/*
 * Copyright 2012-2019 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.boot.context.properties.bind;

import org.springframework.boot.context.properties.source.ConfigurationPropertyName;

Callback interface that can be used to handle additional logic during element binding. 
Author:
Phillip Webb, Madhura Bhave
Since:
2.0.0/**
 * Callback interface that can be used to handle additional logic during element
 * {@link Binder binding}.
 *
 * @author Phillip Webb
 * @author Madhura Bhave
 * @since 2.0.0
 */
public interface BindHandler {

	
Default no-op bind handler.
/**
	 * Default no-op bind handler.
	 */
	BindHandler DEFAULT = new BindHandler() {

	};

	
Called when binding of an element starts but before any result has been determined.
Params:
name – the name of the element being bound
target – the item being bound
context – the bind context
Type parameters:
<T> – the bindable source type
Returns:
the actual item that should be used for binding (may be null)/**
	 * Called when binding of an element starts but before any result has been determined.
	 * @param <T> the bindable source type
	 * @param name the name of the element being bound
	 * @param target the item being bound
	 * @param context the bind context
	 * @return the actual item that should be used for binding (may be {@code null})
	 */
	default <T> Bindable<T> onStart(ConfigurationPropertyName name, Bindable<T> target, BindContext context) {
		return target;
	}

	
Called when binding of an element ends with a successful result. Implementations
may change the ultimately returned result or perform addition validation.
Params:
name – the name of the element being bound
target – the item being bound
context – the bind context
result – the bound result (never null)
Returns:
the actual result that should be used (may be null)/**
	 * Called when binding of an element ends with a successful result. Implementations
	 * may change the ultimately returned result or perform addition validation.
	 * @param name the name of the element being bound
	 * @param target the item being bound
	 * @param context the bind context
	 * @param result the bound result (never {@code null})
	 * @return the actual result that should be used (may be {@code null})
	 */
	default Object onSuccess(ConfigurationPropertyName name, Bindable<?> target, BindContext context, Object result) {
		return result;
	}

	
Called when binding of an element ends with an unbound result and a newly created
instance is about to be returned. Implementations may change the ultimately
returned result or perform addition validation.
Params:
name – the name of the element being bound
target – the item being bound
context – the bind context
result – the newly created instance (never null)
Returns:
the actual result that should be used (must not be null)
Since:
2.2.2/**
	 * Called when binding of an element ends with an unbound result and a newly created
	 * instance is about to be returned. Implementations may change the ultimately
	 * returned result or perform addition validation.
	 * @param name the name of the element being bound
	 * @param target the item being bound
	 * @param context the bind context
	 * @param result the newly created instance (never {@code null})
	 * @return the actual result that should be used (must not be {@code null})
	 * @since 2.2.2
	 */
	default Object onCreate(ConfigurationPropertyName name, Bindable<?> target, BindContext context, Object result) {
		return result;
	}

	
Called when binding fails for any reason (including failures from onSuccess or onCreate calls). Implementations may choose to swallow exceptions and return an alternative result. 
Params:
name – the name of the element being bound
target – the item being bound
context – the bind context
error – the cause of the error (if the exception stands it may be re-thrown)
Throws:
Exception – if the binding isn't valid
Returns:
the actual result that should be used (may be null)./**
	 * Called when binding fails for any reason (including failures from
	 * {@link #onSuccess} or {@link #onCreate} calls). Implementations may choose to
	 * swallow exceptions and return an alternative result.
	 * @param name the name of the element being bound
	 * @param target the item being bound
	 * @param context the bind context
	 * @param error the cause of the error (if the exception stands it may be re-thrown)
	 * @return the actual result that should be used (may be {@code null}).
	 * @throws Exception if the binding isn't valid
	 */
	default Object onFailure(ConfigurationPropertyName name, Bindable<?> target, BindContext context, Exception error)
			throws Exception {
		throw error;
	}

	
Called when binding finishes with either bound or unbound result. This method will not be called when binding failed, even if a handler returns a result from onFailure. 
Params:
name – the name of the element being bound
target – the item being bound
context – the bind context
result – the bound result (may be null)
Throws:
Exception – if the binding isn't valid/**
	 * Called when binding finishes with either bound or unbound result. This method will
	 * not be called when binding failed, even if a handler returns a result from
	 * {@link #onFailure}.
	 * @param name the name of the element being bound
	 * @param target the item being bound
	 * @param context the bind context
	 * @param result the bound result (may be {@code null})
	 * @throws Exception if the binding isn't valid
	 */
	default void onFinish(ConfigurationPropertyName name, Bindable<?> target, BindContext context, Object result)
			throws Exception {
	}

}