/**
*******************************************************************************
* Copyright (C) 1996-2003, International Business Machines Corporation and    *
* others. All Rights Reserved.                                                *
*******************************************************************************
*
* $Source: /xsrl/Nsvn/icu/icu4j/src/com/ibm/icu/text/Collator.java,v $
* $Date: 2003/06/09 23:31:10 $
* $Revision: 1.33 $
*
*******************************************************************************
*/
package com.ibm.icu.text;

import java.util.Comparator;
import java.util.Locale;
import java.util.Set;

import com.ibm.icu.impl.ICULocaleData;
import com.ibm.icu.impl.LocaleUtility;

/**
* <p>Collator performs locale-sensitive string comparison. A concrete
* subclass, RuleBasedCollator, allows customization of the collation
* ordering by the use of rule sets.</p>
*
* <p>Following the <a href=http://www.unicode.org>Unicode
* Consortium</a>'s specifications for the
* <a href="http://www.unicode.org/unicode/reports/tr10/"> Unicode Collation
* Algorithm (UCA)</a>, there are 5 different levels of strength used
* in comparisons:
*
* <ul>
* <li>PRIMARY strength: Typically, this is used to denote differences between
*     base characters (for example, "a" &lt; "b").
*     It is the strongest difference. For example, dictionaries are divided
*     into different sections by base character.
* <li>SECONDARY strength: Accents in the characters are considered secondary
*     differences (for example, "as" &lt; "&agrave;s" &lt; "at"). Other
*     differences
*     between letters can also be considered secondary differences, depending
*     on the language. A secondary difference is ignored when there is a
*     primary difference anywhere in the strings.
* <li>TERTIARY strength: Upper and lower case differences in characters are
*     distinguished at tertiary strength (for example, "ao" &lt; "Ao" &lt;
*     "a&ograve;"). In addition, a variant of a letter differs from the base
*     form on the tertiary strength (such as "A" and "&#9398;"). Another
*     example is the
*     difference between large and small Kana. A tertiary difference is ignored
*     when there is a primary or secondary difference anywhere in the strings.
* <li>QUATERNARY strength: When punctuation is ignored
*     <a href=http://oss.software.ibm.com/icu/userguide/Collate_Concepts.html#Ignoring_Punctuation>
*     (see Ignoring Punctuations in the user guide)</a> at PRIMARY to TERTIARY
*     strength, an additional strength level can
*     be used to distinguish words with and without punctuation (for example,
*     "ab" &lt; "a-b" &lt; "aB").
*     This difference is ignored when there is a PRIMARY, SECONDARY or TERTIARY
*     difference. The QUATERNARY strength should only be used if ignoring
*     punctuation is required.
* <li>IDENTICAL strength:
*     When all other strengths are equal, the IDENTICAL strength is used as a
*     tiebreaker. The Unicode code point values of the NFD form of each string
*     are compared, just in case there is no difference.
*     For example, Hebrew cantellation marks are only distinguished at this
*     strength. This strength should be used sparingly, as only code point
*     value differences between two strings is an extremely rare occurrence.
*     Using this strength substantially decreases the performance for both
*     comparison and collation key generation APIs. This strength also
*     increases the size of the collation key.
* </ul>
*
* Unlike the JDK, ICU4J's Collator deals only with 2 decomposition modes,
* the canonical decomposition mode and one that does not use any decomposition.
* The compatibility decomposition mode, java.text.Collator.FULL_DECOMPOSITION
* is not supported here. If the canonical
* decomposition mode is set, the Collator handles un-normalized text properly,
* producing the same results as if the text were normalized in NFD. If
* canonical decomposition is turned off, it is the user's responsibility to
* ensure that all text is already in the appropriate form before performing
* a comparison or before getting a CollationKey.</p>
*
* <p>For more information about the collation service see the
* <a href="http://oss.software.ibm.com/icu/userguide/Collate_Intro.html">users
* guide</a>.</p>
*
* <p>Examples of use
* <pre>
* // Get the Collator for US English and set its strength to PRIMARY
* Collator usCollator = Collator.getInstance(Locale.US);
* usCollator.setStrength(Collator.PRIMARY);
* if (usCollator.compare("abc", "ABC") == 0) {
*     System.out.println("Strings are equivalent");
* }
*
* The following example shows how to compare two strings using the
* Collator for the default locale.
*
* // Compare two strings in the default locale
* Collator myCollator = Collator.getInstance();
* myCollator.setDecomposition(NO_DECOMPOSITION);
* if (myCollator.compare("&agrave;&#92;u0325", "a&#92;u0325&#768;") != 0) {
*     System.out.println("&agrave;&#92;u0325 is not equals to a&#92;u0325&#768; without decomposition");
*     myCollator.setDecomposition(CANONICAL_DECOMPOSITION);
*     if (myCollator.compare("&agrave;&#92;u0325", "a&#92;u0325&#768;") != 0) {
*         System.out.println("Error: &agrave;&#92;u0325 should be equals to a&#92;u0325&#768; with decomposition");
*     }
*     else {
*         System.out.println("&agrave;&#92;u0325 is equals to a&#92;u0325&#768; with decomposition");
*     }
* }
* else {
*     System.out.println("Error: &agrave;&#92;u0325 should be not equals to a&#92;u0325&#768; without decomposition");
* }
* </pre>
* </p>
* @see RuleBasedCollator
* @see CollationKey
* @author Syn Wee Quek
* @draft ICU 2.2
*/
public abstract class Collator implements Comparator, Cloneable
{
    // public data members ---------------------------------------------------

    /**
     * Strongest collator strength value. Typically used to denote differences
     * between base characters. See class documentation for more explanation.
     * @see #setStrength
     * @see #getStrength
     * @draft ICU 2.2
     */
    public final static int PRIMARY = 0;

    /**
     * Second level collator strength value.
     * Accents in the characters are considered secondary differences.
     * Other differences between letters can also be considered secondary
     * differences, depending on the language.
     * See class documentation for more explanation.
     * @see #setStrength
     * @see #getStrength
     * @draft ICU 2.2
     */
    public final static int SECONDARY = 1;

    /**
     * Third level collator strength value.
     * Upper and lower case differences in characters are distinguished at this
     * strength level. In addition, a variant of a letter differs from the base
     * form on the tertiary level.
     * See class documentation for more explanation.
     * @see #setStrength
     * @see #getStrength
     * @draft ICU 2.2
     */
    public final static int TERTIARY = 2;

    /**
     * Fourth level collator strength value.
     * When punctuation is ignored
     * <a href="http://oss.software.ibm.com/icu/userguide/Collate_Concepts.html#Ignoring_Punctuation">
     * (see Ignoring Punctuations in the user guide)</a> at PRIMARY to TERTIARY
     * strength, an additional strength level can
     * be used to distinguish words with and without punctuation.
     * See class documentation for more explanation.
     * @see #setStrength
     * @see #getStrength
     * @draft ICU 2.2
     */
    public final static int QUATERNARY = 3;

    /**
     * <p>
     * Smallest Collator strength value. When all other strengths are equal,
     * the IDENTICAL strength is used as a tiebreaker. The Unicode code point
     * values of the NFD form of each string are compared, just in case there
     * is no difference.
     * See class documentation for more explanation.
     * </p>
     * <p>
     * Note this value is different from JDK's
     * </p>
     * @draft ICU 2.2
     */
    public final static int IDENTICAL = 15;

    /**
     * <p>Decomposition mode value. With NO_DECOMPOSITION set, Strings
     * will not be decomposed for collation. This is the default
     * decomposition setting unless otherwise specified by the locale
     * used to create the Collator.</p>
     *
     * <p><strong>Note</strong> this value is different from the JDK's.</p>
     * @see #CANONICAL_DECOMPOSITION
     * @see #getDecomposition
     * @see #setDecomposition
     * @draft ICU 2.2
     */
    public final static int NO_DECOMPOSITION = 16;

    /**
     * <p>Decomposition mode value. With CANONICAL_DECOMPOSITION set,
     * characters that are canonical variants according to the Unicode standard
     * will be decomposed for collation.</p>
     *
     * <p>CANONICAL_DECOMPOSITION corresponds to Normalization Form D as
     * described in <a href="http://www.unicode.org/unicode/reports/tr15/">
     * Unicode Technical Report #15</a>.
     * </p>
     * @see #NO_DECOMPOSITION
     * @see #getDecomposition
     * @see #setDecomposition
     * @draft ICU 2.2
     */
    public final static int CANONICAL_DECOMPOSITION = 17;

    // public methods --------------------------------------------------------

    // public setters --------------------------------------------------------

    /**
     * <p>Sets this Collator's strength property. The strength property
     * determines the minimum level of difference considered significant
     * during comparison.</p>
     *
     * <p>The default strength for the Collator is TERTIARY, unless specified
     * otherwise by the locale used to create the Collator.</p>
     *
     * <p>See the Collator class description for an example of use.</p>
     * @param new Strength the new strength value.
     * @see #getStrength
     * @see #PRIMARY
     * @see #SECONDARY
     * @see #TERTIARY
     * @see #QUATERNARY
     * @see #IDENTICAL
     * @exception IllegalArgumentException if the new strength value is not one
     *                of PRIMARY, SECONDARY, TERTIARY, QUATERNARY or IDENTICAL.
     * @draft ICU 2.2
     */
    public void setStrength(int newStrength)
    {
        if ((newStrength != PRIMARY) &&
            (newStrength != SECONDARY) &&
            (newStrength != TERTIARY) &&
            (newStrength != QUATERNARY) &&
            (newStrength != IDENTICAL)) {
            throw new IllegalArgumentException("Incorrect comparison level.");
        }
        m_strength_ = newStrength;
    }

    /**
     * <p>Set the decomposition mode of this Collator.  Setting this
     * decomposition property with CANONICAL_DECOMPOSITION allows the
     * Collator to handle un-normalized text properly, producing the
     * same results as if the text were normalized. If
     * NO_DECOMPOSITION is set, it is the user's responsibility to
     * insure that all text is already in the appropriate form before
     * a comparison or before getting a CollationKey. Adjusting
     * decomposition mode allows the user to select between faster and
     * more complete collation behavior.</p>
     *
     * <p>Since a great many of the world's languages do not require
     * text normalization, most locales set NO_DECOMPOSITION as the
     * default decomposition mode.</p>
     *
     * The default decompositon mode for the Collator is
     * NO_DECOMPOSITON, unless specified otherwise by the locale used
     * to create the Collator.</p>
     *
     * <p>See getDecomposition for a description of decomposition
     * mode.</p>
     *
     * @param decomposition the new decomposition mode
     * @see #getDecomposition
     * @see #NO_DECOMPOSITION
     * @see #CANONICAL_DECOMPOSITION
     * @exception IllegalArgumentException If the given value is not a valid
     *            decomposition mode.
     * @draft ICU 2.2
     */
    public void setDecomposition(int decomposition)
    {
        if ((decomposition != NO_DECOMPOSITION) &&
            (decomposition != CANONICAL_DECOMPOSITION)) {
            throw new IllegalArgumentException("Wrong decomposition mode.");
        }
        m_decomposition_ = decomposition;
    }

    // public getters --------------------------------------------------------

    /**
     * Gets the Collator for the current default locale.
     * The default locale is determined by java.util.Locale.getDefault().
     * @return the Collator for the default locale (for example, en_US) if it
     *         is created successfully. Otherwise if there is no Collator
     *         associated with the current locale, the default UCA collator
     *         will be returned.
     * @see java.util.Locale#getDefault()
     * @see #getInstance(Locale)
     * @draft ICU 2.2
     */
    public static final Collator getInstance()
    {
        return getInstance(Locale.getDefault());
    }

    /**
     * Clone the collator.
     * @draft ICU 2.6
     * @return a clone of this collator.
     */
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    // begin registry stuff

    /**
     * A factory used with registerFactory to register multiple collators and provide
     * display names for them.  If standard locale display names are sufficient, 
     * Collator instances may be registered instead.
     * @draft ICU 2.6
     */
    public static abstract class CollatorFactory {
        /**
         * Return true if this factory will be visible.  Default is true.
         * If not visible, the locales supported by this factory will not
         * be listed by getAvailableLocales.
         *
         * @return true if this factory is visible
         * @draft ICU 2.6
         */
        public boolean visible() {
            return true;
        }

        /**
         * Return an instance of the appropriate collator.  If the locale
         * is not supported, return null.
         * @param loc the locale for which this collator is to be created.
         * @return the newly created collator.
         * @draft ICU 2.6
         */
        public abstract Collator createCollator(Locale loc);

        /**
         * Return the name of the collator for the objectLocale, localized for the displayLocale.
         * If objectLocale is not visible or not defined by the factory, return null.
         * @param objectLocale the locale identifying the collator
         * @param displayLocale the locale for which the display name of the collator should be localized
         * @return the display name
         * @draft ICU 2.6
         */
        public String getDisplayName(Locale objectLocale, Locale displayLocale) {
            if (visible()) {
                Set supported = getSupportedLocaleIDs();
                String name = LocaleUtility.canonicalLocaleString(objectLocale.toString());
                if (supported.contains(name)) {
                    return objectLocale.getDisplayName(displayLocale);
                }
            }
            return null;
        }

        /**
         * Return an unmodifiable collection of the locale names directly 
         * supported by this factory.
         *
         * @return the set of supported locale IDs.
         * @draft ICU 2.6
         */
        public abstract Set getSupportedLocaleIDs();

        /**
         * Empty default constructor.
         * @draft ICU 2.6
         */
        protected CollatorFactory() {
        }
    }

    static abstract class ServiceShim {
        abstract Collator getInstance(Locale l);
        abstract Object registerInstance(Collator c, Locale l);
        abstract Object registerFactory(CollatorFactory f);
        abstract boolean unregister(Object k);
        abstract Locale[] getAvailableLocales();
        abstract String getDisplayName(Locale ol, Locale dl);
    }
    
    private static ServiceShim shim;
    private static ServiceShim getShim() {
        // Note: this instantiation is safe on loose-memory-model configurations
        // despite lack of synchronization, since the shim instance has no state--
        // it's all in the class init.  The worst problem is we might instantiate
        // two shim instances, but they'll share the same state so that's ok.
        if (shim == null) {
            try {
                Class cls = Class.forName("com.ibm.icu.text.CollatorServiceShim");
                shim = (ServiceShim)cls.newInstance();
            }
            catch (Exception e) {
		///CLOVER:OFF
                e.printStackTrace();
                throw new RuntimeException(e.getMessage());
		///CLOVER:ON
            }
        }
        return shim;
    }

    /**
     * Gets the Collator for the desired locale.
     * @param locale the desired locale.
     * @return Collator for the desired locale if it is created successfully.
     *         Otherwise if there is no Collator
     *         associated with the current locale, a default UCA collator will
     *         be returned.
     * @see java.util.Locale
     * @see java.util.ResourceBundle
     * @see #getInstance()
     * @draft ICU 2.2
     */
    public static final Collator getInstance(Locale locale)
    {
        if (shim == null) {
            return new RuleBasedCollator(locale);
        }
        return shim.getInstance(locale);
    }

    /**
     * Register a collator as the default collator for the provided locale.  The
     * collator should not be modified after it is registered.
     *
     * @param collator the collator to register
     * @param locale the locale for which this is the default collator
     * @return an object that can be used to unregister the registered collator.
     *
     * @draft ICU 2.6
     */
    public static final Object registerInstance(Collator collator, Locale locale) {
        return getShim().registerInstance(collator, locale);
    }

    /**
     * Register a collator factory.
     *
     * @param factory the factory to register
     * @return an object that can be used to unregister the registered factory.
     *
     * @draft ICU 2.6
     */
    public static final Object registerFactory(CollatorFactory factory) {
        return getShim().registerFactory(factory);
    }

    /**
     * Unregister a collator previously registered using registerInstance.
     * @param registryKey the object previously returned by registerInstance.
     * @return true if the collator was successfully unregistered.
     * @draft ICU 2.6
     */
    public static final boolean unregister(Object registryKey) {
        if (shim == null) {
            return false;
        }
        return shim.unregister(registryKey);
    }

    /**
     * Get the set of Locales for which Collators are installed.
     * @return the list of available locales in which collators are installed.
     *         The list of Locales returned will include any that have been registered,
     *         in addition to those Locales that are installed with ICU4J.
     * @draft ICU 2.4
     */
    public static Locale[] getAvailableLocales() {
        if (shim == null) {
            return ICULocaleData.getAvailableLocales();
        }
        return shim.getAvailableLocales();
    }

    /**
     * Get the name of the collator for the objectLocale, localized for the displayLocale.
     * @param objectLocale the locale of the collator
     * @param displayLocale the locale for the collator's display name
     * @return the display name
     * @draft ICU 2.6
     */
    static public String getDisplayName(Locale objectLocale, Locale displayLocale) {
        return getShim().getDisplayName(objectLocale, displayLocale);
    }

    /**
     * Get the name of the collator for the objectLocale, localized for the current locale.
     * @param objectLocale the locale of the collator
     * @return the display name
     * @draft ICU 2.6
     */
    static public String getDisplayName(Locale objectLocale) {
        return getShim().getDisplayName(objectLocale, Locale.getDefault());
    }

    /**
     * <p>Returns this Collator's strength property. The strength property
     * determines the minimum level of difference considered significant.
     * </p>
     * <p>
     * See the Collator class description for more details.
     * </p>
     * @return this Collator's current strength property.
     * @see #setStrength
     * @see #PRIMARY
     * @see #SECONDARY
     * @see #TERTIARY
     * @see #QUATERNARY
     * @see #IDENTICAL
     * @draft ICU 2.2
     */
    public int getStrength()
    {
        return m_strength_;
    }

    /**
     * <p>
     * Get the decomposition mode of this Collator. Decomposition mode
     * determines how Unicode composed characters are handled.
     * </p>
     * <p>
     * See the Collator class description for more details.
     * </p>
     * @return the decomposition mode
     * @see #setDecomposition
     * @see #NO_DECOMPOSITION
     * @see #CANONICAL_DECOMPOSITION
     * @draft ICU 2.2
     */
    public int getDecomposition()
    {
        return m_decomposition_;
    }

    /**
     * <p>
     * Compares the source text String to the target text String according to
     * this Collator's rules, strength and decomposition mode.
     * Returns an integer less than,
     * equal to or greater than zero depending on whether the source String is
     * less than, equal to or greater than the target String. See the Collator
     * class description for an example of use.
     * </p>
     * @param source the source String.
     * @param target the target String.
     * @return Returns an integer value. Value is less than zero if source is
     *         less than target, value is zero if source and target are equal,
     *         value is greater than zero if source is greater than target.
     * @see CollationKey
     * @see #getCollationKey
     * @exception NullPointerException thrown if either arguments is null.
     *            IllegalArgumentException thrown if either source or target is
     *            not of the class String.
     * @draft ICU 2.2
     */
    public int compare(Object source, Object target)
    {
        if (!(source instanceof String) || !(target instanceof String)) {
            throw new IllegalArgumentException("Arguments have to be of type String");
        }
        return compare((String)source, (String)target);
    }

    // public other methods -------------------------------------------------

    /**
     * Convenience method for comparing the equality of two text Strings using
     * this Collator's rules, strength and decomposition mode.
     * @param source the source string to be compared.
     * @param target the target string to be compared.
     * @return true if the strings are equal according to the collation
     *         rules, otherwise false.
     * @see #compare
     * @exception NullPointerException thrown if either arguments is null.
     * @draft ICU 2.2
     */
    public boolean equals(String source, String target)
    {
        return (compare(source, target) == 0);
    }

      /**
       * Get an UnicodeSet that contains all the characters and sequences
       * tailored in this collator.
       * @return a pointer to a UnicodeSet object containing all the
       *         code points and sequences that may sort differently than
       *         in the UCA.
       * @draft ICU 2.4
       */
    public UnicodeSet getTailoredSet()
    {
        return new UnicodeSet(0, 0x10FFFF);
    }

    /**
     * Compares the equality of two Collators.
     * @param that the Collator to be compared with this.
     * @return true if this Collator is the same as that Collator;
     *         false otherwise.
     * @draft ICU 2.2
     */
    public abstract boolean equals(Object that);

    // public abstract methods -----------------------------------------------

    /**
     * Generates a unique hash code for this Collator.
     * @draft ICU 2.2
     * @return 32 bit unique hash code
     */
    public abstract int hashCode();

    /**
     * <p>
     * Compares the source text String to the target text String according to
     * this Collator's rules, strength and decomposition mode.
     * Returns an integer less than,
     * equal to or greater than zero depending on whether the source String is
     * less than, equal to or greater than the target String. See the Collator
     * class description for an example of use.
     * </p>
     * @param source the source String.
     * @param target the target String.
     * @return Returns an integer value. Value is less than zero if source is
     *         less than target, value is zero if source and target are equal,
     *         value is greater than zero if source is greater than target.
     * @see CollationKey
     * @see #getCollationKey
     * @exception NullPointerException thrown if either arguments is null.
     * @draft ICU 2.2
     */
    public abstract int compare(String source, String target);

    /**
     * <p>
     * Transforms the String into a CollationKey suitable for efficient
     * repeated comparison.  The resulting key depends on the collator's
     * rules, strength and decomposition mode.
     * </p>
     * <p>See the CollationKey class documentation for more information.</p>
     * @param source the string to be transformed into a CollationKey.
     * @return the CollationKey for the given String based on this Collator's
     *         collation rules. If the source String is null, a null
     *         CollationKey is returned.
     * @see CollationKey
     * @see #compare(String, String)
     * @draft ICU 2.2
     */
    public abstract CollationKey getCollationKey(String source);
    
      /** 
     * <p>
     * Variable top is a two byte primary value which causes all the codepoints 
     * with primary values that are less or equal than the variable top to be 
     * shifted when alternate handling is set to SHIFTED.
     * </p>
     * <p>
     * Sets the variable top to a collation element value of a string supplied.
     * </p> 
     * @param varTop one or more (if contraction) characters to which the 
     *               variable top should be set
     * @return a int value containing the value of the variable top in upper 16
     *         bits. Lower 16 bits are undefined.
     * @exception IllegalArgumentException is thrown if varTop argument is not 
     *            a valid variable top element. A variable top element is 
     *            invalid when it is a contraction that does not exist in the
     *            Collation order or when the PRIMARY strength collation 
     *            element for the variable top has more than two bytes
     * @see #getVariableTop
     * @see RuleBasedCollator#setAlternateHandlingShifted
     * @draft ICU 2.6
     */
    public abstract int setVariableTop(String varTop);
    
    /** 
     * Gets the variable top value of a Collator. 
     * Lower 16 bits are undefined and should be ignored.
     * @return the variable top value of a Collator.
     * @see #setVariableTop
     * @draft ICU 2.6
     */
    public abstract int getVariableTop();
    
    /** 
     * Sets the variable top to a collation element value supplied.
     * Variable top is set to the upper 16 bits. 
     * Lower 16 bits are ignored.
     * @param varTop Collation element value, as returned by setVariableTop or 
     *               getVariableTop
     * @see #getVariableTop
     * @see #setVariableTop
     * @draft ICU 2.6
     */
    public abstract void setVariableTop(int varTop);

    // protected constructor -------------------------------------------------

    /**
     * Empty default constructor to make javadocs happy
     * @draft ICU 2.4
     */
    protected Collator()
    {
    }
    
    // package private methods -----------------------------------------------

    // private data members --------------------------------------------------

    /**
     * Collation strength
     */
    private int m_strength_ = TERTIARY;

    /**
     * Decomposition mode
     */
    private int m_decomposition_ = CANONICAL_DECOMPOSITION;
    
    // private methods -------------------------------------------------------
    
    // end registry stuff
}