IterableQueryable.java

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package pt.isel.mpd14.iters;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Function;
import java.util.function.Predicate;

/**
 *
 * @author Miguel Gamboa at CCISEL
 */
class IterableQueryable<T> implements Queryable<T> {
    
    final Iterable<T> src;
    
    public IterableQueryable(Iterable<T> src) {
        this.src = src;
    }

    @Override
    public Queryable<T> filter(Predicate<T> p) {
        return new IterableQueryable<>(new Iterable<T>() {

            @Override
            public Iterator<T> iterator() {
                return new Iterator<T>() {
                    
                    private final Iterator<T> srcIter = src.iterator();
                    private T nextElem = null;
                    private boolean valueReady = false;

                    @Override
                    public boolean hasNext() {
                        if (valueReady) {
                            return true;
                        }
                        
                        while (srcIter.hasNext()) {
                            T elem = srcIter.next();
                            
                            if (p.test(elem)) {
                                nextElem = elem;
                                valueReady = true;
                                return true;
                            }
                        }
                        
                        return false;
                    }

                    @Override
                    public T next() {
                        if (!valueReady && !hasNext())
                            throw new NoSuchElementException();
                        else {
                            valueReady = false;
                            return nextElem;
                        }
                    }
                    
                };
            }
            
        });
    }

    @Override
    public <R> Queryable<R> map(Function<T, R> mapper) {
        return new IterableQueryable<>(new Iterable<R>() {

            @Override
            public Iterator<R> iterator() {
                return new Iterator<R>(){

                    private final Iterator<T> srcIter = src.iterator();
                    
                    @Override
                    public boolean hasNext() {
                        return srcIter.hasNext();
                    }

                    @Override
                    public R next() {
                        return mapper.apply(srcIter.next());
                    }
                    
                };
            }
            
        });
    }

    @Override
    public Queryable<T> skip(int n) {
        return new IterableQueryable<>(new Iterable<T>() {

            @Override
            public Iterator<T> iterator() {
                return new Iterator<T>() {

                    private final Iterator<T> srcIter = src.iterator();
                    private int skips = n;
                    
                    @Override
                    public boolean hasNext() {
                        while (skips > 0 && srcIter.hasNext()) {
                            srcIter.next();
                            skips--;
                        }
                        
                        return srcIter.hasNext();
                    }

                    @Override
                    public T next() {
                        if (!hasNext()) {
                            throw new NoSuchElementException();
                        }
                        
                        return srcIter.next();
                    }
                    
                };
            }
            
        });
    }

    @Override
    public Iterator<T> iterator() {
        return src.iterator();
    }
    
}