package org.springframework.social.dto.ser;

import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

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;

/**
 * Deserializes documents without a specific field designated for Polymorphic Type
 * identification, when the document contains a field registered to be unique to that type
 *
 * @author robin
 */
public class UniquePropertyPolymorphicDeserializer<T> extends StdDeserializer<T> {

	private static final long serialVersionUID = 1L;

	// the registry of unique field names to Class types
	private Map<String, Class<? extends T>> registry;

	public UniquePropertyPolymorphicDeserializer(Class<T> clazz) {
		super(clazz);
		registry = new HashMap<String, Class<? extends T>>();
	}

	public void register(String uniqueProperty, Class<? extends T> clazz) {
		registry.put(uniqueProperty, clazz);
	}

	/* (non-Javadoc)
	 * @see com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)
	 */
	@Override
	public T deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
		Class<? extends T> clazz = null;

		ObjectMapper mapper = (ObjectMapper) jp.getCodec();
		ObjectNode obj = (ObjectNode) mapper.readTree(jp);
	    Iterator<Entry<String, JsonNode>> elementsIterator = obj.fields();

	    while (elementsIterator.hasNext()) {
	    	Entry<String, JsonNode> element = elementsIterator.next();
	    	String name = element.getKey();
	    	if (registry.containsKey(name)) {
	    		clazz = registry.get(name);
	    		break;
	    	}
	    }

	    if (clazz == null) {
	    	throw ctxt.mappingException("No registered unique properties found for polymorphic deserialization");
	    }

	    return mapper.treeToValue(obj, clazz);
	}

}