/*
 * Copyright 2010-2015 JetBrains s.r.o.
 *
 * 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 org.jetbrains.kotlin.types

import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor

// Composition works as it's expected: Composition(outer, inner)(type) = outer(inner(type))
// Note that when a substitution returns null it means that type shouldn't be changed (i.e. it works like the identity function in that case)
// Currently it's only works if the inner substitution is a mapping from type parameter to another type parameter.
// Otherwise composition semantics become a little bit complicated.
class CompositionTypeSubstitution(
        private val outer: TypeSubstitution, private val inner: Map<TypeParameterDescriptor, TypeParameterDescriptor>
) : DelegatedTypeSubstitution(outer) {

    override fun get(key: KotlinType) = inner[key.constructor.declarationDescriptor]?.let { outer[it.defaultType] } ?: outer[key]
}
