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package org.hsqldb.map;

import java.util.Arrays;

A chained bucket hash index implementation.
hashTable and linkTable are arrays of signed integral types. This
implementation uses int as the type but short or byte can be used for
smaller index sizes (cardinality).
hashTable[index] contains the pointer to the first node with
(index == hash modulo hashTable.length) or -1 if there is no corresponding
node. linkTable[{0,newNodePointer}] (the range between 0 and newNodePointer)
contains either the pointer to the next node or -1 if there is no
such node. reclaimedNodeIndex contains a pointer to an element
of linkTable which is the first element in the list of reclaimed nodes
(nodes no longer in index) or -1 if there is no such node.
elements at and above linkTable[newNodePointer] have never been used
as a node and their contents is not significant.
Author:
Fred Toussi (fredt@users dot sourceforge.net)
Version:
2.3.4
Since:
1.7.2/**
 * A chained bucket hash index implementation.
 *
 * hashTable and linkTable are arrays of signed integral types. This
 * implementation uses int as the type but short or byte can be used for
 * smaller index sizes (cardinality).
 *
 * hashTable[index] contains the pointer to the first node with
 * (index == hash modulo hashTable.length) or -1 if there is no corresponding
 * node. linkTable[{0,newNodePointer}] (the range between 0 and newNodePointer)
 * contains either the pointer to the next node or -1 if there is no
 * such node. reclaimedNodeIndex contains a pointer to an element
 * of linkTable which is the first element in the list of reclaimed nodes
 * (nodes no longer in index) or -1 if there is no such node.
 *
 * elements at and above linkTable[newNodePointer] have never been used
 * as a node and their contents is not significant.
 *
 * @author Fred Toussi (fredt@users dot sourceforge.net)
 * @version 2.3.4
 * @since 1.7.2
 */
public class HashIndex {

    int[]   hashTable;
    int[]   linkTable;
    int     newNodePointer;
    int     elementCount;
    int     reclaimedNodePointer = -1;
    boolean fixedSize;
    boolean modified;

    public HashIndex(int hashTableSize, int capacity, boolean fixedSize) {

        if (capacity < hashTableSize) {
            capacity = hashTableSize;
        }

        reset(hashTableSize, capacity);

        this.fixedSize = fixedSize;
    }

    
Reset the structure with a new size as empty.
Params:
hashTableSize – 
capacity – /**
     * Reset the structure with a new size as empty.
     *
     * @param hashTableSize
     * @param capacity
     */
    public void reset(int hashTableSize, int capacity) {

        int[] newHT = new int[hashTableSize];
        int[] newLT = new int[capacity];

        // allocate memory before assigning
        hashTable = newHT;
        linkTable = newLT;

        Arrays.fill(hashTable, -1);
        resetTables();
    }

    public void resetTables() {

        newNodePointer       = 0;
        elementCount         = 0;
        reclaimedNodePointer = -1;
        modified             = false;
    }

    
Reset the index as empty.
/**
     * Reset the index as empty.
     */
    public void clear() {

        Arrays.fill(linkTable, 0, newNodePointer, 0);
        Arrays.fill(hashTable, -1);
        resetTables();
    }

    
Params:
hash – /**
     * @param hash
     */
    public int getHashIndex(int hash) {
        return (hash & 0x7fffffff) % hashTable.length;
    }

    
Return the array index for a hash.
Params:
hash – the hash value used for indexing
Returns:
either -1 or the first node for this hash value/**
     * Return the array index for a hash.
     *
     * @param hash the hash value used for indexing
     * @return either -1 or the first node for this hash value
     */
    public int getLookup(int hash) {

        if (elementCount == 0) {
            return -1;
        }

        int index = (hash & 0x7fffffff) % hashTable.length;

        return hashTable[index];
    }

    
Return the pointer
/**
     * Return the pointer
     */
    public int getNewNodePointer() {
        return newNodePointer;
    }

    
This looks from a given node, so the parameter is always > -1.
Params:
lookup – A valid node to look from
Returns:
either -1 or the next node from this node/**
     * This looks from a given node, so the parameter is always > -1.
     *
     * @param lookup A valid node to look from
     * @return either -1 or the next node from this node
     */
    public int getNextLookup(int lookup) {
        return linkTable[lookup];
    }

    
Link a new node into the linked list for a hash index.
Params:
index – an index into hashTable
lastLookup – either -1 or the node to which the new node will be linked
Returns:
the new node/**
     * Link a new node into the linked list for a hash index.
     *
     * @param index an index into hashTable
     * @param lastLookup either -1 or the node to which the new node will be linked
     * @return the new node
     */
    public int linkNode(int index, final int lastLookup) {

        // get the first reclaimed slot
        int lookup = reclaimedNodePointer;

        if (lookup == -1) {
            lookup = newNodePointer++;
        } else {

            // reset the first reclaimed slot
            reclaimedNodePointer = linkTable[lookup];
        }

        // link the node
        int nextLookup;

        if (lastLookup == -1) {
            nextLookup       = hashTable[index];
            hashTable[index] = lookup;
        } else {
            nextLookup            = linkTable[lastLookup];
            linkTable[lastLookup] = lookup;
        }

        linkTable[lookup] = nextLookup;

        elementCount++;

        modified = true;

        return lookup;
    }

    
Unlink a node from a linked list and link into the reclaimed list.
Params:
index – an index into hashTable
lastLookup – either -1 or the node to which the target node is linked
lookup – the node to remove/**
     * Unlink a node from a linked list and link into the reclaimed list.
     *
     * @param index an index into hashTable
     * @param lastLookup either -1 or the node to which the target node is linked
     * @param lookup the node to remove
     */
    public void unlinkNode(int index, int lastLookup, int lookup) {

        // unlink the node
        if (lastLookup == -1) {
            hashTable[index] = linkTable[lookup];
        } else {
            linkTable[lastLookup] = linkTable[lookup];
        }

        // add to reclaimed list
        linkTable[lookup]    = reclaimedNodePointer;
        reclaimedNodePointer = lookup;

        elementCount--;

        if (elementCount == 0) {
            Arrays.fill(linkTable, 0, newNodePointer, 0);
            resetTables();
        }
    }

    
Remove a node that has already been unlinked. This is not required
for index operations. It is used only when the row needs to be removed
from the data structures that store the actual indexed data and the
nodes need to be contiguous.
Params:
lookup – the node to remove
Returns:
true if node found in unlinked state/**
     * Remove a node that has already been unlinked. This is not required
     * for index operations. It is used only when the row needs to be removed
     * from the data structures that store the actual indexed data and the
     * nodes need to be contiguous.
     *
     * @param lookup the node to remove
     * @return true if node found in unlinked state
     */
    public boolean removeEmptyNode(int lookup) {

        boolean found      = false;
        int     lastLookup = -1;

        for (int i = reclaimedNodePointer; i >= 0;
                lastLookup = i, i = linkTable[i]) {
            if (i == lookup) {
                if (lastLookup == -1) {
                    reclaimedNodePointer = linkTable[lookup];
                } else {
                    linkTable[lastLookup] = linkTable[lookup];
                }

                found = true;

                break;
            }
        }

        if (!found) {
            return false;
        }

        for (int i = 0; i < newNodePointer; i++) {
            if (linkTable[i] > lookup) {
                linkTable[i]--;
            }
        }

        System.arraycopy(linkTable, lookup + 1, linkTable, lookup,
                         newNodePointer - lookup - 1);

        linkTable[newNodePointer - 1] = 0;

        newNodePointer--;

        for (int i = 0; i < hashTable.length; i++) {
            if (hashTable[i] > lookup) {
                hashTable[i]--;
            }
        }

        return true;
    }
}