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/*******************************************************************
 * © 2019 SAP SE or an SAP affiliate company. All rights reserved. *
 *******************************************************************/
package com.sap.cds.ql.cqn;

import java.util.Optional;
import java.util.stream.Stream;

public interface CqnValue extends CqnToken {

	/**
	 * Returns the optional CDS type of this value.
	 * 
	 * @return the optional CDS type
	 */
	default Optional type() {
		return Optional.empty();
	}

	/**
	 * Returns {@code true} if this is a {@link CqnElementRef}.
	 * 
	 * @return {@code true} if this is an element ref, otherwise {@code false}
	 */
	default boolean isRef() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnExpression}.
	 * 
	 * @return {@code true} if this is an expression, otherwise {@code false}
	 */
	default boolean isExpression() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnFunc}.
	 * 
	 * @return {@code true} if this is a function, otherwise {@code false}
	 */
	default boolean isFunction() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnLiteral}.
	 * 
	 * @return {@code true} if this is a literal, otherwise {@code false}
	 */
	default boolean isLiteral() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnNullValue}.
	 * 
	 * @return {@code true} if this is a null value, otherwise {@code false}
	 */
	default boolean isNullValue() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnParameter}.
	 * 
	 * @return {@code true} if this is a parameter, otherwise {@code false}
	 */
	default boolean isParameter() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnPlain} value.
	 * 
	 * @return {@code true} if this is a plain value, otherwise {@code false}
	 */
	default boolean isPlain() {
		return false;
	}

	/**
	 * Returns {@code true} if this is a {@link CqnListValue} value.
	 * 
	 * @return {@code true} if this is a list value, otherwise {@code false}
	 */
	default boolean isList() {
		return false;
	}

	/**
	 * Casts this value to {@code CqnElementRef}.
	 * 
	 * @throws ClassCastException if this value is not an element ref
	 * @return this value as an element ref
	 */
	default CqnElementRef asRef() {
		throw new ClassCastException("Cannot cast to CqnElementRef");
	}

	default Stream ofRef() {
		return Stream.empty();
	}

	/**
	 * Casts this value to {@code CqnExpression}.
	 * 
	 * @throws ClassCastException if this value is not an expression
	 * @return this value as an expression
	 */
	default CqnExpression asExpression() {
		throw new ClassCastException("Cannot cast to CqnExpression");
	}

	/**
	 * Casts this value to {@code CqnFunc}.
	 * 
	 * @throws ClassCastException if this value is not a function
	 * @return this value as a function
	 */
	default CqnFunc asFunction() {
		throw new ClassCastException("Cannot cast to CqnFunc");
	}

	/**
	 * Casts this value to {@code CqnLiteral}.
	 * 
	 * @throws ClassCastException if this value is not a literal
	 * @return this value as a literal
	 */
	default CqnLiteral asLiteral() {
		throw new ClassCastException("Cannot cast to CqnLiteral");
	}

	default Stream> ofLiteral() {
		return Stream.empty();
	}

	/**
	 * Casts this value to {@code CqnNullValue}.
	 * 
	 * @throws ClassCastException if this value is not a null value
	 * @return this value as a null value
	 */
	default CqnNullValue asNullValue() {
		throw new ClassCastException("Cannot cast to CqnNullValue");
	}

	/**
	 * Casts this value to {@code CqnParameter}.
	 * 
	 * @throws ClassCastException if this value is not a parameter
	 * @return this value as a parameter
	 */
	default CqnParameter asParameter() {
		throw new ClassCastException("Cannot cast to CqnParameter");
	}

	/**
	 * Casts this value to {@code CqnPlain}.
	 * 
	 * @throws ClassCastException if this value is not a plain value
	 * @return this value as a plain value
	 */
	default CqnPlain asPlain() {
		throw new ClassCastException("Cannot cast to CqnPlain");
	}

	/**
	 * Casts this value to {@code CqnListValue}.
	 * 
	 * @throws ClassCastException if this value is not a list value
	 * @return this value as a list value
	 */
	default CqnListValue asList() {
		throw new ClassCastException("Cannot cast to CqnListValue");
	}

	/**
	 * Casts this type to the given {@code type}.
	 * 
	 * @param   the return type
	 * @param type the subtype of {@code CqnValue} to cast to
	 * @return this type casted to the given {@code type} class
	 */
	@SuppressWarnings("unchecked")
	default  T as(Class type) {
		return (T) this;
	}

}