#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dlfcn.h>
#include <unistd.h>

static FILE *(*real_fopen)(const char *path, const char *mode) = NULL;

static void init_real_fopen(void) {
    if (!real_fopen) {
        real_fopen = dlsym(RTLD_NEXT, "fopen");
        if (!real_fopen) {
            fprintf(stderr, "proc_redirect: dlsym(fopen) failed: %s\n", dlerror());
            abort();
        }
    }
}

FILE *fopen(const char *path, const char *mode) {
    init_real_fopen();

    if (path && strncmp(path, "/proc/", 6) == 0) {
        const char *rel_suffix = path + 1;
        size_t len = strlen(rel_suffix) + 4;
        char *new_path = malloc(len);
        if (!new_path) {
            fprintf(stderr, "proc_redirect: malloc failed\n");
            abort();
        }
        new_path[0] = '.';
        new_path[1] = '/';
        new_path[2] = '.';
        strcpy(new_path + 3, rel_suffix);

        FILE *f = real_fopen(new_path, mode);
        free(new_path);
        return f;
    }

    return real_fopen(path, mode);
}

FILE *tmpfile(void) {
    char path[] = "./tmpfile_XXXXXX";
    int fd = mkstemp(path);
    if (fd == -1) {
        fprintf(stderr, "proc_redirect: mkstemp failed\n");
        abort();
    }
    fprintf(stderr, "proc_redirect: tmpfile created at %s\n", path);
    FILE *f = fdopen(fd, "w+");
    if (!f) {
        close(fd);
        abort();
    }
    return f;
}