#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <eeprom.h>
#define DEV "/dev/i2c/0"
#define EEPROM_ADDR 0x50

static int i2cdev;

void raw_writepage(unsigned char page_start, unsigned char *src) {
	// Write 8-byte page
	unsigned char buf[9];
	
	buf[0] = page_start;
	memcpy(buf + 1, src, 8);
	
	if (write(i2cdev, buf, 9) != 9)
		perror("data_write");
	
	while (write(i2cdev, "\x00", 1) != 1) // Busy loop
		usleep(1000);
	
	eeprom_readpage(page_start, buf); // Verify
	
	if (memcmp(buf, src, 8) != 0)
		fprintf(stderr, "I2C eeprom data compare failed at page 0x%02x\n", page_start);
}

void check_journal() {
	/* Control page:
	1st byte: 0 if clean, 1 if dirty
	2st byte: write address
	*/
	
	unsigned char buf[8];
	int dirty, destaddr;
	eeprom_readpage(PAGE_CONTROL, buf);
	dirty = buf[0];
	destaddr = buf[1];
	
	if (dirty == 0) // Memory is clean
		return;
	
	fprintf(stderr, "Replaying journal to page 0x%02x\n", destaddr);
	
	eeprom_readpage(PAGE_JOURNAL, buf);
	
	// If we lose power again, journal will be intact
	raw_writepage(destaddr, buf);
	
	// Clear control
	memset(buf, 0, 8);
	raw_writepage(PAGE_CONTROL, buf);
}

/* Public functions */

void eeprom_initialize() {
	i2cdev = open(DEV, O_RDWR);
	
	if (i2cdev < 0)
		perror("eeprom_open");
	
	if (ioctl(i2cdev, I2C_SLAVE, EEPROM_ADDR) < 0)
		perror("eeprom_ioctl");
	
	check_journal();
}

void eeprom_readpage(unsigned char page_start, unsigned char *dest) {
	// Read 8-byte page
	
	if (write(i2cdev, &page_start, 1) != 1)
		perror("address_write");
	
	if (read(i2cdev, dest, 8) != 8)
		perror("data_read");
}

void eeprom_writepage(unsigned char page_start, unsigned char *src) {
	// Journalled write or 8-byte page
	unsigned char buf[8] = {0};
	
	// Write journal
	raw_writepage(PAGE_JOURNAL, src);
	
	// Write control page
	buf[0] = 1;
	buf[1] = page_start;
	raw_writepage(PAGE_CONTROL, buf);
	
	// Write memory
	raw_writepage(page_start, src);
	
	// Clear control
	memset(buf, 0, 8);
	raw_writepage(PAGE_CONTROL, buf);
}