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Closure Stylesheets is an extension to CSS that adds variables, functions, conditionals, and mixins to standard CSS. The tool also supports minification, linting, RTL flipping, and CSS class renaming.
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/*
 * Copyright 2009 Google Inc.
 *
 * 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.
 */

// TODO(bolinfest): Move this to com.google.common.css.compiler.passes.
package com.google.common.css;

import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.common.css.MultipleMappingSubstitutionMap.ValueWithMappings;

import java.util.Map;

/**
 * A decorator for a {@link SubstitutionMap} that records which values it maps.
 *
 * @author [email protected] (Michael Bolin)
 */
public class RecordingSubstitutionMap implements SubstitutionMap.Initializable {

    private final SubstitutionMap delegate;

    private final Predicate shouldRecordMappingForCodeGeneration;

    // Use a LinkedHashMap so getMappings() is deterministic.
    private final Map mappings = Maps.newLinkedHashMap();

    private RecordingSubstitutionMap(
            SubstitutionMap map, Predicate shouldRecordMappingForCodeGeneration) {
        this.delegate = map;
        this.shouldRecordMappingForCodeGeneration = shouldRecordMappingForCodeGeneration;
    }

    /**
     * {@inheritDoc}
     *
     * @throws NullPointerException if key is null.
     */
    @Override
    public String get(String key) {
        Preconditions.checkNotNull(key);
        if (!shouldRecordMappingForCodeGeneration.apply(key)) {
            return key;
        }

        if (delegate instanceof MultipleMappingSubstitutionMap) {
            // The final value only bears a loose relationship to the mappings.
            // For example, PrefixingSubstitutionMap applied to a MinimalSubstitutionMap
            // minimizes all components but only prefixes the first.
            // We can't memoize the value here, so don't look up in mappings first.
            ValueWithMappings valueWithMappings =
                    ((MultipleMappingSubstitutionMap) delegate).getValueWithMappings(key);
            mappings.putAll(valueWithMappings.mappings);
            return valueWithMappings.value;
        } else {
            return mappings.computeIfAbsent(key, delegate::get);
        }
    }

    /**
     * @return The recorded mappings in the order they were created. This output may be used with
     * {@link OutputRenamingMapFormat#writeRenamingMap}
     */
    public Map getMappings() {
        return ImmutableMap.copyOf(mappings);
    }

    @Override
    public void initializeWithMappings(Map newMappings) {
        Preconditions.checkState(mappings.isEmpty());
        if (!newMappings.isEmpty()) {
            mappings.putAll(newMappings);
            ((SubstitutionMap.Initializable) delegate).initializeWithMappings(newMappings);
        }
    }

    /**
     * A-la-carte builder.
     */
    public static final class Builder {
        private SubstitutionMap delegate = new IdentitySubstitutionMap();
        private Predicate shouldRecordMappingForCodeGeneration =
                Predicates.alwaysTrue();
        private final Map mappings = Maps.newLinkedHashMap();

        /**
         * Specifies the underlying map. Multiple calls clobber.
         */
        public Builder withSubstitutionMap(SubstitutionMap d) {
            this.delegate = Preconditions.checkNotNull(d);
            return this;
        }

        /**
         * True keys that should be treated mapped to themselves instead of passing through Multiple
         * calls AND.
         */
        public Builder shouldRecordMappingForCodeGeneration(Predicate p) {
            shouldRecordMappingForCodeGeneration =
                    Predicates.and(shouldRecordMappingForCodeGeneration, p);
            return this;
        }

        /**
         * Specifies mappings to {@linkplain Initializable initialize} the delegate with. Multiple calls
         * putAll. This can be used to reconstitute a map that was written out by {@link
         * OutputRenamingMapFormat#writeRenamingMap} from the output of {@link
         * OutputRenamingMapFormat#readRenamingMap}.
         */
        public Builder withMappings(Map m) {
            this.mappings.putAll(m);
            return this;
        }

        /**
         * Builds the substitution map based on previous operations on this builder.
         */
        public RecordingSubstitutionMap build() {
            // TODO(msamuel): if delegate instanceof MultipleMappingSubstitutionMap
            // should this return a RecordingSubstitutionMap that is itself
            // a MultipleMappingSubstitutionMap.
            RecordingSubstitutionMap built =
                    new RecordingSubstitutionMap(delegate, shouldRecordMappingForCodeGeneration);
            built.initializeWithMappings(mappings);
            return built;
        }
    }
}