source: trunk/org.modelica.mdt.ui/src/org/modelica/mdt/ui/hover/ContentAssistInvocationContext.java

/*******************************************************************************
 * Copyright (c) 2005, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.modelica.mdt.ui.hover;

import org.eclipse.core.runtime.Assert;

import org.eclipse.jface.text.BadLocationException;
import org.eclipse.jface.text.IDocument;
import org.eclipse.jface.text.ITextViewer;

/**
 * Describes the context of an invocation of content assist in a text viewer. The context knows the
 * document, the invocation offset and can lazily compute the identifier prefix preceding the
 * invocation offset. It may know the viewer.
 * <p>
 * Subclasses may add information to their environment. For example, source code editors may provide
 * specific context information such as an AST.
 * </p>
 * <p>
 * Clients may instantiate and subclass.
 * </p>
 * 
 * @since 3.2
 */
public class ContentAssistInvocationContext {
    
    /* state */
    private final ITextViewer fViewer;
    private final IDocument fDocument;
    private final int fOffset;
    
    /* cached additional info */
    private CharSequence fPrefix;
    
    /**
     * Equivalent to
     * {@linkplain #ContentAssistInvocationContext(ITextViewer, int) ContentAssistInvocationContext(viewer, viewer.getSelectedRange().x)}.
     * 
     * @param viewer the text viewer that content assist is invoked in
     */
    public ContentAssistInvocationContext(ITextViewer viewer) {
        this(viewer, viewer.getSelectedRange().x);
    }

    /**
     * Creates a new context for the given viewer and offset.
     * 
     * @param viewer the text viewer that content assist is invoked in
     * @param offset the offset into the viewer's document where content assist is invoked at
     */
    public ContentAssistInvocationContext(ITextViewer viewer, int offset) {
        Assert.isNotNull(viewer);
        fViewer= viewer;
        fDocument= null;
        fOffset= offset;
    }
    
    /**
     * Creates a new context with no viewer or invocation offset set.
     */
    protected ContentAssistInvocationContext() {
        fDocument= null;
        fViewer= null;
        fOffset= -1;
    }
    
    /**
     * Creates a new context for the given document and offset.
     * 
     * @param document the document that content assist is invoked in
     * @param offset the offset into the document where content assist is invoked at
     */
    public ContentAssistInvocationContext(IDocument document, int offset) {
        Assert.isNotNull(document);
        Assert.isTrue(offset >= 0);
        fViewer= null;
        fDocument= document;
        fOffset= offset;
    }
    
    /**
     * Returns the invocation offset.
     * 
     * @return the invocation offset
     */
    public final int getInvocationOffset() {
        return fOffset;
    }
    
    /**
     * Returns the viewer, <code>null</code> if not available.
     * 
     * @return the viewer, possibly <code>null</code>
     */
    public final ITextViewer getViewer() {
        return fViewer;
    }
    
    /**
     * Returns the document that content assist is invoked on, or <code>null</code> if not known.
     * 
     * @return the document or <code>null</code>
     */
    public IDocument getDocument() {
        if (fDocument == null) {
            if (fViewer == null)
                return null;
            return fViewer.getDocument();
        }
        return fDocument;
    }
    
    /**
     * Computes the identifier (as specified by {@link Character#isJavaIdentifierPart(char)}) that
     * immediately precedes the invocation offset.
     * 
     * @return the prefix preceding the content assist invocation offset, <code>null</code> if
     *         there is no document
     * @throws BadLocationException if accessing the document fails
     */
    public CharSequence computeIdentifierPrefix() throws BadLocationException {
        if (fPrefix == null) {
            IDocument document= getDocument();
            if (document == null)
                return null;
            int end= getInvocationOffset();
            int start= end;
            while (--start >= 0) {
                if (!Character.isJavaIdentifierPart(document.getChar(start)))
                    break;
            }
            start++;
            fPrefix= document.get(start, end - start);
        }
        
        return fPrefix;
    }
    
    /**
     * Invocation contexts are equal if they describe the same context and are of the same type.
     * This implementation checks for <code>null</code> values and class equality. Subclasses
     * should extend this method by adding checks for their context relevant fields (but not
     * necessarily cached values).
     * <p>
     * Example:
     * 
     * <pre>
     * class MyContext extends ContentAssistInvocationContext {
     *  private final Object fState;
     *  private Object fCachedInfo;
     * 
     *  ...
     * 
     *  public boolean equals(Object obj) {
     *      if (!super.equals(obj))
     *          return false;
     *      MyContext other= (MyContext) obj;
     *      return fState.equals(other.fState);
     *  }
     * }
     * </pre>
     * 
     * </p>
     * <p>
     * Subclasses should also extend {@link Object#hashCode()}.
     * </p>
     * 
     * @param obj {@inheritDoc}
     * @return {@inheritDoc}
     */
    public boolean equals(Object obj) {
        if (obj == null)
            return false;
        if (!getClass().equals(obj.getClass()))
            return false;
        ContentAssistInvocationContext other= (ContentAssistInvocationContext) obj;
        return (fViewer == null && other.fViewer == null || fViewer != null && fViewer.equals(other.fViewer)) && fOffset == other.fOffset && (fDocument == null && other.fDocument == null || fDocument != null && fDocument.equals(other.fDocument));
    }
    
    /*
     * @see java.lang.Object#hashCode()
     */
    public int hashCode() {
        return 23459213 << 5 | (fViewer == null ? 0 : fViewer.hashCode() << 3) | fOffset;
    }
}