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

#define MAX_INPUT_LENGTH 80
#define MAX_TOKENS 20
#define DEFAULT_PROMPT "osh> "
#define NULL_CHAR '\0'

typedef char *  String;
typedef char ** StringArray;

/* Enumerated list for valid commands.  Add to list as language grows */
enum Commands { INVALID, EXIT, FILES };  

/* Returns numeric code corresponding to string containing command name 
 */

enum Commands getCommand(String comName) {
   if (!strcmp("exit",comName)) {
       return EXIT;
   } else if (!strcmp("files",comName)) {
       return FILES;
   } else  /* expand as command language grows */
       return INVALID;
}


/* Separate input into its component words - assume space(s) as delimiter
 *
 * First param is String (char array) containing input.
 * Second param is array of String (array of char arrays).  
 * This function will extract each word from input, copying it into next
 * element of array of Strings, starting at element 0.
 * Since both parameters are arrays, they alias the corresponding argument 
 * and any changes made here also affect the caller's argument.
 *
 * Return value is word count.
 */

int inputParse(String line,  StringArray words) {
   int count = 0;
   int i=0;
   int position=0;
   int done = 0;
   while (!done) {
      words[count] = (String) malloc((strlen(line)+1) * sizeof(char));
      while (i < strlen(line) && line[i] != ' ' && line[i] != '\t') {
         words[count][position] = line[i];
         position++;
         i++;
      }
      words[count][position] = NULL_CHAR;
      count++; 
      position=0;
      while (i < strlen(line) && (line[i] == ' ' || line[i] == '\t')) {
         i++;
      }
      if (i >= strlen(line)) {
         done = 1;
      }
   }
   return count;
}


/* handy utility to deallocate space allocated in inputParse
 */

void freeTheTokens(int count, StringArray theTokens) {
   int i;
   for (i=0; i<count; i++) {
      free(theTokens[i]);
   }
}


/* Function to implement the "files" command
 */

/* THIS IS A PROTOTYPE: MERELY ECHOES THE FIRST WORD FROM COMMAND LINE. 
 * YOU NEED TO REMOVE printf and MODIFY IT TO DO WHAT IT IS SUPPOSED TO DO. 
 */

void files(int numWords, StringArray commLine) {
   printf("got %d word command: %s\n", numWords, commLine[0]);
}


int main() {
   String input = (String) malloc(MAX_INPUT_LENGTH * sizeof(char));
   StringArray tokens = (StringArray) malloc(MAX_TOKENS * sizeof(String));

   int numTokens;
   String prompt = DEFAULT_PROMPT;
   int finished = 0;

   while (!finished) {
       printf("%s", prompt);
       fgets(input, MAX_INPUT_LENGTH, stdin); /* enforces buffer length */
       input[strlen(input)-1] = NULL_CHAR;    /* replace newline with null */
       numTokens = inputParse(input, tokens);
       if (numTokens > 0) {
          switch (getCommand(tokens[0])) {  /* first word contains command */
            case EXIT  :  finished = 1;
                          break;
            case FILES :  files(numTokens, tokens); /* do files command */
                          break;
            case INVALID: printf("Invalid command: %s\n", tokens[0]);
                          break;
          }
          freeTheTokens(numTokens, tokens);
       }

   }
   return 0;
}