/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.support;

import java.util.LinkedHashSet;
import java.util.Locale;
import java.util.Set;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**
 * Abstract base class for {@code MessageSource} implementations based on
 * resource bundle conventions, such as {@link ResourceBundleMessageSource}
 * and {@link ReloadableResourceBundleMessageSource}. Provides common
 * configuration methods and corresponding semantic definitions.
 *
 * @author Juergen Hoeller
 * @since 4.3
 * @see ResourceBundleMessageSource
 * @see ReloadableResourceBundleMessageSource
 */
public abstract class AbstractResourceBasedMessageSource extends AbstractMessageSource {

        private final Set<String> basenameSet = new LinkedHashSet<>(4);

        @Nullable
        private String defaultEncoding;

        private boolean fallbackToSystemLocale = true;

        @Nullable
        private Locale defaultLocale;

        private long cacheMillis = -1;


        /**
         * Set a single basename, following the basic ResourceBundle convention
         * of not specifying file extension or language codes. The resource location
         * format is up to the specific {@code MessageSource} implementation.
         * <p>Regular and XMl properties files are supported: e.g. "messages" will find
         * a "messages.properties", "messages_en.properties" etc arrangement as well
         * as "messages.xml", "messages_en.xml" etc.
         * @param basename the single basename
         * @see #setBasenames
         * @see org.springframework.core.io.ResourceEditor
         * @see java.util.ResourceBundle
         */
        public void setBasename(String basename) {
                setBasenames(basename);
        }

        /**
         * Set an array of basenames, each following the basic ResourceBundle convention
         * of not specifying file extension or language codes. The resource location
         * format is up to the specific {@code MessageSource} implementation.
         * <p>Regular and XMl properties files are supported: e.g. "messages" will find
         * a "messages.properties", "messages_en.properties" etc arrangement as well
         * as "messages.xml", "messages_en.xml" etc.
         * <p>The associated resource bundles will be checked sequentially when resolving
         * a message code. Note that message definitions in a <i>previous</i> resource
         * bundle will override ones in a later bundle, due to the sequential lookup.
         * <p>Note: In contrast to {@link #addBasenames}, this replaces existing entries
         * with the given names and can therefore also be used to reset the configuration.
         * @param basenames an array of basenames
         * @see #setBasename
         * @see java.util.ResourceBundle
         */
        public void setBasenames(String... basenames) {
                this.basenameSet.clear();
                addBasenames(basenames);
        }

        /**
         * Add the specified basenames to the existing basename configuration.
         * <p>Note: If a given basename already exists, the position of its entry
         * will remain as in the original set. New entries will be added at the
         * end of the list, to be searched after existing basenames.
         * @since 4.3
         * @see #setBasenames
         * @see java.util.ResourceBundle
         */
        public void addBasenames(String... basenames) {
                if (!ObjectUtils.isEmpty(basenames)) {
                        for (String basename : basenames) {
                                Assert.hasText(basename, "Basename must not be empty");
                                this.basenameSet.add(basename.trim());
                        }
                }
        }

        /**
         * Return this {@code MessageSource}'s basename set, containing entries
         * in the order of registration.
         * <p>Calling code may introspect this set as well as add or remove entries.
         * @since 4.3
         * @see #addBasenames
         */
        public Set<String> getBasenameSet() {
                return this.basenameSet;
        }

        /**
         * Set the default charset to use for parsing properties files.
         * Used if no file-specific charset is specified for a file.
         * <p>The effective default is the {@code java.util.Properties}
         * default encoding: ISO-8859-1. A {@code null} value indicates
         * the platform default encoding.
         * <p>Only applies to classic properties files, not to XML files.
         * @param defaultEncoding the default charset
         */
        public void setDefaultEncoding(@Nullable String defaultEncoding) {
                this.defaultEncoding = defaultEncoding;
        }

        /**
         * Return the default charset to use for parsing properties files, if any.
         * @since 4.3
         */
        @Nullable
        protected String getDefaultEncoding() {
                return this.defaultEncoding;
        }

        /**
         * Set whether to fall back to the system Locale if no files for a specific
         * Locale have been found. Default is "true"; if this is turned off, the only
         * fallback will be the default file (e.g. "messages.properties" for
         * basename "messages").
         * <p>Falling back to the system Locale is the default behavior of
         * {@code java.util.ResourceBundle}. However, this is often not desirable
         * in an application server environment, where the system Locale is not relevant
         * to the application at all: set this flag to "false" in such a scenario.
         * @see #setDefaultLocale
         */
        public void setFallbackToSystemLocale(boolean fallbackToSystemLocale) {
                this.fallbackToSystemLocale = fallbackToSystemLocale;
        }

        /**
         * Return whether to fall back to the system Locale if no files for a specific
         * Locale have been found.
         * @since 4.3
         * @deprecated as of 5.2.2, in favor of {@link #getDefaultLocale()}
         */
        @Deprecated
        protected boolean isFallbackToSystemLocale() {
                return this.fallbackToSystemLocale;
        }

        /**
         * Specify a default Locale to fall back to, as an alternative to falling back
         * to the system Locale.
         * <p>Default is to fall back to the system Locale. You may override this with
         * a locally specified default Locale here, or enforce no fallback locale at all
         * through disabling {@link #setFallbackToSystemLocale "fallbackToSystemLocale"}.
         * @since 5.2.2
         * @see #setFallbackToSystemLocale
         * @see #getDefaultLocale()
         */
        public void setDefaultLocale(@Nullable Locale defaultLocale) {
                this.defaultLocale = defaultLocale;
        }

        /**
         * Determine a default Locale to fall back to: either a locally specified default
         * Locale or the system Locale, or {@code null} for no fallback locale at all.
         * @since 5.2.2
         * @see #setDefaultLocale
         * @see #setFallbackToSystemLocale
         * @see Locale#getDefault()
         */
        @Nullable
        protected Locale getDefaultLocale() {
                if (this.defaultLocale != null) {
                        return this.defaultLocale;
                }
                if (this.fallbackToSystemLocale) {
                        return Locale.getDefault();
                }
                return null;
        }

        /**
         * Set the number of seconds to cache loaded properties files.
         * <ul>
         * <li>Default is "-1", indicating to cache forever (matching the default behavior
         * of {@code java.util.ResourceBundle}). Note that this constant follows Spring
         * conventions, not {@link java.util.ResourceBundle.Control#getTimeToLive}.
         * <li>A positive number will cache loaded properties files for the given
         * number of seconds. This is essentially the interval between refresh checks.
         * Note that a refresh attempt will first check the last-modified timestamp
         * of the file before actually reloading it; so if files don't change, this
         * interval can be set rather low, as refresh attempts will not actually reload.
         * <li>A value of "0" will check the last-modified timestamp of the file on
         * every message access. <b>Do not use this in a production environment!</b>
         * </ul>
         * <p><b>Note that depending on your ClassLoader, expiration might not work reliably
         * since the ClassLoader may hold on to a cached version of the bundle file.</b>
         * Prefer {@link ReloadableResourceBundleMessageSource} over
         * {@link ResourceBundleMessageSource} in such a scenario, in combination with
         * a non-classpath location.
         */
        public void setCacheSeconds(int cacheSeconds) {
                this.cacheMillis = cacheSeconds * 1000L;
        }

        /**
         * Set the number of milliseconds to cache loaded properties files.
         * Note that it is common to set seconds instead: {@link #setCacheSeconds}.
         * <ul>
         * <li>Default is "-1", indicating to cache forever (matching the default behavior
         * of {@code java.util.ResourceBundle}). Note that this constant follows Spring
         * conventions, not {@link java.util.ResourceBundle.Control#getTimeToLive}.
         * <li>A positive number will cache loaded properties files for the given
         * number of milliseconds. This is essentially the interval between refresh checks.
         * Note that a refresh attempt will first check the last-modified timestamp
         * of the file before actually reloading it; so if files don't change, this
         * interval can be set rather low, as refresh attempts will not actually reload.
         * <li>A value of "0" will check the last-modified timestamp of the file on
         * every message access. <b>Do not use this in a production environment!</b>
         * </ul>
         * @since 4.3
         * @see #setCacheSeconds
         */
        public void setCacheMillis(long cacheMillis) {
                this.cacheMillis = cacheMillis;
        }

        /**
         * Return the number of milliseconds to cache loaded properties files.
         * @since 4.3
         */
        protected long getCacheMillis() {
                return this.cacheMillis;
        }

}