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A library for Java that provides re-usable components commonly used by Flow libraries.
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/*
 * This file is part of Flow Commons, licensed under the MIT License (MIT).
 *
 * Copyright (c) 2013 Flow Powered 
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.flowpowered.commons.concurrent;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicReferenceArray;

/**
 * A 3d int based Object map that is backed by AtomicReferenceArrays arranged in a tree structure.
 
 The Map operates in a tree structure.  The bits variable indicates the number of bits used
 * per level of the tree.  This is used to mask the input coordinates.
 
 The length of the internal arrays are determined by the bits parameter.
 
 If bits is set to 4, then each
 * coordinate provides 4 bits for the array index. That gives a total array length of 16 * 16 * 16 = 4096.
 
 Inserting a new object with a random key would probably require new arrays to be
 * created for the entire depth of the tree.
 
 A given depth can be guaranteed by keeping ensuring that all elements are within a cube that has an edge of 2 ^ (depth * bits) or smaller.
 * Increasing the bits variable reduces the depth of the internal tree at the expense of more memory used per array.
 
 The map is thread-safe.  Map update operations can not be carried out by
 * more than one thread at the same time.  However, read operations are concurrent.
 
 The map is optimised for use where all the coordinates occur in a small number of contiguous cuboids.
 *
 * @param  the value type
 */
public class TripleIntObjectReferenceArrayMap {

    private final int bits;
    private final int doubleBits;
    private final int bitMask;
    private final int arraySize;
    private final AtomicReference> root;
    private final LinkedHashSet values;
    private final LinkedHashSet leafEntries;
    private final AtomicReference> valuesSnapshot = new AtomicReference<>(null);

    public TripleIntObjectReferenceArrayMap(int bits) {
        this(bits, 1);
    }

    private TripleIntObjectReferenceArrayMap(int bits, int depth) {
        this.bits = bits;
        this.doubleBits = bits << 1;
        int width = 1 << bits;
        this.bitMask = width - 1;
        this.arraySize = (width) * (width) * (width);
        this.root = new AtomicReference<>(null);
        this.root.set(new AtomicReferenceArrayEntry(depth));
        this.values = new LinkedHashSet<>();
        this.leafEntries = new LinkedHashSet<>();
    }

    public T get(int x, int y, int z) {
        Entry entry = getEntryRaw(x, y, z);
        if (entry != null) {
            return entry.getValue();
        } else {
            return null;
        }
    }

    public synchronized T remove(int x, int y, int z) {
        Entry entry = getEntryRaw(x, y, z);
        if (entry != null) {
            T value = entry.remove();
            if (value != null) {
                valuesSnapshot.set(null);
                if (!values.remove(value)) {
                    throw new IllegalStateException("Item removed from map was not in item set");
                }
            }
            return value;
        } else {
            return null;
        }
    }

    public synchronized boolean remove(int x, int y, int z, T value) {
        Entry entry = getEntryRaw(x, y, z);
        if (entry != null) {
            boolean b = entry.remove(value);
            if (b) {
                valuesSnapshot.set(null);
                if (!values.remove(value)) {
                    throw new IllegalStateException("Item removed from map was not in item set");
                }
            }
            return b;
        } else {
            return false;
        }
    }

    public synchronized T put(int x, int y, int z, T value) {
        if (value == null) {
            throw new NullPointerException("Null values are not permitted");
        }
        Entry entry = getOrCreateEntry(x, y, z);
        if (entry != null) {
            T old = entry.put(value);
            valuesSnapshot.set(null);
            if (!values.add(value)) {
                throw new IllegalStateException("Failed to add item to the value set, items may only be added once to the map");
            }
            if (old != null) {
                if (!values.remove(old)) {
                    throw new IllegalStateException("Item removed from map was not in item set");
                }
            }
            return old;
        } else {
            throw new IllegalStateException("Unable to create entry for put");
        }
    }

    public synchronized T putIfAbsent(int x, int y, int z, T value) {
        if (value == null) {
            throw new NullPointerException("Null values are not permitted");
        }
        Entry entry = getOrCreateEntry(x, y, z);
        if (entry != null) {
            T old = entry.putIfAbsent(value);
            if (old == null) {
                valuesSnapshot.set(null);
                if (!values.add(value)) {
                    throw new IllegalStateException("Failed to add item to the value set, items may only be added once to the map");
                }
            }
            return old;
        } else {
            throw new IllegalStateException("Unable to create entry for put");
        }
    }

    public Collection valueCollection() {
        Collection newValues = this.valuesSnapshot.get();
        if (newValues != null) {
            return newValues;
        }
        synchronized (this) {
            newValues = this.valuesSnapshot.get();
            if (newValues != null) {
                return newValues;
            }
            newValues = Collections.unmodifiableCollection(new LinkedHashSet<>(this.values));
            this.valuesSnapshot.set(newValues);
            return newValues;
        }
    }

    private synchronized Entry getOrCreateEntry(int x, int y, int z) {
        Entry entry = getEntryRaw(x, y, z);
        if (entry != null) {
            return entry;
        }
        entry = this.root.get();
        int depth = entry.getDepth();
        int shift = entry.getInitialShift();
        Entry prevEntry = null;

        int keyDepth = 0;
        while (true) {
            prevEntry = entry;
            entry = entry.getSubEntry(x, y, z, shift);
            shift -= bits;
            if (entry == null) {
                break;
            }
            keyDepth++;
        }

        // Map must be resized if we hit a leaf node (collision) or the map was already at max depth
        if (keyDepth > depth || prevEntry instanceof TripleIntObjectReferenceArrayMap.LeafEntry) {
            resizeMap();
            return getOrCreateEntry(x, y, z);
        } else if (keyDepth > depth) {
            throw new IllegalStateException("Map has a depth that exceeds the depth variable");
        }

        entry = prevEntry;
        shift += bits;

        for (int i = keyDepth; i < depth; i++) {
            Entry newEntry = new AtomicReferenceArrayEntry(depth);
            if (!((AtomicReferenceArrayEntry) entry).addNewEntry(x, y, z, shift, newEntry)) {
                throw new IllegalStateException("Unable to add new map entry");
            }
            shift -= bits;
            entry = newEntry;
        }
        if (shift != 0) {
            throw new IllegalStateException("Shift counter in illegal state: " + shift);
        }
        LeafEntry newEntry = new LeafEntry(x, y, z);
        if (!((AtomicReferenceArrayEntry) entry).addNewEntry(x, y, z, 0, newEntry)) {
            throw new IllegalStateException("Unable to add new leaf entry");
        }
        this.leafEntries.add(newEntry);
        return newEntry;
    }

    private synchronized void resizeMap() {
        TripleIntObjectReferenceArrayMap.Entry oldRoot = this.root.get();
        int newDepth = oldRoot.getDepth() + 1;
        TripleIntObjectReferenceArrayMap temp = new TripleIntObjectReferenceArrayMap<>(bits, newDepth);

        for (LeafEntry le : leafEntries) {
            T value = le.getValue();
            if (value != null) {
                int x = le.getX();
                int y = le.getY();
                int z = le.getZ();
                temp.put(x, y, z, value);
                if (!values.remove(value)) {
                    throw new IllegalStateException("Value moved to other map on resize was not in value list");
                }
            }
        }

        if (!this.values.isEmpty()) {
            throw new IllegalStateException("Some values were not transferred to the new map on resize");
        }

        this.leafEntries.clear();
        this.leafEntries.addAll(temp.leafEntries);

        this.values.addAll(temp.values);
        if (!this.root.compareAndSet(oldRoot, temp.root.get())) {
            throw new IllegalStateException("Old root changed while resizing");
        }
    }

    private Entry getEntryRaw(int x, int y, int z) {
        Entry entry = this.root.get();
        int depth = entry.getDepth();
        int shift = entry.getInitialShift();

        for (int i = 0; i <= depth; i++) {
            entry = entry.getSubEntry(x, y, z, shift);
            if (entry == null) {
                return null;
            }
            shift -= bits;
        }
        if (entry.testKey(x, y, z)) {
            return entry;
        } else {
            return null;
        }
    }

    private static interface Entry {

        public Entry getSubEntry(int x, int y, int z, int shift);

        public boolean testKey(int x, int y, int z);

        public T getValue();

        public T remove();

        public boolean remove(T value);

        public T putIfAbsent(T value);

        public T put(T value);

        public int getDepth();

        public int getInitialShift();
    }

    private class AtomicReferenceArrayEntry implements Entry {

        private final int depth;
        private final int initialShift;
        private final AtomicReferenceArray> array;

        public AtomicReferenceArrayEntry(int depth) {
            this.depth = depth;
            this.array = new AtomicReferenceArray<>(arraySize);
            this.initialShift = depth * bits;
        }

        @Override
        public Entry getSubEntry(int x, int y, int z, int shift) {
            return array.get(getIndex(x, y, z, shift));
        }

        @Override
        public T getValue() {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class cannot store values directly");
        }

        @Override
        public int getDepth() {
            return depth;
        }

        @Override
        public int getInitialShift() {
            return initialShift;
        }

        @Override
        public boolean testKey(int x, int y, int z) {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class does not contain key/value pairs");
        }

        @Override
        public T remove() {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class does not contain key/value pairs");
        }

        @Override
        public boolean remove(T value) {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class does not contain key/value pairs");
        }

        @Override
        public T putIfAbsent(T value) {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class does not contain key/value pairs");
        }

        @Override
        public T put(T value) {
            throw new UnsupportedOperationException("The AtomicReferenceArrayEntry class does not contain key/value pairs");
        }

        public boolean addNewEntry(int x, int y, int z, int shift, Entry subEntry) {
            int index = getIndex(x, y, z, shift);
            return array.compareAndSet(index, null, subEntry);
        }
    }

    private class LeafEntry implements Entry {

        private final AtomicReference value;
        private final int x;
        private final int y;
        private final int z;

        public LeafEntry(int x, int y, int z) {
            this.x = x;
            this.y = y;
            this.z = z;
            this.value = new AtomicReference<>();
        }

        @Override
        public Entry getSubEntry(int x, int y, int z, int shift) {
            return null;
        }

        @Override
        public boolean testKey(int x, int y, int z) {
            return (x == this.x) && (y == this.y) && (z == this.z);
        }

        @Override
        public T getValue() {
            return this.value.get();
        }

        @Override
        public T remove() {
            return this.value.getAndSet(null);
        }

        @Override
        public boolean remove(T value) {
            return this.value.compareAndSet(value, null);
        }

        @Override
        public T putIfAbsent(T value) {
            while (true) {
                T old = this.value.get();
                if (old != null) {
                    return old;
                }
                if (this.value.compareAndSet(null, value)) {
                    return null;
                }
            }
        }

        @Override
        public T put(T value) {
            return this.value.getAndSet(value);
        }

        @Override
        public int getDepth() {
            throw new UnsupportedOperationException("The LeafEntry class does not support this method");
        }

        @Override
        public int getInitialShift() {
            throw new UnsupportedOperationException("The LeafEntry class does not support this method");
        }

        @Override
        public String toString() {
            return "{" + x + ", " + y + ", " + z + "}";
        }

        public int getX() {
            return x;
        }

        public int getY() {
            return y;
        }

        public int getZ() {
            return z;
        }
    }

    private int getIndex(int x, int y, int z, int shift) {
        x >>= shift;
        y >>= shift;
        z >>= shift;
        x &= bitMask;
        y &= bitMask;
        z &= bitMask;
        return ((x & bitMask) << doubleBits) | ((y & bitMask) << bits) | (z & bitMask);
    }
}