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package com.ajjpj.afoundation.collection.immutable;

import com.ajjpj.afoundation.collection.AEquality;
import com.ajjpj.afoundation.function.AFunction1;

import java.util.*;


/**
 * An immutable BTree implementation
 *
 * @author arno
 */
public abstract class ABTreeMap extends AbstractAMap {
    public final ABTreeSpec spec;
    transient private Integer cachedHashcode = null; // intentionally not volatile: This class is immutable, so recalculating per thread works

    @SuppressWarnings ("unchecked")
    public static  ABTreeMap empty (ABTreeSpec spec) {
        return new LeafNode (spec, new Object[0], new Object[0]);
    }

    ABTreeMap (ABTreeSpec spec) {
        this.spec = spec;
    }

    public abstract AOption get (K key);
//    public Iterable keys ();
//    public Iterable values ();
//    public Iterable keys (K keyMin, K keyMax);
//    public Iterable values (K keyMin, K keyMax);

    @SuppressWarnings ("unchecked")
    public ABTreeMap updated (K key, V value) {
        final UpdateResult result = _updated (key, value);

        if (result.optRight == null) {
            return result.left;
        }

        // This is the only place where the tree depth can grow.
        // The 'minimum number of children' constraint does not apply to root nodes.
        return new IndexNode (spec, new Object[] {result.separator}, new ABTreeMap[] {result.left, result.optRight});
    }

    @SuppressWarnings ("unchecked")
    public ABTreeMap removed (K key) {
        final RemoveResult removeResult = _removed (key, null);
        if (removeResult.underflowed &&
                removeResult.newNode instanceof IndexNode &&
                ((IndexNode) removeResult.newNode).children.length == 1) {
            return ((IndexNode) removeResult.newNode).children[0];
        }
        return _removed (key, null).newNode;
    }

    abstract UpdateResult _updated (Object key, Object value);
    abstract RemoveResult _removed (Object key, Object leftSeparator);
    abstract UpdateResult merge (ABTreeMap rightNeighbour, Object separator);

    @Override public ASet keys () {
        return ABTreeSet.create (this);
    }

    @Override public AMap clear () {
        return empty (spec);
    }
    @Override public AEquality keyEquality () {
        return new AEquality.ComparatorBased (spec.comparator);
    }

    @Override public Iterator> iterator () {
        return new BTreeIterator<> (this);
    }

    private static class BTreeIterator implements Iterator>, AMapEntry {
        private final Deque