/*

 * Copyright (c) 1999, 2007, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * Licensed Materials - Property of IBM

 * RMI-IIOP v1.0

 * Copyright IBM Corp. 1998 1999  All Rights Reserved

 *

 */

package sun.rmi.rmic.iiop;

/**

 * StaticStringsHash takes an array of constant strings and

 * uses several different hash methods to try to find the

 * 'best' one for that set. The set of methods is currently

 * fixed, but with a little work could be made extensible thru

 * subclassing.

 * <p>

 * The current set of methods is:

 * <ol>

 * <li> length() - works well when all strings are different length.</li>

 * <li> charAt(n) - works well when one offset into all strings is different.</li>

 * <li> hashCode() - works well with larger arrays.</li>

 * </ol>

 * After constructing an instance over the set of strings, the

 * <code>getKey(String)</code> method can be used to use the selected hash

 * method to produce a key.  The <code>method</code> string will contain

 * "length()", "charAt(n)", or "hashCode()", and is intended for use by

 * code generators.

 * <p>

 * The <code>keys</code> array will contain the full set of unique keys.

 * <p>

 * The <code>buckets</code> array will contain a set of arrays, one for

 * each key in the <code>keys</code>, where <code>buckets[x][y]</code>

 * is an index into the <code>strings</code> array.

 * @author      Bryan Atsatt

 */

public class StaticStringsHash {

    /** The set of strings upon which the hash info is created */

    public String[] strings = null;

    /** Unique hash keys */

    public int[] keys = null;

    /** Buckets for each key, where buckets[x][y] is an index

     * into the strings[] array. */

    public int[][] buckets = null;

    /** The method to invoke on String to produce the hash key */

    public String method = null;

    /** Get a key for the given string using the

     * selected hash method.

     * @param str the string to return a key for.

     * @return the key.

     */

    public int getKey(String str) {

        switch (keyKind) {

        case LENGTH: return str.length();

        case CHAR_AT: return str.charAt(charAt);

        case HASH_CODE: return str.hashCode();

        }

        throw new Error("Bad keyKind");

    }

    /** Constructor

     * @param strings the set of strings upon which to

     * find an optimal hash method. Must not contain

     * duplicates.

     */

    public StaticStringsHash(String[] strings) {

        this.strings = strings;

        length = strings.length;

        tempKeys = new int[length];

        bucketSizes = new int[length];

        setMinStringLength();

        // Decide on the best algorithm based on

        // which one has the smallest maximum

        // bucket depth. First, try length()...

        int currentMaxDepth = getKeys(LENGTH);

        int useCharAt = -1;

        boolean useHashCode = false;

        if (currentMaxDepth > 1) {

            // At least one bucket had more than one

            // entry, so try charAt(i).  If there

            // are a lot of strings in the array,

            // and minStringLength is large, limit

            // the search to a smaller number of

            // characters to avoid spending a lot

            // of time here that is most likely to

            // be pointless...

            int minLength = minStringLength;

            if (length > CHAR_AT_MAX_LINES &&

                length * minLength > CHAR_AT_MAX_CHARS) {

                minLength = length/CHAR_AT_MAX_CHARS;

            }

            charAt = 0;

            for (int i = 0; i < minLength; i++) {

                int charAtDepth = getKeys(CHAR_AT);

                if (charAtDepth < currentMaxDepth) {

                    currentMaxDepth = charAtDepth;

                    useCharAt = i;

                    if (currentMaxDepth == 1) {

                        break;

                    }

                }

                charAt++;

            }

            charAt = useCharAt;

            if (currentMaxDepth > 1) {

                // At least one bucket had more than one

                // entry, try hashCode().

                //

                // Since the cost of computing a full hashCode

                // (for the runtime target string) is much higher

                // than the previous methods, use it only if it is

                // substantially better. The definition of 'substantial'

                // here is not very well founded, and could be improved

                // with some further analysis ;^)

                int hashCodeDepth = getKeys(HASH_CODE);

                if (hashCodeDepth < currentMaxDepth-3) {

                    // Using the full hashCode results in at least

                    // 3 fewer entries in the worst bucket, so will

                    // therefore avoid at least 3 calls to equals()

                    // in the worst case.

                    //

                    // Note that using a number smaller than 3 could

                    // result in using a hashCode when there are only

                    // 2 strings in the array, and that would surely

                    // be a poor performance choice.

                    useHashCode = true;

                }

            }

            // Reset keys if needed...

            if (!useHashCode) {

                if (useCharAt >= 0) {

                    // Use the charAt(i) method...

                    getKeys(CHAR_AT);

                } else {

                    // Use length method...

                    getKeys(LENGTH);

                }

            }

        }

        // Now allocate and fill our real hashKeys array...

        keys = new int[bucketCount];

        System.arraycopy(tempKeys,0,keys,0,bucketCount);

        // Sort keys and bucketSizes arrays...

        boolean didSwap;

        do {

            didSwap = false;

            for (int i = 0; i < bucketCount - 1; i++) {

                if (keys[i] > keys[i+1]) {

                    int temp = keys[i];

                    keys[i] = keys[i+1];

                    keys[i+1] = temp;

                    temp = bucketSizes[i];

                    bucketSizes[i] = bucketSizes[i+1];

                    bucketSizes[i+1] = temp;

                    didSwap = true;

                }

            }

        }

        while (didSwap == true);

        // Allocate our buckets array. Fill the string

        // index slot with an unused key so we can

        // determine which are free...

        int unused = findUnusedKey();

        buckets = new int[bucketCount][];

        for (int i = 0; i < bucketCount; i++) {

            buckets[i] = new int[bucketSizes[i]];

            for (int j = 0; j < bucketSizes[i]; j++) {

                buckets[i][j] = unused;

            }

        }

        // And fill it in...

        for(int i = 0; i < strings.length; i++) {

            int key = getKey(strings[i]);

            for (int j = 0; j < bucketCount; j++) {

                if (keys[j] == key) {

                    int k = 0;

                    while (buckets[j][k] != unused) {

                        k++;

                    }

                    buckets[j][k] = i;

                    break;

                }

            }

        }

    }

    /** Print an optimized 'contains' method for the

     * argument strings

     */

    public static void main (String[] args) {

        StaticStringsHash hash = new StaticStringsHash(args);

        System.out.println();

        System.out.println("    public boolean contains(String key) {");

        System.out.println("        switch (key."+hash.method+") {");

        for (int i = 0; i < hash.buckets.length; i++) {

            System.out.println("            case "+hash.keys[i]+": ");

            for (int j = 0; j < hash.buckets[i].length; j++) {

                if (j > 0) {

                    System.out.print("                } else ");

                } else {

                    System.out.print("                ");

                }

                System.out.println("if (key.equals(\""+ hash.strings[hash.buckets[i][j]] +"\")) {");

                System.out.println("                    return true;");

            }

            System.out.println("                }");

        }

        System.out.println("        }");

        System.out.println("        return false;");

        System.out.println("    }");

    }

    private int length;

    private int[] tempKeys;

    private int[] bucketSizes;

    private int bucketCount;

    private int maxDepth;

    private int minStringLength = Integer.MAX_VALUE;

    private int keyKind;

    private int charAt;

    private static final int LENGTH = 0;

    private static final int CHAR_AT = 1;

    private static final int HASH_CODE = 2;

    /* Determines the maximum number of charAt(i)

     * tests that will be done. The search is

     * limited because if the number of characters

     * is large enough, the likelyhood of finding

     * a good hash key  based on this method is

     * low. The CHAR_AT_MAX_CHARS limit only

     * applies f there are more strings than

     * CHAR_AT_MAX_LINES.

     */

    private static final int CHAR_AT_MAX_LINES = 50;

    private static final int CHAR_AT_MAX_CHARS = 1000;

    private void resetKeys(int keyKind) {

        this.keyKind = keyKind;

        switch (keyKind) {

        case LENGTH: method = "length()"; break;

        case CHAR_AT: method = "charAt("+charAt+")"; break;

        case HASH_CODE: method = "hashCode()"; break;

        }

        maxDepth = 1;

        bucketCount = 0;

        for (int i = 0; i < length; i++) {

            tempKeys[i] = 0;

            bucketSizes[i] = 0;

        }

    }

    private void setMinStringLength() {

        for (int i = 0; i < length; i++) {

            if (strings[i].length() < minStringLength) {

                minStringLength = strings[i].length();

            }

        }

    }

    private int findUnusedKey() {

        int unused = 0;

        int keysLength = keys.length;

        // Note that we just assume that resource

        // exhaustion will occur rather than an

        // infinite loop here if the set of keys

        // is very large.

        while (true) {

            boolean match = false;

            for (int i = 0; i < keysLength; i++) {

                if (keys[i] == unused) {

                    match = true;

                    break;

                }

            }

            if (match) {

                unused--;

            } else {

                break;

            }

        }

        return unused;

    }

    private int getKeys(int methodKind) {

        resetKeys(methodKind);

        for(int i = 0; i < strings.length; i++) {

            addKey(getKey(strings[i]));

        }

        return maxDepth;

    }

    private void addKey(int key) {

        // Have we seen this one before?

        boolean addIt = true;

        for (int j = 0; j < bucketCount; j++) {

            if (tempKeys[j] == key) {

                addIt = false;

                bucketSizes[j]++;

                if (bucketSizes[j] > maxDepth) {

                    maxDepth = bucketSizes[j];

                }

                break;

            }

        }

        if (addIt) {

            tempKeys[bucketCount] = key;

            bucketSizes[bucketCount] = 1;

            bucketCount++;

        }

    }

}