/*******************************************************************************
 * Copyright (c) 2000, 2005 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.eclipse.jdt.internal.debug.core.hcr;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IFileState;
import org.eclipse.core.resources.ResourcesPlugin;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.jdt.core.ICompilationUnit;
import org.eclipse.jdt.core.dom.AST;
import org.eclipse.jdt.core.dom.ASTMatcher;
import org.eclipse.jdt.core.dom.ASTParser;
import org.eclipse.jdt.core.dom.CompilationUnit;
import org.eclipse.jdt.core.dom.MethodDeclaration;

/**
 * A <code>CompilationUnitDelta</code> represents the source code changes between
 * a CU in the workspace and the same CU at some point in the past
 * (from the local history).
 * <p>
 * This functionality is used in the context of Hot Code Replace
 * to determine which stack frames are affected (and need to be dropped)
 * by a class reload in the Java VM.
 * <p>
 * Typically a <code>CompilationUnitDelta</code> object is generated for a CU
 * when the associated class is replaced in the VM.
 */
public class CompilationUnitDelta {
    
    /**
     * AST of the current source code
     */
    private CompilationUnit fCurrentAst;
    /**
     * AST of the previous source code
     */
    private CompilationUnit fPrevAst;
	
    /**
     * AST parser
     */
    private ASTParser fParser = null;
    
    /**
     * AST matcher
     */
    private ASTMatcher fMatcher = null;
    
	private boolean fHasHistory= false;
	
	/**
	 * Creates a new <code>CompilationUnitDelta object that calculates and stores
	 * the changes of the given CU since some point in time.
	 */
	public CompilationUnitDelta(ICompilationUnit cu, long timestamp) throws CoreException {
		
		if (cu.isWorkingCopy()) {
			cu= cu.getPrimary();
		}
		
		// find underlying file
		IFile file= (IFile) cu.getUnderlyingResource();

		// get available editions
		IFileState[] states= file.getHistory(null);
		if (states == null || states.length <= 0) {
			return;
		}
		fHasHistory= true;
		
		IFileState found= null;
		// find edition just before the given time stamp
		for (int i= 0; i < states.length; i++) {
			IFileState state= states[i];
			long d= state.getModificationTime();
			if (d < timestamp) {
				found= state;
				break;
			}
		}
		
		if (found == null) {
			found= states[states.length-1];
		}
		
		InputStream oldContents= null;
		InputStream newContents= null;
		try {
			oldContents= found.getContents();
			newContents= file.getContents();
		} catch (CoreException ex) {
			return;
		}
		
		fPrevAst = parse(oldContents, cu);
		fCurrentAst = parse(newContents, cu);		
	}
	
	/**
	 * Returns <code>true</code>
	 * <ul>
	 * <li>if the source of the given member has been changed, or
	 * <li>if the element has been deleted, or
	 * <li>if the element has been newly created
	 * </ul>
	 * after the initial timestamp.
	 */
	public boolean hasChanged(String methodName, String signature) {
	    if (!fHasHistory) {
	        return false;	// optimistic: we have no history, so assume that member hasn't changed
	    }
	    if (fPrevAst == null || fCurrentAst == null) {
	        return true; // pessimistic: unable to build parse trees
	    }
	    MethodSearchVisitor visitor = new MethodSearchVisitor();
	    MethodDeclaration prev = findMethod(fPrevAst, visitor, methodName, signature);
	    if (prev != null) {
	        MethodDeclaration curr = findMethod(fCurrentAst, visitor, methodName, signature);
	        if (curr != null) {
	            return !getMatcher().match(prev, curr);
	        }
	    }
	    return true;
	}
	
	private MethodDeclaration findMethod(CompilationUnit cu, MethodSearchVisitor visitor, String name, String signature) {
	    visitor.setTargetMethod(name, signature);
	    cu.accept(visitor);
	    return visitor.getMatch();
	}
	
	//---- private stuff ----------------------------------------------------------------
	
	/**
	 * Parses the given input stream and returns a tree of JavaNodes
	 * or a null in case of failure.
	 */
	private CompilationUnit parse(InputStream input, ICompilationUnit cu) {
		
		char[] buffer= readString(input);		
		if (buffer != null) {
		    if (fParser == null) {
		        fParser = ASTParser.newParser(AST.JLS3);
		    }
		    fParser.setSource(buffer);
		    fParser.setProject(cu.getJavaProject());
		    fParser.setResolveBindings(true);
		    fParser.setKind(ASTParser.K_COMPILATION_UNIT);
		    fParser.setUnitName(cu.getElementName());
			return (CompilationUnit) fParser.createAST(null);
		} 
		return null;
	}
	
	/**
	 * Returns an AST matcher
	 * 
	 * @return AST matcher
	 */
	private ASTMatcher getMatcher() {
	    if (fMatcher == null) {
	        fMatcher = new ASTMatcher();
	    }
	    return fMatcher;
	}
			
	/**
	 * Returns null if an error occurred.
	 */
	private char[] readString(InputStream is) {
		if (is == null) {
			return null;
		}
		BufferedReader reader= null;
		try {
			StringBuffer buffer= new StringBuffer();
			char[] part= new char[2048];
			int read= 0;
			reader= new BufferedReader(new InputStreamReader(is, ResourcesPlugin.getEncoding()));

			while ((read= reader.read(part)) != -1) {
				buffer.append(part, 0, read);
			}
			
			char[] b= new char[buffer.length()];
			buffer.getChars(0, b.length, b, 0);
			return b;
			
		} catch (IOException ex) {
		} finally {
			if (reader != null) {
				try {
					reader.close();
				} catch (IOException ex) {
				}
			}
		}
		return null;
	}
}