server/protocols/jmap-draft/src/main/java/org/apache/james/jmap/draft/json/FilterDeserializer.java

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package org.apache.james.jmap.draft.json;

import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.Optional;

import org.apache.james.jmap.draft.model.Filter;
import org.apache.james.jmap.draft.model.FilterCondition;
import org.apache.james.jmap.draft.model.FilterOperator;
import org.apache.james.util.streams.Iterators;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.node.ObjectNode;

public class FilterDeserializer extends StdDeserializer<Filter> {

    public FilterDeserializer() {
        super(Filter.class);
    }

    @Override
    public Filter deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        ObjectMapper mapper = (ObjectMapper) p.getCodec();
        ObjectNode obj = (ObjectNode) mapper.readTree(p);

        return mapper.treeToValue(obj, detectClass(obj.fields()));
    }

    private Class<? extends Filter> detectClass(Iterator<Map.Entry<String, JsonNode>> elements) {
        Optional<Class<? extends Filter>> maybeFilterOperator = Iterators.toStream(elements)
                .map(Map.Entry::getKey)
                .filter(name -> name.equals("operator"))
                .findFirst()
                .map(x -> FilterOperator.class);

        return maybeFilterOperator.orElse(FilterCondition.class);
    }
}