#include <dlfcn.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

//#define DEBUG

#ifdef DEBUG
#define DEBUG_PRINT(x) printf x;
#else
#define DEBUG_PRINT(x) ;
#endif

typedef struct {
    sem_t request_ready;
    sem_t response_ready;
    char func_name[20];
    double value;
    double result;
} shared_data_t;

typedef double (*dd_func_t)(double);

const char SHM_NAME[] = "/maximmum_shm";
enum { SHM_PERMS = 0644 };

void prepare_shared_data(shared_data_t* data) {
    memset(data, 0, sizeof(shared_data_t));

    sem_init(&data->request_ready, 1, 0);
    sem_init(&data->response_ready, 1, 0);
}

int main(int argc, char** argv)
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <library name>", argv[0]);
        return 1;
    }

    void* lib = dlopen(argv[1], RTLD_NOW);
    if (!lib) {
        fprintf(stderr, "Error on dlopen: %s\n", dlerror());
        return 1;
    }

    const size_t page_size = sysconf(_SC_PAGESIZE);
    int shm_fd = shm_open(SHM_NAME, O_CREAT | O_RDWR, SHM_PERMS);
    const size_t needed_size = sizeof(shared_data_t);
    const size_t shm_size = (needed_size % page_size == 0 ?
                            needed_size :
                            (needed_size / page_size + 1) * page_size);
    ftruncate(shm_fd, shm_size);

    shared_data_t* data =
        mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    prepare_shared_data(data);

    sem_t* request_ready_sem = &data->request_ready;
    sem_t* response_ready_sem = &data->response_ready;

    printf("%s\n", SHM_NAME);
    fflush(stdout);

    do {
        DEBUG_PRINT(("1: sem_wait...\n"));
        sem_wait(request_ready_sem);
        DEBUG_PRINT(("1: sem waited\n"));

        if (data->func_name[0] == '\0') {
            DEBUG_PRINT(("1: func_name is empty, exiting...\n"));
            break;
        }

        void* sym = dlsym(lib, data->func_name);
        if (!sym) {
            fprintf(stderr, "Error on dlsym: %s\n", dlerror());
            break;
        }

        dd_func_t func = sym;

        data->result = func(data->value);

        sem_post(response_ready_sem);
        DEBUG_PRINT(("1: sem posted\n"));
    } while (data->func_name[0] != '\0');

    sem_destroy(response_ready_sem);
    sem_destroy(request_ready_sem);
    munmap((void*)data, shm_size);
    close(shm_fd);
    shm_unlink(SHM_NAME);
    dlclose(lib);

    return 0;
}