/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
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 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
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 *    this list of conditions and the following disclaimer.
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 *    this list of conditions and the following disclaimer in the documentation
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package org.scijava.module.process;

import org.scijava.convert.ConvertService;
import org.scijava.module.Module;
import org.scijava.module.ModuleItem;
import org.scijava.module.ModuleService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.util.ConversionUtils;
import org.scijava.widget.InputHarvester;

/**
 * A preprocessor for loading populated input values from persistent storage.
 * <p>
 * This preprocessor runs late in the chain, to give other preprocessors a
 * chance to populate the inputs first. However, its priority immediately
 * precedes the {@link org.scijava.widget.InputHarvester}'s, so that user-specified
 * values from last time are populated in the user dialog.
 * </p>
 * 
 * @author Curtis Rueden
 */
@Plugin(type = PreprocessorPlugin.class,
	priority = InputHarvester.PRIORITY + 1)
public class LoadInputsPreprocessor extends AbstractPreprocessorPlugin {

	@Parameter
	private ModuleService moduleService;

	@Parameter
	private ConvertService conversionService;

	// -- ModuleProcessor methods --

	@Override
	public void process(final Module module) {
		final Iterable<ModuleItem<?>> inputs = module.getInfo().inputs();
		for (final ModuleItem<?> item : inputs) {
			loadValue(module, item);
		}
	}

	// -- Helper methods --

	/** Loads the value of the given module item from persistent storage. */
	private <T> void loadValue(final Module module, final ModuleItem<T> item) {
		// skip input that has already been resolved
		if (module.isInputResolved(item.getName())) return;

		final T prefValue = moduleService.load(item);
		final Class<T> type = item.getType();
		final T defaultValue = item.getValue(module);
		final T value = getBestValue(prefValue, defaultValue, type);
		item.setValue(module, value);
	}

	private <T> T getBestValue(final Object prefValue,
		final Object defaultValue, final Class<T> type)
	{
		if (prefValue != null) return conversionService.convert(prefValue, type);
		if (defaultValue != null) {
			return conversionService.convert(defaultValue, type);
		}
		return ConversionUtils.getNullValue(type);
	}

}
