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CDS4J API
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/*******************************************************************
 * © 2019 SAP SE or an SAP affiliate company. All rights reserved. *
 *******************************************************************/
package com.sap.cds;

import static java.util.Collections.unmodifiableMap;

import java.util.HashMap;
import java.util.Map;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * Struct provides static helper methods to access data given as {@code Map} via
 * an accessor interface.
 */
public final class Struct {

	private static final ProxyFactory proxyFactory = Cds4jServiceLoader.load(ProxyFactory.class);

	private Struct() {
	}

	/**
	 * Creates a data container for the given accessor interface.
	 * 
	 * @param       the return type
	 * @param type the accessor interface
	 * @return a typed data container
	 */
	public static  T create(Class type) {
		return proxyFactory.proxy(new HashMap<>(), type);
	}

	/**
	 * Provides typed access on the given data map.
	 * 
	 * @param data the data map to access
	 * @return a factory, that provides typed access on the underlying data
	 */
	public static MapViewFactory access(Map data) {
		return new MapViewFactory(data);
	}

	/**
	 * Provides typed stream access on the given data maps.
	 * 
	 * @param data the data maps to be streamed
	 * @return a factory, that provides typed access on the underlying data
	 */
	public static IterableViewFactory stream(Iterable> data) {
		return new IterableViewFactory(data);
	}

	public interface ProxyFactory {
		 T proxy(Map data, Class type);
	}

	public static final class MapViewFactory {
		private final Map data;

		private MapViewFactory(Map data) {
			this.data = data; // NOSONAR
		}

		/**
		 * Provides typed access on the underlying data map.
		 * 
		 * @param       the return type
		 * @param view the accessor interface
		 * @return a typed writable view on the underlying data map
		 */
		public  T as(Class view) {
			return proxyFactory.proxy(data, view);
		}

		/**
		 * Provides typed read-only access on the underlying data map.
		 * 
		 * @param       the return type
		 * @param view the accessor interface
		 * @return a typed read-only view on the underlying data map
		 */
		public  T asReadOnly(Class view) {
			return proxyFactory.proxy(unmodifiableMap(data), view);
		}
	}

	public static final class IterableViewFactory {
		private final Iterable> data;

		private IterableViewFactory(Iterable> data) {
			this.data = data;
		}

		/**
		 * Provides typed stream access on the underlying data maps.
		 * 
		 * @param       the type of the returned {@code Stream}
		 * @param view the accessor interface
		 * @return a typed {@code Stream} of the underlying data maps
		 */
		public  Stream as(Class view) {
			return StreamSupport.stream(data.spliterator(), false).map(d -> proxyFactory.proxy(d, view));
		}
	}

}