/*
 * Copyright 2016-2018 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 com.tick42.varandb.boot.env;

import java.io.File;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Collections;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.env.EnvironmentPostProcessor;
import org.springframework.boot.env.OriginTrackedMapPropertySource;
import org.springframework.boot.origin.Origin;
import org.springframework.boot.origin.OriginTrackedValue;
import org.springframework.boot.origin.TextResourceOrigin;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
import org.springframework.core.io.FileSystemResource;

import static java.util.stream.Collectors.toMap;

/**
 * An {@link EnvironmentPostProcessor} that knows how to load docker/kubernetes secrets.
 *
 * The contents of every file under {@code /run/secrets} can be easily consumed
 * by {@link ConfigurableEnvironment Environment} users via {@code secret.*} properties.
 *
 * @author Vladimir Tsanev
 */
public class SecretEnvironmentPostProcessor implements EnvironmentPostProcessor {
    private static final Logger log = LoggerFactory.getLogger(SecretEnvironmentPostProcessor.class);

    private String prefix = "secret.";
    private final Path directory;

    public SecretEnvironmentPostProcessor() {
        this(new File("/run/secrets").toPath());
    }

    public SecretEnvironmentPostProcessor(Path directory) {
        this.directory = directory;
    }

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        Map<String, OriginTrackedValue> map;
        map = createSecretsMap();
        if (!map.isEmpty()) {
            MutablePropertySources sources = environment.getPropertySources();
            PropertySource<?> source = new OriginTrackedMapPropertySource("secrets", map);
            sources.addFirst(source);
        }
    }

    Map<String, OriginTrackedValue> createSecretsMap() {
        try {
            if (this.directory.toFile().exists()) {
                return Files.walk(this.directory, 1)
                    .filter(p -> p.toFile().isFile())
                    .collect(toMap(this::getSecretName, this::readValueFromFile));
            }
        }
        catch (Exception e) {
            log.error("Cloud not create secrets map", e);
        }
        return Collections.emptyMap();
    }

    private String getSecretName(Path path) {
        return this.prefix + path.getFileName().toString();
    }

    private OriginTrackedValue readValueFromFile(Path path) {
        char[] secret;
        try {
            byte[] bytes = Files.readAllBytes(path);
            secret = new String(bytes, StandardCharsets.UTF_8).toCharArray();
        }
        catch (Exception e) {
            log.error("Could not read secret value from " + path, e);
            secret = null;
        }
        Origin origin = new TextResourceOrigin(new FileSystemResource(path.toFile()), null);
        return OriginTrackedValue.of(secret, origin);
    }

}