//----------------------------------------------------------------------
//  IMPLEMENTATION FILE (cqueue.cpp)
//  This module exports an ADT for a queue of at most MAX_LENG-1
//  characters.
//  Queue representation: a vector (ring buffer) of size MAX_LENG
//----------------------------------------------------------------------
#include "cqueue.h"

// Private members of class:
//    int  front;            // Subscript of queue front - 1
//    int  rear;             // Subscript of queue rear
//    char data[MAX_LENG];   // Vector representing the queue
//
// CLASSINV:  At all times, at least one element of "data"
//            remains unused

CharQueue::CharQueue()
    //..................................................................
    // Constructor
    // POST: front == 0  &&  rear == 0
    //..................................................................
{
    front = rear = 0;
}

Boolean CharQueue::IsEmpty() const
    //..................................................................
    // POST: FCTVAL == (rear == front)
    //..................................................................
{
    return (rear == front);
}

Boolean CharQueue::IsFull() const
    //..................................................................
    // POST: FCTVAL == ((rear+1) MOD MAX_LENG == front)
    //..................................................................
{
    return ((rear+1) % MAX_LENG == front);
}

void CharQueue::Enqueue( /* in */ char newItem )
    //..................................................................
    // PRE:  (rear + 1) MOD MAX_LENG != front
    //    && Assigned(newItem)
    // POST: rear == (rear<entry> + 1) MOD MAX_LENG
    //    && data[rear] == newItem
    //..................................................................
{
    rear = (rear + 1) % MAX_LENG;
    data[rear] = newItem;
}

char CharQueue::Front() const
    //..................................................................
    // PRE:  rear != front
    // POST: FCTVAL == data[(front+1) MOD MAX_LENG]
    //..................................................................
{
    return data[(front+1) % MAX_LENG];
}

void CharQueue::Dequeue()
    //..................................................................
    // PRE:  rear != front
    // POST: front == (front<entry> + 1) MOD MAX_LENG
    //..................................................................
{
    front = (front + 1) % MAX_LENG;
}