// Stack in C language

#include <stdio.h>
#include <stdlib.h>
 
#include "person.h"                           // use person from before
 
#define STACK_SIZE 100                        // constant for array size
#define EMPTY_TOS  -1                         // top-of-stack starts at -1

struct stack{                                 // data structure is encapsulated into struct
  int top;                                    // stack has a top
  person_ptr stack_array[STACK_SIZE];         // and an array of person ptrs
};
typedef struct stack *stack_ptr;              // stack accessed via this ptr

int isEmpty(stack_ptr s) {                    // function returns "boolean" 
  return(s->top == EMPTY_TOS);
}

int isFull(stack_ptr s) {                     // stack is full if all elements used
  return(s->top == STACK_SIZE-1);
}

void push(stack_ptr s, person_ptr p) {        // give stack ptr, and person ptr
  if (!isFull(s))                             // use s to tell if full
    s->stack_array[++s->top] = p;             // s-> allows us to examine array and top
}                                             // pre-increment the top, and then add ptr

person_ptr pop(stack_ptr s) {                 // return a ptr that is on top of stack
  if (isEmpty(s))                             // return default if empty
    return NULL;
  else
    return(s->stack_array[s->top--]);         // access the top, then post-decrement
}

stack_ptr stackConstructor() {                // artificial C constructor
  stack_ptr s;
  s = (stack_ptr) malloc(sizeof(struct stack)); // allocate storage
  s->top = EMPTY_TOS;                           // initialize top field
  return(s);
}

void stackDestructor(stack_ptr s) {           // artificial C deconstructor
  while (!isEmpty(s))                         // iterate through all ptrs
    personDestructor(pop(s));                 // memory leak - all persons have been popped already in main 
  free(s);
}
  
 

int main(int argc, char *argv[]) {
  stack_ptr s = stackConstructor();           // allocate memory
  push(s, personConstructor("Name 1",10));    // push 3 persons onto stack
  push(s, personConstructor("Name 2",20));    // note its push(ptr,person)
  push(s, personConstructor("Name 3",30));    // Opposite of OO: obj.push(person)

  while (!isEmpty(s))                         // pop 3 persons in opposite order
    printf("%s\n",toString(pop(s)));
}