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Build time optimizations for Micronaut
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/*
 * Copyright 2017-2021 original 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 io.micronaut.aot.std.sourcegen;

import com.squareup.javapoet.ClassName;
import com.squareup.javapoet.ParameterizedTypeName;
import io.micronaut.aot.core.AOTContext;
import io.micronaut.aot.core.AOTModule;
import io.micronaut.aot.core.codegen.AbstractCodeGenerator;
import io.micronaut.context.env.CachedEnvironment;
import io.micronaut.context.env.ConstantPropertySources;
import io.micronaut.context.env.PropertySource;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.util.EnvironmentProperties;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

/**
 * Generates a "constant" property source, that is to say a
 * {@link PropertySource} which properties are known at build time
 * (and constant).
 */
@AOTModule(
        id = ConstantPropertySourcesSourceGenerator.ID,
        description = ConstantPropertySourcesSourceGenerator.DESCRIPTION,
        dependencies = {
                JitStaticServiceLoaderSourceGenerator.ID,
                NativeStaticServiceLoaderSourceGenerator.ID
        }
)
public class ConstantPropertySourcesSourceGenerator extends AbstractCodeGenerator {
    public static final String ID = "sealed.property.source";
    public static final String DESCRIPTION = "Precomputes property sources at build time";

    @Override
    public void generate(@NonNull AOTContext context) {
        Optional maybeSubstitutes = context.get(AbstractStaticServiceLoaderSourceGenerator.Substitutes.class);
        List substitutes = maybeSubstitutes.map(s -> s.findSubstitutesFor("io.micronaut.context.env.PropertySourceLoader")).orElse(Collections.emptyList())
                .stream()
                .map(javaFile -> javaFile.packageName + "." + javaFile.typeSpec.name)
                .collect(Collectors.toList());

        context.registerStaticOptimization("AotConstantPropertySources", ConstantPropertySources.class, initializer -> {
            EnvironmentProperties env = EnvironmentProperties.empty();
            CachedEnvironment.getenv().keySet().forEach(env::findPropertyNamesForEnvironmentVariable);

            initializer.addStatement("$T propertySources = new $T()",
                    ParameterizedTypeName.get(ClassName.get(List.class), ClassName.get(PropertySource.class)),
                    ParameterizedTypeName.get(ClassName.get(ArrayList.class), ClassName.get(PropertySource.class))
            );
            for (String substitute : substitutes) {
                initializer.addStatement("propertySources.add(new $T())", ClassName.bestGuess(substitute));
            }
            initializer.addStatement("return new $T(propertySources)", ConstantPropertySources.class);
        });
    }
}