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Server-side library used by applications created with the JHipster generator, see https://www.jhipster.tech/ for more information on JHipster

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package tech.jhipster.config.cache;

import java.lang.reflect.Method;
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.util.Objects;
import org.apache.commons.lang3.ObjectUtils;
import org.apache.commons.lang3.RandomStringUtils;
import org.springframework.boot.info.BuildProperties;
import org.springframework.boot.info.GitProperties;
import org.springframework.cache.interceptor.KeyGenerator;

/**
 * PrefixedKeyGenerator class.
 * 
 * This class is responsible for generating cache keys that are specific to a version of the application
 * by prefixing them with git commit hash.
 * 
 * 
 * This allows multiple versions of an application to "share" the same distributed cache even when the structure
 * of the values has changed between those versions of the software.
 * 
 * 
 * This case typically occurs in production to ensure zero-downtime updates across a cluster
 * requiring that two different versions of the application have to run concurrently for some time.
 * 
 */
public class PrefixedKeyGenerator implements KeyGenerator {

    private final String prefix;
    private String shortCommitId = null;
    private Instant time = null;
    private String version = null;

    /**
     * Constructor for PrefixedKeyGenerator.
     *
     * @param gitProperties a {@link org.springframework.boot.info.GitProperties} object.
     * @param buildProperties a {@link org.springframework.boot.info.BuildProperties} object.
     */
    public PrefixedKeyGenerator(GitProperties gitProperties, BuildProperties buildProperties) {
        prefix = generatePrefix(gitProperties, buildProperties);
    }

    String getPrefix() {
        return prefix;
    }

    private String generatePrefix(GitProperties gitProperties, BuildProperties buildProperties) {
        if (Objects.nonNull(gitProperties)) {
            shortCommitId = gitProperties.getShortCommitId();
        }

        if (Objects.nonNull(buildProperties)) {
            time = buildProperties.getTime();
            version = buildProperties.getVersion();
        }
        Object p = ObjectUtils.firstNonNull(shortCommitId, time, version, RandomStringUtils.randomAlphanumeric(12));

        if (p instanceof Instant) {
            return DateTimeFormatter.ISO_INSTANT.format((Instant) p);
        }
        return p.toString();
    }

    /** {@inheritDoc} */
    @Override
    public Object generate(Object target, Method method, Object... params) {
        return new PrefixedSimpleKey(prefix, method.getName(), params);
    }
}