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/**
 * Copyright 2012-2019 The Feign 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
 *
 * http://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 feign.template;

import feign.Util;
import java.nio.charset.Charset;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;

/**
 * Template for HTTP Headers. Variables that are unresolved are ignored and
 * Literals are not encoded.
 */
public final class HeaderTemplate extends Template {

	/* cache a copy of the variables for lookup later */
	private Set values;
	private String name;

	public static HeaderTemplate create(String name, Iterable values) {
		if (name == null || name.isEmpty()) {
			throw new IllegalArgumentException("name is required.");
		}

		if (values == null) {
			throw new IllegalArgumentException("values are required");
		}

		/* construct a uri template from the name and values */
		StringBuilder template = new StringBuilder();
		template.append(name).append(" ");

		/* create a comma separated template for the header values */
		Iterator iterator = values.iterator();
		while (iterator.hasNext()) {
			template.append(iterator.next());
			if (iterator.hasNext()) {
				template.append(", ");
			}
		}
		return new HeaderTemplate(template.toString(), name, values, Util.UTF_8);
	}

	/**
	 * Append values to a Header Template.
	 *
	 * @param headerTemplate
	 *            to append to.
	 * @param values
	 *            to append.
	 * @return a new Header Template with the values added.
	 */
	public static HeaderTemplate append(HeaderTemplate headerTemplate, Iterable values) {
		Set headerValues = new LinkedHashSet<>(headerTemplate.getValues());
		headerValues.addAll(
				StreamSupport.stream(values.spliterator(), false).filter(Util::isNotBlank).collect(Collectors.toSet()));
		return create(headerTemplate.getName(), headerValues);
	}

	/**
	 * Creates a new Header Template.
	 *
	 * @param template
	 *            to parse.
	 */
	private HeaderTemplate(String template, String name, Iterable values, Charset charset) {
		super(template, ExpansionOptions.REQUIRED, EncodingOptions.NOT_REQUIRED, false, charset);
		this.values = StreamSupport.stream(values.spliterator(), false).filter(Util::isNotBlank)
				.collect(Collectors.toSet());
		this.name = name;
	}

	public Collection getValues() {
		return Collections.unmodifiableCollection(values);
	}

	public String getName() {
		return name;
	}
}