#include <avr/interrupt.h>
#include <avr/io.h>
#include <stdint.h>
#include <avr/pgmspace.h>

#include "board.h"
#include "setpoints.h"

/*! ADMUX setting for selecting 1.1V reference */
#define ADC_REF_1V1	(2 << REFS0)
/*! ADMUX setting for mains input voltage reading */
#define ADC_MUX_MAINS	(ADC_REF_1V1 | 0x00)
/*! ADMUX setting for solar input voltage reading */
#define ADC_MUX_SOLAR	(ADC_REF_1V1 | 0x01)
/*! ADMUX setting for battery input voltage reading */
#define ADC_MUX_BATT	(ADC_REF_1V1 | 0x02)
/*! ADMUX setting for temperature reading */
#define ADC_MUX_TEMP	(ADC_REF_1V1 | 0x22)

/*!
 * Macro for computing ADC measurements.  This assumes the input to the
 * ADC pin is via a voltage divider made up of resistors R1 and R2, with
 * the input voltage applied across both resistors and the ADC measuring
 * across R2.
 *
 * @param	mv	Voltage in millivolts
 * @returns		Approximate ADC reading
 */
# define ADC_READ(mv) (						\
	(ADC_MAX * ((uint64_t)(mv)) * VDIV_R2)			\
	 /							\
	(ADC_REF * (VDIV_R1 + VDIV_R2))				\
)

/* --- Thresholds --- */
#define V_H_ADC		ADC_READ(V_H_MV)
#define V_L_ADC		ADC_READ(V_L_MV)
#define V_CL_ADC	ADC_READ(V_CL_MV)
#define V_SOL_MIN_ADC	ADC_READ(V_SOL_MIN_MV)

/* --- Timeouts --- */
#define T_ADC_TICKS	TIMER_TICKS(T_ADC_MS)
#define T_LED_TICKS	TIMER_TICKS(T_LED_MS)

#define STATE_INIT	(0)	/*!< Initial start-up state */
#define STATE_SOLAR	(1)	/*!< Running from solar */
#define STATE_MAINS_CHG	(2)	/*!< Charging from mains */
#define STATE_MAINS_FLT	(3)	/*!< Floating on mains */

/*!
 * Charger state machine state.  We have four states we can be in.
 */
static volatile uint8_t charger_state = STATE_INIT;

/*!
 * For state machine, the last state of the ADC MUX so we know whether
 * to ignore the sample or not.  Datasheet recommends discarding samples
 * to let things stabalise when switching sources/references.
 */
static volatile uint8_t last_admux = 0;

/*!
 * Current reading of the battery voltage in ADC units.
 */
static volatile uint16_t v_bat_adc = 0;

/*!
 * Current reading of the solar voltage in ADC units.
 */
static volatile uint16_t v_sol_adc = 0;

/*!
 * Current reading of the internal temperature sensor in ADC units.
 */
static volatile uint16_t temp_adc = 0;

/*!
 * One-second event timer
 */
static volatile uint16_t t_second = 0;

/*!
 * How long before we next take a reading?
 */
static volatile uint16_t t_adc = 0;

/*!
 * Battery voltage timeout, used for:
 * - low voltage timeout
 * - charge timeout
 * - float timeout
 */
static volatile uint16_t t_batt = 0;

/*!
 * Fan kick-start timeout
 */
static volatile uint8_t t_fan = 0;

/*!
 * LED blink interval
 */
static volatile uint8_t t_led = 0;

/*!
 * HAL state
 */
static volatile uint8_t hal_state = 0;
#define HAL_STATE_ADC_CHECKED	(1 << 0)
#define HAL_STATE_LED_BLINK_POL	(1 << 7)

/*!
 * LED blink state
 */
static volatile uint8_t led_blink = 0;

/*!
 * Switch to charging from mains power.
 */
static void enter_mains_chg(void) {
	/* Reset timer */
	t_batt = T_CHARGE_S;

	/* Enable mains power */
	FET_PORT &= ~FET_MAINS;

	/* Indicate via LEDs */
	if (charger_state == STATE_MAINS_FLT) {
		/* We have regressed from floating state */
		led_blink &= ~LED_BATT_CHG;
		led_blink |= LED_BATT_FLT;
	} else {
		led_blink &= ~(LED_BATT_CHG | LED_BATT_FLT);
	}
	LED_PORT |= LED_BATT_CHG;
	LED_PORT &= ~LED_BATT_FLT;

	/* Enter state */
	charger_state = STATE_MAINS_CHG;
}

/*!
 * Switch to floating on mains power.
 */
static void enter_mains_float(void) {
	/* Reset timer */
	t_batt = T_FLOAT_S;

	/* Indicate via LEDs */
	led_blink &= ~(LED_BATT_CHG | LED_BATT_FLT);
	LED_PORT &= ~LED_BATT_CHG;
	LED_PORT |= LED_BATT_FLT;

	/* Enter state */
	charger_state = STATE_MAINS_FLT;
}

/*!
 * Switch to running on solar.
 */
static void enter_solar(void) {
	/* Inhibit mains */
	FET_PORT |= FET_MAINS;

	/* Indicate via LEDs */
	led_blink &= ~(LED_BATT_CHG | LED_BATT_FLT);
	LED_PORT &= ~(LED_BATT_FLT | LED_BATT_CHG);

	/* Enter state */
	charger_state = STATE_SOLAR;
}

/*!
 * Checks at start-up
 */
static void init_check(void) {
	/* Wait until we have our first readings from the ADC */
	if (!(hal_state & HAL_STATE_ADC_CHECKED))
		return;

	if (
			/* Battery is low */
			(v_bat_adc < V_L_ADC)
			/* Solar voltage is low */
			|| (v_sol_adc < V_SOL_MIN_ADC)
	)
		/* Battery/solar is low, begin charging */
		enter_mains_chg();
	else
		/* Run from solar */
		enter_solar();
}

/*!
 * Checks whilst running on solar
 */
static void solar_check(void) {
	if (v_bat_adc > V_L_ADC) {
		/* Battery is above low threshold, reset low timer */
		t_batt = T_LOW_S;
	} else if (
			/* Battery is low */
			v_bat_adc < V_L_ADC
	) {
		if (
				/* Battery is critically low */
				(v_bat_adc < V_CL_ADC)
				/* Battery is low for >T_LOW_S seconds */
				|| (!t_batt)
				/* Solar voltage is low */
				|| (v_sol_adc < V_SOL_MIN_ADC)
		) {
			/* Move to mains power */
			enter_mains_chg();
			return;
		} else {
			/*
			 * Blink charge LED to indicate we consider
			 * the battery low.
			 */
			led_blink |= LED_BATT_CHG;
		}
	}
}

/*!
 * Checks whilst charging from mains
 */
static void mains_chg_check(void) {
	if (
			/* Charger has been active for T_CHARGE_S seconds */
			(!t_batt)
			/* Battery has reached the floating voltage */
			&& (v_bat_adc >= V_H_ADC)
	) {
		/* We've reached the float voltage */
		enter_mains_float();
		return;
	}
}

/*!
 * Checks whilst floating on mains
 */
static void mains_float_check(void) {
	if (v_bat_adc < V_H_ADC) {
		/* We've regressed, go back to charging state! */
		enter_mains_chg();
		return;
	} else if (
			/* Battery is high for ≥T_FLOAT_S seconds */
			!t_batt
	) {
		/* Solar can take it from here */
		enter_solar();
	}
}

/*!
 * Check the state of the solar input, and update the output state
 * accordingly.
 */
static void adc_check_solar(void) {
	/*
	 * The "SOLAR" FET is no longer fitted, so this is more
	 * an indication of whether we consider solar to be
	 * "good enough".  In short, it's just controlling the
	 * LED where the MOSFET was now.
	 */
	if (v_sol_adc < V_SOL_MIN_ADC)
		FET_PORT |= FET_SOLAR;
	else
		FET_PORT &= ~FET_SOLAR;
}

/*!
 * Check the state of the temperature sensor and the fan.  Adjust
 * motor PWM and LED outputs as required.
 */
static void adc_check_temp(void) {
	/* Temperature LED and Fan control */
	if (t_fan) {
		/* Kick-start mode */
		OCR0A = FAN_PWM_MAX;
	} else if (temp_adc > TEMP_MAX) {
		/* We're at the maximum temperature, FULL SPEED! */
		OCR0A = FAN_PWM_MAX;
		led_blink &= (LED_TEMP_HIGH | LED_TEMP_LOW);
		LED_PORT &= ~LED_TEMP_LOW;
		LED_PORT |= LED_TEMP_HIGH;
	} else if (temp_adc > TEMP_MIN) {
		/* Scale fan speed linearly with temperature */
		uint8_t pwm = (((temp_adc - TEMP_MIN)
					* FAN_PWM_MAX)
				/ (TEMP_MAX - TEMP_MIN));

		LED_PORT &= ~LED_TEMP_HIGH;
		if (OCR0A < FAN_PWM_MIN) {
			/* Enter kick-start mode */
			t_fan = T_FAN_S;
			led_blink |= LED_TEMP_LOW;
		} else {
			led_blink &= ~LED_TEMP_LOW;
			LED_PORT |= LED_TEMP_LOW;

			if (pwm > FAN_PWM_MIN) {
				OCR0A = pwm;
			} else {
				OCR0A = FAN_PWM_MIN;
			}
		}
	} else {
		/* Turn fans off completely. */
		OCR0A = 0;
		led_blink &= (LED_TEMP_HIGH | LED_TEMP_LOW);
		LED_PORT &= (LED_TEMP_HIGH | LED_TEMP_LOW);
	}
}

/*!
 * Check the battery voltage and update the battery LEDs accordingly.
 */
static void adc_check_batt(void) {
	/* Battery state LED control */
	if (v_bat_adc <= V_CL_ADC) {
		/* Battery is critically low */
		led_blink |= LED_BATT_GOOD;
	} else if (v_bat_adc <= V_L_ADC) {
		/* Battery is low */
		led_blink &= ~LED_BATT_GOOD;
		LED_PORT &= ~LED_BATT_GOOD;
	} else {
		led_blink &= ~LED_BATT_GOOD;
		LED_PORT |= LED_BATT_GOOD;
	}
}

/*!
 * Check to see if a second has elapsed, if it has, tick down each of
 * the one-second resolution timers.
 */
static void loop_second_tasks(void) {
	if (!t_second) {
		/* One second passed, tick down the 1-second timers. */
		t_second = TIMER_FREQ;

		if (t_batt)
			t_batt--;

		if (t_fan)
			t_fan--;
	}
}

/*!
 * Check to see if our ADC state machine has advanced,  If so,
 * check the state of all our ADC-dependent inputs.
 */
static void loop_adc_tasks(void) {
	if (!t_adc) {
		t_adc = T_ADC_TICKS;
		ADCSRA |= (1 << ADEN) | (1 << ADSC);

		while(ADCSRA & (1 << ADEN));

		adc_check_solar();
		adc_check_temp();
		adc_check_batt();

		/* Charger control */
		switch (charger_state) {
		case STATE_INIT:
			init_check();
			break;
		case STATE_SOLAR:
			solar_check();
			break;
		case STATE_MAINS_CHG:
			mains_chg_check();
			break;
		case STATE_MAINS_FLT:
			mains_float_check();
			break;
		default:
			charger_state = STATE_INIT;
		}
	}
}

/*!
 * Check to see if our LED control timer has elapsed.  If so
 * blink the LEDs that have been selected for blinking.
 */
static void loop_led_tasks(void) {
	if (!t_led) {
		/*
		 * Decide whether we're turning blinking LEDs on
		 * or off.  One bit keeps all blinking LEDs in phase.
		 */
		hal_state ^= HAL_STATE_LED_BLINK_POL;

		/* Apply that state to all selected LEDs */
		if (hal_state & HAL_STATE_LED_BLINK_POL)
			LED_PORT |= led_blink;
		else
			LED_PORT &= ~led_blink;

		/* Reset timer */
		t_led = T_LED_TICKS;
	}
}

/*!
 * Main entrypoint
 */
int main(void) {
	/* Configure LEDs */
	LED_PORT_DDR_REG = LED_PORT_DDR_VAL;
	LED_PORT = 0;

	/* Configure MOSFETs */
	FET_PORT_DDR_REG = FET_PORT_DDR_VAL;
	FET_PORT = FET_MAINS | FET_SOLAR;

	/* Turn on ADC and timers */
	PRR &= ~((1 << PRTIM0) | (1 << PRTIM1) | (1 << PRADC));

	/* Configure Timer0: Fan PWM */
	TCCR0A = (1 << COM0A1) | (1 << WGM01) | (1 << WGM00);
	TCCR0B = (1 << CS00);
	OCR0A = 0;

	/*
	 * Configure Timer1: TIMER_FREQ System tick timer
	 * / baud rate generator for debug output
	 */
	TCCR1A = 0;
	TCCR1B = (1 << WGM12) | (1 << CS10);
	TCCR1C = 0;
	OCR1A = F_CPU/TIMER_FREQ;
	TIMSK1 = (1 << OCIE1A);

	/* ADC configuration */
	DIDR0 = ADC_CH_EN;
	ADMUX = ADC_MUX_TEMP;
	ADCSRB = (1 << ADLAR);
	ADCSRA = (1 << ADIE)
		| (1 << ADPS2)
		| (1 << ADPS1)
		| (1 << ADPS0);

	/* Start interrupts */
	sei();
	MCUSR = 0;

	/* Enter core loop */
	while(1) {
		loop_second_tasks();
		loop_adc_tasks();
		loop_led_tasks();
	}
	return 0;
}

ISR(TIM1_COMPA_vect) {
	/* One-second timer for longer events */
	if (t_second)
		t_second--;

	/* ADC tick events */
	if (t_adc)
		t_adc--;
}

ISR(ADC_vect) {
	uint16_t adc = ADCW;
	if (last_admux == ADMUX) {
		switch(last_admux) {
		case ADC_MUX_TEMP:
			temp_adc = adc;
			ADMUX = ADC_MUX_BATT;
			ADCSRA |= (1 << ADSC);
			break;
		case ADC_MUX_BATT:
			v_bat_adc = adc;
			ADMUX = ADC_MUX_SOLAR;
			ADCSRA |= (1 << ADSC);
			break;
		case ADC_MUX_SOLAR:
			v_sol_adc = adc;
			/* Once we get here, we've done a full cycle */
			hal_state |= HAL_STATE_ADC_CHECKED;
		default:
			ADMUX = ADC_MUX_TEMP;
			ADCSRA &= ~(1 << ADEN);
		}
	} else {
		ADCSRA |= (1 << ADSC);
		last_admux = ADMUX;
	}
}