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The AWS Java SDK for Amazon AppSync module holds the client classes that are used for communicating with Amazon AppSync.

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/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with
 * the License. A copy of the License is located at
 * 
 * http://aws.amazon.com/apache2.0
 * 
 * or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.services.appsync.endpoints.internal;

import software.amazon.awssdk.annotations.SdkInternalApi;

/**
 * For code generating from a template, use a `TemplateVisitor`. Template visitor is written to enable optimized
 * behavior for static templates with no dynamic components.
 * 
 * @param 
 *        The return type of this visitor
 */
@SdkInternalApi
public interface TemplateVisitor {
    /**
     * The template contains a single static string, eg. `"https://mystaticendpoing.com"`
     * 
     * @param value
     *        : The static value of the template.
     * @return T
     */
    T visitStaticTemplate(String value);

    /**
     * The template contains a single dynamic element, eg. `{Region}`. In this case, string formatting is not required.
     * The type of the value is guaranteed to be a string.
     * 
     * @param value
     *        : The single expression that represents this template.
     * @return T
     */
    T visitSingleDynamicTemplate(Expr value);

    /**
     * Visit a static element within a multipart template. This will only be called after
     * {@link #startMultipartTemplate()} has been invoked.
     * 
     * @param value
     *        A static element within a larger template
     * @return T
     */
    T visitStaticElement(String value);

    /**
     * Visit a dynamic element within a multipart template. This will only be called after
     * {@link #startMultipartTemplate()} has been invoked.
     * 
     * @param value
     *        The dynamic template value
     * @return T
     */
    T visitDynamicElement(Expr value);

    /**
     * Invoked prior to visiting a multipart template like `https://{Region}.{dnsSuffix}`. This function will be
     * followed by invocations of {@link #visitStaticTemplate(String)} and {@link #visitDynamicElement(Expr)}.
     * 
     * @return T
     */
    T startMultipartTemplate();

    /**
     * Invoked at the conclusion of visiting a multipart template like `https://{Region}.{dnsSuffix}`. This allows
     * implementations to do something like call `string.join()` or `stringbuilder.toString()`.
     * 
     * @return T
     */
    T finishMultipartTemplate();
}