/*
 * @file eeprom.cpp
 * @brief EEPROM management with dual-partition wear leveling.
 *
 * Created: 21.09.2025
 * Author: ThePetrovich
 *
 * Copyright YKSA - Sakha Aerospace Systems, LLC.
 * See the LICENSE file for details.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "eeprom.h"
#include "config.h"
#include <Arduino.h>
#include <EEPROM.h>

config_t config;

/*
 * Each partition occupies sizeof(config_t)+1 bytes:
 *   [0 .. sizeof(config_t)-1]  config_t struct
 *   [sizeof(config_t)]         generation counter (uint8_t)
 */
#define PARTITION_SIZE ((uint16_t)(sizeof(config_t) + 1))
#define PARTITION_A_ADDR 0
#define PARTITION_B_ADDR PARTITION_SIZE
#define GEN_OFFSET ((uint16_t)sizeof(config_t))

/**
 * @brief Track which partition was last written so saves alternate.
 *        0 = partition A is current, 1 = partition B is current.
 */
static uint8_t g_active_partition = 0;

/**
 * @brief Check whether the partition at @p base contains a valid magic pair.
 */
static bool partition_valid(uint16_t base)
{
	uint8_t m1 = EEPROM.read(base + offsetof(config_t, magic1));
	uint8_t m2 = EEPROM.read(base + offsetof(config_t, magic2));
	return (m1 == 0xA5 && m2 == 0x5A);
}

/**
 * @brief Read a config_t struct from the partition at @p base into @p dst.
 */
static void read_partition(uint16_t base, config_t *dst)
{
	uint8_t *p = (uint8_t *)dst;
	for (uint16_t i = 0; i < sizeof(config_t); i++) {
		p[i] = EEPROM.read(base + i);
	}
}

/**
 * @brief Write @p src and a generation byte to the partition at @p base.
 *        Uses EEPROM.update() so unchanged cells incur no wear.
 */
static void write_partition(uint16_t base, const config_t *src, uint8_t generation)
{
	const uint8_t *p = (const uint8_t *)src;
	for (uint16_t i = 0; i < sizeof(config_t); i++) {
		EEPROM.update(base + i, p[i]);
	}
	EEPROM.update(base + GEN_OFFSET, generation);
}

/**
 * @brief Populate @p cfg with safe factory defaults.
 *        Used on first boot or when both partitions are corrupt.
 */
static void set_defaults(config_t *cfg)
{
	cfg->magic1 = 0xA5;
	cfg->magic2 = 0x5A;
	cfg->pots.pot_hv = DEFAULT_POT_VALUE;
	cfg->pots.pot_amp = DEFAULT_POT_VALUE;
	cfg->pots.pot_det = DEFAULT_POT_VALUE;
	cfg->calibration.adccal0 = 0xFFFF;
	cfg->calibration.adccal3 = 0xFFFF;
	cfg->calibration.tempcal = 0;
	cfg->flags.value = 0;
	/* pot_low == pot_high disables drift compensation per channel. */
	cfg->temp_drift_compensation.temp_drift = 0;
	cfg->temp_drift_compensation.vbias_drift = 0;
	cfg->temp_drift_compensation.gain_drift = 0;
	cfg->temp_drift_compensation.threshold_drift = 0;
	cfg->temp_drift_compensation.drift_period_ms = 5000;
	cfg->temp_drift_compensation.pot_hv_low = DEFAULT_POT_VALUE;
	cfg->temp_drift_compensation.pot_hv_high = DEFAULT_POT_VALUE;
	cfg->temp_drift_compensation.pot_amp_low = DEFAULT_POT_VALUE;
	cfg->temp_drift_compensation.pot_amp_high = DEFAULT_POT_VALUE;
	cfg->temp_drift_compensation.pot_det_low = DEFAULT_POT_VALUE;
	cfg->temp_drift_compensation.pot_det_high = DEFAULT_POT_VALUE;
}

void eeprom_init(void)
{
	bool a_valid = partition_valid(PARTITION_A_ADDR);
	bool b_valid = partition_valid(PARTITION_B_ADDR);

	if (a_valid && b_valid) {
		uint8_t gen_a = EEPROM.read(PARTITION_A_ADDR + GEN_OFFSET);
		uint8_t gen_b = EEPROM.read(PARTITION_B_ADDR + GEN_OFFSET);
		/* Signed delta handles wrap-around: B is newer if (gen_b - gen_a) > 0 mod 256. */
		if ((int8_t)(gen_b - gen_a) > 0) {
			read_partition(PARTITION_B_ADDR, &config);
			g_active_partition = 1;
		} else {
			read_partition(PARTITION_A_ADDR, &config);
			g_active_partition = 0;
		}
	} else if (a_valid) {
		read_partition(PARTITION_A_ADDR, &config);
		g_active_partition = 0;
	} else if (b_valid) {
		read_partition(PARTITION_B_ADDR, &config);
		g_active_partition = 1;
	} else {
		set_defaults(&config);
		write_partition(PARTITION_A_ADDR, &config, 0);
		g_active_partition = 0;
	}
}

void eeprom_save_config(void)
{
	/* Write to whichever partition is NOT currently active. */
	uint8_t target_partition = (g_active_partition == 0) ? 1 : 0;
	uint16_t target_base = (target_partition == 0) ? PARTITION_A_ADDR : PARTITION_B_ADDR;
	uint16_t active_base = (g_active_partition == 0) ? PARTITION_A_ADDR : PARTITION_B_ADDR;

	uint8_t old_gen = EEPROM.read(active_base + GEN_OFFSET);
	uint8_t new_gen = old_gen + 1;

	config.magic1 = 0xA5;
	config.magic2 = 0x5A;

	write_partition(target_base, &config, new_gen);
	g_active_partition = target_partition;
}