/*
 * @file adc.cpp
 * @brief ATmega4809 ADC0 driver: configuration profiles, oversampling reads,
 *        and conversions to engineering units.
 *
 * Created: 27.09.2025 05:06:33
 * Author: ThePetrovich
 *
 * Copyright YKSA - Sakha Aerospace Systems, LLC.
 * See the LICENSE file for details.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "adc.h"
#include "config.h"
#include <Arduino.h>
#include <util/atomic.h>

/**
 * @brief Internal driver state.
 *        Bit 0 = fast mode currently enabled.
 */
static uint8_t adc_flags = 0;

int16_t adc_to_temperature_c(uint16_t adc_value)
{
	/*
	 * MCP9700: 500 mV at 0 °C, 10 mV/°C, result returned in 0.1 °C units.
	 * Use calibration points when available (adccal3 != 0xFFFF):
	 *   adccal0 = ADC reading at GND (offset),
	 *   adccal3 = ADC reading at 3.0 V reference.
	 * Falls back to nominal constants when uncalibrated.
	 */
	uint16_t cal0 = config.calibration.adccal0;
	uint16_t cal3 = config.calibration.adccal3;
	int16_t tempcal = (int16_t)config.calibration.tempcal;

	int32_t mv;
	if (cal3 != 0xFFFF && cal3 != cal0) {
		mv = (int32_t)(adc_value - cal0) * ADC_VREF_MV / (int32_t)(cal3 - cal0);
	} else {
		uint16_t adc_resolution = ADC_RESOLUTION << config.flags.fields.adc_oversample_bits;
		mv = (int32_t)adc_value * ADC_VREF_MV / adc_resolution;
	}

	/* Result in 0.1 °C: (mv - 500 - tempcal_offset) * 10 / 10. */
	return (int16_t)((mv - MCP9700_OFFSET_MV - tempcal) * 10L / MCP9700_SCALE_MV);
}

uint16_t adc_to_voltage_mv(uint16_t adc_value) { return (uint16_t)(adc_value * VOLTAGE_MV_PER_STEP); }

uint16_t adc_read_oversampled(uint8_t pin, uint8_t samples)
{
	uint32_t sum = 0;
	uint8_t shift = ((samples == 64) ? 3 : (samples == 16) ? 2 : (samples == 4) ? 1 : 0);

	for (uint8_t i = 0; i < samples; i++) {
		sum += analogRead(pin);
	}
	return (uint16_t)(sum >> shift);
}

void adc_enable_fast(void)
{
	ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
	{
		ADC0.CTRLA |= ADC_ENABLE_bm;

		/* Oversampling factor selected by config.flags.adc_oversample_bits. */
		ADC0.CTRLB |= (config.flags.fields.adc_oversample_bits << 2);

		ADC0.CTRLC = 0;
		ADC0.CTRLC |= ADC_PRESC_DIV32_gc | ADC_REFSEL_VREFA_gc; /* CLK_PER/32, VREFA reference */

		ADC0.EVCTRL |= ADC_STARTEI_bm; /* EVSYS input starts conversion */
		ADC0.INTCTRL |= ADC_RESRDY_bm; /* result-ready interrupt */

		/* Microchip DS40002015B p. 424. */
		VREF.CTRLA |= VREF_ADC0REFSEL_4V34_gc;

		ADC0.MUXPOS = ADC_MUXPOS_AIN3_gc; /* DET_SIG_PIN */

		adc_flags |= 0x01;
	}
}

void adc_restore_default(void)
{
	ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
	{
		ADC0.CTRLB &= ~ADC_SAMPNUM_gm;

		ADC0.CTRLC &= ~ADC_REFSEL_gm;
		ADC0.CTRLC |= ADC_REFSEL_VREFA_gc;

		ADC0.EVCTRL &= ~ADC_STARTEI_bm;
		ADC0.INTCTRL &= ~ADC_RESRDY_bm;

		adc_flags &= ~0x01;
	}
}

/**
 * @brief Trigger a single conversion and block until the result is ready.
 */
static uint16_t adc_conversion(void)
{
	ADC0.COMMAND = ADC_STCONV_bm;
	while (!(ADC0.INTFLAGS & ADC_RESRDY_bm))
		;
	return ADC0.RES;
}

uint16_t adc_read_tempsense(void)
{
	/*
	 * Microchip DS40002015B p. 425 procedure:
	 *   1. Configure VREF to 1.1 V via the VREF peripheral.
	 *   2. Select internal voltage reference (REFSEL = 0x0 in ADCn.CTRLC).
	 *   3. Select the temperature sensor channel via ADCn.MUXPOS.
	 *   4. Set INITDLY ≥ 32 µs × CLK_ADC in ADCn.SAMPCTRL.
	 *   5. Set SAMPLEN ≥ 32 µs × CLK_ADC in ADCn.CTRLC.
	 *   6. Start a conversion to acquire the sensor output voltage.
	 *   7. Process the result as below.
	 */
	ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
	{
		ADC0.CTRLA |= ADC_ENABLE_bm;

		ADC0.CTRLB |= ADC_SAMPNUM_ACC16_gc;

		ADC0.CTRLC = 0;
		ADC0.CTRLC |= ADC_PRESC_DIV32_gc | ADC_REFSEL_INTREF_gc;

		VREF.CTRLA |= VREF_ADC0REFSEL_1V1_gc;

		ADC0.MUXPOS = ADC_MUXPOS_TEMPSENSE_gc;
	}

	delay(10);

	int8_t sigrow_offset = SIGROW.TEMPSENSE1;
	uint8_t sigrow_gain = SIGROW.TEMPSENSE0;
	uint16_t adc_reading = adc_conversion() >> 4;

	/* Conversion result with 1.1 V internal reference; result may exceed 16
	 * bits during the multiply (10-bit reading × 8-bit gain). */
	uint32_t temp = adc_reading - sigrow_offset;
	temp *= sigrow_gain;
	temp += 0x80; /* Round-half-up before the >>8 division. */
	temp >>= 8;
	uint16_t temperature_in_C = temp - 273; /* Convert from Kelvin to Celsius. */

	adc_restore_default();

	if (adc_flags & 0x01) {
		adc_enable_fast();
	}

	return temperature_in_C * 10; /* Return in 0.1 °C for consistency */
}