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package org.apache.james.backends.cassandra.utils;

import javax.inject.Inject;

import org.apache.james.core.healthcheck.ComponentName;
import org.apache.james.core.healthcheck.HealthCheck;
import org.apache.james.core.healthcheck.Result;

import com.datastax.driver.core.Session;
import com.datastax.driver.core.SimpleStatement;

import reactor.core.publisher.Mono;

/**
 * Health check for the Cassandra backend.
 *
 */
public class CassandraHealthCheck implements HealthCheck {

    private static final ComponentName COMPONENT_NAME = new ComponentName("Cassandra backend");
    private static final String SAMPLE_QUERY = "SELECT NOW() FROM system.local";

    private final CassandraAsyncExecutor queryExecutor;

    @Inject
    public CassandraHealthCheck(Session session) {
        this.queryExecutor = new CassandraAsyncExecutor(session);
    }

    @Override
    public ComponentName componentName() {
        return COMPONENT_NAME;
    }

    @Override
    public Mono<Result> check() {
        // execute a simple query to check if cassandra is responding
        // idea from: https://stackoverflow.com/questions/10246287
        return queryExecutor.execute(new SimpleStatement(SAMPLE_QUERY))
            .map(resultSet -> Result.healthy(COMPONENT_NAME))
            .onErrorResume(e -> Mono.just(Result.unhealthy(COMPONENT_NAME, "Error checking Cassandra backend", e)));
    }
}
