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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2009-2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
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 *    may be used to endorse or promote products derived from this software
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package java.time.format;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.temporal.Chrono;
import java.util.Locale;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * A provider to obtain date-time formatters for a style.
 * <p>
 *
 * <h3>Specification for implementors</h3>
 * This implementation is based on extraction of data from a {@link SimpleDateFormat}.
 * This class is immutable and thread-safe.
 * This Implementations caches the returned formatters.
 *
 * @since 1.8
 */
final class DateTimeFormatStyleProvider {
    // TODO: Better implementation based on CLDR

    /** Cache of formatters. */
    private static final ConcurrentMap<String, Object> FORMATTER_CACHE = new ConcurrentHashMap<>(16, 0.75f, 2);

    private DateTimeFormatStyleProvider() {}

    /**
     * Gets an Instance of the provider of format styles.
     *
     * @return the provider, not null
     */
    static DateTimeFormatStyleProvider getInstance() {
        return new DateTimeFormatStyleProvider();
    }

    /**
     * Gets a localized date, time or date-time formatter.
     * <p>
     * The formatter will be the most appropriate to use for the date and time style in the locale.
     * For example, some locales will use the month name while others will use the number.
     *
     * @param dateStyle  the date formatter style to obtain, null to obtain a time formatter
     * @param timeStyle  the time formatter style to obtain, null to obtain a date formatter
     * @param chrono  the chronology to use, not null
     * @param locale  the locale to use, not null
     * @return the date-time formatter, not null
     * @throws IllegalArgumentException if both format styles are null or if the locale is not recognized
     */
    public DateTimeFormatter getFormatter(
            FormatStyle dateStyle, FormatStyle timeStyle, Chrono<?> chrono, Locale locale) {
        if (dateStyle == null && timeStyle == null) {
            throw new IllegalArgumentException("Date and Time style must not both be null");
        }
        String key = chrono.getId() + '|' + locale.toString() + '|' + dateStyle + timeStyle;
        Object cached = FORMATTER_CACHE.get(key);
        if (cached != null) {
            if (cached.equals("")) {
                throw new IllegalArgumentException("Unable to convert DateFormat to DateTimeFormatter");
            }
            return (DateTimeFormatter) cached;
        }
        DateFormat dateFormat;
        if (dateStyle != null) {
            if (timeStyle != null) {
                dateFormat = DateFormat.getDateTimeInstance(convertStyle(dateStyle), convertStyle(timeStyle), locale);
            } else {
                dateFormat = DateFormat.getDateInstance(convertStyle(dateStyle), locale);
            }
        } else {
            dateFormat = DateFormat.getTimeInstance(convertStyle(timeStyle), locale);
        }
        if (dateFormat instanceof SimpleDateFormat) {
            String pattern = ((SimpleDateFormat) dateFormat).toPattern();
            DateTimeFormatter formatter = new DateTimeFormatterBuilder().appendPattern(pattern).toFormatter(locale);
            FORMATTER_CACHE.putIfAbsent(key, formatter);
            return formatter;
        }
        FORMATTER_CACHE.putIfAbsent(key, "");
        throw new IllegalArgumentException("Unable to convert DateFormat to DateTimeFormatter");
    }

    /**
     * Converts the enum style to the old format style.
     * @param style  the enum style, not null
     * @return the int style
     */
    private int convertStyle(FormatStyle style) {
        return style.ordinal();  // indices happen to align
    }

}