#define __AVR_ATmega2560__
#define F_CPU 16000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <stdbool.h>
#include <avr/interrupt.h>

volatile uint16_t tick_timer_start = 0xffff - (F_CPU / 1024 / 1000);
volatile bool speaker_disabled = true;

uint16_t notes[][3] = {
    { 1000, 200, 30 },
    { 1200, 200, 30 },
    { 1500, 200, 30 },
    { 1600, 200, 30 },
    { 1500, 200, 30 },
    { 1200, 100, 10 },
    { 1000, 300, 100 },
};

void ADC_Setup() {
    // AVCC with external capacitor at AREF pin
    ADMUX = _BV(REFS0);

    // Enable ADC, set prescaler to 8tick_timer_start
    ADCSRA = _BV(ADEN) | _BV(ADPS0) | _BV(ADPS1);

    // Perform dummy readout
    ADCSRA |= _BV(ADSC); // Start conversion
    while (ADCSRA & _BV(ADSC)); // Await result
    (void) ADCW; // Read out result
}

uint16_t ADC_Read(uint8_t channel) {
    // Select chosen channel
    ADMUX = (ADMUX & ~(0x1F)) | (channel & 0x1F);
    // Start conversion
    ADCSRA |= _BV(ADSC);
    // Await the result
    while (ADCSRA & _BV(ADSC));
    // Although it doesn't appear to be documented, ADCW holds the covnersion result
    return ADCW;
}

uint16_t ADC_Read_Avg(uint8_t channel, uint8_t samples) {
    uint32_t sum = 0;
    for (int i = 0; i < samples; i++) {
        sum += ADC_Read(channel);
    }
    return (uint16_t)(sum / samples);
}

void TIMER_Setup() {
    TCCR1B |= _BV(CS10) | _BV(CS12); // clk/1024

    // Set the TOIE (Timer Overflow Interrupt Enable) bit
    // on TIMSK1 (Timer 1 Interrupt Mask Register).
    TIMSK1 |= _BV(TOIE1);

    // Sets the current timer value
    TCNT1 = tick_timer_start;

    // Enable interrupts
    sei();
}

// ISR is used to handle interrupts. TIMER1_OVF_vect
// is triggered whenever timer 1 (16 bit) overflows.
ISR(TIMER1_OVF_vect) {
    TCNT1 = tick_timer_start;
    PORTB ^= 0b10000000;

    if (speaker_disabled) PORTK &= 0b11111110;
    else PORTK ^= 0b00000001;
}

void play_note(uint16_t freq, uint8_t delay, uint8_t delay_silence) {
    speaker_disabled = false;
    tick_timer_start = 0xffff - (F_CPU / freq / 1000);
    for (int i = 0; i < delay; i++) _delay_ms(1);
    speaker_disabled = true;
    for (int i = 0; i < delay_silence; i++) _delay_ms(1);
}

void main() {
    DDRK = 0b00000001;
    PORTB = 0b10000000; // Start with LED enabled

    ADC_Setup();
    TIMER_Setup();

    long rows = sizeof(notes) / sizeof(notes[0]);

    while (true) {
        for (int i = 0; i < rows; i++) {
            play_note(notes[i][0], notes[i][1], notes[i][2]);
        }

        //uint16_t value = ADC_Read_Avg(0, 4);
        //speaker_disabled = value == 0;
        //if  (value < 100) value = 100; // Anything lower than this causes issues
        //tick_timer_start = 0xffff - (F_CPU / value / 1000);
    }
}