/*
*******************************************************************************
*   Copyright (C) 2010-2012, International Business Machines
*   Corporation and others.  All Rights Reserved.
*******************************************************************************
*   created on: 2010aug21
*   created by: Markus W. Scherer
*/

package com.ibm.icu.text;

import java.util.ArrayList;

import com.ibm.icu.impl.ICUConfig;
import com.ibm.icu.impl.PatternProps;
import com.ibm.icu.util.Freezable;

//Note: Minimize ICU dependencies, only use a very small part of the ICU core.
//In particular, do not depend on *Format classes.

/**
 * Parses and represents ICU MessageFormat patterns.
 * Also handles patterns for ChoiceFormat, PluralFormat and SelectFormat.
 * Used in the implementations of those classes as well as in tools
 * for message validation, translation and format conversion.
 * <p>
 * The parser handles all syntax relevant for identifying message arguments.
 * This includes "complex" arguments whose style strings contain
 * nested MessageFormat pattern substrings.
 * For "simple" arguments (with no nested MessageFormat pattern substrings),
 * the argument style is not parsed any further.
 * <p>
 * The parser handles named and numbered message arguments and allows both in one message.
 * <p>
 * Once a pattern has been parsed successfully, iterate through the parsed data
 * with countParts(), getPart() and related methods.
 * <p>
 * The data logically represents a parse tree, but is stored and accessed
 * as a list of "parts" for fast and simple parsing and to minimize object allocations.
 * Arguments and nested messages are best handled via recursion.
 * For every _START "part", {@link #getLimitPartIndex(int)} efficiently returns
 * the index of the corresponding _LIMIT "part".
 * <p>
 * List of "parts":
 * <pre>
 * message = MSG_START (SKIP_SYNTAX | INSERT_CHAR | REPLACE_NUMBER | argument)* MSG_LIMIT
 * argument = noneArg | simpleArg | complexArg
 * complexArg = choiceArg | pluralArg | selectArg
 *
 * noneArg = ARG_START.NONE (ARG_NAME | ARG_NUMBER) ARG_LIMIT.NONE
 * simpleArg = ARG_START.SIMPLE (ARG_NAME | ARG_NUMBER) ARG_TYPE [ARG_STYLE] ARG_LIMIT.SIMPLE
 * choiceArg = ARG_START.CHOICE (ARG_NAME | ARG_NUMBER) choiceStyle ARG_LIMIT.CHOICE
 * pluralArg = ARG_START.PLURAL (ARG_NAME | ARG_NUMBER) pluralStyle ARG_LIMIT.PLURAL
 * selectArg = ARG_START.SELECT (ARG_NAME | ARG_NUMBER) selectStyle ARG_LIMIT.SELECT
 *
 * choiceStyle = ((ARG_INT | ARG_DOUBLE) ARG_SELECTOR message)+
 * pluralStyle = [ARG_INT | ARG_DOUBLE] (ARG_SELECTOR [ARG_INT | ARG_DOUBLE] message)+
 * selectStyle = (ARG_SELECTOR message)+
 * </pre>
 * <ul>
 *   <li>Literal output text is not represented directly by "parts" but accessed
 *       between parts of a message, from one part's getLimit() to the next part's getIndex().
 *   <li><code>ARG_START.CHOICE</code> stands for an ARG_START Part with ArgType CHOICE.
 *   <li>In the choiceStyle, the ARG_SELECTOR has the '<', the '#' or
 *       the less-than-or-equal-to sign (U+2264).
 *   <li>In the pluralStyle, the first, optional numeric Part has the "offset:" value.
 *       The optional numeric Part between each (ARG_SELECTOR, message) pair
 *       is the value of an explicit-number selector like "=2",
 *       otherwise the selector is a non-numeric identifier.
 *   <li>The REPLACE_NUMBER Part can occur only in an immediate sub-message of the pluralStyle.
 * <p>
 * This class is not intended for public subclassing.
 *
 * @stable ICU 4.8
 * @author Markus Scherer
 */
public final class MessagePattern implements Cloneable, Freezable<MessagePattern> {
    /**
     * Mode for when an apostrophe starts quoted literal text for MessageFormat output.
     * The default is DOUBLE_OPTIONAL unless overridden via ICUConfig
     * (/com/ibm/icu/ICUConfig.properties).
     * <p>
     * A pair of adjacent apostrophes always results in a single apostrophe in the output,
     * even when the pair is between two single, text-quoting apostrophes.
     * <p>
     * The following table shows examples of desired MessageFormat.format() output
     * with the pattern strings that yield that output.
     * <p>
     * <table>
     *   <tr>
     *     <th>Desired output</th>
     *     <th>DOUBLE_OPTIONAL</th>
     *     <th>DOUBLE_REQUIRED</th>
     *   </tr>
     *   <tr>
     *     <td>I see {many}</td>
     *     <td>I see '{many}'</td>
     *     <td>(same)</td>
     *   </tr>
     *   <tr>
     *     <td>I said {'Wow!'}</td>
     *     <td>I said '{''Wow!''}'</td>
     *     <td>(same)</td>
     *   </tr>
     *   <tr>
     *     <td>I don't know</td>
     *     <td>I don't know OR<br> I don''t know</td>
     *     <td>I don''t know</td>
     *   </tr>
     * </table>
     * @stable ICU 4.8
     */
    public enum ApostropheMode {
        /**
         * A literal apostrophe is represented by
         * either a single or a double apostrophe pattern character.
         * Within a MessageFormat pattern, a single apostrophe only starts quoted literal text
         * if it immediately precedes a curly brace {},
         * or a pipe symbol | if inside a choice format,
         * or a pound symbol # if inside a plural format.
         * <p>
         * This is the default behavior starting with ICU 4.8.
         * @stable ICU 4.8
         */
        DOUBLE_OPTIONAL,
        /**
         * A literal apostrophe must be represented by
         * a double apostrophe pattern character.
         * A single apostrophe always starts quoted literal text.
         * <p>
         * This is the behavior of ICU 4.6 and earlier, and of the JDK.
         * @stable ICU 4.8
         */
        DOUBLE_REQUIRED
    }

    /**
     * Constructs an empty MessagePattern with default ApostropheMode.
     * @stable ICU 4.8
     */
    public MessagePattern() {
        aposMode=defaultAposMode;
    }

    /**
     * Constructs an empty MessagePattern.
     * @param mode Explicit ApostropheMode.
     * @stable ICU 4.8
     */
    public MessagePattern(ApostropheMode mode) {
        aposMode=mode;
    }

    /**
     * Constructs a MessagePattern with default ApostropheMode and
     * parses the MessageFormat pattern string.
     * @param pattern a MessageFormat pattern string
     * @throws IllegalArgumentException for syntax errors in the pattern string
     * @throws IndexOutOfBoundsException if certain limits are exceeded
     *         (e.g., argument number too high, argument name too long, etc.)
     * @throws NumberFormatException if a number could not be parsed
     * @stable ICU 4.8
     */
    public MessagePattern(String pattern) {
        aposMode=defaultAposMode;
        parse(pattern);
    }

    /**
     * Parses a MessageFormat pattern string.
     * @param pattern a MessageFormat pattern string
     * @return this
     * @throws IllegalArgumentException for syntax errors in the pattern string
     * @throws IndexOutOfBoundsException if certain limits are exceeded
     *         (e.g., argument number too high, argument name too long, etc.)
     * @throws NumberFormatException if a number could not be parsed
     * @stable ICU 4.8
     */
    public MessagePattern parse(String pattern) {
        preParse(pattern);
        parseMessage(0, 0, 0, ArgType.NONE);
        postParse();
        return this;
    }

    /**
     * Parses a ChoiceFormat pattern string.
     * @param pattern a ChoiceFormat pattern string
     * @return this
     * @throws IllegalArgumentException for syntax errors in the pattern string
     * @throws IndexOutOfBoundsException if certain limits are exceeded
     *         (e.g., argument number too high, argument name too long, etc.)
     * @throws NumberFormatException if a number could not be parsed
     * @stable ICU 4.8
     */
    public MessagePattern parseChoiceStyle(String pattern) {
        preParse(pattern);
        parseChoiceStyle(0, 0);
        postParse();
        return this;
    }

    /**
     * Parses a PluralFormat pattern string.
     * @param pattern a PluralFormat pattern string
     * @return this
     * @throws IllegalArgumentException for syntax errors in the pattern string
     * @throws IndexOutOfBoundsException if certain limits are exceeded
     *         (e.g., argument number too high, argument name too long, etc.)
     * @throws NumberFormatException if a number could not be parsed
     * @stable ICU 4.8
     */
    public MessagePattern parsePluralStyle(String pattern) {
        preParse(pattern);
        parsePluralOrSelectStyle(ArgType.PLURAL, 0, 0);
        postParse();
        return this;
    }

    /**
     * Parses a SelectFormat pattern string.
     * @param pattern a SelectFormat pattern string
     * @return this
     * @throws IllegalArgumentException for syntax errors in the pattern string
     * @throws IndexOutOfBoundsException if certain limits are exceeded
     *         (e.g., argument number too high, argument name too long, etc.)
     * @throws NumberFormatException if a number could not be parsed
     * @stable ICU 4.8
     */
    public MessagePattern parseSelectStyle(String pattern) {
        preParse(pattern);
        parsePluralOrSelectStyle(ArgType.SELECT, 0, 0);
        postParse();
        return this;
    }

    /**
     * Clears this MessagePattern.
     * countParts() will return 0.
     * @stable ICU 4.8
     */
    public void clear() {
        // Mostly the same as preParse().
        if(isFrozen()) {
            throw new UnsupportedOperationException(
                "Attempt to clear() a frozen MessagePattern instance.");
        }
        msg=null;
        hasArgNames=hasArgNumbers=false;
        needsAutoQuoting=false;
        parts.clear();
        if(numericValues!=null) {
            numericValues.clear();
        }
    }

    /**
     * Clears this MessagePattern and sets the ApostropheMode.
     * countParts() will return 0.
     * @param mode The new ApostropheMode.
     * @stable ICU 4.8
     */
    public void clearPatternAndSetApostropheMode(ApostropheMode mode) {
        clear();
        aposMode=mode;
    }

    /**
     * @param other another object to compare with.
     * @return true if this object is equivalent to the other one.
     * @stable ICU 4.8
     */
    @Override
    public boolean equals(Object other) {
        if(this==other) {
            return true;
        }
        if(other==null || getClass()!=other.getClass()) {
            return false;
        }
        MessagePattern o=(MessagePattern)other;
        return
            aposMode.equals(o.aposMode) &&
            (msg==null ? o.msg==null : msg.equals(o.msg)) &&
            parts.equals(o.parts);
        // No need to compare numericValues if msg and parts are the same.
    }

    /**
     * {@inheritDoc}
     * @stable ICU 4.8
     */
    @Override
    public int hashCode() {
        return (aposMode.hashCode()*37+(msg!=null ? msg.hashCode() : 0))*37+parts.hashCode();
    }

    /**
     * @return this instance's ApostropheMode.
     * @stable ICU 4.8
     */
    public ApostropheMode getApostropheMode() {
        return aposMode;
    }

    /**
     * @return true if getApostropheMode() == ApostropheMode.DOUBLE_REQUIRED
     * @internal
     */
    /* package */ boolean jdkAposMode() {
        return aposMode == ApostropheMode.DOUBLE_REQUIRED;
    }

    /**
     * @return the parsed pattern string (null if none was parsed).
     * @stable ICU 4.8
     */
    public String getPatternString() {
        return msg;
    }

    /**
     * Does the parsed pattern have named arguments like {first_name}?
     * @return true if the parsed pattern has at least one named argument.
     * @stable ICU 4.8
     */
    public boolean hasNamedArguments() {
        return hasArgNames;
    }

    /**
     * Does the parsed pattern have numbered arguments like {2}?
     * @return true if the parsed pattern has at least one numbered argument.
     * @stable ICU 4.8
     */
    public boolean hasNumberedArguments() {
        return hasArgNumbers;
    }

    /**
     * {@inheritDoc}
     * @stable ICU 4.8
     */
    @Override
    public String toString() {
        return msg;
    }

    /**
     * Validates and parses an argument name or argument number string.
     * An argument name must be a "pattern identifier", that is, it must contain
     * no Unicode Pattern_Syntax or Pattern_White_Space characters.
     * If it only contains ASCII digits, then it must be a small integer with no leading zero.
     * @param name Input string.
     * @return &gt;=0 if the name is a valid number,
     *         ARG_NAME_NOT_NUMBER (-1) if it is a "pattern identifier" but not all ASCII digits,
     *         ARG_NAME_NOT_VALID (-2) if it is neither.
     * @stable ICU 4.8
     */
    public static int validateArgumentName(String name) {
        if(!PatternProps.isIdentifier(name)) {
            return ARG_NAME_NOT_VALID;
        }
        return parseArgNumber(name, 0, name.length());
    }

    /**
     * Return value from {@link #validateArgumentName(String)} for when
     * the string is a valid "pattern identifier" but not a number.
     * @stable ICU 4.8
     */
    public static final int ARG_NAME_NOT_NUMBER=-1;

    /**
     * Return value from {@link #validateArgumentName(String)} for when
     * the string is invalid.
     * It might not be a valid "pattern identifier",
     * or it have only ASCII digits but there is a leading zero or the number is too large.
     * @stable ICU 4.8
     */
    public static final int ARG_NAME_NOT_VALID=-2;

    /**
     * Returns a version of the parsed pattern string where each ASCII apostrophe
     * is doubled (escaped) if it is not already, and if it is not interpreted as quoting syntax.
     * <p>
     * For example, this turns "I don't '{know}' {gender,select,female{h''er}other{h'im}}."
     * into "I don''t '{know}' {gender,select,female{h''er}other{h''im}}."
     * @return the deep-auto-quoted version of the parsed pattern string.
     * @see MessageFormat#autoQuoteApostrophe(String)
     * @stable ICU 4.8
     */
    public String autoQuoteApostropheDeep() {
        if(!needsAutoQuoting) {
            return msg;
        }
        StringBuilder modified=null;
        // Iterate backward so that the insertion indexes do not change.
        int count=countParts();
        for(int i=count; i>0;) {
            Part part;
            if((part=getPart(--i)).getType()==Part.Type.INSERT_CHAR) {
                if(modified==null) {
                    modified=new StringBuilder(msg.length()+10).append(msg);
                }
                modified.insert(part.index, (char)part.value);
            }
        }
        if(modified==null) {
            return msg;
        } else {
            return modified.toString();
        }
    }

    /**
     * Returns the number of "parts" created by parsing the pattern string.
     * Returns 0 if no pattern has been parsed or clear() was called.
     * @return the number of pattern parts.
     * @stable ICU 4.8
     */
    public int countParts() {
        return parts.size();
    }

    /**
     * Gets the i-th pattern "part".
     * @param i The index of the Part data. (0..countParts()-1)
     * @return the i-th pattern "part".
     * @throws IndexOutOfBoundsException if i is outside the (0..countParts()-1) range
     * @stable ICU 4.8
     */
    public Part getPart(int i) {
        return parts.get(i);
    }

    /**
     * Returns the Part.Type of the i-th pattern "part".
     * Convenience method for getPart(i).getType().
     * @param i The index of the Part data. (0..countParts()-1)
     * @return The Part.Type of the i-th Part.
     * @throws IndexOutOfBoundsException if i is outside the (0..countParts()-1) range
     * @stable ICU 4.8
     */
    public Part.Type getPartType(int i) {
        return parts.get(i).type;
    }

    /**
     * Returns the pattern index of the specified pattern "part".
     * Convenience method for getPart(partIndex).getIndex().
     * @param partIndex The index of the Part data. (0..countParts()-1)
     * @return The pattern index of this Part.
     * @throws IndexOutOfBoundsException if partIndex is outside the (0..countParts()-1) range
     * @stable ICU 4.8
     */
    public int getPatternIndex(int partIndex) {
        return parts.get(partIndex).index;
    }

    /**
     * Returns the substring of the pattern string indicated by the Part.
     * Convenience method for getPatternString().substring(part.getIndex(), part.getLimit()).
     * @param part a part of this MessagePattern.
     * @return the substring associated with part.
     * @stable ICU 4.8
     */
    public String getSubstring(Part part) {
        int index=part.index;
        return msg.substring(index, index+part.length);
    }

    /**
     * Compares the part's substring with the input string s.
     * @param part a part of this MessagePattern.
     * @param s a string.
     * @return true if getSubstring(part).equals(s).
     * @stable ICU 4.8
     */
    public boolean partSubstringMatches(Part part, String s) {
        return msg.regionMatches(part.index, s, 0, part.length);
    }

    /**
     * Returns the numeric value associated with an ARG_INT or ARG_DOUBLE.
     * @param part a part of this MessagePattern.
     * @return the part's numeric value, or NO_NUMERIC_VALUE if this is not a numeric part.
     * @stable ICU 4.8
     */
    public double getNumericValue(Part part) {
        Part.Type type=part.type;
        if(type==Part.Type.ARG_INT) {
            return part.value;
        } else if(type==Part.Type.ARG_DOUBLE) {
            return numericValues.get(part.value);
        } else {
            return NO_NUMERIC_VALUE;
        }
    }

    /**
     * Special value that is returned by getNumericValue(Part) when no
     * numeric value is defined for a part.
     * @see #getNumericValue
     * @stable ICU 4.8
     */
    public static final double NO_NUMERIC_VALUE=-123456789;

    /**
     * Returns the "offset:" value of a PluralFormat argument, or 0 if none is specified.
     * @param pluralStart the index of the first PluralFormat argument style part. (0..countParts()-1)
     * @return the "offset:" value.
     * @throws IndexOutOfBoundsException if pluralStart is outside the (0..countParts()-1) range
     * @stable ICU 4.8
     */
    public double getPluralOffset(int pluralStart) {
        Part part=parts.get(pluralStart);
        if(part.type.hasNumericValue()) {
            return getNumericValue(part);
        } else {
            return 0;
        }
    }

    /**
     * Returns the index of the ARG|MSG_LIMIT part corresponding to the ARG|MSG_START at start.
     * @param start The index of some Part data (0..countParts()-1);
     *        this Part should be of Type ARG_START or MSG_START.
     * @return The first i>start where getPart(i).getType()==ARG|MSG_LIMIT at the same nesting level,
     *         or start itself if getPartType(msgStart)!=ARG|MSG_START.
     * @throws IndexOutOfBoundsException if start is outside the (0..countParts()-1) range
     * @stable ICU 4.8
     */
    public int getLimitPartIndex(int start) {
        int limit=parts.get(start).limitPartIndex;
        if(limit<start) {
            return start;
        }
        return limit;
    }

    /**
     * A message pattern "part", representing a pattern parsing event.
     * There is a part for the start and end of a message or argument,
     * for quoting and escaping of and with ASCII apostrophes,
     * and for syntax elements of "complex" arguments.
     * @stable ICU 4.8
     */
    public static final class Part {
        private Part(Type t, int i, int l, int v) {
            type=t;
            index=i;
            length=(char)l;
            value=(short)v;
        }

        /**
         * Returns the type of this part.
         * @return the part type.
         * @stable ICU 4.8
         */
        public Type getType() {
            return type;
        }

        /**
         * Returns the pattern string index associated with this Part.
         * @return this part's pattern string index.
         * @stable ICU 4.8
         */
        public int getIndex() {
            return index;
        }

        /**
         * Returns the length of the pattern substring associated with this Part.
         * This is 0 for some parts.
         * @return this part's pattern substring length.
         * @stable ICU 4.8
         */
        public int getLength() {
            return length;
        }

        /**
         * Returns the pattern string limit (exclusive-end) index associated with this Part.
         * Convenience method for getIndex()+getLength().
         * @return this part's pattern string limit index, same as getIndex()+getLength().
         * @stable ICU 4.8
         */
        public int getLimit() {
            return index+length;
        }

        /**
         * Returns a value associated with this part.
         * See the documentation of each part type for details.
         * @return the part value.
         * @stable ICU 4.8
         */
        public int getValue() {
            return value;
        }

        /**
         * Returns the argument type if this part is of type ARG_START or ARG_LIMIT,
         * otherwise ArgType.NONE.
         * @return the argument type for this part.
         * @stable ICU 4.8
         */
        public ArgType getArgType() {
            Type type=getType();
            if(type==Type.ARG_START || type==Type.ARG_LIMIT) {
                return argTypes[value];
            } else {
                return ArgType.NONE;
            }
        }

        /**
         * Part type constants.
         * @stable ICU 4.8
         */
        public enum Type {
            /**
             * Start of a message pattern (main or nested).
             * The length is 0 for the top-level message
             * and for a choice argument sub-message, otherwise 1 for the '{'.
             * The value indicates the nesting level, starting with 0 for the main message.
             * <p>
             * There is always a later MSG_LIMIT part.
             * @stable ICU 4.8
             */
            MSG_START,
            /**
             * End of a message pattern (main or nested).
             * The length is 0 for the top-level message and
             * the last sub-message of a choice argument,
             * otherwise 1 for the '}' or (in a choice argument style) the '|'.
             * The value indicates the nesting level, starting with 0 for the main message.
             * @stable ICU 4.8
             */
            MSG_LIMIT,
            /**
             * Indicates a substring of the pattern string which is to be skipped when formatting.
             * For example, an apostrophe that begins or ends quoted text
             * would be indicated with such a part.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            SKIP_SYNTAX,
            /**
             * Indicates that a syntax character needs to be inserted for auto-quoting.
             * The length is 0.
             * The value is the character code of the insertion character. (U+0027=APOSTROPHE)
             * @stable ICU 4.8
             */
            INSERT_CHAR,
            /**
             * Indicates a syntactic (non-escaped) # symbol in a plural variant.
             * When formatting, replace this part's substring with the
             * (value-offset) for the plural argument value.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            REPLACE_NUMBER,
            /**
             * Start of an argument.
             * The length is 1 for the '{'.
             * The value is the ordinal value of the ArgType. Use getArgType().
             * <p>
             * This part is followed by either an ARG_NUMBER or ARG_NAME,
             * followed by optional argument sub-parts (see ArgType constants)
             * and finally an ARG_LIMIT part.
             * @stable ICU 4.8
             */
            ARG_START,
            /**
             * End of an argument.
             * The length is 1 for the '}'.
             * The value is the ordinal value of the ArgType. Use getArgType().
             * @stable ICU 4.8
             */
            ARG_LIMIT,
            /**
             * The argument number, provided by the value.
             * @stable ICU 4.8
             */
            ARG_NUMBER,
            /**
             * The argument name.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            ARG_NAME,
            /**
             * The argument type.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            ARG_TYPE,
            /**
             * The argument style text.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            ARG_STYLE,
            /**
             * A selector substring in a "complex" argument style.
             * The value is undefined and currently always 0.
             * @stable ICU 4.8
             */
            ARG_SELECTOR,
            /**
             * An integer value, for example the offset or an explicit selector value
             * in a PluralFormat style.
             * The part value is the integer value.
             * @stable ICU 4.8
             */
            ARG_INT,
            /**
             * A numeric value, for example the offset or an explicit selector value
             * in a PluralFormat style.
             * The part value is an index into an internal array of numeric values;
             * use getNumericValue().
             * @stable ICU 4.8
             */
            ARG_DOUBLE;

            /**
             * Indicates whether this part has a numeric value.
             * If so, then that numeric value can be retrieved via {@link MessagePattern#getNumericValue(Part)}.
             * @return true if this part has a numeric value.
             * @stable ICU 4.8
             */
            public boolean hasNumericValue() {
                return this==ARG_INT || this==ARG_DOUBLE;
            }
        }

        /**
         * @return a string representation of this part.
         * @stable ICU 4.8
         */
        @Override
        public String toString() {
            String valueString=(type==Type.ARG_START || type==Type.ARG_LIMIT) ?
                getArgType().name() : Integer.toString(value);
            return type.name()+"("+valueString+")@"+index;
        }

        /**
         * @param other another object to compare with.
         * @return true if this object is equivalent to the other one.
         * @stable ICU 4.8
         */
        @Override
        public boolean equals(Object other) {
            if(this==other) {
                return true;
            }
            if(other==null || getClass()!=other.getClass()) {
                return false;
            }
            Part o=(Part)other;
            return
                type.equals(o.type) &&
                index==o.index &&
                length==o.length &&
                value==o.value &&
                limitPartIndex==o.limitPartIndex;
        }

        /**
         * {@inheritDoc}
         * @stable ICU 4.8
         */
        @Override
        public int hashCode() {
            return ((type.hashCode()*37+index)*37+length)*37+value;
        }

        private static final int MAX_LENGTH=0xffff;
        private static final int MAX_VALUE=Short.MAX_VALUE;

        // Some fields are not final because they are modified during pattern parsing.
        // After pattern parsing, the parts are effectively immutable.
        private final Type type;
        private final int index;
        private final char length;
        private short value;
        private int limitPartIndex;
    }

    /**
     * Argument type constants.
     * Returned by Part.getArgType() for ARG_START and ARG_LIMIT parts.
     *
     * Messages nested inside an argument are each delimited by MSG_START and MSG_LIMIT,
     * with a nesting level one greater than the surrounding message.
     * @stable ICU 4.8
     */
    public enum ArgType {
        /**
         * The argument has no specified type.
         * @stable ICU 4.8
         */
        NONE,
        /**
         * The argument has a "simple" type which is provided by the ARG_TYPE part.
         * An ARG_STYLE part might follow that.
         * @stable ICU 4.8
         */
        SIMPLE,
        /**
         * The argument is a ChoiceFormat with one or more
         * ((ARG_INT | ARG_DOUBLE), ARG_SELECTOR, message) tuples.
         * @stable ICU 4.8
         */
        CHOICE,
        /**
         * The argument is a PluralFormat with an optional ARG_INT or ARG_DOUBLE offset
         * (e.g., offset:1)
         * and one or more (ARG_SELECTOR [explicit-value] message) tuples.
         * If the selector has an explicit value (e.g., =2), then
         * that value is provided by the ARG_INT or ARG_DOUBLE part preceding the message.
         * Otherwise the message immediately follows the ARG_SELECTOR.
         * @stable ICU 4.8
         */
        PLURAL,
        /**
         * The argument is a SelectFormat with one or more (ARG_SELECTOR, message) pairs.
         * @stable ICU 4.8
         */
        SELECT
    }

    /**
     * Creates and returns a copy of this object.
     * @return a copy of this object (or itself if frozen).
     * @stable ICU 4.8
     */
    @Override
    public Object clone() {
        if(isFrozen()) {
            return this;
        } else {
            return cloneAsThawed();
        }
    }

    /**
     * Creates and returns an unfrozen copy of this object.
     * @return a copy of this object.
     * @stable ICU 4.8
     */
    @SuppressWarnings("unchecked")
    public MessagePattern cloneAsThawed() {
        MessagePattern newMsg;
        try {
            newMsg=(MessagePattern)super.clone();
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException(e);
        }
        newMsg.parts=(ArrayList<Part>)parts.clone();
        if(numericValues!=null) {
            newMsg.numericValues=(ArrayList<Double>)numericValues.clone();
        }
        newMsg.frozen=false;
        return newMsg;
    }

    /**
     * Freezes this object, making it immutable and thread-safe.
     * @return this 
     * @stable ICU 4.8
     */
    public MessagePattern freeze() {
        frozen=true;
        return this;
    }

    /**
     * Determines whether this object is frozen (immutable) or not.
     * @return true if this object is frozen.
     * @stable ICU 4.8
     */
    public boolean isFrozen() {
        return frozen;
    }

    private void preParse(String pattern) {
        if(isFrozen()) {
            throw new UnsupportedOperationException(
                "Attempt to parse(\""+prefix(pattern)+"\") on frozen MessagePattern instance.");
        }
        msg=pattern;
        hasArgNames=hasArgNumbers=false;
        needsAutoQuoting=false;
        parts.clear();
        if(numericValues!=null) {
            numericValues.clear();
        }
    }

    private void postParse() {
        // Nothing to be done currently.
    }

    private int parseMessage(int index, int msgStartLength, int nestingLevel, ArgType parentType) {
        if(nestingLevel>Part.MAX_VALUE) {
            throw new IndexOutOfBoundsException();
        }
        int msgStart=parts.size();
        addPart(Part.Type.MSG_START, index, msgStartLength, nestingLevel);
        index+=msgStartLength;
        while(index<msg.length()) {
            char c=msg.charAt(index++);
            if(c=='\'') {
                if(index==msg.length()) {
                    // The apostrophe is the last character in the pattern. 
                    // Add a Part for auto-quoting.
                    addPart(Part.Type.INSERT_CHAR, index, 0, '\'');  // value=char to be inserted
                    needsAutoQuoting=true;
                } else {
                    c=msg.charAt(index);
                    if(c=='\'') {
                        // double apostrophe, skip the second one
                        addPart(Part.Type.SKIP_SYNTAX, index++, 1, 0);
                    } else if(
                        aposMode==ApostropheMode.DOUBLE_REQUIRED ||
                        c=='{' || c=='}' ||
                        (parentType==ArgType.CHOICE && c=='|') ||
                        (parentType==ArgType.PLURAL && c=='#')
                    ) {
                        // skip the quote-starting apostrophe
                        addPart(Part.Type.SKIP_SYNTAX, index-1, 1, 0);
                        // find the end of the quoted literal text
                        for(;;) {
                            index=msg.indexOf('\'', index+1);
                            if(index>=0) {
                                if((index+1)<msg.length() && msg.charAt(index+1)=='\'') {
                                    // double apostrophe inside quoted literal text
                                    // still encodes a single apostrophe, skip the second one
                                    addPart(Part.Type.SKIP_SYNTAX, ++index, 1, 0);
                                } else {
                                    // skip the quote-ending apostrophe
                                    addPart(Part.Type.SKIP_SYNTAX, index++, 1, 0);
                                    break;
                                }
                            } else {
                                // The quoted text reaches to the end of the of the message.
                                index=msg.length();
                                // Add a Part for auto-quoting.
                                addPart(Part.Type.INSERT_CHAR, index, 0, '\'');  // value=char to be inserted
                                needsAutoQuoting=true;
                                break;
                            }
                        }
                    } else {
                        // Interpret the apostrophe as literal text.
                        // Add a Part for auto-quoting.
                        addPart(Part.Type.INSERT_CHAR, index, 0, '\'');  // value=char to be inserted
                        needsAutoQuoting=true;
                    }
                }
            } else if(parentType==ArgType.PLURAL && c=='#') {
                // The unquoted # in a plural message fragment will be replaced
                // with the (number-offset).
                addPart(Part.Type.REPLACE_NUMBER, index-1, 1, 0);
            } else if(c=='{') {
                index=parseArg(index-1, 1, nestingLevel);
            } else if((nestingLevel>0 && c=='}') || (parentType==ArgType.CHOICE && c=='|')) {
                // Finish the message before the terminator.
                // In a choice style, report the "}" substring only for the following ARG_LIMIT,
                // not for this MSG_LIMIT.
                int limitLength=(parentType==ArgType.CHOICE && c=='}') ? 0 : 1;
                addLimitPart(msgStart, Part.Type.MSG_LIMIT, index-1, limitLength, nestingLevel);
                if(parentType==ArgType.CHOICE) {
                    // Let the choice style parser see the '}' or '|'.
                    return index-1;
                } else {
                    // continue parsing after the '}'
                    return index;
                }
            }  // else: c is part of literal text
        }
        if(nestingLevel>0 && !inTopLevelChoiceMessage(nestingLevel, parentType)) {
            throw new IllegalArgumentException(
                "Unmatched '{' braces in message \""+prefix()+"\"");
        }
        addLimitPart(msgStart, Part.Type.MSG_LIMIT, index, 0, nestingLevel);
        return index;
    }

    private int parseArg(int index, int argStartLength, int nestingLevel) {
        int argStart=parts.size();
        ArgType argType=ArgType.NONE;
        addPart(Part.Type.ARG_START, index, argStartLength, argType.ordinal());
        int nameIndex=index=skipWhiteSpace(index+argStartLength);
        if(index==msg.length()) {
            throw new IllegalArgumentException(
                "Unmatched '{' braces in message \""+prefix()+"\"");
        }
        // parse argument name or number
        index=skipIdentifier(index);
        int number=parseArgNumber(nameIndex, index);
        if(number>=0) {
            int length=index-nameIndex;
            if(length>Part.MAX_LENGTH || number>Part.MAX_VALUE) {
                throw new IndexOutOfBoundsException(
                    "Argument number too large: "+prefix(nameIndex));
            }
            hasArgNumbers=true;
            addPart(Part.Type.ARG_NUMBER, nameIndex, length, number);
        } else if(number==ARG_NAME_NOT_NUMBER) {
            int length=index-nameIndex;
            if(length>Part.MAX_LENGTH) {
                throw new IndexOutOfBoundsException(
                    "Argument name too long: "+prefix(nameIndex));
            }
            hasArgNames=true;
            addPart(Part.Type.ARG_NAME, nameIndex, length, 0);
        } else {  // number<-1 (ARG_NAME_NOT_VALID)
            throw new IllegalArgumentException("Bad argument syntax: "+prefix(nameIndex));
        }
        index=skipWhiteSpace(index);
        if(index==msg.length()) {
            throw new IllegalArgumentException(
                "Unmatched '{' braces in message \""+prefix()+"\"");
        }
        char c=msg.charAt(index);
        if(c=='}') {
            // all done
        } else if(c!=',') {
            throw new IllegalArgumentException("Bad argument syntax: "+prefix(nameIndex));
        } else /* ',' */ {
            // parse argument type: case-sensitive a-zA-Z
            int typeIndex=index=skipWhiteSpace(index+1);
            while(index<msg.length() && isArgTypeChar(msg.charAt(index))) {
                ++index;
            }
            int length=index-typeIndex;
            index=skipWhiteSpace(index);
            if(index==msg.length()) {
                throw new IllegalArgumentException(
                    "Unmatched '{' braces in message \""+prefix()+"\"");
            }
            if(length==0 || ((c=msg.charAt(index))!=',' && c!='}')) {
                throw new IllegalArgumentException("Bad argument syntax: "+prefix(nameIndex));
            }
            if(length>Part.MAX_LENGTH) {
                throw new IndexOutOfBoundsException(
                    "Argument type name too long: "+prefix(nameIndex));
            }
            argType=ArgType.SIMPLE;
            if(length==6) {
                // case-insensitive comparisons for complex-type names
                if(isChoice(typeIndex)) {
                    argType=ArgType.CHOICE;
                } else if(isPlural(typeIndex)) {
                    argType=ArgType.PLURAL;
                } else if(isSelect(typeIndex)) {
                    argType=ArgType.SELECT;
                }
            }
            // change the ARG_START type from NONE to argType
            parts.get(argStart).value=(short)argType.ordinal();
            if(argType==ArgType.SIMPLE) {
                addPart(Part.Type.ARG_TYPE, typeIndex, length, 0);
            }
            // look for an argument style (pattern)
            if(c=='}') {
                if(argType!=ArgType.SIMPLE) {
                    throw new IllegalArgumentException(
                        "No style field for complex argument: "+prefix(nameIndex));
                }
            } else /* ',' */ {
                ++index;
                if(argType==ArgType.SIMPLE) {
                    index=parseSimpleStyle(index);
                } else if(argType==ArgType.CHOICE) {
                    index=parseChoiceStyle(index, nestingLevel);
                } else {
                    index=parsePluralOrSelectStyle(argType, index, nestingLevel);
                }
            }
        }
        // Argument parsing stopped on the '}'.
        addLimitPart(argStart, Part.Type.ARG_LIMIT, index, 1, argType.ordinal());
        return index+1;
    }

    private int parseSimpleStyle(int index) {
        int start=index;
        int nestedBraces=0;
        while(index<msg.length()) {
            char c=msg.charAt(index++);
            if(c=='\'') {
                // Treat apostrophe as quoting but include it in the style part.
                // Find the end of the quoted literal text.
                index=msg.indexOf('\'', index);
                if(index<0) {
                    throw new IllegalArgumentException(
                        "Quoted literal argument style text reaches to the end of the message: \""+
                        prefix(start)+"\"");
                }
                // skip the quote-ending apostrophe
                ++index;
            } else if(c=='{') {
                ++nestedBraces;
            } else if(c=='}') {
                if(nestedBraces>0) {
                    --nestedBraces;
                } else {
                    int length=--index-start;
                    if(length>Part.MAX_LENGTH) {
                        throw new IndexOutOfBoundsException(
                            "Argument style text too long: "+prefix(start));
                    }
                    addPart(Part.Type.ARG_STYLE, start, length, 0);
                    return index;
                }
            }  // c is part of literal text
        }
        throw new IllegalArgumentException(
            "Unmatched '{' braces in message \""+prefix()+"\"");
    }

    private int parseChoiceStyle(int index, int nestingLevel) {
        int start=index;
        index=skipWhiteSpace(index);
        if(index==msg.length() || msg.charAt(index)=='}') {
            throw new IllegalArgumentException(
                "Missing choice argument pattern in \""+prefix()+"\"");
        }
        for(;;) {
            // The choice argument style contains |-separated (number, separator, message) triples.
            // Parse the number.
            int numberIndex=index;
            index=skipDouble(index);
            int length=index-numberIndex;
            if(length==0) {
                throw new IllegalArgumentException("Bad choice pattern syntax: "+prefix(start));
            }
            if(length>Part.MAX_LENGTH) {
                throw new IndexOutOfBoundsException(
                    "Choice number too long: "+prefix(numberIndex));
            }
            parseDouble(numberIndex, index, true);  // adds ARG_INT or ARG_DOUBLE
            // Parse the separator.
            index=skipWhiteSpace(index);
            if(index==msg.length()) {
                throw new IllegalArgumentException("Bad choice pattern syntax: "+prefix(start));
            }
            char c=msg.charAt(index);
            if(!(c=='#' || c=='<' || c=='\u2264')) {  // U+2264 is <=
                throw new IllegalArgumentException(
                    "Expected choice separator (#<\u2264) instead of '"+c+
                    "' in choice pattern "+prefix(start));
            }
            addPart(Part.Type.ARG_SELECTOR, index, 1, 0);
            // Parse the message fragment.
            index=parseMessage(++index, 0, nestingLevel+1, ArgType.CHOICE);
            // parseMessage(..., CHOICE) returns the index of the terminator, or msg.length().
            if(index==msg.length()) {
                return index;
            }
            if(msg.charAt(index)=='}') {
                if(!inMessageFormatPattern(nestingLevel)) {
                    throw new IllegalArgumentException(
                        "Bad choice pattern syntax: "+prefix(start));
                }
                return index;
            }  // else the terminator is '|'
            index=skipWhiteSpace(index+1);
        }
    }

    private int parsePluralOrSelectStyle(ArgType argType, int index, int nestingLevel) {
        int start=index;
        boolean isEmpty=true;
        boolean hasOther=false;
        for(;;) {
            // First, collect the selector looking for a small set of terminators.
            // It would be a little faster to consider the syntax of each possible
            // token right here, but that makes the code too complicated.
            index=skipWhiteSpace(index);
            boolean eos=index==msg.length();
            if(eos || msg.charAt(index)=='}') {
                if(eos==inMessageFormatPattern(nestingLevel)) {
                    throw new IllegalArgumentException(
                        "Bad "+
                        (argType==ArgType.PLURAL ? "plural" : "select")+
                        " pattern syntax: "+prefix(start));
                }
                if(!hasOther) {
                    throw new IllegalArgumentException(
                        "Missing 'other' keyword in "+
                        (argType==ArgType.PLURAL ? "plural" : "select")+
                        " pattern in \""+prefix()+"\"");
                }
                return index;
            }
            int selectorIndex=index;
            if(argType==ArgType.PLURAL && msg.charAt(selectorIndex)=='=') {
                // explicit-value plural selector: =double
                index=skipDouble(index+1);
                int length=index-selectorIndex;
                if(length==1) {
                    throw new IllegalArgumentException(
                        "Bad "+
                        (argType==ArgType.PLURAL ? "plural" : "select")+
                        " pattern syntax: "+prefix(start));
                }
                if(length>Part.MAX_LENGTH) {
                    throw new IndexOutOfBoundsException(
                        "Argument selector too long: "+prefix(selectorIndex));
                }
                addPart(Part.Type.ARG_SELECTOR, selectorIndex, length, 0);
                parseDouble(selectorIndex+1, index, false);  // adds ARG_INT or ARG_DOUBLE
            } else {
                index=skipIdentifier(index);
                int length=index-selectorIndex;
                if(length==0) {
                    throw new IllegalArgumentException(
                        "Bad "+
                        (argType==ArgType.PLURAL ? "plural" : "select")+
                        " pattern syntax: "+prefix(start));
                }
                // Note: The ':' in "offset:" is just beyond the skipIdentifier() range.
                if( argType==ArgType.PLURAL && length==6 && index<msg.length() &&
                    msg.regionMatches(selectorIndex, "offset:", 0, 7)
                ) {
                    // plural offset, not a selector
                    if(!isEmpty) {
                        throw new IllegalArgumentException(
                            "Plural argument 'offset:' (if present) must precede key-message pairs: "+
                            prefix(start));
                    }
                    // allow whitespace between offset: and its value
                    int valueIndex=skipWhiteSpace(index+1);  // The ':' is at index.
                    index=skipDouble(valueIndex);
                    if(index==valueIndex) {
                        throw new IllegalArgumentException(
                            "Missing value for plural 'offset:' at "+prefix(start));
                    }
                    if((index-valueIndex)>Part.MAX_LENGTH) {
                        throw new IndexOutOfBoundsException(
                            "Plural offset value too long: "+prefix(valueIndex));
                    }
                    parseDouble(valueIndex, index, false);  // adds ARG_INT or ARG_DOUBLE
                    isEmpty=false;
                    continue;  // no message fragment after the offset
                } else {
                    // normal selector word
                    if(length>Part.MAX_LENGTH) {
                        throw new IndexOutOfBoundsException(
                            "Argument selector too long: "+prefix(selectorIndex));
                    }
                    addPart(Part.Type.ARG_SELECTOR, selectorIndex, length, 0);
                    if(msg.regionMatches(selectorIndex, "other", 0, length)) {
                        hasOther=true;
                    }
                }
            }

            // parse the message fragment following the selector
            index=skipWhiteSpace(index);
            if(index==msg.length() || msg.charAt(index)!='{') {
                throw new IllegalArgumentException(
                    "No message fragment after "+
                    (argType==ArgType.PLURAL ? "plural" : "select")+
                    " selector: "+prefix(selectorIndex));
            }
            index=parseMessage(index, 1, nestingLevel+1, argType);
            isEmpty=false;
        }
    }

    /**
     * Validates and parses an argument name or argument number string.
     * This internal method assumes that the input substring is a "pattern identifier".
     * @return &gt;=0 if the name is a valid number,
     *         ARG_NAME_NOT_NUMBER (-1) if it is a "pattern identifier" but not all ASCII digits,
     *         ARG_NAME_NOT_VALID (-2) if it is neither.
     * @see #validateArgumentName(String)
     */
    private static int parseArgNumber(CharSequence s, int start, int limit) {
        // If the identifier contains only ASCII digits, then it is an argument _number_
        // and must not have leading zeros (except "0" itself).
        // Otherwise it is an argument _name_.
        if(start>=limit) {
            return ARG_NAME_NOT_VALID;
        }
        int number;
        // Defer numeric errors until we know there are only digits.
        boolean badNumber;
        char c=s.charAt(start++);
        if(c=='0') {
            if(start==limit) {
                return 0;
            } else {
                number=0;
                badNumber=true;  // leading zero
            }
        } else if('1'<=c && c<='9') {
            number=c-'0';
            badNumber=false;
        } else {
            return ARG_NAME_NOT_NUMBER;
        }
        while(start<limit) {
            c=s.charAt(start++);
            if('0'<=c && c<='9') {
                if(number>=Integer.MAX_VALUE/10) {
                    badNumber=true;  // overflow
                }
                number=number*10+(c-'0');
            } else {
                return ARG_NAME_NOT_NUMBER;
            }
        }
        // There are only ASCII digits.
        if(badNumber) {
            return ARG_NAME_NOT_VALID;
        } else {
            return number;
        }
    }

    private int parseArgNumber(int start, int limit) {
        return parseArgNumber(msg, start, limit);
    }

    /**
     * Parses a number from the specified message substring.
     * @param start start index into the message string
     * @param limit limit index into the message string, must be start<limit
     * @param allowInfinity true if U+221E is allowed (for ChoiceFormat)
     */
    private void parseDouble(int start, int limit, boolean allowInfinity) {
        assert start<limit;
        // fake loop for easy exit and single throw statement
        for(;;) {
            // fast path for small integers and infinity
            int value=0;
            int isNegative=0;  // not boolean so that we can easily add it to value
            int index=start;
            char c=msg.charAt(index++);
            if(c=='-') {
                isNegative=1;
                if(index==limit) {
                    break;  // no number
                }
                c=msg.charAt(index++);
            } else if(c=='+') {
                if(index==limit) {
                    break;  // no number
                }
                c=msg.charAt(index++);
            }
            if(c==0x221e) {  // infinity
                if(allowInfinity && index==limit) {
                    addArgDoublePart(
                        isNegative!=0 ? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY,
                        start, limit-start);
                    return;
                } else {
                    break;
                }
            }
            // try to parse the number as a small integer but fall back to a double
            while('0'<=c && c<='9') {
                value=value*10+(c-'0');
                if(value>(Part.MAX_VALUE+isNegative)) {
                    break;  // not a small-enough integer
                }
                if(index==limit) {
                    addPart(Part.Type.ARG_INT, start, limit-start, isNegative!=0 ? -value : value);
                    return;
                }
                c=msg.charAt(index++);
            }
            // Let Double.parseDouble() throw a NumberFormatException.
            double numericValue=Double.parseDouble(msg.substring(start, limit));
            addArgDoublePart(numericValue, start, limit-start);
            return;
        }
        throw new NumberFormatException(
            "Bad syntax for numeric value: "+msg.substring(start, limit));
    }

    /**
     * Appends the s[start, limit[ substring to sb, but with only half of the apostrophes
     * according to JDK pattern behavior.
     * @internal
     */
    /* package */ static void appendReducedApostrophes(String s, int start, int limit,
                                                       StringBuilder sb) {
        int doubleApos=-1;
        for(;;) {
            int i=s.indexOf('\'', start);
            if(i<0 || i>=limit) {
                sb.append(s, start, limit);
                break;
            }
            if(i==doubleApos) {
                // Double apostrophe at start-1 and start==i, append one.
                sb.append('\'');
                ++start;
                doubleApos=-1;
            } else {
                // Append text between apostrophes and skip this one.
                sb.append(s, start, i);
                doubleApos=start=i+1;
            }
        }
    }

    private int skipWhiteSpace(int index) {
        return PatternProps.skipWhiteSpace(msg, index);
    }

    private int skipIdentifier(int index) {
        return PatternProps.skipIdentifier(msg, index);
    }

    /**
     * Skips a sequence of characters that could occur in a double value.
     * Does not fully parse or validate the value.
     */
    private int skipDouble(int index) {
        while(index<msg.length()) {
            char c=msg.charAt(index);
            // U+221E: Allow the infinity symbol, for ChoiceFormat patterns.
            if((c<'0' && "+-.".indexOf(c)<0) || (c>'9' && c!='e' && c!='E' && c!=0x221e)) {
                break;
            }
            ++index;
        }
        return index;
    }

    private static boolean isArgTypeChar(int c) {
        return ('a'<=c && c<='z') || ('A'<=c && c<='Z');
    }

    private boolean isChoice(int index) {
        char c;
        return
            ((c=msg.charAt(index++))=='c' || c=='C') &&
            ((c=msg.charAt(index++))=='h' || c=='H') &&
            ((c=msg.charAt(index++))=='o' || c=='O') &&
            ((c=msg.charAt(index++))=='i' || c=='I') &&
            ((c=msg.charAt(index++))=='c' || c=='C') &&
            ((c=msg.charAt(index))=='e' || c=='E');
    }

    private boolean isPlural(int index) {
        char c;
        return
            ((c=msg.charAt(index++))=='p' || c=='P') &&
            ((c=msg.charAt(index++))=='l' || c=='L') &&
            ((c=msg.charAt(index++))=='u' || c=='U') &&
            ((c=msg.charAt(index++))=='r' || c=='R') &&
            ((c=msg.charAt(index++))=='a' || c=='A') &&
            ((c=msg.charAt(index))=='l' || c=='L');
    }

    private boolean isSelect(int index) {
        char c;
        return
            ((c=msg.charAt(index++))=='s' || c=='S') &&
            ((c=msg.charAt(index++))=='e' || c=='E') &&
            ((c=msg.charAt(index++))=='l' || c=='L') &&
            ((c=msg.charAt(index++))=='e' || c=='E') &&
            ((c=msg.charAt(index++))=='c' || c=='C') &&
            ((c=msg.charAt(index))=='t' || c=='T');
    }

    /**
     * @return true if we are inside a MessageFormat (sub-)pattern,
     *         as opposed to inside a top-level choice/plural/select pattern.
     */
    private boolean inMessageFormatPattern(int nestingLevel) {
        return nestingLevel>0 || parts.get(0).type==Part.Type.MSG_START;
    }

    /**
     * @return true if we are in a MessageFormat sub-pattern
     *         of a top-level ChoiceFormat pattern.
     */
    private boolean inTopLevelChoiceMessage(int nestingLevel, ArgType parentType) {
        return
            nestingLevel==1 &&
            parentType==ArgType.CHOICE &&
            parts.get(0).type!=Part.Type.MSG_START;
    }

    private void addPart(Part.Type type, int index, int length, int value) {
        parts.add(new Part(type, index, length, value));
    }

    private void addLimitPart(int start, Part.Type type, int index, int length, int value) {
        parts.get(start).limitPartIndex=parts.size();
        addPart(type, index, length, value);
    }

    private void addArgDoublePart(double numericValue, int start, int length) {
        int numericIndex;
        if(numericValues==null) {
            numericValues=new ArrayList<Double>();
            numericIndex=0;
        } else {
            numericIndex=numericValues.size();
            if(numericIndex>Part.MAX_VALUE) {
                throw new IndexOutOfBoundsException("Too many numeric values");
            }
        }
        numericValues.add(numericValue);
        addPart(Part.Type.ARG_DOUBLE, start, length, numericIndex);
    }

    private static final int MAX_PREFIX_LENGTH=24;

    /**
     * Returns a prefix of s.substring(start). Used for Exception messages.
     * @param s
     * @param start start index in s
     * @return s.substring(start) or a prefix of that
     */
    private static String prefix(String s, int start) {
        int substringLength=s.length()-start;
        if(substringLength<=MAX_PREFIX_LENGTH) {
            return start==0 ? s : s.substring(start);
        } else {
            StringBuilder prefix=new StringBuilder(MAX_PREFIX_LENGTH);
            prefix.append(s, start, start+MAX_PREFIX_LENGTH-4);
            if(Character.isHighSurrogate(prefix.charAt(MAX_PREFIX_LENGTH-5))) {
                // remove lead surrogate from the end of the prefix
                prefix.setLength(MAX_PREFIX_LENGTH-5);
            }
            return prefix.append(" ...").toString();
        }
    }

    private static String prefix(String s) {
        return prefix(s, 0);
    }

    private String prefix(int start) {
        return prefix(msg, start);
    }

    private String prefix() {
        return prefix(msg, 0);
    }

    private ApostropheMode aposMode;
    private String msg;
    private ArrayList<Part> parts=new ArrayList<Part>();
    private ArrayList<Double> numericValues;
    private boolean hasArgNames;
    private boolean hasArgNumbers;
    private boolean needsAutoQuoting;
    private boolean frozen;

    private static final ApostropheMode defaultAposMode=
        ApostropheMode.valueOf(
            ICUConfig.get("com.ibm.icu.text.MessagePattern.ApostropheMode", "DOUBLE_OPTIONAL"));

    private static final ArgType[] argTypes=ArgType.values();
}