#include "headers/nstdo.h"
extern long sys_read(int fd, void *buf, size_t cnt);
extern long sys_write(int fd, const void *buf, size_t cnt);
extern long sys_fork(void);
extern long sys_execve(const char *filename, char *const argv[], char *const envp[]);
extern long sys_wait4(int pid, int *wstatus, int options, void *rusage);
extern void sys_exit(int status);

static int streq(const char *a, const char *b) {
    while (*a && *b) {
        if (*a != *b) return 0;
        a++; b++;
    }
    return *a == *b;
}

static long str_len(const char *s) {
    long len = 0;
    while (s[len]) len++;
    return len;
}

int main(int argc, char *argv[], char *envp[]) {
    (void)argc; (void)argv;
    const char prompt[] = "$ ";
    char buf[512];
    while (1) {
        sys_write(1, prompt, sizeof(prompt)-1);
        long n = sys_read(0, buf, sizeof(buf)-1);
        if (n <= 0) break;
        buf[n-1] = '\0';
        if (streq(buf, "help")) {
            const char *h1 = "  help  - display this help message\n";
            const char *h2 = "  exit  - exit the shell\n";
            sys_write(1, h1, str_len(h1));
            sys_write(1, h2, str_len(h2));
            continue;
        }
        if (streq(buf, "exit")) {
            break;
        }
        char *args[] = { buf, NULL };
        long pid = sys_fork();
        if (pid == 0) {
            sys_execve(buf, args, envp);
            sys_exit(1);
        } else {
            sys_wait4(pid, 0, 0, 0);
        }
    }
    return 0;
}