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package org.milyn.cdr;

import java.util.List;

import org.milyn.delivery.ContentDeliveryConfig;
import org.w3c.dom.Element;

/**
 * SmooksResourceConfiguration Parameter.
 * 
 * Wrapper for a param.  Handles decoding.
 * @author tfennelly
 */
public class Parameter {
	public static final String PARAM_TYPE_PREFIX = "param-type:";
	private final String name;
	String value;
	private String type;
	private Object objValue;

    private Element xml;

    /**
	 * Public constructor.
	 * @param name Parameter name.
	 * @param value Parameter value.
	 */
	public Parameter(String name, String value) {
		if(name == null || (name = name.trim()).equals("")) {
			throw new IllegalArgumentException("null or empty 'name' arg in constructor call.");
		}
		if(value == null) {
			throw new IllegalArgumentException("null 'value' arg in constructor call.");
		}
		this.name = name;
		this.value = value;
	}

    /**
	 * Public constructor.
	 * @param name Parameter name.
	 * @param value Parameter value.
	 */
	public Parameter(String name, Object value) {
		if(name == null || (name = name.trim()).equals("")) {
			throw new IllegalArgumentException("null or empty 'name' arg in constructor call.");
		}
		if(value == null) {
			throw new IllegalArgumentException("null 'value' arg in constructor call.");
		}
		this.name = name;
        this.value = value.toString();
		this.objValue = value;
	}

	/**
	 * Public constructor.
	 * @param name Parameter name.
	 * @param value Parameter value.
	 * @param type Parameter type.  This argument identifies the
	 * {@link ParameterDecoder} to use for decoding the param value.
	 */
	public Parameter(String name, String value, String type) {
		this(name, value);

		// null type attribute is OK - means no decoder is used on the value
		this.type = type;
	}

	/**
	 * Get the parameter name.
	 * @return The parameter name.
	 */
	public String getName() {
		return name;
	}

	/**
	 * Get the parameter type.
	 * @return The parameter type.
	 */
	public String getType() {
		return type;
	}

	/**
	 * Get the parameter value "undecoded".
	 * @return Parameter value.
	 */
	public String getValue() {
		return value;
	}

	/**
	 * Get the parameter value "decoded" into an Object.
	 * 

	 * Uses the supplied deliveryConfig to get the {@link ParameterDecoder}
	 * implementation to be used to decode the parameter value.  Looks up the
	 * {@link ParameterDecoder} using the parameter type - selector="decoder-<type>".
	 * @param deliveryConfig Requesting device {@link ContentDeliveryConfig}.
	 * @return Decoded value.
	 * @throws ParameterDecodeException Unable to decode parameter value.
	 */
	public Object getValue(ContentDeliveryConfig deliveryConfig) throws ParameterDecodeException {
		if(objValue == null) {
			synchronized (value) {
				if(objValue == null) {
					if(type == null) {
						objValue = value;
					} else {
						List decoders = deliveryConfig.getObjects(PARAM_TYPE_PREFIX + type);
						if(!decoders.isEmpty()) {
							try {
								ParameterDecoder paramDecoder = (ParameterDecoder)decoders.get(0);
								objValue = paramDecoder.decodeValue(value);
							} catch(ClassCastException cast) {
								throw new ParameterDecodeException("Configured ParameterDecoder '" + PARAM_TYPE_PREFIX + type + "' for device must be of type " + ParameterDecoder.class);
							}
						} else {
							throw new ParameterDecodeException("ParameterDecoder '" + PARAM_TYPE_PREFIX + type + "' not defined for requesting device.");
						}
					}
				}
			}
		}

		return objValue;
	}

    /**
     * Get the object value associated with this parameter.
     * @return The object value, or null if not set.
     */
    public Object getObjValue() {
        return objValue;
    }

    /* (non-Javadoc)
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		return value;
	}

    /**
     * Set the DOM element node associated with the parameter definition.
     * 

     * Only relevant for XML based configs.
     *
     * @param xml Parameter configuration xml.
     */
    public Parameter setXML(Element xml) {
        this.xml = xml;
        return this;
    }

    /**
     * Get the DOM element node associated with the parameter definition.
     * 
     * Only relevant for XML based configs.
     *
     * @return Parameter configuration xml.
     */
    public Element getXml() {
        return xml;
    }
}