package org.opendaylight.yangtools.yang.model.util.repo;

import org.opendaylight.yangtools.concepts.Delegator;
import org.opendaylight.yangtools.concepts.Registration;

import com.google.common.base.Optional;

import static com.google.common.base.Preconditions.*;

public abstract class AbstractCachingSchemaSourceProvider<I, O> implements SchemaSourceProvider<O>,
        Delegator<SchemaSourceProvider<I>> {

    private final SchemaSourceProvider<I> defaultDelegate;

    protected AbstractCachingSchemaSourceProvider(SchemaSourceProvider<I> delegate) {
        this.defaultDelegate = delegate;
    }

    @Override
    public Optional<O> getSchemaSource(String moduleName, Optional<String> revision) {
        return getSchemaSourceImpl(moduleName, revision, defaultDelegate);
    }

    private Optional<O> getSchemaSourceImpl(String moduleName, Optional<String> revision,
            SchemaSourceProvider<I> delegate) {
        checkNotNull(moduleName, "Module name should not be null.");
        checkNotNull(revision, "Revision should not be null");

        Optional<O> cached = getCachedSchemaSource(moduleName, revision);
        if (cached.isPresent()) {
            return cached;
        }
        Optional<I> live = delegate.getSchemaSource(moduleName, revision);
        return cacheSchemaSource(moduleName, revision, live);
    }

    abstract protected Optional<O> cacheSchemaSource(String moduleName, Optional<String> revision, Optional<I> stream);

    abstract protected Optional<O> getCachedSchemaSource(String moduleName, Optional<String> revision);

    public SchemaSourceProvider<I> getDelegate() {
        return defaultDelegate;
    }

    public SchemaSourceProvider<O> createInstanceFor(SchemaSourceProvider<I> delegate) {
        checkNotNull(delegate, "Delegate should not be null");
        return new SchemaSourceProviderInstance(delegate);
    }

    private class SchemaSourceProviderInstance implements SchemaSourceProvider<O>, Delegator<SchemaSourceProvider<I>> {

        private final SchemaSourceProvider<I> delegate;

        protected SchemaSourceProviderInstance(SchemaSourceProvider<I> delegate) {
            super();
            this.delegate = delegate;
        }

        @Override
        public Optional<O> getSchemaSource(String moduleName, Optional<String> revision) {
            return getSchemaSourceImpl(moduleName, revision, getDelegate());
        }

        @Override
        public SchemaSourceProvider<I> getDelegate() {
            return delegate;
        }
    }
}