// Make a shell which supports
// exiting the shell with exit or Ctrl D
// changing the current directory with cd
// printing directory with getcwd
// run the specificed program in the current dir using posix_spawn
// should work for full path or relative path
// simple args, separated by spaces

#include <linux/limits.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <spawn.h>
#include <sys/wait.h>
#include <limits.h>
#include <errno.h>

#define BUFFER_SIZE 8192

extern char **environ;

int main(void) {
    char buffer[BUFFER_SIZE];
    while (1) {
        printf(":) ");
        if (fgets(buffer, BUFFER_SIZE, stdin) == NULL){
            printf("\n");
            break;
        }
        // Get rid of trailing newline character;
        size_t len_input = strlen(buffer);
        if (buffer[len_input - 1] == '\n' ){
            buffer[len_input - 1] = '\0';
        }

        if (strcmp(buffer,"exit") == 0) {
            break;
        }
        // cd XXXXXXXXXXXX
        if (strncmp(buffer, "cd ", 3) == 0) {
            chdir(buffer+3);
        } else if (strcmp(buffer, "pwd") == 0) {
            char path_buffer[PATH_MAX];
            getcwd(path_buffer, PATH_MAX);
            printf("%s\n", path_buffer);
        } else {
            //ls -l asdf 
            pid_t process_id;
                           //"/bin/ls"
            char *args[128];
            char *tokens = strtok(buffer, " ");
            int argc = 0;
            while (tokens != NULL && argc < 127) {
                args[argc++] = tokens;
                tokens = strtok(NULL, " ");
            }
            args[argc++]= NULL;

            int ret = posix_spawnp(&process_id, args[0], NULL, NULL, args, environ);
            if (ret != 0) {
                errno = ret;
                fprintf(stderr, "No %s\n", strerror(errno));
            } else {
                waitpid(process_id, NULL, 0);
            }                                
        }
    }
    return 0;
}