CLK/Storage/MassStorage/Encodings/ApplePartitionMap.hpp

//
//  ApplePartitionMap.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 23/08/2022.
//  Copyright © 2022 Thomas Harte. All rights reserved.
//

#pragma once

#include <cstddef>
#include <cstdint>
#include <cstring>
#include <sys/types.h>
#include <vector>

namespace Storage::MassStorage::Encodings::Apple {

enum class DriveType {
	SCSI
};

/*!
	Implements a device to volume mapping with an Apple Partition Map.

	The @c VolumeProvider provides both the volume to be embedded into a device,
	and device driver information if applicable.
*/
template <typename VolumeProvider> class PartitionMap {
public:
	/*!
		Sets the drive type to map to and the number of blocks in the underlying partition.
	*/
	void set_drive_type(DriveType drive_type, size_t number_of_blocks) {
		drive_type_ = drive_type;
		number_of_blocks_ = number_of_blocks;
	}

	/*!
		@returns The total number of blocks on the entire volume.
	*/
	size_t get_number_of_blocks() const {
		return
			number_of_blocks_ +				// Size of the volume.
			size_t(non_volume_blocks());	// Size of everything else.
	}

	/*!
		Maps from a mass-storage device address to an address
		in the underlying volume.
	*/
	ssize_t to_source_address(size_t address) const {
		// The embedded volume is always the last thing on the device.
		return ssize_t(address) - ssize_t(non_volume_blocks());
	}

	/*!
		Converts from a source data block to one properly encoded for the drive type.

		Expected usage:

			const size_t source_address = mapper.to_source_address(unit_address);
			if(is_in_range_for_partition(source_address)) {
				return mapper.convert_source_block(source_address, get_block_contents(source_address));
			} else {
				return mapper.convert_source_block(source_address);
			}
	*/
	std::vector<uint8_t> convert_source_block(ssize_t source_address, std::vector<uint8_t> source_data = {}) {
		// Addresses greater than or equal to zero map to the actual disk image.
		if(source_address >= 0) return source_data;

		// Switch to mapping relative to 0, for personal sanity.
		source_address += non_volume_blocks();

		// Block 0 is the device descriptor, which lists the total number of blocks,
		// and provides an offset to the driver, if any.
		if(!source_address) {
			const uint32_t total_device_blocks = uint32_t(get_number_of_blocks());
			const auto driver_size = uint16_t(driver_block_size());
			const auto driver_offset = uint16_t(predriver_blocks());
			const uint8_t driver_count = driver_size > 0 ? 1 : 0;

			/* The driver descriptor. */
			std::vector<uint8_t> driver_description = {
				0x45, 0x52,		/* device signature */
				0x02, 0x00,		/* block size, in bytes */

				uint8_t(total_device_blocks >> 24),
				uint8_t(total_device_blocks >> 16),
				uint8_t(total_device_blocks >> 8),
				uint8_t(total_device_blocks),
								/* number of blocks on device */

				0x00, 0x01,		/* reserved (formerly: device type) */
				0x00, 0x01,		/* reserved (formerly: device ID) */
				0x00, 0x00,
				0x00, 0x00,		/* reserved ('sbData', no further explanation given) */

				0x00, driver_count,		/* number of device descriptor entries */
				0x00, 0x00,

				/* first device descriptor's starting block */
				uint8_t(driver_offset >> 8), uint8_t(driver_offset),

				/* size of device driver */
				uint8_t(driver_size >> 8), uint8_t(driver_size),

				0x00, 0x01,		/*
									More modern documentation: operating system (MacOS = 1)
									Inside Macintosh IV: system type (Mac Plus = 1)
								*/
			};
			driver_description.resize(512);

			return driver_description;
		}

		// Blocks 1 and 2 contain entries of the partition map; there's also possibly an entry
		// for the driver.
		if(source_address < 3 + volume_provider_.HasDriver) {
			struct Partition {
				const char *name, *type;
				uint32_t start_block, size;
				uint8_t status;
			} partitions[3] = {
				{
					volume_provider_.name(),
					volume_provider_.type(),
					uint32_t(non_volume_blocks()),
					uint32_t(number_of_blocks_),
					0xb7
				},
				{
					"Apple",
					"Apple_partition_map",
					0x01,
					uint32_t(predriver_blocks()) - 1,
					0x37
				},
				{
					"Macintosh",
					"Apple_Driver",
					uint32_t(predriver_blocks()),
					uint32_t(driver_block_size()),
					0x7f
				},
			};

			std::vector<uint8_t> partition(512);

			// Fill in the fixed fields.
			partition[0] = 'P';	partition[1] = 'M';	/* Signature. */
			partition[7] = 3;						/* Number of partitions. */

			const Partition &details = partitions[source_address-1];

			partition[8] = uint8_t(details.start_block >> 24);
			partition[9] = uint8_t(details.start_block >> 16);
			partition[10] = uint8_t(details.start_block >> 8);
			partition[11] = uint8_t(details.start_block);

			partition[84] = partition[12] = uint8_t(details.size >> 24);
			partition[85] = partition[13] = uint8_t(details.size >> 16);
			partition[86] = partition[14] = uint8_t(details.size >> 8);
			partition[87] = partition[15] = uint8_t(details.size);

			// 32 bytes are allocated for each of the following strings.
			memcpy(&partition[16], details.name, strlen(details.name));
			memcpy(&partition[48], details.type, strlen(details.type));

			partition[91] = details.status;

			// The third entry in this constructed partition map is the driver;
			// add some additional details.
			if constexpr (VolumeProvider::HasDriver) {
				if(source_address == 3) {
					const auto driver_size = uint16_t(volume_provider_.driver_size());
					const auto driver_checksum = uint16_t(volume_provider_.driver_checksum());

					/* Driver size in bytes. */
					partition[98] = uint8_t(driver_size >> 8);
					partition[99] = uint8_t(driver_size);

					/* Driver checksum. */
					partition[118] = uint8_t(driver_checksum >> 8);
					partition[119] = uint8_t(driver_checksum);

					/* Driver target processor. */
					const char *driver_target = volume_provider_.driver_target();
					memcpy(&partition[120], driver_target, strlen(driver_target));

					// Various non-zero values that Apple HD SC Tool wrote are below; they are
					// documented as reserved officially, so I don't know their meaning.
					partition[137] = 0x01;
					partition[138] = 0x06;
					partition[143] = 0x01;
					partition[147] = 0x02;
					partition[149] = 0x07;
				}
			}

			return partition;
		}

		if constexpr (VolumeProvider::HasDriver) {
			// The remainder of the non-volume area is the driver.
			if(source_address >= predriver_blocks() && source_address < non_volume_blocks()) {
				const uint8_t *driver = volume_provider_.driver();
				const auto offset = (source_address - predriver_blocks()) * 512;
				return std::vector<uint8_t>(&driver[offset], &driver[offset + 512]);
			}
		}

		// Default: return an empty block.
		return std::vector<uint8_t>(512);
	}

private:
	DriveType drive_type_;
	size_t number_of_blocks_;

	VolumeProvider volume_provider_;

	ssize_t predriver_blocks() const {
		return
			0x40;					// Holding:
									//	(i) the driver descriptor;
									//	(ii) the partition table; and
									//	(iii) the partition entries.
	}

	ssize_t non_volume_blocks() const {
		return
			predriver_blocks() +
			driver_block_size();	// Size of device driver (if any).
	}

	ssize_t driver_block_size() const {
		if constexpr (VolumeProvider::HasDriver) {
			return (volume_provider_.driver_size() + 511) >> 9;
		} else {
			return 0;
		}
	}
};

}