PagingIterator.java

package com.stripe.model;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

import com.stripe.Stripe;
import com.stripe.net.APIResource;
import com.stripe.net.RequestOptions;

public class PagingIterator<T extends HasId> extends APIResource implements Iterator<T> {
	private final String url;
	
	@SuppressWarnings("rawtypes")
	private final Class<? extends StripeCollectionInterface> collectionType;
	
	private StripeCollectionInterface<T> currentCollection;
	private Iterator<T> currentDataIterator;
	
	private String lastId;
	
	PagingIterator(final StripeCollectionInterface<T> stripeCollection) {
		this.url = Stripe.getApiBase() + stripeCollection.getURL();

		this.collectionType = stripeCollection.getClass();
		
		this.currentCollection = stripeCollection;
		this.currentDataIterator = stripeCollection.getData().iterator();
	}

	@Override
	public boolean hasNext() {
		return currentDataIterator.hasNext() ||
			currentCollection.getHasMore();
	}

	@Override
	public T next() {
		// if we've run out of data on the current page, try to fetch another
		// one
		if (!currentDataIterator.hasNext() && currentCollection.getHasMore()) {
			try {
				Map<String, Object> params = new HashMap<String, Object>();

				// copy all the parameters from the initial request
				Map<String, Object> initialParams = currentCollection.getRequestParams();
				if (initialParams != null) {
					params.putAll(initialParams);
				}

				// then put our new page start in
				params.put("starting_after", lastId);

				this.currentCollection = list(params, currentCollection.getRequestOptions());
				
				this.currentDataIterator =
					currentCollection.getData().iterator();
			} catch (final Exception e) {
				throw new RuntimeException("Unable to lazy-load stripe objects", e);
			}
		}

		if (currentDataIterator.hasNext()) {
			final T next = currentDataIterator.next();
			this.lastId = next.getId();
			return next;
		}

		throw new NoSuchElementException();
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException();
	}

	@SuppressWarnings("unchecked")
	private StripeCollectionInterface<T> list(
		final Map<String, Object> params, 
		final RequestOptions options
	) throws Exception {
		return APIResource.requestCollection(url, params, collectionType, options);
	}
}