plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/core/model/InstallOperation.java

package org.eclipse.epp.installer.core.model;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.epp.installer.core.IErrorConstants;


/**
 * Abstract base class for all install operations that actually install bits onto the drive.
 * These operations consume information placed into {@link org.eclipse.epp.installer.core.InstallOptions}
 * by {@link org.eclipse.epp.installer.core.model.IInstallStep}s.
 */
public abstract class InstallOperation implements IErrorConstants {

	/**
	 * List of prerequisites executed before operation.
	 * Operation should fill with needed prerequisite operations.
	 */	
	private List prerequisites;

	/**
	 * Invoked by InstallModel in Prepare Phase.
	 * 
	 * Why prepare? Well, installer may require relatively long steps (analyze
	 * files, etc) to decide (build) installation model, so it's recommended to
	 * add child operations in prepare method instead of constructor (etc) - to
	 * keep user updated with UI.
	 * @throws Exception
	 */
	protected void prepare() throws Exception {

	}

	/**
	 * Execure operation.
	 * 
	 * @param installer Installation Context
	 * @return IStatus return operation execution status.
	 */
	protected IStatus run(Context installer) {
		return Status.OK_STATUS;
	}

	/**
	 * Add prerequisite to list of prerequsites.
	 * 
	 * If one prerequisite are added second time, if will be ignored.<br/>
	 * If derived class implemens {@link org.eclipse.epp.installer.core.model.ISequence} interface then
	 * last prerequisite before adding new will be added into <code>op</code> list of prerequisites.
	 * 
	 * @param op InstallOperation prerequisite to add.
	 */
	protected void addPrerequisite(InstallOperation op) {
		if (prerequisites == null) {
			prerequisites = new ArrayList();
		}

		// check if operation already added.
		// (we don't use Set to find last added operation for sequences)
		if (prerequisites.contains(op)) {
			return;
		}

		if (this instanceof ISequence) {
			int size = prerequisites.size();
			if (size > 0) {
				InstallOperation last = (InstallOperation) prerequisites
						.get(size - 1);
				op.addPrerequisite(last);
			}
		}
		prerequisites.add(op);
	}

	/**
	 * Return true if prerequisites list contains elements.
	 * @return boolean true if prerequisites not null. 
	 */
	protected boolean hasPrerequisites() {
		if( prerequisites == null ) {
			return false;
		}
		return prerequisites.size() > 0;
	}

	/**
	 * Return current list of prerequisites.
	 * @return List of current prerequisites.
	 */
	protected List prerequisites() {
		if (prerequisites == null) {
			return Collections.EMPTY_LIST;
		}
		return prerequisites;
	}

	/*
	 * TODO think about API clearance (at this point only prerequisity type of
	 * relation exists)
	 */
	/**
	 * Add prerequisite operation.
	 * @param op InstallOperation
	 */
	public final void add(InstallOperation op) {
		addPrerequisite(op);
	}
	
}