArray()
{
	int index;

	/* After reading in the whole array inside the loop
	 * we must have read in all the data, so we must be at end of current block. */
	if (_next_offs != 0 && SlGetBytesRead() != _next_offs) SlErrorCorrupt("Invalid chunk size");

	for (;;) {
		uint length = SlReadArrayLength();
		if (length == 0) {
			assert(!_sl.expect_table_header);
			_next_offs = 0;
			return -1;
		}

		_sl.obj_len = --length;
		_next_offs = SlGetBytesRead() + length;

		if (_sl.expect_table_header) {
			_sl.expect_table_header = false;
			return INT32_MAX;
		}

		switch (_sl.block_mode) {
			case CH_SPARSE_TABLE:
			case CH_SPARSE_ARRAY: index = (int)SlReadSparseIndex(); break;
			case CH_TABLE:
			case CH_ARRAY:        index = _sl.array_index++; break;
			default:
				DEBUG(sl, 0, "SlIterateArray error");
				return -1; // error
		}

		if (length != 0) return index;
	}
}

/**
 * Skip an array or sparse array
 */
void SlSkipArray()
{
	while (SlIterateArray() != -1) {
		SlSkipBytes(_next_offs - SlGetBytesRead());
	}
}

/**
 * Sets the length of either a RIFF object or the number of items in an array.
 * This lets us load an object or an array of arbitrary size
 * @param length The length of the sought object/array
 */
void SlSetLength(size_t length)
{
	assert(_sl.action == SLA_SAVE);

	switch (_sl.need_length) {
		case NL_WANTLENGTH:
			_sl.need_length = NL_NONE;
			if ((_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE) && _sl.expect_table_header) {
				_sl.expect_table_header = false;
				SlWriteArrayLength(length + 1);
				break;
			}

			switch (_sl.block_mode) {
				case CH_RIFF:
					/* Ugly encoding of >16M RIFF chunks
					 * The lower 24 bits are normal
					 * The uppermost 4 bits are bits 24:27 */
					assert(length < (1 << 28));
					SlWriteUint32((uint32_t)((length & 0xFFFFFF) | ((length >> 24) << 28)));
					break;
				case CH_TABLE:
				case CH_ARRAY:
					assert(_sl.last_array_index <= _sl.array_index);
					while (++_sl.last_array_index <= _sl.array_index) {
						SlWriteArrayLength(1);
					}
					SlWriteArrayLength(length + 1);
					break;
				case CH_SPARSE_TABLE:
				case CH_SPARSE_ARRAY:
					SlWriteArrayLength(length + 1 + SlGetArrayLength(_sl.array_index)); // Also include length of sparse index.
					SlWriteSparseIndex(_sl.array_index);
					break;
				default: NOT_REACHED();
			}
			break;

		case NL_CALCLENGTH:
			_sl.obj_len += (int)length;
			break;

		default: NOT_REACHED();
	}
}

/**
 * Save/Load bytes. These do not need to be converted to Little/Big Endian
 * so directly write them or read them to/from file
 * @param ptr The source or destination of the object being manipulated
 * @param length number of bytes this fast CopyBytes lasts
 */
static void SlCopyBytes(void *ptr, size_t length)
{
	switch (_sl.action) {
		case SLA_LOAD_CHECK:
		case SLA_LOAD:
			SlCopyBytesRead(ptr, length);
			break;
		case SLA_SAVE:
			SlCopyBytesWrite(ptr, length);
			break;
		default: NOT_REACHED();
	}
}

/** Get the length of the current object */
size_t SlGetFieldLength()
{
	return _sl.obj_len;
}

/**
 * Return a signed-long version of the value of a setting
 * @param ptr pointer to the variable
 * @param conv type of variable, can be a non-clean
 * type, eg one with other flags because it is parsed
 * @return returns the value of the pointer-setting
 */
int64_t ReadValue(const void *ptr, VarType conv)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL:  return (*(const bool   *)ptr != 0);
		case SLE_VAR_I8:  return *(const int8_t  *)ptr;
		case SLE_VAR_U8:  return *(const byte    *)ptr;
		case SLE_VAR_I16: return *(const int16_t *)ptr;
		case SLE_VAR_U16: return *(const uint16_t*)ptr;
		case SLE_VAR_I32: return *(const int32_t *)ptr;
		case SLE_VAR_U32: return *(const uint32_t*)ptr;
		case SLE_VAR_I64: return *(const int64_t *)ptr;
		case SLE_VAR_U64: return *(const uint64_t*)ptr;
		case SLE_VAR_NULL:return 0;
		default: NOT_REACHED();
	}
}

/**
 * Write the value of a setting
 * @param ptr pointer to the variable
 * @param conv type of variable, can be a non-clean type, eg
 *             with other flags. It is parsed upon read
 * @param val the new value being given to the variable
 */
void WriteValue(void *ptr, VarType conv, int64_t val)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL:  *(bool    *)ptr = (val != 0);  break;
		case SLE_VAR_I8:  *(int8_t  *)ptr = val; break;
		case SLE_VAR_U8:  *(byte    *)ptr = val; break;
		case SLE_VAR_I16: *(int16_t *)ptr = val; break;
		case SLE_VAR_U16: *(uint16_t*)ptr = val; break;
		case SLE_VAR_I32: *(int32_t *)ptr = val; break;
		case SLE_VAR_U32: *(uint32_t*)ptr = val; break;
		case SLE_VAR_I64: *(int64_t *)ptr = val; break;
		case SLE_VAR_U64: *(uint64_t*)ptr = val; break;
		case SLE_VAR_NAME: *reinterpret_cast<std::string *>(ptr) = CopyFromOldName(val); break;
		case SLE_VAR_NULL: break;
		default: NOT_REACHED();
	}
}

/**
 * Handle all conversion and typechecking of variables here.
 * In the case of saving, read in the actual value from the struct
 * and then write them to file, endian safely. Loading a value
 * goes exactly the opposite way
 * @param ptr The object being filled/read
 * @param conv VarType type of the current element of the struct
 */
static void SlSaveLoadConv(void *ptr, VarType conv)
{
	switch (_sl.action) {
		case SLA_SAVE: {
			int64_t x = ReadValue(ptr, conv);

			/* Write the value to the file and check if its value is in the desired range */
			switch (GetVarFileType(conv)) {
				case SLE_FILE_I8: assert(x >= -128 && x <= 127);     SlWriteByte(x);break;
				case SLE_FILE_U8: assert(x >= 0 && x <= 255);        SlWriteByte(x);break;
				case SLE_FILE_I16:assert(x >= -32768 && x <= 32767); SlWriteUint16(x);break;
				case SLE_FILE_STRINGID:
				case SLE_FILE_U16:assert(x >= 0 && x <= 65535);      SlWriteUint16(x);break;
				case SLE_FILE_I32:
				case SLE_FILE_U32:                                   SlWriteUint32((uint32_t)x);break;
				case SLE_FILE_I64:
				case SLE_FILE_U64:                                   SlWriteUint64(x);break;
				default: NOT_REACHED();
			}
			break;
		}
		case SLA_LOAD_CHECK:
		case SLA_LOAD: {
			int64_t x;
			/* Read a value from the file */
			switch (GetVarFileType(conv)) {
				case SLE_FILE_I8:  x = (int8_t  )SlReadByte();   break;
				case SLE_FILE_U8:  x = (byte    )SlReadByte();   break;
				case SLE_FILE_I16: x = (int16_t )SlReadUint16(); break;
				case SLE_FILE_U16: x = (uint16_t)SlReadUint16(); break;
				case SLE_FILE_I32: x = (int32_t )SlReadUint32(); break;
				case SLE_FILE_U32: x = (uint32_t)SlReadUint32(); break;
				case SLE_FILE_I64: x = (int64_t )SlReadUint64(); break;
				case SLE_FILE_U64: x = (uint64_t)SlReadUint64(); break;
				case SLE_FILE_STRINGID: x = RemapOldStringID((uint16_t)SlReadUint16()); break;
				default: NOT_REACHED();
			}

			/* Write The value to the struct. These ARE endian safe. */
			WriteValue(ptr, conv, x);
			break;
		}
		case SLA_PTRS: break;
		case SLA_NULL: break;
		default: NOT_REACHED();
	}
}

/**
 * Calculate the net length of a string. This is in almost all cases
 * just strlen(), but if the string is not properly terminated, we'll
 * resort to the maximum length of the buffer.
 * @param ptr pointer to the stringbuffer
 * @param length maximum length of the string (buffer). If -1 we don't care
 * about a maximum length, but take string length as it is.
 * @return return the net length of the string
 */
static inline size_t SlCalcNetStringLen(const char *ptr, size_t length)
{
	if (ptr == nullptr) return 0;
	return std::min(strlen(ptr), length - 1);
}

/**
 * Calculate the gross length of the string that it
 * will occupy in the savegame. This includes the real length, returned
 * by SlCalcNetStringLen and the length that the index will occupy.
 * @param ptr pointer to the stringbuffer
 * @param length maximum length of the string (buffer size, etc.)
 * @param conv type of data been used
 * @return return the gross length of the string
 */
static inline size_t SlCalcStringLen(const void *ptr, size_t length, VarType conv)
{
	size_t len;
	const char *str;

	switch (GetVarMemType(conv)) {
		default: NOT_REACHED();
		case SLE_VAR_STR:
		case SLE_VAR_STRQ:
			str = *(const char * const *)ptr;
			len = SIZE_MAX;
			break;
		case SLE_VAR_STRB:
			str = (const char *)ptr;
			len = length;
			break;
	}

	len = SlCalcNetStringLen(str, len);
	return len + SlGetArrayLength(len); // also include the length of the index
}

/**
 * Calculate the gross length of the string that it
 * will occupy in the savegame. This includes the real length, returned
 * by SlCalcNetStringLen and the length that the index will occupy.
 * @param ptr Pointer to the \c std::string.
 * @return The gross length of the string.
 */
static inline size_t SlCalcStdStringLen(const void *ptr)
{
	const std::string *str = reinterpret_cast<const std::string *>(ptr);

	size_t len = str->length();
	return len + SlGetArrayLength(len); // also include the length of the index
}

/**
 * Save/Load a string.
 * @param ptr the string being manipulated
 * @param length of the string (full length)
 * @param conv must be SLE_FILE_STRING
 */
static void SlString(void *ptr, size_t length, VarType conv)
{
	switch (_sl.action) {
		case SLA_SAVE: {
			size_t len;
			switch (GetVarMemType(conv)) {
				default: NOT_REACHED();
				case SLE_VAR_STRB:
					len = SlCalcNetStringLen((char *)ptr, length);
					break;
				case SLE_VAR_STR:
				case SLE_VAR_STRQ:
					ptr = *(char **)ptr;
					len = SlCalcNetStringLen((char *)ptr, SIZE_MAX);
					break;
			}

			SlWriteArrayLength(len);
			SlCopyBytes(ptr, len);
			break;
		}
		case SLA_LOAD_CHECK:
		case SLA_LOAD: {
			size_t len = SlReadArrayLength();

			switch (GetVarMemType(conv)) {
				default: NOT_REACHED();
				case SLE_VAR_NULL:
					SlSkipBytes(len);
					return;
				case SLE_VAR_STRB:
					if (len >= length) {
						DEBUG(sl, 1, "String length in savegame is bigger than buffer, truncating");
						SlCopyBytes(ptr, length);
						SlSkipBytes(len - length);
						len = length - 1;
					} else {
						SlCopyBytes(ptr, len);
					}
					break;
				case SLE_VAR_STR:
				case SLE_VAR_STRQ: // Malloc'd string, free previous incarnation, and allocate
					free(*(char **)ptr);
					if (len == 0) {
						*(char **)ptr = nullptr;
						return;
					} else {
						*(char **)ptr = MallocT<char>(len + 1); // terminating '\0'
						ptr = *(char **)ptr;
						SlCopyBytes(ptr, len);
					}
					break;
			}

			((char *)ptr)[len] = '\0'; // properly terminate the string
			StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK;
			if ((conv & SLF_ALLOW_CONTROL) != 0) {
				settings = settings | SVS_ALLOW_CONTROL_CODE;
				if (IsSavegameVersionBefore(SLV_169)) {
					str_fix_scc_encoded((char *)ptr, (char *)ptr + len);
				}
			}
			if ((conv & SLF_ALLOW_NEWLINE) != 0) {
				settings = settings | SVS_ALLOW_NEWLINE;
			}
			StrMakeValidInPlace((char *)ptr, (char *)ptr + len, settings);
			break;
		}
		case SLA_PTRS: break;
		case SLA_NULL: break;
		default: NOT_REACHED();
	}
}

/**
 * Save/Load a \c std::string.
 * @param ptr the string being manipulated
 * @param conv must be SLE_FILE_STRING
 */
static void SlStdString(void *ptr, VarType conv)
{
	std::string *str = reinterpret_cast<std::string *>(ptr);

	switch (_sl.action) {
		case SLA_SAVE: {
			size_t len = str->length();
			SlWriteArrayLength(len);
			SlCopyBytes(const_cast<void *>(static_cast<const void *>(str->c_str())), len);
			break;
		}

		case SLA_LOAD_CHECK:
		case SLA_LOAD: {
			size_t len = SlReadArrayLength();
			if (GetVarMemType(conv) == SLE_VAR_NULL) {
				SlSkipBytes(len);
				return;
			}

			str->resize(len);
			SlCopyBytes(str->data(), len);

			StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK;
			if ((conv & SLF_ALLOW_CONTROL) != 0) {
				settings = settings | SVS_ALLOW_CONTROL_CODE;
				if (IsSavegameVersionBefore(SLV_169)) {
					char *buf = str->data();
					str->resize(str_fix_scc_encoded(buf, buf + str->size()) - buf);
				}
			}
			if ((conv & SLF_ALLOW_NEWLINE) != 0) {
				settings = settings | SVS_ALLOW_NEWLINE;
			}

			StrMakeValidInPlace(*str, settings);
		}

		case SLA_PTRS: break;
		case SLA_NULL: break;
		default: NOT_REACHED();
	}
}

/**
 * Internal function to save/Load a list of SL_VARs.
 * SlCopy() and SlArray() are very similar, with the exception of the header.
 * This function represents the common part.
 * @param object The object being manipulated.
 * @param length The length of the object in elements
 * @param conv VarType type of the items.
 */
static void SlCopyInternal(void *object, size_t length, VarType conv)
{
	if (GetVarMemType(conv) == SLE_VAR_NULL) {
		assert(_sl.action != SLA_SAVE); // Use SL_NULL if you want to write null-bytes
		SlSkipBytes(length * SlCalcConvFileLen(conv));
		return;
	}

	/* NOTICE - handle some buggy stuff, in really old versions everything was saved
	 * as a byte-type. So detect this, and adjust object size accordingly */
	if (_sl.action != SLA_SAVE && _sl_version == 0) {
		/* all objects except difficulty settings */
		if (conv == SLE_INT16 || conv == SLE_UINT16 || conv == SLE_STRINGID ||
				conv == SLE_INT32 || conv == SLE_UINT32) {
			SlCopyBytes(object, length * SlCalcConvFileLen(conv));
			return;
		}
		/* used for conversion of Money 32bit->64bit */
		if (conv == (SLE_FILE_I32 | SLE_VAR_I64)) {
			for (uint i = 0; i < length; i++) {
				((int64_t*)object)[i] = (int32_t)BSWAP32(SlReadUint32());
			}
			return;
		}
	}

	/* If the size of elements is 1 byte both in file and memory, no special
	 * conversion is needed, use specialized copy-copy function to speed up things */
	if (conv == SLE_INT8 || conv == SLE_UINT8) {
		SlCopyBytes(object, length);
	} else {
		byte *a = (byte*)object;
		byte mem_size = SlCalcConvMemLen(conv);

		for (; length != 0; length --) {
			SlSaveLoadConv(a, conv);
			a += mem_size; // get size
		}
	}
}

/**
 * Copy a list of SL_VARs to/from a savegame.
 * These entries are copied as-is, and you as caller have to make sure things
 * like length-fields are calculated correctly.
 * @param object The object being manipulated.
 * @param length The length of the object in elements
 * @param conv VarType type of the items.
 */
void SlCopy(void *object, size_t length, VarType conv)
{
	if (_sl.action == SLA_PTRS || _sl.action == SLA_NULL) return;

	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(length * SlCalcConvFileLen(conv));
		/* Determine length only? */
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	SlCopyInternal(object, length, conv);
}

/**
 * Return the size in bytes of a certain type of atomic array
 * @param length The length of the array counted in elements
 * @param conv VarType type of the variable that is used in calculating the size
 */
static inline size_t SlCalcArrayLen(size_t length, VarType conv)
{
	return SlCalcConvFileLen(conv) * length + SlGetArrayLength(length);
}

/**
 * Save/Load the length of the array followed by the array of SL_VAR elements.
 * @param array The array being manipulated
 * @param length The length of the array in elements
 * @param conv VarType type of the atomic array (int, byte, uint64_t, etc.)
 */
static void SlArray(void *array, size_t length, VarType conv)
{
	switch (_sl.action) {
		case SLA_SAVE:
			SlWriteArrayLength(length);
			SlCopyInternal(array, length, conv);
			return;

		case SLA_LOAD_CHECK:
		case SLA_LOAD: {
			if (!IsSavegameVersionBefore(SLV_SAVELOAD_LIST_LENGTH)) {
				size_t sv_length = SlReadArrayLength();
				if (GetVarMemType(conv) == SLE_VAR_NULL) {
					/* We don't know this field, so we assume the length in the savegame is correct. */
					length = sv_length;
				} else if (sv_length != length) {
					/* If the SLE_ARR changes size, a savegame bump is required
					 * and the developer should have written conversion lines.
					 * Error out to make this more visible. */
					SlErrorCorrupt("Fixed-length array is of wrong length");
				}
			}

			SlCopyInternal(array, length, conv);
			return;
		}

		case SLA_PTRS:
		case SLA_NULL:
			return;

		default:
			NOT_REACHED();
	}
}

/**
 * Pointers cannot be saved to a savegame, so this functions gets
 * the index of the item, and if not available, it hussles with
 * pointers (looks really bad :()
 * Remember that a nullptr item has value 0, and all
 * indices have +1, so vehicle 0 is saved as index 1.
 * @param obj The object that we want to get the index of
 * @param rt SLRefType type of the object the index is being sought of
 * @return Return the pointer converted to an index of the type pointed to
 */
static size_t ReferenceToInt(const void *obj, SLRefType rt)
{
	assert(_sl.action == SLA_SAVE);

	if (obj == nullptr) return 0;

	switch (rt) {
		case REF_VEHICLE_OLD: // Old vehicles we save as new ones
		case REF_VEHICLE:   return ((const  Vehicle*)obj)->index + 1;
		case REF_STATION:   return ((const  Station*)obj)->index + 1;
		case REF_TOWN:      return ((const     Town*)obj)->index + 1;
		case REF_ORDER:     return ((const    Order*)obj)->index + 1;
		case REF_ROADSTOPS: return ((const RoadStop*)obj)->index + 1;
		case REF_ENGINE_RENEWS:  return ((const       EngineRenew*)obj)->index + 1;
		case REF_CARGO_PACKET:   return ((const       CargoPacket*)obj)->index + 1;
		case REF_ORDERLIST:      return ((const         OrderList*)obj)->index + 1;
		case REF_STORAGE:        return ((const PersistentStorage*)obj)->index + 1;
		case REF_LINK_GRAPH:     return ((const         LinkGraph*)obj)->index + 1;
		case REF_LINK_GRAPH_JOB: return ((const      LinkGraphJob*)obj)->index + 1;
		default: NOT_REACHED();
	}
}

/**
 * Pointers cannot be loaded from a savegame, so this function
 * gets the index from the savegame and returns the appropriate
 * pointer from the already loaded base.
 * Remember that an index of 0 is a nullptr pointer so all indices
 * are +1 so vehicle 0 is saved as 1.
 * @param index The index that is being converted to a pointer
 * @param rt SLRefType type of the object the pointer is sought of
 * @return Return the index converted to a pointer of any type
 */
static void *IntToReference(size_t index, SLRefType rt)
{
	static_assert(sizeof(size_t) <= sizeof(void *));

	assert(_sl.action == SLA_PTRS);

	/* After version 4.3 REF_VEHICLE_OLD is saved as REF_VEHICLE,
	 * and should be loaded like that */
	if (rt == REF_VEHICLE_OLD && !IsSavegameVersionBefore(SLV_4, 4)) {
		rt = REF_VEHICLE;
	}

	/* No need to look up nullptr pointers, just return immediately */
	if (index == (rt == REF_VEHICLE_OLD ? 0xFFFF : 0)) return nullptr;

	/* Correct index. Old vehicles were saved differently:
	 * invalid vehicle was 0xFFFF, now we use 0x0000 for everything invalid. */
	if (rt != REF_VEHICLE_OLD) index--;

	switch (rt) {
		case REF_ORDERLIST:
			if (OrderList::IsValidID(index)) return OrderList::Get(index);
			SlErrorCorrupt("Referencing invalid OrderList");

		case REF_ORDER:
			if (Order::IsValidID(index)) return Order::Get(index);
			/* in old versions, invalid order was used to mark end of order list */
			if (IsSavegameVersionBefore(SLV_5, 2)) return nullptr;
			SlErrorCorrupt("Referencing invalid Order");

		case REF_VEHICLE_OLD:
		case REF_VEHICLE:
			if (Vehicle::IsValidID(index)) return Vehicle::Get(index);
			SlErrorCorrupt("Referencing invalid Vehicle");

		case REF_STATION:
			if (Station::IsValidID(index)) return Station::Get(index);
			SlErrorCorrupt("Referencing invalid Station");

		case REF_TOWN:
			if (Town::IsValidID(index)) return Town::Get(index);
			SlErrorCorrupt("Referencing invalid Town");

		case REF_ROADSTOPS:
			if (RoadStop::IsValidID(index)) return RoadStop::Get(index);
			SlErrorCorrupt("Referencing invalid RoadStop");

		case REF_ENGINE_RENEWS:
			if (EngineRenew::IsValidID(index)) return EngineRenew::Get(index);
			SlErrorCorrupt("Referencing invalid EngineRenew");

		case REF_CARGO_PACKET:
			if (CargoPacket::IsValidID(index)) return CargoPacket::Get(index);
			SlErrorCorrupt("Referencing invalid CargoPacket");

		case REF_STORAGE:
			if (PersistentStorage::IsValidID(index)) return PersistentStorage::Get(index);
			SlErrorCorrupt("Referencing invalid PersistentStorage");

		case REF_LINK_GRAPH:
			if (LinkGraph::IsValidID(index)) return LinkGraph::Get(index);
			SlErrorCorrupt("Referencing invalid LinkGraph");

		case REF_LINK_GRAPH_JOB:
			if (LinkGraphJob::IsValidID(index)) return LinkGraphJob::Get(index);
			SlErrorCorrupt("Referencing invalid LinkGraphJob");

		default: NOT_REACHED();
	}
}

/**
 * Handle conversion for references.
 * @param ptr The object being filled/read.
 * @param conv VarType type of the current element of the struct.
 */
void SlSaveLoadRef(void *ptr, VarType conv)
{
	switch (_sl.action) {
		case SLA_SAVE:
			SlWriteUint32((uint32_t)ReferenceToInt(*(void **)ptr, (SLRefType)conv));
			break;
		case SLA_LOAD_CHECK:
		case SLA_LOAD:
			*(size_t *)ptr = IsSavegameVersionBefore(SLV_69) ? SlReadUint16() : SlReadUint32();
			break;
		case SLA_PTRS:
			*(void **)ptr = IntToReference(*(size_t *)ptr, (SLRefType)conv);
			break;
		case SLA_NULL:
			*(void **)ptr = nullptr;
			break;
		default: NOT_REACHED();
	}
}

template <typename T, typename U>
using ring_buffer_sl = ring_buffer<T>;

/**
 * Template class to help with list-like types.
 */
template <template<typename, typename> typename Tstorage, typename Tvar, typename Tallocator = std::allocator<Tvar>>
class SlStorageHelper {
	typedef Tstorage<Tvar, Tallocator> SlStorageT;
public:
	/**
	 * Internal templated helper to return the size in bytes of a list-like type.
	 * @param storage The storage to find the size of
	 * @param conv VarType type of variable that is used for calculating the size
	 * @param cmd The SaveLoadType ware are saving/loading.
	 */
	static size_t SlCalcLen(const void *storage, VarType conv, SaveLoadType cmd = SL_VAR)
	{
		assert(cmd == SL_VAR || cmd == SL_REF);

		const SlStorageT *list = static_cast<const SlStorageT *>(storage);

		int type_size = SlGetArrayLength(list->size());
		int item_size = SlCalcConvFileLen(cmd == SL_VAR ? conv : (VarType)SLE_FILE_U32);
		return list->size() * item_size + type_size;
	}

	static void SlSaveLoadMember(SaveLoadType cmd, Tvar *item, VarType conv)
	{
		switch (cmd) {
			case SL_VAR: SlSaveLoadConv(item, conv); break;
			case SL_REF: SlSaveLoadRef(item, conv); break;
			default:
				NOT_REACHED();
		}
	}

	/**
	 * Internal templated helper to save/load a list-like type.
	 * @param storage The storage being manipulated.
	 * @param conv VarType type of variable that is used for calculating the size.
	 * @param cmd The SaveLoadType ware are saving/loading.
	 */
	static void SlSaveLoad(void *storage, VarType conv, SaveLoadType cmd = SL_VAR)
	{
		assert(cmd == SL_VAR || cmd == SL_REF);

		SlStorageT *list = static_cast<SlStorageT *>(storage);

		switch (_sl.action) {
			case SLA_SAVE:
				SlWriteArrayLength(list->size());

				for (auto &item : *list) {
					SlSaveLoadMember(cmd, &item, conv);
				}
				break;

			case SLA_LOAD_CHECK:
			case SLA_LOAD: {
				size_t length;
				switch (cmd) {
					case SL_VAR: length = IsSavegameVersionBefore(SLV_SAVELOAD_LIST_LENGTH) ? SlReadUint32() : SlReadArrayLength(); break;
					case SL_REF: length = IsSavegameVersionBefore(SLV_69) ? SlReadUint16() : IsSavegameVersionBefore(SLV_SAVELOAD_LIST_LENGTH) ? SlReadUint32() : SlReadArrayLength(); break;
					default: NOT_REACHED();
				}

				/* Load each value and push to the end of the storage. */
				for (size_t i = 0; i < length; i++) {
					Tvar &data = list->emplace_back();
					SlSaveLoadMember(cmd, &data, conv);
				}
				break;
			}

			case SLA_PTRS:
				for (auto &item : *list) {
					SlSaveLoadMember(cmd, &item, conv);
				}
				break;

			case SLA_NULL:
				list->clear();
				break;

			default: NOT_REACHED();
		}
	}
};

/**
 * Return the size in bytes of a list.
 * @param list The std::list to find the size of.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static inline size_t SlCalcRefListLen(const void *list, VarType conv)
{
	return SlStorageHelper<std::list, void *>::SlCalcLen(list, conv, SL_REF);
}

/**
 * Return the size in bytes of a ring buffer.
 * @param list The ring buffer to find the size of.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static inline size_t SlCalcRefRingLen(const void *list, VarType conv)
{
	return SlStorageHelper<ring_buffer_sl, void *>::SlCalcLen(list, conv, SL_REF);
}

/**
 * Return the size in bytes of a vector.
 * @param list The std::vector to find the size of.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static inline size_t SlCalcRefVectorLen(const void *list, VarType conv)
{
	return SlStorageHelper<std::vector, void *>::SlCalcLen(list, conv, SL_REF);
}

/**
 * Save/Load a list.
 * @param list The list being manipulated.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static void SlRefList(void *list, VarType conv)
{
	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(SlCalcRefListLen(list, conv));
		/* Determine length only? */
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	SlStorageHelper<std::list, void *>::SlSaveLoad(list, conv, SL_REF);
}

/**
 * Save/Load a ring buffer.
 * @param list The list being manipulated.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static void SlRefRing(void *list, VarType conv)
{
	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(SlCalcRefRingLen(list, conv));
		/* Determine length only? */
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	SlStorageHelper<ring_buffer_sl, void *>::SlSaveLoad(list, conv, SL_REF);
}

/**
 * Save/Load a vector.
 * @param list The list being manipulated.
 * @param conv VarType type of variable that is used for calculating the size.
 */
static void SlRefVector(void *list, VarType conv)
{
	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(SlCalcRefVectorLen(list, conv));
		/* Determine length only? */
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	SlStorageHelper<std::vector, void *>::SlSaveLoad(list, conv, SL_REF);
}

/**
 * Return the size in bytes of a ring buffer.
 * @param ring The ring buffer to find the size of
 * @param conv VarType type of variable that is used for calculating the size
 */
static inline size_t SlCalcRingLen(const void *ring, VarType conv)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL: return SlStorageHelper<ring_buffer_sl, bool>::SlCalcLen(ring, conv);
		case SLE_VAR_I8: return SlStorageHelper<ring_buffer_sl, int8_t>::SlCalcLen(ring, conv);
		case SLE_VAR_U8: return SlStorageHelper<ring_buffer_sl, uint8_t>::SlCalcLen(ring, conv);
		case SLE_VAR_I16: return SlStorageHelper<ring_buffer_sl, int16_t>::SlCalcLen(ring, conv);
		case SLE_VAR_U16: return SlStorageHelper<ring_buffer_sl, uint16_t>::SlCalcLen(ring, conv);
		case SLE_VAR_I32: return SlStorageHelper<ring_buffer_sl, int32_t>::SlCalcLen(ring, conv);
		case SLE_VAR_U32: return SlStorageHelper<ring_buffer_sl, uint32_t>::SlCalcLen(ring, conv);
		case SLE_VAR_I64: return SlStorageHelper<ring_buffer_sl, int64_t>::SlCalcLen(ring, conv);
		case SLE_VAR_U64: return SlStorageHelper<ring_buffer_sl, uint64_t>::SlCalcLen(ring, conv);
		default: NOT_REACHED();
	}
}

/**
 * Save/load a ring buffer.
 * @param ring The ring buffer being manipulated
 * @param conv VarType type of variable that is used for calculating the size
 */
static void SlRing(void *ring, VarType conv)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL: SlStorageHelper<ring_buffer_sl, bool>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_I8: SlStorageHelper<ring_buffer_sl, int8_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_U8: SlStorageHelper<ring_buffer_sl, uint8_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_I16: SlStorageHelper<ring_buffer_sl, int16_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_U16: SlStorageHelper<ring_buffer_sl, uint16_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_I32: SlStorageHelper<ring_buffer_sl, int32_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_U32: SlStorageHelper<ring_buffer_sl, uint32_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_I64: SlStorageHelper<ring_buffer_sl, int64_t>::SlSaveLoad(ring, conv); break;
		case SLE_VAR_U64: SlStorageHelper<ring_buffer_sl, uint64_t>::SlSaveLoad(ring, conv); break;
		default: NOT_REACHED();
	}
}

/**
 * Return the size in bytes of a std::vector.
 * @param vector The std::vector to find the size of
 * @param conv VarType type of variable that is used for calculating the size
 */
static inline size_t SlCalcVectorLen(const void *vector, VarType conv)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL: NOT_REACHED(); // Not supported
		case SLE_VAR_I8: return SlStorageHelper<std::vector, int8_t>::SlCalcLen(vector, conv);
		case SLE_VAR_U8: return SlStorageHelper<std::vector, uint8_t>::SlCalcLen(vector, conv);
		case SLE_VAR_I16: return SlStorageHelper<std::vector, int16_t>::SlCalcLen(vector, conv);
		case SLE_VAR_U16: return SlStorageHelper<std::vector, uint16_t>::SlCalcLen(vector, conv);
		case SLE_VAR_I32: return SlStorageHelper<std::vector, int32_t>::SlCalcLen(vector, conv);
		case SLE_VAR_U32: return SlStorageHelper<std::vector, uint32_t>::SlCalcLen(vector, conv);
		case SLE_VAR_I64: return SlStorageHelper<std::vector, int64_t>::SlCalcLen(vector, conv);
		case SLE_VAR_U64: return SlStorageHelper<std::vector, uint64_t>::SlCalcLen(vector, conv);
		default: NOT_REACHED();
	}
}

/**
 * Save/load a std::vector.
 * @param vector The std::vector being manipulated
 * @param conv VarType type of variable that is used for calculating the size
 */
static void SlVector(void *vector, VarType conv)
{
	switch (GetVarMemType(conv)) {
		case SLE_VAR_BL: NOT_REACHED(); // Not supported
		case SLE_VAR_I8: SlStorageHelper<std::vector, int8_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_U8: SlStorageHelper<std::vector, uint8_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_I16: SlStorageHelper<std::vector, int16_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_U16: SlStorageHelper<std::vector, uint16_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_I32: SlStorageHelper<std::vector, int32_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_U32: SlStorageHelper<std::vector, uint32_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_I64: SlStorageHelper<std::vector, int64_t>::SlSaveLoad(vector, conv); break;
		case SLE_VAR_U64: SlStorageHelper<std::vector, uint64_t>::SlSaveLoad(vector, conv); break;
		default: NOT_REACHED();
	}
}

/** Are we going to save this object or not? */
static inline bool SlIsObjectValidInSavegame(const SaveLoad &sld)
{
	return (_sl_version >= sld.version_from && _sl_version < sld.version_to);
}

/**
 * Calculate the size of the table header.
 * @param slt The SaveLoad table with objects to save/load.
 * @return size of given object.
 */
static size_t SlCalcTableHeader(const SaveLoadTable &slt)
{
	size_t length = 0;

	for (auto &sld : slt) {
		if (!SlIsObjectValidInSavegame(sld)) continue;

		length += SlCalcConvFileLen(SLE_UINT8);
		length += SlCalcStdStringLen(&sld.name);
	}

	length += SlCalcConvFileLen(SLE_UINT8); // End-of-list entry.

	for (auto &sld : slt) {
		if (!SlIsObjectValidInSavegame(sld)) continue;
		if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
			length += SlCalcTableHeader(sld.handler->GetDescription());
		}
	}

	return length;
}

/**
 * Calculate the size of an object.
 * @param object to be measured.
 * @param slt The SaveLoad table with objects to save/load.
 * @return size of given object.
 */
size_t SlCalcObjLength(const void *object, const SaveLoadTable &slt)
{
	size_t length = 0;

	/* Need to determine the length and write a length tag. */
	for (auto &sld : slt) {
		length += SlCalcObjMemberLength(object, sld);
	}
	return length;
}

size_t SlCalcObjMemberLength(const void *object, const SaveLoad &sld)
{
	assert(_sl.action == SLA_SAVE);

	if (!SlIsObjectValidInSavegame(sld)) return 0;

	switch (sld.cmd) {
		case SL_VAR: return SlCalcConvFileLen(sld.conv);
		case SL_REF: return SlCalcRefLen();
		case SL_ARR: return SlCalcArrayLen(sld.length, sld.conv);
		case SL_STR: return SlCalcStringLen(GetVariableAddress(object, sld), sld.length, sld.conv);
		case SL_REFLIST: return SlCalcRefListLen(GetVariableAddress(object, sld), sld.conv);
		case SL_REFRING: return SlCalcRefRingLen(GetVariableAddress(object, sld), sld.conv);
		case SL_REFVEC: return SlCalcRefVectorLen(GetVariableAddress(object, sld), sld.conv);
		case SL_RING: return SlCalcRingLen(GetVariableAddress(object, sld), sld.conv);
		case SL_VECTOR: return SlCalcVectorLen(GetVariableAddress(object, sld), sld.conv);
		case SL_STDSTR: return SlCalcStdStringLen(GetVariableAddress(object, sld));
		case SL_SAVEBYTE: return 1; // a byte is logically of size 1
		case SL_NULL: return SlCalcConvFileLen(sld.conv) * sld.length;

		case SL_STRUCT:
		case SL_STRUCTLIST: {
			NeedLength old_need_length = _sl.need_length;
			size_t old_obj_len = _sl.obj_len;

			_sl.need_length = NL_CALCLENGTH;
			_sl.obj_len = 0;

			/* Pretend that we are saving to collect the object size. Other
			 * means are difficult, as we don't know the length of the list we
			 * are about to store. */
			sld.handler->Save(const_cast<void *>(object));
			size_t length = _sl.obj_len;

			_sl.obj_len = old_obj_len;
			_sl.need_length = old_need_length;

			if (sld.cmd == SL_STRUCT) {
				length += SlGetArrayLength(1);
			}

			return length;
		}

		default: NOT_REACHED();
	}
	return 0;
}

static bool SlObjectMember(void *object, const SaveLoad &sld)
{
	if (!SlIsObjectValidInSavegame(sld)) return false;

	VarType conv = GB(sld.conv, 0, 8);
	switch (sld.cmd) {
		case SL_VAR:
		case SL_REF:
		case SL_ARR:
		case SL_STR:
		case SL_REFLIST:
		case SL_REFRING:
		case SL_REFVEC:
		case SL_RING:
		case SL_VECTOR:
		case SL_STDSTR: {
			void *ptr = GetVariableAddress(object, sld);

			switch (sld.cmd) {
				case SL_VAR: SlSaveLoadConv(ptr, conv); break;
				case SL_REF: SlSaveLoadRef(ptr, conv); break;
				case SL_ARR: SlArray(ptr, sld.length, conv); break;
				case SL_STR: SlString(ptr, sld.length, sld.conv); break;
				case SL_REFLIST: SlRefList(ptr, conv); break;
				case SL_REFRING: SlRefRing(ptr, conv); break;
				case SL_REFVEC: SlRefVector(ptr, conv); break;
				case SL_RING: SlRing(ptr, conv); break;
				case SL_VECTOR: SlVector(ptr, conv); break;
				case SL_STDSTR: SlStdString(ptr, sld.conv); break;
				default: NOT_REACHED();
			}
			break;
		}

		/* SL_SAVEBYTE writes a value to the savegame to identify the type of an object.
		 * When loading, the value is read explicitly with SlReadByte() to determine which
		 * object description to use. */
		case SL_SAVEBYTE: {
			void *ptr = GetVariableAddress(object, sld);

			switch (_sl.action) {
				case SLA_SAVE: SlWriteByte(*(uint8_t *)ptr); break;
				case SLA_LOAD_CHECK:
				case SLA_LOAD:
				case SLA_PTRS:
				case SLA_NULL: break;
				default: NOT_REACHED();
			}
			break;
		}

		case SL_NULL: {
			assert(GetVarMemType(sld.conv) == SLE_VAR_NULL);

			switch (_sl.action) {
				case SLA_LOAD_CHECK:
				case SLA_LOAD: SlSkipBytes(SlCalcConvFileLen(sld.conv) * sld.length); break;
				case SLA_SAVE: for (int i = 0; i < SlCalcConvFileLen(sld.conv) * sld.length; i++) SlWriteByte(0); break;
				case SLA_PTRS:
				case SLA_NULL: break;
				default: NOT_REACHED();
			}
			break;
		}

		case SL_STRUCT:
		case SL_STRUCTLIST:
			switch (_sl.action) {
				case SLA_SAVE: {
					if (sld.cmd == SL_STRUCT) {
						/* Store in the savegame if this struct was written or not. */
						SlSetStructListLength(SlCalcObjMemberLength(object, sld) > SlGetArrayLength(1) ? 1 : 0);
					}
					sld.handler->Save(object);
					break;
				}

				case SLA_LOAD_CHECK: {
					if (sld.cmd == SL_STRUCT && !IsSavegameVersionBefore(SLV_SAVELOAD_LIST_LENGTH)) {
						SlGetStructListLength(1);
					}
					sld.handler->LoadCheck(object);
					break;
				}

				case SLA_LOAD: {
					if (sld.cmd == SL_STRUCT && !IsSavegameVersionBefore(SLV_SAVELOAD_LIST_LENGTH)) {
						SlGetStructListLength(1);
					}
					sld.handler->Load(object);
					break;
				}

				case SLA_PTRS:
					sld.handler->FixPointers(object);
					break;

				case SLA_NULL: break;
				default: NOT_REACHED();
			}
			break;

		default: NOT_REACHED();
	}
	return true;
}

/**
 * Set the length of this list.
 * @param The length of the list.
 */
void SlSetStructListLength(size_t length)
{
	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(SlGetArrayLength(length));
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	SlWriteArrayLength(length);
}

/**
 * Get the length of this list; if it exceeds the limit, error out.
 * @param limit The maximum size the list can be.
 * @return The length of the list.
 */
size_t SlGetStructListLength(size_t limit)
{
	size_t length = SlReadArrayLength();
	if (length > limit) SlErrorCorrupt("List exceeds storage size");

	return length;
}

/**
 * Main SaveLoad function.
 * @param object The object that is being saved or loaded.
 * @param slt The SaveLoad table with objects to save/load.
 */
void SlObject(void *object, const SaveLoadTable &slt)
{
	/* Automatically calculate the length? */
	if (_sl.need_length != NL_NONE) {
		SlSetLength(SlCalcObjLength(object, slt));
		if (_sl.need_length == NL_CALCLENGTH) return;
	}

	for (auto &sld : slt) {
		SlObjectMember(object, sld);
	}
}

/**
 * Handler that is assigned when there is a struct read in the savegame which
 * is not known to the code. This means we are going to skip it.
 */
class SlSkipHandler : public SaveLoadHandler {
	void Save(void *) const override
	{
		NOT_REACHED();
	}

	void Load(void *object) const override
	{
		size_t length = SlGetStructListLength(UINT32_MAX);
		for (; length > 0; length--) {
			SlObject(object, this->GetLoadDescription());
		}
	}

	void LoadCheck(void *object) const override
	{
		this->Load(object);
	}

	virtual SaveLoadTable GetDescription() const override
	{
		return {};
	}

	virtual SaveLoadCompatTable GetCompatDescription() const override
	{
		NOT_REACHED();
	}
};

/**
 * Save or Load a table header.
 * @note a table-header can never contain more than 65535 fields.
 * @param slt The SaveLoad table with objects to save/load.
 * @return When loading, the ordered SaveLoad array to use; otherwise an empty list.
 */
std::vector<SaveLoad> SlTableHeader(const SaveLoadTable &slt)
{
	/* You can only use SlTableHeader if you are a CH_TABLE. */
	assert(_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE);

	switch (_sl.action) {
		case SLA_LOAD_CHECK:
		case SLA_LOAD: {
			std::vector<SaveLoad> saveloads;

			/* Build a key lookup mapping based on the available fields. */
			std::map<std::string, const SaveLoad *> key_lookup;
			for (auto &sld : slt) {
				if (!SlIsObjectValidInSavegame(sld)) continue;

				/* Check that there is only one active SaveLoad for a given name. */
				assert(key_lookup.find(sld.name) == key_lookup.end());
				key_lookup[sld.name] = &sld;
			}

			while (true) {
				uint8_t type = 0;
				SlSaveLoadConv(&type, SLE_UINT8);
				if (type == SLE_FILE_END) break;

				std::string key;
				SlStdString(&key, SLE_STR);

				auto sld_it = key_lookup.find(key);
				if (sld_it == key_lookup.end()) {
					/* SLA_LOADCHECK triggers this debug statement a lot and is perfectly normal. */
					DEBUG(sl, _sl.action == SLA_LOAD ? 2 : 6, "Field '%s' of type 0x%02X not found, skipping", key.c_str(), type);

					std::shared_ptr<SaveLoadHandler> handler = nullptr;
					SaveLoadType saveload_type;
					switch (type & SLE_FILE_TYPE_MASK) {
						case SLE_FILE_STRING:
							/* Strings are always marked with SLE_FILE_HAS_LENGTH_FIELD, as they are a list of chars. */
							saveload_type = SL_STR;
							break;

						case SLE_FILE_STRUCT:
							/* Structs are always marked with SLE_FILE_HAS_LENGTH_FIELD as SL_STRUCT is seen as a list of 0/1 in length. */
							saveload_type = SL_STRUCTLIST;
							handler = std::make_shared<SlSkipHandler>();
							break;

						default:
							saveload_type = (type & SLE_FILE_HAS_LENGTH_FIELD) ? SL_ARR : SL_VAR;
							break;
					}

					/* We don't know this field, so read to nothing. */
					saveloads.push_back({key, saveload_type, ((VarType)type & SLE_FILE_TYPE_MASK) | SLE_VAR_NULL, 1, SL_MIN_VERSION, SL_MAX_VERSION, 0, nullptr, 0, handler});
					continue;
				}

				/* Validate the type of the field. If it is changed, the
				 * savegame should have been bumped so we know how to do the
				 * conversion. If this error triggers, that clearly didn't
				 * happen and this is a friendly poke to the developer to bump
				 * the savegame version and add conversion code. */
				uint8_t correct_type = GetSavegameFileType(*sld_it->second);
				if (correct_type != type) {
					DEBUG(sl, 1, "Field type for '%s' was expected to be 0x%02X but 0x%02X was found", key.c_str(), correct_type, type);
					SlErrorCorrupt("Field type is different than expected");
				}
				saveloads.push_back(*sld_it->second);
			}

			for (auto &sld : saveloads) {
				if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
					sld.handler->load_description = SlTableHeader(sld.handler->GetDescription());
				}
			}

			return saveloads;
		}

		case SLA_SAVE: {
			/* Automatically calculate the length? */
			if (_sl.need_length != NL_NONE) {
				SlSetLength(SlCalcTableHeader(slt));
				if (_sl.need_length == NL_CALCLENGTH) break;
			}

			for (auto &sld : slt) {
				if (!SlIsObjectValidInSavegame(sld)) continue;
				/* Make sure we are not storing empty keys. */
				assert(!sld.name.empty());

				uint8_t type = GetSavegameFileType(sld);
				assert(type != SLE_FILE_END);

				SlSaveLoadConv(&type, SLE_UINT8);
				SlStdString(const_cast<std::string *>(&sld.name), SLE_STR);
			}

			/* Add an end-of-header marker. */
			uint8_t type = SLE_FILE_END;
			SlSaveLoadConv(&type, SLE_UINT8);

			/* After the table, write down any sub-tables we might have. */
			for (auto &sld : slt) {
				if (!SlIsObjectValidInSavegame(sld)) continue;
				if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
					/* SlCalcTableHeader already looks in sub-lists, so avoid the length being added twice. */
					NeedLength old_need_length = _sl.need_length;
					_sl.need_length = NL_NONE;

					SlTableHeader(sld.handler->GetDescription());

					_sl.need_length = old_need_length;
				}
			}

			break;
		}

		default: NOT_REACHED();
	}

	return std::vector<SaveLoad>();
}

/**
 * Load a table header in a savegame compatible way. If the savegame was made
 * before table headers were added, it will fall back to the
 * SaveLoadCompatTable for the order of fields while loading.
 *
 * @note You only have to call this function if the chunk existed as a
 * non-table type before converting it to a table. New chunks created as
 * table can call SlTableHeader() directly.
 *
 * @param slt The SaveLoad table with objects to save/load.
 * @param slct The SaveLoadCompat table the original order of the fields.
 * @return When loading, the ordered SaveLoad array to use; otherwise an empty list.
 */
std::vector<SaveLoad> SlCompatTableHeader(const SaveLoadTable &slt, const SaveLoadCompatTable &slct)
{
	assert(_sl.action == SLA_LOAD || _sl.action == SLA_LOAD_CHECK);
	/* CH_TABLE / CH_SPARSE_TABLE always have a header. */
	if (_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE) return SlTableHeader(slt);

	std::vector<SaveLoad> saveloads;

	/* Build a key lookup mapping based on the available fields. */
	std::map<std::string, std::vector<const SaveLoad *>> key_lookup;
	for (auto &sld : slt) {
		/* All entries should have a name; otherwise the entry should just be removed. */
		assert(!sld.name.empty());

		key_lookup[sld.name].push_back(&sld);
	}

	for (auto &slc : slct) {
		if (slc.name.empty()) {
			/* In old savegames there can be data we no longer care for. We
			 * skip this by simply reading the amount of bytes indicated and
			 * send those to /dev/null. */
			saveloads.push_back({"", SL_NULL, SLE_FILE_U8 | SLE_VAR_NULL, slc.length, slc.version_from, slc.version_to, 0, nullptr, 0, nullptr});
		} else {
			auto sld_it = key_lookup.find(slc.name);
			/* If this branch triggers, it means that an entry in the
			 * SaveLoadCompat list is not mentioned in the SaveLoad list. Did
			 * you rename a field in one and not in the other? */
			if (sld_it == key_lookup.end()) {
				/* This isn't an assert, as that leaves no information what
				 * field was to blame. This way at least we have breadcrumbs. */
				DEBUG(sl, 0, "internal error: saveload compatibility field '%s' not found", slc.name.c_str());
				SlErrorCorrupt("Internal error with savegame compatibility");
			}
			for (auto &sld : sld_it->second) {
				saveloads.push_back(*sld);
			}
		}
	}

	for (auto &sld : saveloads) {
		if (!SlIsObjectValidInSavegame(sld)) continue;
		if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
			sld.handler->load_description = SlCompatTableHeader(sld.handler->GetDescription(), sld.handler->GetCompatDescription());
		}
	}

	return saveloads;
}

/**
 * Save or Load (a list of) global variables.
 * @param slt The SaveLoad table with objects to save/load.
 */
void SlGlobList(const SaveLoadTable &slt)
{
	SlObject(nullptr, slt);
}

/**
 * Do something of which I have no idea what it is :P
 * @param proc The callback procedure that is called
 * @param arg The variable that will be used for the callback procedure
 */
void SlAutolength(AutolengthProc *proc, void *arg)
{
	assert(_sl.action == SLA_SAVE);
	assert(_sl.need_length == NL_WANTLENGTH);

	_sl.need_length = NL_NONE;
	uint8_t state = SlSaveToTempBufferSetup();
	proc(arg);
	std::span<byte> result = SlSaveToTempBufferRestore(state);
	_sl.need_length = NL_WANTLENGTH;
	SlSetLength(result.size());
	SlCopyBytesWrite(result.data(), result.size());
}

void ChunkHandler::LoadCheck(size_t len) const
{
	switch (_sl.block_mode) {
		case CH_TABLE:
		case CH_SPARSE_TABLE:
			SlTableHeader({});
			[[fallthrough]];
		case CH_ARRAY:
		case CH_SPARSE_ARRAY:
			SlSkipArray();
			break;
		case CH_RIFF:
			SlSkipBytes(len);
			break;
		default:
			NOT_REACHED();
	}
}

/**
 * Load a chunk of data (eg vehicles, stations, etc.)
 * @param ch The chunkhandler that will be used for the operation
 */
static void SlLoadChunk(const ChunkHandler &ch)
{
	byte m = SlReadByte();
	size_t len;
	size_t endoffs;

	_sl.block_mode = m & CH_TYPE_MASK;
	_sl.obj_len = 0;
	_sl.expect_table_header = (_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE);

	/* The header should always be at the start. Read the length; the
	 * Load() should as first action process the header. */
	if (_sl.expect_table_header) {
		SlIterateArray();
	}

	switch (_sl.block_mode) {
		case CH_TABLE:
		case CH_ARRAY:
			_sl.array_index = 0;
			ch.Load();
			if (_next_offs != 0) SlErrorCorrupt("Invalid array length");
			break;
		case CH_SPARSE_TABLE:
		case CH_SPARSE_ARRAY:
			ch.Load();
			if (_next_offs != 0) SlErrorCorrupt("Invalid array length");
			break;
		case CH_RIFF:
			/* Read length */
			len = (SlReadByte() << 16) | ((m >> 4) << 24);
			len += SlReadUint16();
			_sl.obj_len = len;
			endoffs = SlGetBytesRead() + len;
			ch.Load();
			if (SlGetBytesRead() != endoffs) SlErrorCorrupt("Invalid chunk size");
			break;
		default:
			SlErrorCorrupt("Invalid chunk type");
			break;
	}

	if (_sl.expect_table_header) SlErrorCorrupt("Table chunk without header");
}

/**
 * Load a chunk of data for checking savegames.
 * If the chunkhandler is nullptr, the chunk is skipped.
 * @param ch The chunkhandler that will be used for the operation
 */
static void SlLoadCheckChunk(const ChunkHandler &ch)
{
	byte m = SlReadByte();
	size_t len;
	size_t endoffs;

	_sl.block_mode = m & CH_TYPE_MASK;
	_sl.obj_len = 0;
	_sl.expect_table_header = (_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE);

	/* The header should always be at the start. Read the length; the
	 * LoadCheck() should as first action process the header. */
	if (_sl.expect_table_header) {
		SlIterateArray();
	}

	switch (_sl.block_mode) {
		case CH_TABLE:
		case CH_ARRAY:
			_sl.array_index = 0;
			ch.LoadCheck();
			break;
		case CH_SPARSE_TABLE:
		case CH_SPARSE_ARRAY:
			ch.LoadCheck();
			break;
		case CH_RIFF:
			/* Read length */
			len = (SlReadByte() << 16) | ((m >> 4) << 24);
			len += SlReadUint16();
			_sl.obj_len = len;
			endoffs = SlGetBytesRead() + len;
			ch.LoadCheck(len);
			if (SlGetBytesRead() != endoffs) SlErrorCorrupt("Invalid chunk size");
			break;
		default:
			SlErrorCorrupt("Invalid chunk type");
			break;
	}

	if (_sl.expect_table_header) SlErrorCorrupt("Table chunk without header");
}

/**
 * Find the ChunkHandler that will be used for processing the found
 * chunk in the savegame or in memory
 * @param id the chunk in question
 * @return returns the appropriate chunkhandler
 */
static const ChunkHandler *SlFindChunkHandler(uint32_t id)
{
	for (const ChunkHandler &ch : ChunkHandlers()) if (ch.id == id) return &ch;
	return nullptr;
}

/** Load all chunks */
void SlLoadChunks()
{
	_sl.action = SLA_LOAD;

	uint32_t id;
	const ChunkHandler *ch;

	for (id = SlReadUint32(); id != 0; id = SlReadUint32()) {
		DEBUG(sl, 2, "Loading chunk %c%c%c%c", id >> 24, id >> 16, id >> 8, id);

		ch = SlFindChunkHandler(id);
		if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
		SlLoadChunk(*ch);
	}
}

/** Load a chunk */
void SlLoadChunkByID(uint32_t id)
{
	_sl.action = SLA_LOAD;

	DEBUG(sl, 2, "Loading chunk %c%c%c%c", id >> 24, id >> 16, id >> 8, id);

	const ChunkHandler *ch = SlFindChunkHandler(id);
	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
	SlLoadChunk(*ch);
}

/** Load all chunks for savegame checking */
void SlLoadCheckChunks()
{
	_sl.action = SLA_LOAD_CHECK;

	uint32_t id;
	const ChunkHandler *ch;

	for (id = SlReadUint32(); id != 0; id = SlReadUint32()) {
		DEBUG(sl, 2, "Loading chunk %c%c%c%c", id >> 24, id >> 16, id >> 8, id);

		ch = SlFindChunkHandler(id);
		if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
		SlLoadCheckChunk(*ch);
	}
}

/** Load a chunk for savegame checking */
void SlLoadCheckChunkByID(uint32_t id)
{
	_sl.action = SLA_LOAD_CHECK;

	DEBUG(sl, 2, "Loading chunk %c%c%c%c", id >> 24, id >> 16, id >> 8, id);

	const ChunkHandler *ch = SlFindChunkHandler(id);
	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
	SlLoadCheckChunk(*ch);
}

/** Fix all pointers (convert index -> pointer) */
void SlFixPointers()
{
	_sl.action = SLA_PTRS;

	for (const ChunkHandler &ch : ChunkHandlers()) {
		DEBUG(sl, 3, "Fixing pointers for %c%c%c%c", ch.id >> 24, ch.id >> 16, ch.id >> 8, ch.id);
		ch.FixPointers();
	}

	assert(_sl.action == SLA_PTRS);
}

void SlFixPointerChunkByID(uint32_t id)
{
	const ChunkHandler *ch = SlFindChunkHandler(id);
	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");
	DEBUG(sl, 3, "Fixing pointers for %c%c%c%c", ch->id >> 24, ch->id >> 16, ch->id >> 8, ch->id);
	ch->FixPointers();
}

/**
 * Save a chunk of data (eg. vehicles, stations, etc.). Each chunk is
 * prefixed by an ID identifying it, followed by data, and terminator where appropriate
 * @param ch The chunkhandler that will be used for the operation
 */
static void SlSaveChunk(const ChunkHandler &ch)
{
	if (ch.type == CH_READONLY) return;

	SlWriteUint32(ch.id);
	DEBUG(sl, 2, "Saving chunk %c%c%c%c", ch.id >> 24, ch.id >> 16, ch.id >> 8, ch.id);

	_sl.block_mode = ch.type;
	_sl.expect_table_header = (_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE);

	_sl.need_length = (_sl.expect_table_header || _sl.block_mode == CH_RIFF) ? NL_WANTLENGTH : NL_NONE;

	switch (_sl.block_mode) {
		case CH_RIFF:
			ch.Save();
			break;
		case CH_TABLE:
		case CH_ARRAY:
			_sl.last_array_index = 0;
			SlWriteByte(_sl.block_mode);
			ch.Save();
			SlWriteArrayLength(0); // Terminate arrays
			break;
		case CH_SPARSE_TABLE:
		case CH_SPARSE_ARRAY:
			SlWriteByte(_sl.block_mode);
			ch.Save();
			SlWriteArrayLength(0); // Terminate arrays
			break;
		default: NOT_REACHED();
	}

	if (_sl.expect_table_header) SlErrorCorrupt("Table chunk without header");
}

/** Save a chunk of data */
void SlSaveChunkChunkByID(uint32_t id)
{
	const ChunkHandler *ch = SlFindChunkHandler(id);
	if (ch == nullptr) SlErrorCorrupt("Unknown chunk type");

	_sl.action = SLA_SAVE;
	SlSaveChunk(*ch);
}

/** Reset state prior to a load */
void SlResetLoadState()
{
	_next_offs = 0;
}

SaveLoadTable SaveLoadHandler::GetLoadDescription() const
{
	assert(this->load_description.has_value());
	return *this->load_description;
}

}