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Set of codecs to add support for json-values in the Java MongoDB driver, abstracting the process of decoding a BSON into a JsObj and encoding a JsObj into a BSON.

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package mongovalues;

import jsonvalues.JsInstant;
import jsonvalues.JsStr;
import jsonvalues.JsValue;
import org.bson.BsonReader;
import org.bson.BsonType;
import org.bson.codecs.BsonTypeClassMap;
import org.bson.codecs.BsonTypeCodecMap;
import org.bson.codecs.Codec;
import org.bson.codecs.DecoderContext;
import org.bson.codecs.configuration.CodecRegistry;
import org.bson.types.ObjectId;

import java.time.Instant;


abstract class JsonCodec {

    private final BsonTypeCodecMap bsonTypeCodecMap;
    CodecRegistry registry;
    BsonTypeClassMap bsonTypeClassMap;


    public JsonCodec(final CodecRegistry registry,
                     final BsonTypeClassMap bsonTypeClassMap) {
        this.registry = registry;
        this.bsonTypeClassMap = bsonTypeClassMap;
        this.bsonTypeCodecMap = new BsonTypeCodecMap(bsonTypeClassMap,
                registry
        );
    }

    protected JsValue readValue(final BsonReader reader,
                                final DecoderContext context) {

        BsonType bsonType = reader.getCurrentBsonType();

        if (bsonType == BsonType.OBJECT_ID) {
            ObjectId objectId = reader.readObjectId();
            return JsStr.of(objectId.toHexString());
        }

        //not supported for writing, date-time is the format supported
        // for reading is transformed into an instant
        if (bsonType == BsonType.TIMESTAMP) {
            long value = reader.readTimestamp()
                    .getValue();
            return JsInstant.of(Instant.ofEpochMilli(value));
        }

        @SuppressWarnings("unchecked")
        Codec codec = (Codec) bsonTypeCodecMap.get(bsonType);
        if (codec == null) throw new IllegalArgumentException("The bson type " + bsonType.name() + " is not supported");
        return codec.decode(reader,
                context
        );
    }
}