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package net.digitalid.utility.functional.iterators;

import java.util.Iterator;

import javax.annotation.Nonnull;

import net.digitalid.utility.annotations.generics.Specifiable;
import net.digitalid.utility.annotations.method.Impure;
import net.digitalid.utility.annotations.method.Pure;
import net.digitalid.utility.annotations.ownership.Capturable;
import net.digitalid.utility.annotations.ownership.NonCapturable;
import net.digitalid.utility.functional.iterables.FiniteIterable;
import net.digitalid.utility.validation.annotations.type.Mutable;

/**
 * This class implements a cycling iterator that iterates over the elements of the given iterable indefinitely.
 */
@Mutable
public class CyclingIterator<@Specifiable ELEMENT> extends ReadOnlyIterator {
    
    /* -------------------------------------------------- Iterable -------------------------------------------------- */
    
    protected final @Nonnull FiniteIterable iterable;
    
    /* -------------------------------------------------- Constructors -------------------------------------------------- */
    
    protected CyclingIterator(@Nonnull FiniteIterable iterable) {
        this.iterable = iterable;
        this.iterator = iterable.iterator();
        this.hasNext = iterator.hasNext();
    }
    
    /**
     * Returns a new cycling iterator that iterates over the elements of the given iterable indefinitely.
     */
    @Pure
    public static @Capturable <@Specifiable ELEMENT> @Nonnull CyclingIterator with(@Nonnull FiniteIterable iterable) {
        return new CyclingIterator<>(iterable);
    }
    
    /* -------------------------------------------------- Methods -------------------------------------------------- */
    
    private @Nonnull Iterator iterator;
    
    private final boolean hasNext;
    
    @Pure
    @Override
    public boolean hasNext() {
        return hasNext;
    }
    
    @Impure
    @Override
    public @NonCapturable ELEMENT next() {
        if (!iterator.hasNext()) { iterator = iterable.iterator(); }
        return iterator.next();
    }
    
}