/**
 * array-stack.c
 *   An array-based implementation of stacks.
 */

// +---------+--------------------------------------------------------
// | Headers |
// +---------+

#include <stdlib.h>     // For malloc

#include "linear.h"     // Signatures of the methods we provide.


// +-------+----------------------------------------------------------
// | Types |
// +-------+

struct linear
  {
    char **contents;    // Contents of the stack (an array of strings)
    int capacity;       // Capacity of the stack
    int size;           // Number of elements in the stack
  };


// +---------+--------------------------------------------------------
// | Helpers |
// +---------+


// +----------------------------+-------------------------------------
// | Constructors & Destructors |
// +----------------------------+

struct linear *
construct (int minimum_capacity)
{
  // Allocate the enclosing structure
  struct linear *linear = (struct linear *) malloc (sizeof (struct linear));
  if (linear == NULL)
    return NULL;

  // Allocate the array of strings
  linear->contents = calloc (minimum_capacity, sizeof (char *));
  if (linear->contents == NULL)
    {
      free (linear);
      return NULL;
    }

  // Fill in the fields.  (Note that calloc zeroes memory, so we don't
  // have to set things to 0.)
  linear->capacity = minimum_capacity;
  linear->size = 0;

  // And we're done
  return linear;
} // construct

void 
destruct (struct linear *linear)
{
  free (linear->contents);
  linear->contents = NULL;
  free (linear);
} // destruct


// +-----------+------------------------------------------------------
// | Observers |
// +-----------+

int 
is_empty (struct linear *linear)
{
  return linear->size == 0;
} // is_empty

int 
is_full (struct linear *linear)
{
  return linear->size == linear->capacity;
} // is_full

char *
peek (struct linear *linear)
{
  if (linear->size == 0)
    return NULL;
  return linear->contents[linear->size-1];
} // peek


// +----------+-------------------------------------------------------
// | Mutators |
// +----------+

int 
add (struct linear *linear, char *str)
{
  linear->contents[(linear->size)++] = str;
  return 1;
} // add

char *
get (struct linear *linear)
{
  return linear->contents[--(linear->size)];
} // get

void 
clear (struct linear *linear)
{
  linear->size = 0;
} // clear