#include "shim-signal.h"
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static pid_t hakurei_shim_param_ppid = -1;
static int hakurei_shim_fd = -1;

/* see shim.go for handling of the message */
static inline ssize_t hakurei_shim_write(hakurei_shim_msg msg) {
    int savedErrno = errno;
    unsigned char buf = (unsigned char)msg;
    ssize_t ret = write(hakurei_shim_fd, &buf, 1);
    if (ret == -1 && errno != EAGAIN)
        exit(EXIT_FAILURE);
    errno = savedErrno;
    return ret;
}

static void hakurei_shim_sigaction(int sig, siginfo_t *si, void *ucontext) {
    if (sig != SIGCONT || si == NULL) {
        hakurei_shim_write(HAKUREI_SHIM_INVALID);
        return;
    }

    if (si->si_pid == hakurei_shim_param_ppid) {
        hakurei_shim_write(HAKUREI_SHIM_EXIT_REQUESTED);
        return;
    }

    hakurei_shim_write(HAKUREI_SHIM_BAD_PID);

    if (getppid() != hakurei_shim_param_ppid)
        hakurei_shim_write(HAKUREI_SHIM_ORPHAN);
}

void hakurei_shim_setup_cont_signal(pid_t ppid, int fd) {
    if (hakurei_shim_param_ppid != -1 || hakurei_shim_fd != -1)
        *(volatile int *)NULL = 0; /* unreachable */

    struct sigaction new_action = {0}, old_action = {0};
    if (sigaction(SIGCONT, NULL, &old_action) != 0)
        return;
    if (old_action.sa_handler != SIG_DFL) {
        errno = ENOTRECOVERABLE;
        return;
    }

    new_action.sa_sigaction = hakurei_shim_sigaction;
    if (sigemptyset(&new_action.sa_mask) != 0)
        return;
    new_action.sa_flags = SA_ONSTACK | SA_SIGINFO;

    if (sigaction(SIGCONT, &new_action, NULL) != 0)
        return;

    errno = 0;
    hakurei_shim_param_ppid = ppid;
    hakurei_shim_fd = fd;
}
