/* Stacks with Arrays Lab
   Version 1:  Stack contains pointers to strings
*/

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

/* MaxStack stands for the size of all stack arrays */
#define MaxStack 50  

typedef struct {
  int topPosition;
  char* items[MaxStack];
} stringStack;      /* type for a stack of strings */

/* index of standard stack operations */

void
initialize(stringStack* stack);

int
size(const stringStack* stack);

int
isEmpty(const stringStack* stack);

int
isFull(const stringStack* stack);

int
push(stringStack* stack, char* item);
/* post-condition:  item string is added to stack
                    length of string is returned 
*/

char*
pop(stringStack* stack);

char*
top(const stringStack* stack);

void
print(const stringStack* stack);

char*
get(const stringStack* stack, int index);
/* assume indexing starts at 1 */

/* ---------------------------------------------------------------------- */
/* Implementation of stack operations */

void
initialize(stringStack* stack)
{
  stack->topPosition = -1;
}

int
size(const stringStack* stack)
{
  return stack->topPosition+1;
}

int
isEmpty(const stringStack* stack)
{
  return (stack->topPosition == -1);
}

int
isFull(const stringStack* stack)
{
  return (stack->topPosition == (MaxStack-1));
}

int
push(stringStack* stack, char* item) {
/* post-condition:  item string is added to stack
                    length of string is returned 
*/
  /* return -1 if stack full */
  if (isFull(stack))
    return -1;
  
  /* add item to stack */
  (stack->topPosition) ++;
  stack->items[stack->topPosition] = item;
  return strlen(item);
}

char*
pop(stringStack *stack)
{
  char* item;  /* string [base address] to return */
  /* return -1 if stack empty */
  if (isEmpty(stack)) 
    return (char *)(-1);
  
  /* remove item from stack */
  item = stack->items[stack->topPosition];
  (stack->topPosition) --;
  return item;
}
  
char*
top(const stringStack* stack)
{
  /* return -1 if stack empty */
  if (isEmpty(stack)) 
    return (char *)(-1);

  /* remove item from stack */
  return stack->items[stack->topPosition];
}

void
print(const stringStack* stack)
{
  int i;
  printf ("contents of stack from top to bottom:\n");
  for (i = stack->topPosition; i >= 0; i--)
    printf ("    %s\n", stack->items[i]);
  printf ("end of stack\n");
}

char*
get(const stringStack* stack, int index)
{
  /* assume nth indexing starts at 1
     translate to 0-indexed arrays, counting from topPosition 
     return -1 if invalid index specified */
  if ( (index < 1) || (index > stack->topPosition+1))
    return (char*)(-1);

  return stack->items[(stack->topPosition) - index + 1];
}