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/*
 * Copyright 2017 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
 *
 *      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.gradle.api.internal.provider;

import org.gradle.api.Transformer;
import org.gradle.api.provider.Provider;
import org.gradle.internal.Cast;

import javax.annotation.Nullable;

public class Providers {
    public static final String NULL_TRANSFORMER_RESULT = "Transformer for this provider returned a null value.";
    public static final String NULL_VALUE = "No value has been specified for this provider.";

    private static final Provider NULL_PROVIDER = new AbstractMinimalProvider() {
        @Override
        public Object get() {
            throw new IllegalStateException(NULL_VALUE);
        }

        @Nullable
        @Override
        public Class getType() {
            return null;
        }

        @Override
        public Object getOrNull() {
            return null;
        }

        @Override
        public Object getOrElse(Object defaultValue) {
            return defaultValue;
        }

        @Override
        public  ProviderInternal map(Transformer transformer) {
            return Cast.uncheckedCast(this);
        }

        @Override
        public boolean isPresent() {
            return false;
        }

        @Override
        public ProviderInternal withFinalValue() {
            return this;
        }

        @Override
        public String toString() {
            return "undefined";
        }
    };

    public static final Provider TRUE = of(true);
    public static final Provider FALSE = of(false);

    public static  ProviderInternal notDefined() {
        return Cast.uncheckedCast(NULL_PROVIDER);
    }

    public static  ProviderInternal of(T value) {
        return new FixedValueProvider(value);
    }

    public static  ProviderInternal internal(final Provider value) {
        return Cast.uncheckedCast(value);
    }

    private static class FixedValueProvider extends AbstractMinimalProvider {
        private final T value;

        FixedValueProvider(T value) {
            this.value = value;
        }

        @Nullable
        @Override
        public Class getType() {
            return Cast.uncheckedCast(value.getClass());
        }

        @Override
        public T get() {
            return value;
        }

        @Override
        public T getOrElse(T defaultValue) {
            return value;
        }

        @Override
        public T getOrNull() {
            return value;
        }

        @Override
        public boolean isPresent() {
            return true;
        }

        @Override
        public ProviderInternal withFinalValue() {
            return this;
        }

        @Override
        public  ProviderInternal map(final Transformer transformer) {
            return new MappedFixedValueProvider(transformer, this);
        }

        @Override
        public String toString() {
            return String.format("fixed(%s, %s)", getType(), value);
        }
    }

    private static class MappedFixedValueProvider extends AbstractMinimalProvider {
        private final Transformer transformer;
        private final Provider provider;
        private S value;

        MappedFixedValueProvider(Transformer transformer, Provider provider) {
            this.transformer = transformer;
            this.provider = provider;
        }

        @Nullable
        @Override
        public Class getType() {
            if (value != null) {
                return Cast.uncheckedCast(value.getClass());
            }
            return null;
        }

        @Override
        public boolean isPresent() {
            return true;
        }

        @Override
        public S get() {
            if (value == null) {
                value = transformer.transform(provider.get());
                if (value == null) {
                    throw new IllegalStateException(NULL_TRANSFORMER_RESULT);
                }
            }
            return value;
        }

        @Override
        public S getOrElse(S defaultValue) {
            return get();
        }

        @Nullable
        @Override
        public S getOrNull() {
            return get();
        }

        @Override
        public  ProviderInternal map(Transformer transformer) {
            return new MappedFixedValueProvider(transformer, this);
        }

        @Override
        public String toString() {
            if (value == null) {
                return String.format("transform(not calculated)");
            }
            return String.format("transform(%s, %s)", getType(), value);
        }
    }
}