#include <math.h>
#include <stdio.h>
#include <complex.h>
#include <stdint.h>
#include <stdlib.h>

complex float* fft(complex float* p, uint32_t N) {
    complex float w = cexpf(-2 * I * M_PI / N);

    if (N == 1)
        return p;

    complex float* pe = (complex float*)malloc(sizeof(complex float) * (N / 2));
    complex float* po = (complex float*)malloc(sizeof(complex float) * (N / 2));
    for (int i = 0; i < N - 1; i += 2) {
       pe[i / 2] = p[i];
       po[i / 2] = p[i + 1];
    }

    complex float* xe = fft(pe, N / 2);
    complex float* xo = fft(po, N / 2);

    complex float* ps = (complex float*)malloc(sizeof(complex float) * N);

    for (int i = 0; i < N / 2; i++) {
        ps[i] = xe[i] + cpowf(w, (complex float)i) * xo[i];
        ps[i + N / 2] = xe[i] - cpowf(w, (complex float)i) * xo[i];
    }
    
    return ps;
}

int main() {
    FILE *f = fopen("signal.csv","r");
    if (!f) { perror("signal.csv"); return 1; }

    double t, a;
    int capacity = 1024, n = 0;
    complex float *samples = malloc(sizeof(complex float) * capacity);

    while (fscanf(f, "%lf;%lf", &t, &a) == 2) {
        if (n >= capacity) {
            capacity *= 2;
            samples = realloc(samples, sizeof(complex float)*capacity);
        }
        samples[n++] = a; 
    }
    fclose(f);

    int fsize = 1 << (int)floorf(log2f((float)n));

    complex float* cwav_data = (complex float*)malloc(sizeof(complex float) * fsize);
    for (int i = 0; i < fsize; i++)
        cwav_data[i] = samples[i];

    complex float* ft = fft(cwav_data, fsize);

    double Fe = 400.0; 

    FILE *gnuplot = popen("gnuplot -persistent", "w");
    fprintf(gnuplot, "set title 'fft'\n");
    fprintf(gnuplot, "set logscale x\n");
    fprintf(gnuplot, "set logscale y\n");
    fprintf(gnuplot, "plot '-' with linespoints title 'fft'\n");

    for (int i = 0; i < fsize/2; i++) {
        double freq = (double)i * Fe / fsize;
        fprintf(gnuplot, "%f %f\n", freq ,cabsf(ft[i])); 
    }
    fprintf(gnuplot, "e\n");
    pclose(gnuplot);

    free(samples);
    free(cwav_data);
    free(ft);

    return 0;
}