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International Component for Unicode for Java (ICU4J) is a mature, widely used Java library providing Unicode and Globalization support

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// © 2017 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
package com.ibm.icu.impl.number.parse;

import com.ibm.icu.impl.StaticUnicodeSets;
import com.ibm.icu.impl.StringSegment;
import com.ibm.icu.text.UnicodeSet;

/**
 * A base class for many matchers that performs a simple match against a UnicodeString and/or UnicodeSet.
 *
 * @author sffc
 */
public abstract class SymbolMatcher implements NumberParseMatcher {
    protected final String string;
    protected final UnicodeSet uniSet;

    // TODO: Implement this class using only UnicodeSet and not String?
    // How to deal with case folding?

    protected SymbolMatcher(String symbolString, UnicodeSet symbolUniSet) {
        string = symbolString;
        uniSet = symbolUniSet;
    }

    protected SymbolMatcher(StaticUnicodeSets.Key key) {
        string = "";
        uniSet = StaticUnicodeSets.get(key);
    }

    public UnicodeSet getSet() {
        return uniSet;
    }

    @Override
    public boolean match(StringSegment segment, ParsedNumber result) {
        // Smoke test first; this matcher might be disabled.
        if (isDisabled(result)) {
            return false;
        }

        // Test the string first in order to consume trailing chars greedily.
        int overlap = 0;
        if (!string.isEmpty()) {
            overlap = segment.getCommonPrefixLength(string);
            if (overlap == string.length()) {
                segment.adjustOffset(string.length());
                accept(segment, result);
                return false;
            }
        }

        if (segment.startsWith(uniSet)) {
            segment.adjustOffsetByCodePoint();
            accept(segment, result);
            return false;
        }

        return overlap == segment.length();
    }

    @Override
    public boolean smokeTest(StringSegment segment) {
        return segment.startsWith(uniSet) || segment.startsWith(string);
    }

    @Override
    public void postProcess(ParsedNumber result) {
        // No-op
    }

    protected abstract boolean isDisabled(ParsedNumber result);

    protected abstract void accept(StringSegment segment, ParsedNumber result);
}