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

/* ST Nucleo Green user LED (PB3)
* As defined in https://www.st.com/resource/en/user_manual/um1956-stm32-nucleo32-boards-mb1180-stmicroelectronics.pdf
*/
#define LED_PORT                GPIOB 
#define LED_PIN                 GPIO_PIN_3
#define LED_PORT_CLK_ENABLE     __HAL_RCC_GPIOB_CLK_ENABLE
#define VCP_TX_Pin GPIO_PIN_2
#define VCP_RX_Pin GPIO_PIN_15

UART_HandleTypeDef UartHandle;

void GPIO_Init();
void Uart_Init();

volatile uint32_t led_ready = 0;

/*
Called by SysTick_Handler
See: https://developer.arm.com/documentation/107565/0101/Use-case-examples/rtos-context-switch/Basic-Building-Blocks/The-SysTick-Timer
*/
void osSystickHandler(void)
{
  static uint32_t tick_count = 0;
  tick_count++;
  //printf("tick count %d\n", tick_count);
  if ((tick_count % 500) == 0)
  {
    printf("led ready!\n");
    led_ready = 1;  // Signal main loop to toggle LED
  }
}

int main(void)
{
  Uart_Init();
  printf("UART initialized.\n");

  HAL_Init();
  printf("HAL initialized.\n");
  GPIO_Init();
  printf("GPIO init\n");
  HAL_GPIO_TogglePin(LED_PORT, LED_PIN);
  printf("TogglePin\n");
  while (1) {
    //printf("here 1\n");
    if (led_ready) {
      HAL_GPIO_TogglePin(LED_PORT, LED_PIN);

      led_ready = 0;
    }
  }

  return 0;
}

/*
Initialize GPIOs
*/
void GPIO_Init()
{
  GPIO_InitTypeDef GPIO_Config;

  GPIO_Config.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_Config.Pull = GPIO_NOPULL;
  GPIO_Config.Speed = GPIO_SPEED_FREQ_HIGH;
  GPIO_Config.Pin = LED_PIN;

  LED_PORT_CLK_ENABLE();
  HAL_GPIO_Init(LED_PORT, &GPIO_Config);
}

/*
Re-routing of the C library printf function to the UART.
The UART outputs a message on the HyperTerminal.

Board: STM32L031K6-Nucleo
Tx Pin: PA.02 (A7 : pin 5 on CN4)
Rx Pin: PA.03 (A2 : pin 10 on CN4)
   _________________________
  |           ______________|                       _______________
  |          |USART         |                      | HyperTerminal |
  |          |              |                      |               |
  |          |           TX |______________________|RX             |
  |          |              |                      |               |
  |          |              |     RS232 Cable      |               |
  |          |              |                      |               |
  |          |           RX |______________________|TX             |
  |          |              |                      |               |
  |          |______________|                      |_______________|
  |                         |
  |                         |
  |                         |
  |                         |
  |_STM32_Board_____________|

The USART2 is configured as follows:
    - BaudRate = 115200 baud
    - Word Length = 8 Bits (7 data bit + 1 parity bit)
    - One Stop Bit
    - Odd parity
    - Hardware flow control disabled (RTS and CTS signals)
    - Both TX and RX are enabled
*/
void Uart_Init(void)
{
  __HAL_RCC_GPIOA_CLK_ENABLE();

  GPIO_InitTypeDef GPIO_InitStruct = {0};
  GPIO_InitStruct.Pin = VCP_TX_Pin|VCP_RX_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF4_USART2;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  UartHandle.Instance        = USART2;
  UartHandle.Init.BaudRate   = 115200;
  UartHandle.Init.WordLength = UART_WORDLENGTH_8B;
  UartHandle.Init.StopBits   = UART_STOPBITS_1;
  UartHandle.Init.Parity     = UART_PARITY_ODD;
  UartHandle.Init.HwFlowCtl  = UART_HWCONTROL_NONE;
  UartHandle.Init.Mode       = UART_MODE_TX_RX;
  if (HAL_UART_Init(&UartHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
}

void Error_Handler(void)
{
  while(1);
}

/*
 * _write function is used to redirect the printf output to the UART.
 * It is called by the C library printf function.
 */
int _write(int file, uint8_t *ptr, int len)
{
  switch (file)
  {
    case STDOUT_FILENO:
    case STDERR_FILENO:
      if (HAL_UART_Transmit(&UartHandle, ptr, len, HAL_MAX_DELAY) != HAL_OK)
      {
        return -1;
      }
      break;
    default:
      return -1;
  }
  return len;
}