/* This program 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, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/** library to read/write internal flash (code)
 *  @file
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @date 2016-2020
 *  @note peripherals used: none
 */
/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdlib.h> // general utilities

/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/flash.h> // flash utilities
#include <libopencm3/stm32/desig.h> // device signature definitions
#include <libopencm3/stm32/dbgmcu.h> // debug definitions

/* own libraries */
#include "flash_internal.h" // flash storage library API
#include "global.h" // global definitions

/** number of flash pages, located at the end of flash memory, to use for EEPROM functionality */
static uint16_t flash_internal_eeprom_pages = 0;
/** start address of flash memory used for the emulated EEPROM */
static uint32_t flash_internal_eeprom_start = 0;
/** start address of emulated EEPROM */
static uint32_t flash_internal_eeprom_address = 0;

/** verify if the data is in the internal flash area
 *  @param[in] address start address of the data to read
 *  @param[in] size how much data to read or write, in bytes
 *  @return if the data is in the internal flash area
 */
static bool flash_internal_range(uint32_t address, size_t size)
{
	if (address > (UINT32_MAX - size)) { // on integer overflow will occur
		return false;
	}
	if (address < FLASH_BASE) { // start address is before the start of the internal flash
		return false;
	}
	if ((uint32_t)&__flash_end >= FLASH_BASE) { // check if the end for the internal flash is enforced by the linker script
		if ((address + size) > (uint32_t)&__flash_end) { // end address is after the end of the enforced internal flash
			return false;
		}
	} else {
		if ((address + size) > (FLASH_BASE + DESIG_FLASH_SIZE * 1024)) { // end address is after the end of the advertised flash
			return false;
		}
	}
	return true;
}

/** get flash page size
 *  @return flash page size (in bytes)
 */
uint16_t flash_internal_page_size(void)
{
	static uint16_t page_size = 0; // remember page size

	if (page_size) { // we already determined the size
		return page_size;
	}
	if (0 == page_size) { // we don't know the page size yet
		if ((0x410 == (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK)) || (0x412 == (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK))) { // low-density (16-32 KB flash) and medium-density (64-128 KB flash) devices have 1 KB flash pages
			page_size = 1024;
		} else if ((0x414 == (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK)) || (0x430 == (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK)) || (0x418 == (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK))) { // high-density (256-512 KB flash), XL-density (768-1024 KB flash) devices and connectivity line have 2 KB flash pages
			page_size = 2048;
		} else { // unknown device type (or unreadable type, see errata), deduce page size from flash size
			if (DESIG_FLASH_SIZE < 256) {
				page_size = 1024;
			} else {
				page_size = 2048;
			}
		}
	}

	return page_size;
}

bool flash_internal_read(uint32_t address, uint8_t *buffer, size_t size)
{
	// sanity checks
	if (buffer == NULL || size == 0) {
		return false;
	}
	if (!flash_internal_range(address, size)) {
		return false;
	}

	// copy data byte per byte (a more efficient way would be to copy words, than the remaining bytes)
	for (size_t i = 0; i < size; i++) {
		buffer[i] = *((uint8_t*)address + i);
	}

	return true;
}

int32_t flash_internal_write(uint32_t address, const uint8_t *buffer, size_t size, bool preserve)
{
	// sanity checks
	if (buffer == NULL || size == 0 || size % 2) {
		return -1;
	}
	if (!flash_internal_range(address, size)) {
		return -2;
	}

	// verify if it's in the flash area
	if (address < FLASH_BASE) {
		return -3;
	} else if ((uint32_t)&__flash_end >= FLASH_BASE && (address + size) > (uint32_t)&__flash_end) {
		return -4;
	} else if ((uint32_t)&__flash_end < FLASH_BASE && (address + size) > (FLASH_BASE + DESIG_FLASH_SIZE * 1024)) {
		return -5;
	}

	uint16_t page_size = flash_internal_page_size(); // get page size
	uint32_t written = 0; // number of bytes written
	flash_unlock(); // unlock flash to be able to write it
	while (size) { // write page by page until all data has been written
		// verify of we need to erase the flash before writing it
		uint32_t page_start = address - (address % page_size); // get start of the current page
		bool erase = false; // verify if we need to erase the page
		bool identical = true; // verify if we actually need to write data, or if the data to be written is the identical to the one already if flash
		for (uint32_t i = 0; i < size && (address + i) < (page_start + page_size); i += 2) { // verify if no bit needs to be flipped to 1 again
			if (*(uint16_t*)(buffer + i) != (*(uint16_t*)(address + i))) { // verify if the data to be written is identical to the one already written
				identical = false;
				// in theory writing flash is only about flipping (individual) bits from 1 (erase state) to 0
				// in practice the micro-controller won't allow to flip individual bits if the whole half-word is erased (set to 0xffff)
				if (*(uint16_t*)(address + i) != 0xffff) { // flash is not erased
					erase = true; // we need to erase it for it to be written
					break; // no need to check further
				}
			}
		}
		if (identical) { // no data needs to be changed
			// go to end of page, or size
			uint32_t remaining = (page_start + page_size) - address;
			if (remaining > size) {
				remaining = size;
			}
			written += remaining;
			buffer += remaining;
			address += remaining;
			size -= remaining;
		} else if (erase && preserve) { // erase before
			uint8_t page_data[page_size]; // a copy of the complete page before the erase it
			uint16_t page_i = 0; // index for page data
			// copy page before address
			for (uint32_t flash = page_start; flash < address && flash < (page_start + page_size) && page_i < page_size; flash++) {
				page_data[page_i++] = *(uint8_t*)(flash);
			}
			// copy data starting at address
			while (size > 0 && page_i < page_size) {
				page_data[page_i++] = *buffer;
				buffer++;
				address++;
				size--;
			}
			// copy data after buffer until end of page
			while (page_i < page_size) {
				page_data[page_i] = *(uint8_t*)(page_start + page_i);
				page_i++;
			}
			flash_erase_page(page_start); // erase current page
			if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
				flash_lock(); // lock back flash to protect it
				return -6;
			}
			for (uint16_t i = 0; i < page_size; i += 2) { // write whole page
				if (*((uint16_t*)(page_data + i)) != 0xffff) { // after an erase the bits are set to one, no need to program them
					flash_program_half_word(page_start + i, *((uint16_t*)(page_data + i)));
					if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
						flash_lock(); // lock back flash to protect it
						return -7;
					}
				}
				if (*((uint16_t*)(page_data + i)) != *((uint16_t*)(page_start + i))) { // verify the programmed data is right
					flash_lock(); // lock back flash to protect it
					return -8;
				}
				written += 2;
			}
		} else { // simply copy data until end of page (or end of data)
			if (erase) {
				flash_erase_page(page_start); // erase current page
				if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
					flash_lock(); // lock back flash to protect it
					return -9;
				}
			}
			while (size > 0 && address < (page_start + page_size)) {
				if (*((uint16_t*)(buffer)) != *((uint16_t*)(address)) && *((uint16_t*)(buffer)) != 0xffff) { // only program when data is different and bits need to be set
					flash_program_half_word(address, *((uint16_t*)(buffer))); // program the data
					if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
						flash_lock(); // lock back flash to protect it
						return -10;
					}
					if (*((uint16_t*)address) != *((uint16_t*)buffer)) { // verify the programmed data is right
						flash_lock(); // lock back flash to protect it
						return -11;
					}
				}
				written += 2;
				buffer += 2;
				address += 2;
				size -= 2;
			}
		}
	}
	flash_lock(); // lock back flash to protect it

	return written;
}

void flash_internal_eeprom_setup(uint16_t pages)
{
	flash_internal_eeprom_pages = pages; // just need to remember the number of pages

	// get allocated memory address
	if ((uint32_t)&__flash_end >= FLASH_BASE) { // check if the end for the internal flash is enforced by the linker script
		flash_internal_eeprom_start = (uint32_t)&__flash_end - flash_internal_eeprom_pages * flash_internal_page_size();
	} else {
		flash_internal_eeprom_start = (FLASH_BASE + DESIG_FLASH_SIZE * 1024) - flash_internal_eeprom_pages * flash_internal_page_size();
	}
	flash_internal_eeprom_start -= flash_internal_eeprom_start % flash_internal_page_size(); // ensure it starts at start of page

	// find EEPROM in flash
	flash_internal_eeprom_address = flash_internal_eeprom_start; // by default start with start of allocated flash memory
	for (uint32_t addr = flash_internal_eeprom_start; addr < flash_internal_eeprom_start + flash_internal_eeprom_pages * flash_internal_page_size() - 2; addr += 2) {
		if (0 != *(uint16_t*)addr) { // 0 is invalidated flash
			flash_internal_eeprom_address = addr; // we found a valid address, which should be the size of the EEPROM
			break;
		}
	}
	uint16_t size = *(uint16_t*)flash_internal_eeprom_address;
	if (size + 2U > flash_internal_eeprom_pages * flash_internal_page_size()) { // there is not enough space
		flash_internal_eeprom_address = flash_internal_eeprom_start; // set back to start
	}
	if (0 != size && flash_internal_eeprom_address + 2U + size > flash_internal_eeprom_start + flash_internal_eeprom_pages * flash_internal_page_size()) { // the size seems to be valid to there is not enough remaining space
		flash_internal_eeprom_address = flash_internal_eeprom_start; // set back to start
	}
}

bool flash_internal_eeprom_read(uint8_t *eeprom, uint16_t size)
{
	// sanity checks
	if (NULL == eeprom || 0 == size || 0 == flash_internal_eeprom_pages || 0 == flash_internal_eeprom_start || 0 == flash_internal_eeprom_address) {
		return false;
	}
	if (size + 2U > flash_internal_eeprom_pages * flash_internal_page_size()) { // not enough space
		return false;
	}

	if (size != *(uint16_t*)flash_internal_eeprom_address) { // check if size match
		return false;
	}

	return flash_internal_read(flash_internal_eeprom_address + 2, eeprom, size); // read data
}

int32_t flash_internal_eeprom_write(const uint8_t *eeprom, uint16_t size)
{
	// sanity checks
	if (NULL == eeprom || 0 == size || 0 == flash_internal_eeprom_pages || 0 == flash_internal_eeprom_start || 0 == flash_internal_eeprom_address) {
		return -1;
	}
	if (size + 2U > flash_internal_eeprom_pages * flash_internal_page_size()) { // not enough space
		return -2;
	}

	uint16_t current_size = *(uint16_t*)flash_internal_eeprom_address;
	if (size == current_size) { // check if it already the same
		bool identical = true;
		for (uint16_t i = 0; i < size; i++) {
			if (eeprom[i] != *((uint8_t*)flash_internal_eeprom_address + 2 + i)) {
				identical = false;
				break;
			}
		}
		if (identical) { // no need to write since it's identical
			return size;
		}
	}

	// one optimisation would be to check if we just need to flip bits to 0, than we could reuse the same location

	// invalidate current EEPROM
	const uint8_t zero[2] = {0, 0};
	flash_internal_write(flash_internal_eeprom_address, zero, 2, false);
	flash_internal_eeprom_address += 2;
	while (current_size && flash_internal_eeprom_address < flash_internal_eeprom_start + flash_internal_eeprom_pages * flash_internal_page_size()) {
		flash_internal_write(flash_internal_eeprom_address, zero, 2, false);
		current_size -= 2;
		flash_internal_eeprom_address += 2;
	}

	// go to start if there is not enough remaining space
	if (flash_internal_eeprom_address + size + 2U > flash_internal_eeprom_start + flash_internal_eeprom_pages * flash_internal_page_size()) {
		flash_internal_eeprom_address = flash_internal_eeprom_start;
	}

	int32_t rc = flash_internal_write(flash_internal_eeprom_address, (uint8_t*)&size, 2, false);
	if (2 != rc) {
		return (-10 + rc);
	}
	rc = flash_internal_write(flash_internal_eeprom_address + 2, eeprom, size, false);
	if (size != rc) {
		return (-10 + rc);
	}
	return rc;
}