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Base classes to create standalone Java applications using picocli
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/*
 * MIT License
 *
 * Copyright (c) 2024 bakdata
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.bakdata.kafka;

import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Map.Entry;
import java.util.StringJoiner;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.Stream;


/**
 * This class is primarily used to inject environment variables to the passed in command line arguments
 * in {@link KafkaPropertiesFactory}.
 *
 * In general a usage would look like this:
 * {@code
 * final String[] environmentArguments = new EnvironmentArgumentsParser(ENV_PREFIX).parseVariables(System.getenv());
 * }
 * The class collects all environment variables starting with {@link #environmentPrefix} and replaces the
 * {@link #environmentDelimiter} with the {@link #commandLineDelimiter}. Furthermore it transforms all words to
 * lowercase and prepends "--" to match the command line argument descriptors.
 * Example:
 * {@code var ENV_PREFIX = "APP_"; Transformation: APP_INPUT_TOPIC --> --input-topic }
 */
public class EnvironmentArgumentsParser {

    private final String environmentPrefix;

    private final String commandLineDelimiter;

    private final String environmentDelimiter;

    /**
     * Create a new parser with a default command line delimiter of {@code -} and a default environment delimiter of
     * {@code _}
     *
     * @param environmentPrefix prefix to use to detect environment variables representing a command line argument
     */
    public EnvironmentArgumentsParser(final String environmentPrefix) {
        this(environmentPrefix, "-", "_");
    }

    /**
     * Create a new parser
     *
     * @param environmentPrefix prefix to use to detect environment variables representing a command line argument
     * @param commandLineDelimiter delimiter to use to concatenate fragments of a command line argument
     * @param environmentDelimiter delimiter to use to detect fragments of a command line argument in an environment
     * variable
     */
    public EnvironmentArgumentsParser(final String environmentPrefix, final String commandLineDelimiter,
            final String environmentDelimiter) {
        this.environmentPrefix = environmentPrefix;
        this.commandLineDelimiter = commandLineDelimiter;
        this.environmentDelimiter = environmentDelimiter;
    }

    /**
     * Parse a list of environment variables as command line arguments. All variables starting with the configured
     * prefix are converted by using the configured delimiters.
     *
     * @param environment map of environment variables
     * @return parsed command line arguments
     */
    public List parseVariables(final Map environment) {
        return environment.entrySet().stream()
                .filter(e -> e.getKey().startsWith(this.environmentPrefix))
                .flatMap(this::convertEnvironmentVariable)
                .collect(Collectors.toList());
    }


    private String convertEnvironmentKeyToCommandLineParameter(final String environmentKey) {
        final StringJoiner sj = new StringJoiner(this.commandLineDelimiter);
        final String[] words = environmentKey.replaceAll("^" + Pattern.quote(this.environmentPrefix), "")
                .split(this.environmentDelimiter);
        for (final String word : words) {
            sj.add(word.toLowerCase(Locale.getDefault()));
        }
        return "--" + sj;
    }

    private Stream convertEnvironmentVariable(final Entry environmentEntry) {
        final String key = this.convertEnvironmentKeyToCommandLineParameter(environmentEntry.getKey());
        return Stream.of(key, environmentEntry.getValue());
    }

}