//
// Written for Computer Networks and Systems lab classes
// AUTHOR : Sergiusz Warga

#include <fcntl.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <time.h>

#include "CircBuffer.h"
#include "funs.h"

void handle_arguments(int argc, char *argv[]) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s REFRESHING_FREQUENCY ALPHA\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    if (strtol(argv[1], NULL, 10) < 2) {
        fprintf(stderr, "Refreshing frequency should be at least 2Hz!\n");
        exit(EXIT_FAILURE);
    }

    if (strtod(argv[2], NULL) > 1 || strtod(argv[2], NULL) < 0) {
        fprintf(stderr, "Alpha coefficient should be in range [0, 1]!\n");
        exit(EXIT_FAILURE);
    }
}

_Noreturn void k_avg(int fd, int refreshing_frequency, double alpha) {
    // Exponential Moving Average
    printf("A k_avg has been called\n");

    //----- Initialize the buffer -----
    struct CircBuffer *buffer;
    buffer = mmap(NULL, sizeof(struct CircBuffer), PROT_READ, MAP_SHARED, fd, 0);
    if (buffer == MAP_FAILED) {
        fprintf(stderr, "mmap: ");
        exit(EXIT_FAILURE);
    }

    struct timespec delay, tic, toc;
    delay.tv_sec = 0;
    delay.tv_nsec = (1./refreshing_frequency * NSEC_PER_SEC); // 1/f in nanoseconds
    clock_gettime(CLOCK_REALTIME, &tic);

    double ema;
    int read_idx;
    
    read_idx = buffer->info.free_idx - 1;
    ema = buffer->data[read_idx];
    printf("Refreshing period = %ldms\n", delay.tv_nsec/1000000);

    while (1) {
        clock_gettime(CLOCK_REALTIME, &toc);
        if (timespec_diff_nano(&toc, &tic) > delay.tv_nsec) {
            printf("EMA = %f\n", ema);
            clock_gettime(CLOCK_REALTIME, &tic);
        }
        while (read_idx == ((buffer->info.free_idx - 1) % buffer->info.size)) {};
        read_idx = ++read_idx % buffer->info.size;
        ema = alpha * buffer->data[read_idx] + (1 - alpha) * ema;
    }
}

int main(int argc, char *argv[]) {

    handle_arguments(argc, argv);

    //----- Open a shared memory -----
	const char *memory_name = "/dsp";
	int fd = shm_open(memory_name, O_RDONLY, 0777);
    if (fd < 0) {
        fprintf(stderr, "shm_open: ");
        exit(EXIT_FAILURE);
    }
    printf("Shared memory file descriptor: %d\n", fd);

    k_avg(fd, strtol(argv[1], NULL, 10), strtod(argv[2], NULL));

	return 0;
}