/**
 * Lab 2
 * Note that this program would print out garbage for the first few characters
 * received. It will work as intended after a few characters are received.
 */

#include <stdio.h>
#include "pico/stdlib.h"

#define UART_ID uart0
#define BAUD_RATE 115200    // Baud rate of UART

#define UART_TX_PIN 16      // GPIO for UART TX pin
#define UART_RX_PIN 17      // GPIO for UART RX pin
#define GPIO_PIN 15         // GPIO for pseudo button

#define SLEEP_TIME 100     // For testing can use a smaller value
                            // 1000ms is based on the lab requirements

/**
 * Sends a character through UART0 based on the state of GPIO15 (Pseudo button)
 * @param uart_input  Pointer to a character to be sent through UART0 (Space optimisation)
 * @return void       Prints the character in uart_receive()
 */
void uart_transmit(char *uart_input) {
    if (gpio_get(GPIO_PIN)) {           // Active low
        uart_putc(UART_ID, '1');
    } else {                                // Active high
        uart_putc(UART_ID, *uart_input);
        *uart_input = (*uart_input - 'A' + 1) % 26 + 'A'; // Next character
                                                          // Wrap around back to A
    }
}

/**
 * Receives a character through UART0 and prints it out
 * Ideally, the buffer should be cleared after each read
 * NOTE: Flipping bit 5 effectively converts a character to lowercase
 * @param uart_output Pointer to a location to store the received character (Space optimisation)
 * @return void       Character is read and printed
 */
void uart_receive(char *uart_output) {
    if (uart_is_readable(UART_ID)) {
        *uart_output = uart_getc(UART_ID);

        if (*uart_output >= 'A' && *uart_output <= 'Z') {
            *uart_output ^= (1 << 5);   // XOR with 32 to convert to lowercase
                                        // This operation flips bit 5
        } else if (*uart_output == '1') {
            *uart_output = '2';         // If '1' is received, print '2'
        }

        printf("%c\n", *uart_output);
    }
}

/**
 * Initializes UART0 and GPIO pins
 * @return void
 */
void pin_init() {
    // UART init
    uart_init(UART_ID, BAUD_RATE);
    gpio_set_function(UART_TX_PIN, GPIO_FUNC_UART);
    gpio_set_function(UART_RX_PIN, GPIO_FUNC_UART);

    // Pseudo button init
    gpio_set_dir(GPIO_PIN, GPIO_IN);
}

int main() {
    stdio_init_all();
    pin_init();

    char uart_input = 'A'; // Initial value of A
    char uart_output;      // To store received character

    while (true) {
        uart_transmit(&uart_input); // Pass by reference to change
                                    // value of uart_input during transmission

        uart_receive(&uart_output); // Pass by reference to change
                                    // value of uart_output during reception

        sleep_ms(SLEEP_TIME); // Sleep based on SLEEP_TIME
    }

}