/** library to read/write internal flash
 *  @file
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @copyright SPDX-License-Identifier: GPL-3.0-or-later
 *  @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 <libopencmsis/core_cm3.h> // Cortex M3 utilities
#include <libopencm3/stm32/flash.h> // flash utilities
#include <libopencm3/stm32/desig.h> // device signature definitions

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

/** flash page size */
static uint16_t flash_internal_page = 0;
/** end address of flash */
static uint32_t flash_internal_end = 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;

/** find out page size and flash end address */
static void flash_internal_init(void)
{
	if (0 == flash_internal_page) {
		flash_internal_page_size(); // get page size
	}
	if (0 == flash_internal_end) {
		if ((uint32_t)&__flash_end >= FLASH_BASE) {
			flash_internal_end = (uint32_t)&__flash_end;
		} else {
			flash_internal_end = FLASH_BASE + desig_get_flash_size() * 1024;
		}
	}
}

/** 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 (0 == flash_internal_page || 0 == flash_internal_end) {
		flash_internal_init();
	}
	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 ((address + size) > flash_internal_end) { // end address is after the end of the internal flash
		return false;
	}
	return true;
}

/** get flash page size
 *  @return flash page size (in bytes)
 */
uint16_t flash_internal_page_size(void)
{
	if (0 == flash_internal_page) { // we don't know the page size yet
		if (desig_get_flash_size() < 256) {
			if ((*(uint32_t*)0x1FFFF000 & 0xFFFE0000) == 0x20000000) { // non-connectivity system memory start detected (MSP address pointing to SRAM
				flash_internal_page = 1024;
			} else { // connectivity system memory start is at 0x1FFFB000
				flash_internal_page = 2048;
			}
		} else {
			flash_internal_page = 2048;
		}
	}

	return flash_internal_page;
}

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;
	} else if (address < FLASH_BASE) {
		return -2;
	} else if (!flash_internal_range(address, size)) {
		return -3;
	}

	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 % flash_internal_page); // 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 + flash_internal_page); i += 2) { // verify if any word in this page needs to be programmed
			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 will only 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 + flash_internal_page) - address;
			if (remaining > size) {
				remaining = size;
			}
			written += remaining;
			buffer += remaining;
			address += remaining;
			size -= remaining;
		} else if (erase && preserve) { // erase before
			uint8_t page_data[flash_internal_page]; // 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 + flash_internal_page) && page_i <flash_internal_page; flash++) {
				page_data[page_i++] = *(uint8_t*)(flash);
			}
			// copy data starting at address
			while (size > 0 && page_i < flash_internal_page) {
				page_data[page_i++] = *buffer;
				buffer++;
				address++;
				size--;
			}
			// copy data after buffer until end of page
			while (page_i < flash_internal_page) {
				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 < flash_internal_page; 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 + flash_internal_page)) {
				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;
}

/* the EEPROM allocated area is erased at first
 * the EEPROM data starts at the end of the allocated memory
 * each time it is written, the next data segment is placed before the existing one
 * a data segment start with the size, which help detecting the segment since the data can be the same as erased data (0xffff)
 */
void flash_internal_eeprom_setup(uint16_t pages)
{
	if (0 == flash_internal_page || 0 == flash_internal_end) {
		flash_internal_init(); // get page size and flash end
	}

	flash_internal_eeprom_start = 0; // reset start address
	flash_internal_eeprom_address = 0; // reset EEPROM address
	if (pages > desig_get_flash_size() * 1024 / flash_internal_page) { // not enough pages are available
		return;
	}
	flash_internal_eeprom_start = flash_internal_end - flash_internal_page * pages; // set EEPROM start (page aligned)

	// find EEPROM in flash (first non-erased word)
	for (flash_internal_eeprom_address = flash_internal_eeprom_start; flash_internal_eeprom_address < flash_internal_end && 0xffff == *(uint16_t*)flash_internal_eeprom_address; flash_internal_eeprom_address += 2);
}

bool flash_internal_eeprom_read(uint8_t *eeprom, uint16_t size)
{
	// sanity checks
	if (NULL == eeprom || 0 == size || 0xffff == size || 0 == flash_internal_eeprom_start || 0 == flash_internal_eeprom_address) {
		return false;
	}
	if (size + 2U > flash_internal_end - flash_internal_eeprom_start) { // not enough space
		return false;
	}
	if (size + 2U > flash_internal_end - flash_internal_eeprom_address) { // EEPROM size is too large
		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 || 0xffff == size || 0 == flash_internal_eeprom_start || 0 == flash_internal_eeprom_address) {
		return -1;
	}
	if (size + 2U > flash_internal_end - flash_internal_eeprom_start) { // not enough space
		return -2;
	}

	if (flash_internal_eeprom_start + size + 2U > flash_internal_eeprom_address) { // there is not enough free space
		// erase all EEPROM allocated pages
		flash_unlock(); // unlock flash to be able to erase it
		for (uint32_t page_start = flash_internal_eeprom_start; page_start < flash_internal_end; page_start += flash_internal_page) {
			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 -3;
			}
		}
		flash_internal_eeprom_address = flash_internal_end; // put address back as the end
	}
	flash_internal_eeprom_address -= (size + 2U); // get new start of data segment
	if (flash_internal_eeprom_address % 2) { // have segment word aligned
		flash_internal_eeprom_address--;
	}
	if (flash_internal_eeprom_address < flash_internal_eeprom_start) { // just to be sure
		return -4;
	}

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

uint32_t flash_internal_probe_read_size(void)
{
	// we will check is a flash address is readable until a bus fault occurs
	cm_disable_faults(); // disable all faults, particularly BusFault
	SCB_CFSR |= SCB_CFSR_BFARVALID; // clear bus fault flag
	SCB_CCR |= SCB_CCR_BFHFNMIGN; // ignore bus faults (but still flag them)
	uint32_t address = FLASH_BASE; // start with the start of flash
	while (0 == (SCB_CFSR & SCB_CFSR_BFARVALID)) { // until a bus fault occurs
		(void)*(volatile uint8_t*)address; // access address
		address++; // got to next address
	}
	SCB_CFSR |= SCB_CFSR_BFARVALID; // clear bus fault flag
	SCB_CCR &= ~SCB_CCR_BFHFNMIGN; // re-enable bus fault
	cm_enable_faults(); // re-enable faults

	return address - 1 - FLASH_BASE;
}

uint32_t flash_internal_probe_write_size(void)
{
	if (0 == desig_get_flash_size()) { // no flash size advertised
		return 0;
	}

	// prepare for reading the flash
	cm_disable_faults(); // disable all faults, particularly BusFault
	SCB_CFSR |= SCB_CFSR_BFARVALID; // clear bus fault flag
	SCB_CCR |= SCB_CCR_BFHFNMIGN; // ignore bus faults (but still flag them)
	// prepare for writing the flash
	flash_unlock(); // unlock flash to be able to write it
	// try reading and writing the flash, page per page
	uint32_t start = FLASH_BASE + desig_get_flash_size() * 1024; // start with the end of the advertised flash
	if ((uint32_t)&__flash_end >= FLASH_BASE) { // use linker flash size if provided
		start = (uint32_t)&__flash_end;
	}
	uint32_t address = start; // address to test
	const uint16_t test_data = 0x2342; // the data we will write and read to test page
	while (address < 0x1FFFEFFF) { // this is where the system memory starts
		// try reading the flash
		(void)*(volatile uint32_t*)address; // access address
		if (0 != (SCB_CFSR & SCB_CFSR_BFARVALID)) { // until a bus fault occurs
			break; // page not readable
		}
		// try writing the flash
		flash_erase_page(address); // erase current page
		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
			break;
		}
		flash_program_half_word(address, test_data); // writes test data
		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
			break;
		}
		if (test_data != *((uint16_t*)address)) { // verify data is written correctly
			break;
		}
		flash_erase_page(address); // erase test data
		if (flash_get_status_flags() != FLASH_SR_EOP) { // operation went wrong
			break;
		}
		address += flash_internal_page_size(); // go to next page
	}
	flash_clear_status_flags(); // clear all flag
	flash_lock(); // protect again from writing
	SCB_CFSR |= SCB_CFSR_BFARVALID; // clear bus fault flag
	SCB_CCR &= ~SCB_CCR_BFHFNMIGN; // re-enable bus fault
	cm_enable_faults(); // re-enable faults

	return address - start;
}