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package org.scijava.module;

import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.List;

import org.scijava.BasicDetails;
import org.scijava.ItemIO;
import org.scijava.ItemVisibility;

/**
 * A ModuleItem represents metadata about one input or output of a module.
 * 
 * @author Aivar Grislis
 * @author Curtis Rueden
 */
public interface ModuleItem<T> extends BasicDetails {

	/** Gets the {@link ModuleInfo} to which this item belongs. */
	ModuleInfo getInfo();

	/** Gets the type of the item. */
	Class<T> getType();

	/**
	 * Gets the type of the item, including Java generic parameters.
	 * <p>
	 * For many modules, this may be the same {@link Class} object returned by
	 * {@link #getType()}, but some module inputs or outputs may be backed by a
	 * generic type such as {@code List<String>} or {@code Iterable<Integer>}.
	 * </p>
	 * 
	 * @see Field#getGenericType()
	 */
	Type getGenericType();

	/** Gets the input/output type of the item. */
	ItemIO getIOType();

	/** Gets whether the item is a module input. */
	boolean isInput();

	/** Gets whether the item is a module output. */
	boolean isOutput();

	/** Gets the visibility of the item. */
	ItemVisibility getVisibility();

	/** Gets whether the item value is allowed to be auto-filled. */
	boolean isAutoFill();

	/** Gets whether the item value must be specified (i.e., no default). */
	boolean isRequired();

	/** Gets whether to remember the most recent value of the parameter. */
	boolean isPersisted();

	/** Gets the key to use for saving the value persistently. */
	String getPersistKey();

	/**
	 * Loads the item's persisted value. This recalls the value last stored using
	 * {@link #saveValue(Object)}.
	 * <p>
	 * Note that this is different than obtaining a module instance's current
	 * value for the input; see {@link #getValue(Module)} for that.
	 * </p>
	 *
	 * @deprecated
	 * @see ModuleService#load(ModuleItem)
	 */
	@Deprecated
	T loadValue();

	/**
	 * Saves the given value to persistent storage. This allows later restoration
	 * of the value via {@link #loadValue()}, even from a different JVM.
	 *
	 * @deprecated
	 * @see ModuleService#save(ModuleItem, Object)
	 */
	@Deprecated
	void saveValue(T value);

	/** Gets the function that is called to initialize the item's value. */
	String getInitializer();

	/**
	 * Invokes this item's initializer function, if any, on the given module.
	 * 
	 * @see #getInitializer()
	 */
	void initialize(Module module) throws MethodCallException;

	/** Gets the function that is called to validate the item's value. */
	String getValidater();

	/**
	 * Invokes this item's validation function, if any, on the given module.
	 * <p>
	 * The validation function may signal failure either by throwing an exception
	 * or by returning a non-empty {@link String} error message.
	 * </p>
	 *
	 * @throws MethodCallException if validation fails or the method cannot be
	 *           invoked. When the validater returns a non-empty String, a
	 *           {@link MethodCallException} is thrown with that string as its
	 *           message.
	 * @see #getValidater()
	 * @see #validateMessage(Module)
	 */
	void validate(Module module) throws MethodCallException;

	/**
	 * Validates this item's value in the given module, returning any error
	 * message rather than throwing.
	 * <p>
	 * The validation function may signal failure either by throwing an exception
	 * or by returning a non-empty {@link String} error message. This method
	 * catches both cases and returns the error message as a string, or
	 * {@code null} if the value is valid.
	 * </p>
	 *
	 * @return an error message if the value is invalid, or {@code null} if valid.
	 * @see #getValidater()
	 * @see #validate(Module)
	 */
	default String validateMessage(final Module module) {
		try {
			validate(module);
			return null;
		}
		catch (final MethodCallException exc) {
			// Unwrap to find the most informative message.
			final Throwable cause = exc.getCause();
			if (cause != null && cause.getMessage() != null &&
				!cause.getMessage().isEmpty())
			{
				return cause.getMessage();
			}
			final String msg = exc.getMessage();
			return msg != null && !msg.isEmpty() ? msg : exc.toString();
		}
	}

	/**
	 * Gets the function that is called whenever this item changes.
	 * <p>
	 * This mechanism enables interdependent items of various types. For example,
	 * two int parameters "width" and "height" could update each other when
	 * another boolean "Preserve aspect ratio" flag is set.
	 * </p>
	 */
	String getCallback();

	/**
	 * Invokes this item's callback function, if any, on the given module.
	 * 
	 * @see #getCallback()
	 */
	void callback(Module module) throws MethodCallException;

	/**
	 * Gets the preferred widget style to use when rendering the item in a user
	 * interface.
	 */
	String getWidgetStyle();

	/** Gets the default value. */
	T getDefaultValue();

	/** Gets the minimum allowed value (if applicable). */
	T getMinimumValue();

	/** Gets the maximum allowed value (if applicable). */
	T getMaximumValue();

	/**
	 * Gets the "soft" minimum value (if applicable).
	 * <p>
	 * The soft minimum is a hint for use in bounded scenarios, such as rendering
	 * in a user interface with a slider or scroll bar widget; the parameter value
	 * will not actually be clamped to the soft bounds, but they may be used in
	 * certain circumstances where appropriate.
	 * </p>
	 */
	T getSoftMinimum();

	/**
	 * Gets the "soft" maximum value (if applicable).
	 * <p>
	 * The soft maximum is a hint for use in bounded scenarios, such as rendering
	 * in a user interface with a slider or scroll bar widget; the parameter value
	 * will not actually be clamped to the soft bounds, but they may be used in
	 * certain circumstances where appropriate.
	 * </p>
	 */
	T getSoftMaximum();

	/**
	 * Gets the preferred step size to use when rendering the item in a user
	 * interface (if applicable).
	 */
	Number getStepSize();

	/**
	 * Gets the preferred width of the input field in characters (if applicable).
	 */
	int getColumnCount();

	/** Gets the list of possible values. */
	List<T> getChoices();

	/** Gets the item's current value with respect to the given module. */
	T getValue(Module module);

	/** Sets the item's current value with respect to the given module. */
	void setValue(Module module, T value);

}
