#include <stdio.h>              // Standard C I/O library (printf, etc.)
#include <stdint.h>             // Standard integer types (uint8_t, uint32_t, etc.)
#include <string.h>             // Standard string handling functions
#include <stm32c0xx_hal.h>      // STM32C0 HAL (Hardware Abstraction Layer) main header

// ST Nucleo Green user LED (PA5)
#define LED_PORT                GPIOA               // GPIO port where the LED is connected
#define LED_PIN                 GPIO_PIN_5          // Pin number for the LED (PA5)
#define LED_PORT_CLK_ENABLE     __HAL_RCC_GPIOA_CLK_ENABLE // Macro to enable GPIOA clock

UART_HandleTypeDef huart2;       // UART handle structure for USART2

void SystemClock_Config(void);   // Prototype for system clock configuration function
static void MX_USART2_UART_Init(void); // Prototype for USART2 initialization function

void osSystickHandler(void)
{
  // This function is intended to be called periodically from SysTick
  // HAL_GetTick() returns the system tick count in milliseconds

  // 1 Hz blinking:
  if ((HAL_GetTick() % 500) == 0) // Check every 500 ms
  {
    HAL_GPIO_TogglePin(LED_PORT, LED_PIN); // Toggle LED state
  }
}

void initGPIO()
{
  GPIO_InitTypeDef GPIO_Config;   // GPIO configuration structure

  GPIO_Config.Mode = GPIO_MODE_OUTPUT_PP; // Configure pin as push-pull output
  GPIO_Config.Pull = GPIO_NOPULL;         // No internal pull-up or pull-down resistor
  GPIO_Config.Speed = GPIO_SPEED_FREQ_HIGH; // High-speed GPIO output

  GPIO_Config.Pin = LED_PIN;      // Select LED pin (PA5)

  LED_PORT_CLK_ENABLE();          // Enable clock for GPIOA peripheral
  HAL_GPIO_Init(LED_PORT, &GPIO_Config); // Initialize GPIOA with the configuration

  __HAL_RCC_GPIOA_CLK_ENABLE();   // (Redundant) Enable GPIOA clock again
}

int main(void)
{
  HAL_Init();                     // Initialize HAL library and SysTick
  SystemClock_Config();           // Configure system clock

  initGPIO();                     // Initialize LED GPIO
  MX_USART2_UART_Init();          // Initialize USART2 for serial communication

  printf("Hello, %s!\n", "Wokwi"); // Send text over USART2 using printf

  HAL_GPIO_TogglePin(LED_PORT, LED_PIN); // Toggle LED once at startup

  while (1);                      // Infinite loop (program runs forever)

  return 0;                       // Never reached
}

/**
    @brief System Clock Configuration
    @retval None
*/
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0}; // Oscillator configuration structure
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0}; // Clock tree configuration structure

  /** Initializes the RCC Oscillators according to the specified parameters */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI; // Use internal HSI oscillator
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;                   // Turn HSI on
  RCC_OscInitStruct.HSIDiv = RCC_HSI_DIV1;                   // No division of HSI
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT; // Default calibration

  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();             // Handle oscillator configuration error
  }

  /** Initializes the CPU, AHB and APB buses clocks */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_SYSCLK
                                | RCC_CLOCKTYPE_PCLK1; // Select clocks to configure
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI; // Use HSI as system clock
  RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;     // SYSCLK = HSI
  RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV1;       // AHB clock = SYSCLK
  RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV1;      // APB1 clock = AHB clock

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
  {
    Error_Handler();             // Handle clock configuration error
  }
}

/**
    @brief USART2 Initialization Function
    @param None
    @retval None
*/
static void MX_USART2_UART_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0}; // GPIO configuration structure

  __HAL_RCC_GPIOA_CLK_ENABLE();   // Enable clock for GPIOA

  // PA2     ------> USART2_TX
  // PA3     ------> USART2_RX
  GPIO_InitStruct.Pin = GPIO_PIN_2 | GPIO_PIN_3; // Select PA2 and PA3
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;        // Alternate function push-pull
  GPIO_InitStruct.Pull = GPIO_NOPULL;            // No pull-up or pull-down
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;   // Low-speed GPIO
  GPIO_InitStruct.Alternate = GPIO_AF1_USART2;   // AF1 maps pins to USART2
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);        // Initialize GPIOA pins
  
  huart2.Instance = USART2;       // Select USART2 peripheral
  huart2.Init.BaudRate = 115200;  // Communication speed: 115200 baud
  huart2.Init.WordLength = UART_WORDLENGTH_8B; // 8-bit data
  huart2.Init.StopBits = UART_STOPBITS_1;      // 1 stop bit
  huart2.Init.Parity = UART_PARITY_NONE;        // No parity bit
  huart2.Init.Mode = UART_MODE_TX_RX;           // Enable TX and RX
  huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;  // No hardware flow control
  huart2.Init.OverSampling = UART_OVERSAMPLING_16; // Oversampling by 16
  huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE; // Disable one-bit sampling
  huart2.Init.ClockPrescaler = UART_PRESCALER_DIV1; // No clock prescaling
  huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT; // No advanced features

  if (HAL_UART_Init(&huart2) != HAL_OK)
  {
    Error_Handler();             // Handle UART initialization error
  }
}

void Error_Handler(void)
{
  /* User can add custom error handling code here */
}

// The following makes printf() write to USART2:

#define STDOUT_FILENO   1         // File descriptor for standard output
#define STDERR_FILENO   2         // File descriptor for standard error

int _write(int file, uint8_t *ptr, int len)
{
  switch (file)
  {
    case STDOUT_FILENO:           // Standard output (printf)
      HAL_UART_Transmit(&huart2, ptr, len, HAL_MAX_DELAY); // Send data via UART
      break;

    case STDERR_FILENO:           // Standard error output
      HAL_UART_Transmit(&huart2, ptr, len, HAL_MAX_DELAY); // Send data via UART
      break;

    default:
      return -1;                  // Unsupported file descriptor
  }

  return len;                     // Return number of bytes written
}