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Kafka Compatible Schema Registry
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/**
 * Copyright (c) 2019 - 2024 StreamNative, Inc.. All Rights Reserved.
 */
/**
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.streamnative.pulsar.handlers.kop.schemaregistry.providers;

import io.streamnative.pulsar.handlers.kop.schemaregistry.model.Schema;
import io.streamnative.pulsar.handlers.kop.schemaregistry.model.SchemaVersionFetcher;
import io.streamnative.pulsar.handlers.kop.schemaregistry.model.rest.SchemaReference;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

public abstract class AbstractSchemaProvider implements SchemaProvider {

    private SchemaVersionFetcher schemaVersionFetcher;

    @Override
    public void configure(Map configs) {
        schemaVersionFetcher =
            (SchemaVersionFetcher) configs.get(SchemaProvider.SCHEMA_VERSION_FETCHER_CONFIG);
    }

    public SchemaVersionFetcher schemaVersionFetcher() {
        return schemaVersionFetcher;
    }

    protected Map resolveReferences(List references) {
        if (references == null) {
            return Collections.emptyMap();
        }
        Map result = new LinkedHashMap<>();
        Set visited = new HashSet<>();
        resolveReferences(references, result, visited);
        return result;
    }

    private void resolveReferences(
        List references, Map schemas, Set visited) {
        for (SchemaReference reference : references) {
            if (reference.getName() == null
                || reference.getSubject() == null
                || reference.getVersion() == null) {
                throw new IllegalStateException("Invalid reference: " + reference);
            }
            if (visited.contains(reference.getName())) {
                continue;
            } else {
                visited.add(reference.getName());
            }
            String subject = reference.getSubject();
            if (!schemas.containsKey(reference.getName())) {
                // TODO: Use async call here.
                Schema schema = schemaVersionFetcher().getByVersion(subject, reference.getVersion(), true).join();
                if (schema == null) {
                    throw new IllegalStateException("No schema reference found for subject \""
                        + subject
                        + "\" and version "
                        + reference.getVersion());
                }
                if (reference.getVersion() == -1) {
                    // Update the version with the latest
                    reference.setVersion(schema.getVersion());
                }
                resolveReferences(schema.getReferences(), schemas, visited);
                schemas.put(reference.getName(), schema.getSchema());
            }
        }
    }
}