#include <stdio.h>
#include <stdlib.h>

typedef struct
{
    const char *data;
} UART;

#define START_ASYNC static int state = 0; switch (state) { case 0:
#define WAIT state = __LINE__; return; case __LINE__:
#define END_ASYNC }

int data_available(UART *in)
{
    return *in->data != '\0' && rand() % 5 == 0;
}

char read_byte(UART *in)
{
    return *in->data++;
}

int ready_for_sending(UART *out)
{
    return rand() % 5 == 0;
}

void write_byte(UART *out, char ch)
{
    printf("%c", ch);
}


void echo_infinite(UART *in, UART *out)
{
    while (1)
    {
        while (!data_available(in))
        {
            // wait
        }
        char ch;
        ch = read_byte(in);
        while (!ready_for_sending(out))
        {
            // wait
        }
        write_byte(out, ch);
    }
}

void echo_state_machine(UART *in, UART *out)
{
    static char ch;
    static int state = 0;
    switch (state)
    {
        case 0:
            if (data_available(in))
            {
                ch = read_byte(in);
                state = 1;
            }
            break;
        case 1:
            if (ready_for_sending(out))
            {
                write_byte(out, ch);
                state = 0;
            }
            break;
    }
}

void echo_async(UART *in, UART *out)
{
    START_ASYNC
    while (1)
    {
        while (!data_available(in))
        {
            WAIT
        }
        static char ch;
        ch = read_byte(in);
        while (!ready_for_sending(out))
        {
            WAIT
        }
        write_byte(out, ch);
    }
    END_ASYNC
}

int main(int argc, char *argv[])
{
    int seed = 0;
    if (argc > 1) seed = atoi(argv[1]);
    if (seed == 0) seed = 1;
    srand(seed); 

    UART in;
    UART out;
    
    printf("function: echo_state_machine\n----\n");
    in.data = "Hello World!\n";
    for (int i = 0; i < 100; i++)
        echo_state_machine(&in, &out);
    printf("-----\n\n");
    
    printf("function: echo_async\n----\n");
    in.data = "Hello World!\n";
    for (int i = 0; i < 100; i++)
        echo_async(&in, &out);
    printf("-----\n\n");

    printf("function: echo_infinite\n----\n");
    in.data = "Hello World!\n";
    echo_infinite(&in, &out);
    printf("-----\n\n");

    
    return 0;
}