server/blob/blob-objectstorage/src/main/java/org/apache/james/blob/objectstorage/ObjectStorageBucketNameResolver.java

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 * distributed with this work for additional information        *
 * regarding copyright ownership.  The ASF licenses this file   *
 * to you under the Apache License, Version 2.0 (the            *
 * "License"); you may not use this file except in compliance   *
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 * software distributed under the License is distributed on an  *
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
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package org.apache.james.blob.objectstorage;

import java.util.Optional;

import org.apache.james.blob.api.BucketName;

import com.google.common.base.Preconditions;

class ObjectStorageBucketNameResolver {

    static class Builder {

        @FunctionalInterface
        interface RequirePrefix {
            RequireNamespace prefix(Optional<String> prefix);

            default RequireNamespace noPrefix() {
                return prefix(Optional.empty());
            }

            default RequireNamespace prefix(String prefix) {
                return prefix(Optional.ofNullable(prefix));
            }
        }

        @FunctionalInterface
        interface RequireNamespace {
            ReadyToBuild namespace(Optional<BucketName> namespace);

            default ReadyToBuild namespace(BucketName namespace) {
                return namespace(Optional.ofNullable(namespace));
            }

            default ReadyToBuild noNamespace() {
                return namespace(Optional.empty());
            }
        }

        static final class ReadyToBuild {
            private final Optional<BucketName> namespace;
            private final Optional<String> prefix;

            ReadyToBuild(Optional<BucketName> namespace, Optional<String> prefix) {
                this.namespace = namespace;
                this.prefix = prefix;
            }

            ObjectStorageBucketNameResolver build() {
                return new ObjectStorageBucketNameResolver(namespace, prefix);
            }
        }
    }

    static Builder.RequirePrefix builder() {
        return prefix -> namespace -> new Builder.ReadyToBuild(namespace, prefix);
    }

    private final Optional<BucketName> namespace;
    private final Optional<String> prefix;

    private ObjectStorageBucketNameResolver(Optional<BucketName> namespace, Optional<String> prefix) {
        Preconditions.checkNotNull(namespace);
        Preconditions.checkNotNull(prefix);

        this.namespace = namespace;
        this.prefix = prefix;
    }

    ObjectStorageBucketName resolve(BucketName bucketName) {
        Preconditions.checkNotNull(bucketName);

        if (isNameSpace(bucketName)) {
            return ObjectStorageBucketName.of(bucketName);
        }
        return prefix
            .map(bucketPrefix -> ObjectStorageBucketName.of(bucketPrefix + bucketName.asString()))
            .orElse(ObjectStorageBucketName.of(bucketName));
    }

    private boolean isNameSpace(BucketName bucketName) {
        return namespace
            .map(existingNamespace -> existingNamespace.equals(bucketName))
            .orElse(false);
    }
}