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/*
 * Copyright (c) 2022, 2023 Oracle and/or its affiliates.
 *
 * 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.helidon.webserver.http2;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import io.helidon.common.buffers.BufferData;
import io.helidon.webserver.ConnectionContext;
import io.helidon.webserver.http2.spi.Http2SubProtocolSelector;
import io.helidon.webserver.spi.ServerConnection;
import io.helidon.webserver.spi.ServerConnectionSelector;

import static io.helidon.http.http2.Http2Util.PREFACE_LENGTH;
import static io.helidon.http.http2.Http2Util.isPreface;

/**
 * HTTP/2 server connection selector.
 */
public class Http2ConnectionSelector implements ServerConnectionSelector {

    private final Http2Config http2Config;
    private final List subProviders;

    // Creates an instance of HTTP/2 server connection selector.
    Http2ConnectionSelector(Http2Config http2Config, List subProviders) {
        this.http2Config = http2Config;
        this.subProviders = subProviders;
    }

    /**
     * Builder to set up this provider.
     *
     * @return a new builder
     */
    public static Builder builder() {
        return new Builder();
    }

    @Override
    public int bytesToIdentifyConnection() {
        return PREFACE_LENGTH;
    }

    @Override
    public Support supports(BufferData request) {
        byte[] prefaceBytes = new byte[PREFACE_LENGTH];
        request.read(prefaceBytes, 0, PREFACE_LENGTH);

        // now we can ask protocol handler to identify this protocol
        if (isPreface(prefaceBytes)) {
            // this is HTTP/2 prior knowledge
            return Support.SUPPORTED;
        }

        return Support.UNSUPPORTED;
    }

    @Override
    public Set supportedApplicationProtocols() {
        return Set.of("h2");
    }

    @Override
    public ServerConnection connection(ConnectionContext ctx) {
        Http2Connection result = new Http2Connection(ctx, http2Config, subProviders);
        result.expectPreface();

        return result;
    }

    /**
     * Fluent API builder for {@link Http2ConnectionProvider}.
     */
    public static class Builder implements io.helidon.common.Builder {
        private final List subProtocolSelectors = new ArrayList<>();

        private Http2Config http2Config;

        private Builder() {
        }

        @Override
        public Http2ConnectionSelector build() {
            return new Http2ConnectionSelector(http2Config, subProtocolSelectors);
        }

        /**
         * Custom configuration of HTTP/2 connection provider.
         * If not defined, it will be configured from config, or defaults would be used.
         *
         * @param http2Config HTTP/2 configuration
         * @return updated builder
         */
        public Builder http2Config(Http2Config http2Config) {
            this.http2Config = http2Config;
            return this;
        }

        /**
         * Add a configured sub-protocol provider. This will replace the instance discovered through service loader (if one
         * exists).
         *
         * @param selector provider to add
         * @return updated builer
         */
        public Builder addSubProtocolSelector(Http2SubProtocolSelector selector) {
            subProtocolSelectors.add(selector);
            return this;
        }
    }
}