#include "stm32c0xx.h"

// Hard delay padding blocks for raw cycle synchronization
void delay_us(volatile uint32_t us) {
    volatile uint32_t count = us * 3UL; 
    while (count > 0) {
        count--;
        __NOP();
    }
}

void delay_ms(volatile uint32_t ms) {
    while (ms > 0) {
        delay_us(1000);
        ms--;
    }
}

// Pure C square-wave toggle engine mapping PA5
void play_tone(uint32_t frequency_hz, uint32_t duration_ms) {
    if (frequency_hz == 0) {
        GPIOA->ODR &= ~GPIO_ODR_OD5; 
        delay_ms(duration_ms);
        return;
    }

    uint32_t half_period_us = 1000000UL / (frequency_hz * 2);
    uint32_t total_cycles = (duration_ms * 1000UL) / (half_period_us * 2);

    for (uint32_t i = 0; i < total_cycles; i++) {
        GPIOA->ODR |= GPIO_ODR_OD5;   // Drive PA5 High
        delay_us(half_period_us);
        GPIOA->ODR &= ~GPIO_ODR_OD5;  // Drive PA5 Low
        delay_us(half_period_us);
    }
    
    // Reduced silent gap (9ms) between faster notes for crisp separation
    GPIOA->ODR &= ~GPIO_ODR_OD5;
    delay_ms(9);
}

void setup(void) {
    // 1. Enable GPIOA peripheral clock
    RCC->IOPENR |= RCC_IOPENR_GPIOAEN;
    delay_ms(5); 

    // 2. Configure PA0 to PA3 explicitly as Input Mode (00)
    GPIOA->MODER &= ~(GPIO_MODER_MODE0 | GPIO_MODER_MODE1 | GPIO_MODER_MODE2 | GPIO_MODER_MODE3);

    // 3. Clear and activate internal Pull-Up Resistors (01) for pins PA0-PA3
    GPIOA->PUPDR &= ~(GPIO_PUPDR_PUPD0 | GPIO_PUPDR_PUPD1 | GPIO_PUPDR_PUPD2 | GPIO_PUPDR_PUPD3);
    GPIOA->PUPDR |= (GPIO_PUPDR_PUPD0_0 | GPIO_PUPDR_PUPD1_0 | GPIO_PUPDR_PUPD2_0 | GPIO_PUPDR_PUPD3_0);

    // 4. Configure PA5 as Output Mode (01)
    GPIOA->MODER &= ~(GPIO_MODER_MODE5);
    GPIOA->MODER |= GPIO_MODER_MODE5_0;
}

void loop(void) {
    // Read lower 4 bits of GPIOA IDR and invert them.
    uint32_t switch_state = (~GPIOA->IDR) & 0x0F;

    switch (switch_state) {
        case 0x01: // Switch 1 Only -> "Drunken Sailor" (Accelerated)
            play_tone(294, 90);  // D4
            play_tone(294, 90);  // D4
            play_tone(294, 90);  // D4
            play_tone(294, 90);  // D4
            play_tone(294, 90);  // D4
            play_tone(294, 90);  // D4
            play_tone(349, 90);  // F4
            play_tone(440, 180); // A4
            play_tone(392, 90);  // G4
            play_tone(392, 90);  // G4
            play_tone(392, 90);  // G4
            play_tone(392, 90);  // G4
            play_tone(330, 90);  // E4
            play_tone(330, 90);  // E4
            play_tone(330, 180); // E4
            break;

        case 0x02: // Switch 2 Only -> "London Bridge Is Falling Down" (Accelerated)
            play_tone(392, 120); // G4
            play_tone(440, 60);  // A4
            play_tone(392, 90);  // G4
            play_tone(349, 90);  // F4
            play_tone(330, 90);  // E4
            play_tone(349, 90);  // F4
            play_tone(392, 180); // G4
            play_tone(294, 90);  // D4
            play_tone(330, 90);  // E4
            play_tone(349, 180); // F4
            play_tone(330, 90);  // E4
            play_tone(349, 90);  // F4
            play_tone(392, 180); // G4
            break;

        case 0x04: // Switch 3 Only -> "Frere Jacques" (Accelerated)
            play_tone(261, 120); // C4
            play_tone(294, 120); // D4
            play_tone(330, 120); // E4
            play_tone(261, 120); // C4
            // Repeat phrase
            play_tone(261, 120); // C4
            play_tone(294, 120); // D4
            play_tone(330, 120); // E4
            play_tone(261, 120); // C4
            // Next phrase
            play_tone(330, 120); // E4
            play_tone(349, 120); // F4
            play_tone(392, 240); // G4
            break;

        case 0x08: // Switch 4 Only -> "US National Anthem" (Accelerated)
            play_tone(392, 90);  // G4
            play_tone(330, 90);  // E4
            play_tone(261, 180); // C4
            play_tone(330, 90);  // E4
            play_tone(392, 90);  // G4
            play_tone(523, 270); // C5
            play_tone(659, 90);  // E5
            play_tone(587, 90);  // D5
            play_tone(523, 180); // C5
            play_tone(330, 90);  // E4
            play_tone(370, 90);  // F#4
            play_tone(392, 270); // G4
            break;

        default:
            // No switches down -> absolute silence
            GPIOA->ODR &= ~GPIO_ODR_OD5; 
            delay_ms(10);                
            break;
    }
}