#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stm32l0xx_hal.h>

// Define ports and pins
#define LED_PORT        GPIOB
#define RED_PIN         GPIO_PIN_3 // D13
#define YELLOW_PIN      GPIO_PIN_4 // D12
#define GREEN_PIN       GPIO_PIN_5 // D11

#define LED_PORT_CLK_ENABLE __HAL_RCC_GPIOB_CLK_ENABLE

void SystemClock_Config(void);
static void MX_GPIO_Init(void);
void HAL_SYSTICK_Callback(void);

int main(void)
{
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();

    while (1)
    {
        // Nothing here, control is interrupt-driven
    }

    return 0;
}

// ============================================================
// GPIO Initialization
static void MX_GPIO_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStruct = {0};
    LED_PORT_CLK_ENABLE();

    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;

    // Configure all three pins
    GPIO_InitStruct.Pin = RED_PIN | YELLOW_PIN | GREEN_PIN;
    HAL_GPIO_Init(LED_PORT, &GPIO_InitStruct);
}

// ============================================================
// SysTick interrupt handler
void HAL_SYSTICK_Callback(void)
{
    static uint32_t counter = 0;
    static uint8_t state = 0;

    counter++;

    if (counter >= 10000) // 1000 ms = 1 second
    {
        counter = 0;

        // Turn off all LEDs first
        HAL_GPIO_WritePin(LED_PORT, RED_PIN | YELLOW_PIN | GREEN_PIN, GPIO_PIN_RESET);

        // Control LED state machine
        switch (state)
        {
            case 0: // RED
                HAL_GPIO_WritePin(LED_PORT, RED_PIN, GPIO_PIN_SET);
                state = 1;
                break;
            case 1: // GREEN
                HAL_GPIO_WritePin(LED_PORT, GREEN_PIN, GPIO_PIN_SET);
                state = 2;
                break;
            case 2: // YELLOW
                HAL_GPIO_WritePin(LED_PORT, YELLOW_PIN, GPIO_PIN_SET);
                state = 0;
                break;
        }
    }
}

// SystemClock_Config remains unchanged (from your image)