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

import static org.apache.james.backends.cassandra.versions.CassandraSchemaVersionManager.SchemaState.TOO_OLD;
import static org.apache.james.backends.cassandra.versions.CassandraSchemaVersionManager.SchemaState.TOO_RECENT;
import static org.apache.james.backends.cassandra.versions.CassandraSchemaVersionManager.SchemaState.UPGRADABLE;
import static org.apache.james.backends.cassandra.versions.CassandraSchemaVersionManager.SchemaState.UP_TO_DATE;

import javax.inject.Inject;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;

import reactor.core.publisher.Mono;

public class CassandraSchemaVersionManager {
    public static final SchemaVersion MIN_VERSION = new SchemaVersion(5);
    public static final SchemaVersion MAX_VERSION = new SchemaVersion(10);
    public static final SchemaVersion DEFAULT_VERSION = MIN_VERSION;

    private static final Logger LOGGER = LoggerFactory.getLogger(CassandraSchemaVersionManager.class);

    private final SchemaVersion minVersion;
    private final SchemaVersion maxVersion;
    private final SchemaVersion initialSchemaVersion;
    private final CassandraSchemaVersionDAO schemaVersionDAO;

    public enum SchemaState {
        UP_TO_DATE,
        TOO_RECENT,
        TOO_OLD,
        UPGRADABLE
    }

    @Inject
    public CassandraSchemaVersionManager(CassandraSchemaVersionDAO schemaVersionDAO) {
        this(schemaVersionDAO, MIN_VERSION, MAX_VERSION);
    }

    @VisibleForTesting
    public CassandraSchemaVersionManager(CassandraSchemaVersionDAO schemaVersionDAO, SchemaVersion minVersion, SchemaVersion maxVersion) {
        Preconditions.checkArgument(maxVersion.isAfterOrEquals(minVersion),
            "maxVersion should not be inferior to minVersion");

        this.schemaVersionDAO = schemaVersionDAO;
        this.minVersion = minVersion;
        this.maxVersion = maxVersion;

        this.initialSchemaVersion = computeVersion().block();
    }

    public Mono<Boolean> isBefore(SchemaVersion minimum) {
        if (initialSchemaVersion.isBefore(minimum)) {
            // If we started with a legacy james then maybe schema version had been updated since then
            return computeVersion()
                .map(computedVersion -> computedVersion.isBefore(minimum));
        }
        return Mono.just(false);
    }

    public Mono<SchemaVersion> computeVersion() {
        return schemaVersionDAO
            .getCurrentSchemaVersion()
            .map(maybeVersion -> maybeVersion.orElseGet(() -> {
                LOGGER.warn("No schema version information found on Cassandra, we assume schema is at version {}",
                    CassandraSchemaVersionManager.DEFAULT_VERSION);
                return DEFAULT_VERSION;
            }));
    }

    public SchemaVersion getMinimumSupportedVersion() {
        return minVersion;
    }

    public SchemaVersion getMaximumSupportedVersion() {
        return maxVersion;
    }

    public SchemaState computeSchemaState() {
        SchemaVersion version = computeVersion().block();
        if (version.isBefore(minVersion)) {
            return TOO_OLD;
        } else if (version.isBefore(maxVersion)) {
            return UPGRADABLE;
        } else if (version.equals(maxVersion)) {
            return UP_TO_DATE;
        } else {
            return TOO_RECENT;
        }
    }
}
