package edu.rice.hj.example.comp322.labs.lab10;

/*
 *  Class SyncList implements a thread-safe sorted list data structure that supports contains(), add() and remove() methods.
 *
 *  Thread safety is guaranteed by declaring each of the methods to be synchronized.
 */

public class SyncList extends ListSet {
    private final Entry head;

    public SyncList() {
        // Add sentinels to start and end
        this.head = new Entry(Integer.MIN_VALUE);
        this.head.next = new Entry(Integer.MAX_VALUE);
    }

    public synchronized boolean contains(final Object object) {
        Entry pred, curr;
        final int key = object.hashCode();
        pred = this.head;
        curr = pred.next;
        while (curr.key < key) {
            pred = curr;
            curr = curr.next;
        }
        return (key == curr.key);
    }

    public synchronized int add(final Object object) {
        Entry pred, curr;
        final int key = object.hashCode();
        pred = this.head;
        curr = pred.next;
        while (curr.key < key) {
            pred = curr;
            curr = curr.next;
        }
        if (key == curr.key) {  // present
            return -1;
        } else {                // not present
            final Entry entry = new Entry(object);
            entry.next = curr;
            pred.next = entry;
            return 1;
        }
    }

    public synchronized int remove(final Object object) {
        Entry pred, curr;
        final int key = object.hashCode();
        pred = this.head;
        curr = pred.next;
        while (curr.key < key) {
            pred = curr;
            curr = curr.next;
        }
        if (key == curr.key) {  // present
            pred.next = curr.next;
            return 1;
        } else {
            return -1;         // not present
        }
    }

    // define list entry class
    private class Entry {
        Object object;
        int key;
        Entry next;

        Entry(final Object object) {     // usual constructor
            this.object = object;
            this.key = object.hashCode();
        }

        Entry(final int key) {           // sentinel constructor
            this.object = null;
            this.key = key;
        }
    }
}