# AbstractJoinNode.java

    package org.codefilarete.stalactite.engine.runtime.load;

    import javax.annotation.Nullable;
    import java.util.ArrayList;
    import java.util.IdentityHashMap;
    import java.util.Iterator;
    import java.util.List;
    import java.util.NoSuchElementException;
    import java.util.Set;

    import org.codefilarete.stalactite.engine.runtime.load.EntityJoinTree.JoinType;
    import org.codefilarete.stalactite.query.api.Fromable;
    import org.codefilarete.stalactite.query.api.JoinLink;
    import org.codefilarete.stalactite.query.api.Selectable;
    import org.codefilarete.stalactite.sql.ddl.structure.Key;
    import org.codefilarete.tool.collection.ReadOnlyList;

    /**
     * Abstraction of relation, merge and passive joins.
     *
     * @author Guillaume Mary
     */
    public abstract class AbstractJoinNode<C, T1 extends Fromable, T2 extends Fromable, JOINTYPE> implements JoinNode<C, T2> {

    	/** Join column with previous strategy table */
    	private final Key<T1, JOINTYPE> leftJoinLink;

    	/** Join column with next strategy table */
    	private final Key<T2, JOINTYPE> rightJoinLink;

    	/** Indicates if the join must be an inner or (left) outer join */
    	private final JoinType joinType;

    	private final Set<Selectable<?>> columnsToSelect;

    	private final JoinNode<?, T1> parent;

    	/** Joins */
    	private final List<AbstractJoinNode<?, ?, ?, ?>> joins = new ArrayList<>();

    	@Nullable
    	protected String tableAlias;

    	@Nullable
    	private EntityTreeJoinNodeConsumptionListener<C> consumptionListener;

    	private final IdentityHashMap<JoinLink<?, ?>, JoinLink<?, ?>> originalColumnsToLocalOnes;

    	protected AbstractJoinNode(JoinNode<?, T1> parent,
    							   JoinLink<T1, JOINTYPE> leftJoinLink,
    							   JoinLink<T2, JOINTYPE> rightJoinLink,
    							   JoinType joinType,
    							   Set<? extends Selectable<?>> columnsToSelect,	// From T2
    							   @Nullable String tableAlias) {
    		this(parent, Key.ofSingleColumn(leftJoinLink), Key.ofSingleColumn(rightJoinLink), joinType, columnsToSelect, tableAlias);
    	}

    	protected AbstractJoinNode(JoinNode<?, T1> parent,
    							   Key<T1, JOINTYPE> leftJoinLink,
    							   Key<T2, JOINTYPE> rightJoinLink,
    							   JoinType joinType,
    							   Set<? extends Selectable<?>> columnsToSelect,	// From T2
    							   @Nullable String tableAlias) {
    		this.parent = parent;
    		this.leftJoinLink = leftJoinLink;
    		this.rightJoinLink = rightJoinLink;
    		this.joinType = joinType;
    		this.columnsToSelect = (Set) columnsToSelect;
    		this.tableAlias = tableAlias;
    		parent.add(this);
    		this.originalColumnsToLocalOnes = new IdentityHashMap<>();
    		rightJoinLink.getTable().getColumns().forEach(column -> {
    			// we clone columns to avoid side effects on the original query
    			this.originalColumnsToLocalOnes.put((JoinLink<?, ?>) column, (JoinLink<?, ?>) column);
    		});
    	}

    	/**
    	 * Constructor dedicated for node cloning
    	 *
    	 * @param parent the node to add the created instance to
    	 * @param leftJoinLink the left joining columns of this node, expected to be taken on parent node table
    	 * @param rightJoinLink the right joining columns of this node, expected to be taken on this node table
    	 * @param joinType inner or outer join type
    	 * @param columnsToSelect additional columns to select from right table (T2), out of the joining columns which are automatically selected
    	 * @param tableAlias optional table alias to use in the query, if null then no alias is used
    	 * @param originalColumnsToLocalOnes a map of original columns to local ones, used to simplify and allow selecting original columns by user
    	 */
    	protected AbstractJoinNode(JoinNode<?, T1> parent,
    							   Key<T1, JOINTYPE> leftJoinLink,
    							   Key<T2, JOINTYPE> rightJoinLink,
    							   JoinType joinType,
    							   Set<? extends Selectable<?>> columnsToSelect,	// From T2
    							   @Nullable String tableAlias,
    							   IdentityHashMap<JoinLink<?, ?>, JoinLink<?, ?>> originalColumnsToLocalOnes) {
    		this.parent = parent;
    		this.leftJoinLink = leftJoinLink;
    		this.rightJoinLink = rightJoinLink;
    		this.joinType = joinType;
    		this.columnsToSelect = (Set) columnsToSelect;
    		this.tableAlias = tableAlias;
    		parent.add(this);
    		this.originalColumnsToLocalOnes = originalColumnsToLocalOnes;
    	}

    	@Override
    	public <ROOT, ID> EntityJoinTree<ROOT, ID> getTree() {
    		// going up to the root to get tree from it because JoinRoot owns the information
    		JoinNodeHierarchyIterator joinNodeHierarchyIterator = new JoinNodeHierarchyIterator(this);
    		AbstractJoinNode<?, ?, ?, ?> currentNode = this;
    		while (joinNodeHierarchyIterator.hasNext()) {
    			currentNode = joinNodeHierarchyIterator.next();
    		}
    		// currentNode is the last before root
    		return currentNode.getParent().getTree();
    	}

    	public JoinNode<?, T1> getParent() {
    		return parent;
    	}

    	@Override
    	public T2 getTable() {
    		return getRightTable();
    	}

    	public Key<T1, JOINTYPE> getLeftJoinLink() {
    		return leftJoinLink;
    	}

    	public Key<T2, JOINTYPE> getRightJoinLink() {
    		return rightJoinLink;
    	}

    	public JoinType getJoinType() {
    		return joinType;
    	}

    	@Override
    	public Set<Selectable<?>> getColumnsToSelect() {
    		return columnsToSelect;
    	}

    	@Override
    	public IdentityHashMap<JoinLink<?, ?>, JoinLink<?, ?>> getOriginalColumnsToLocalOnes() {
    		return originalColumnsToLocalOnes;
    	}

    	@Override
    	public ReadOnlyList<AbstractJoinNode<?, ?, ?, ?>> getJoins() {
    		return new ReadOnlyList<>(joins);
    	}

    	@Nullable
    	EntityTreeJoinNodeConsumptionListener<C> getConsumptionListener() {
    		return consumptionListener;
    	}

    	@Override
    	public AbstractJoinNode<C, T1, T2, JOINTYPE> setConsumptionListener(@Nullable EntityTreeJoinNodeConsumptionListener<C> consumptionListener) {
    		this.consumptionListener = consumptionListener;
    		return this;
    	}

    	@Override
    	public void add(AbstractJoinNode node) {
    		// safeguard
    		if (node.getParent() != this) {
    			throw new IllegalArgumentException("Node is not added as child of right node : parent differs from target owner");
    		}
    		this.joins.add(node);
    	}

    	@Nullable
    	@Override
    	public String getTableAlias() {
    		return tableAlias;
    	}

    	public T2 getRightTable() {
    		return this.rightJoinLink.getTable();
    	}

    	/**
    	 * Iterator over {@link AbstractJoinNode} from given node over parents, except root (because it's not a {@link AbstractJoinNode} so can't be returned)
    	 */
    	static class JoinNodeHierarchyIterator implements Iterator<AbstractJoinNode> {

    		private AbstractJoinNode currentNode;

    		JoinNodeHierarchyIterator(AbstractJoinNode currentNode) {
    			this.currentNode = currentNode;
    		}

    		@Override
    		public boolean hasNext() {
    			return currentNode != null;
    		}

    		@Override
    		public AbstractJoinNode next() {
    			if (!hasNext()) {
    				throw new NoSuchElementException();
    			}
    			AbstractJoinNode toReturn = currentNode;
    			prepareNextIteration();
    			return toReturn;
    		}

    		private void prepareNextIteration() {
    			JoinNode parent = currentNode.getParent();
    			if (parent instanceof AbstractJoinNode) {
    				currentNode = (AbstractJoinNode) parent;
    			} else {
    				currentNode = null;
    			}
    		}
    	}
    }