/*
    * Copyright (C) 2008-2010, Google Inc.
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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  package org.eclipse.jgit.lib;
  
  import java.io.IOException;
  import java.text.MessageFormat;
  
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevWalk;
  
  /**
   * Creates, updates or deletes any reference.
   */
  public abstract class RefUpdate {
  	/** Status of an update request. */
  	public static enum Result {
  		/** The ref update/delete has not been attempted by the caller. */
  		NOT_ATTEMPTED,
  
  		/**
  		 * The ref could not be locked for update/delete.
  		 * <p>
  		 * This is generally a transient failure and is usually caused by
  		 * another process trying to access the ref at the same time as this
  		 * process was trying to update it. It is possible a future operation
  		 * will be successful.
  		 */
  		LOCK_FAILURE,
  
  		/**
  		 * Same value already stored.
  		 * <p>
  		 * Both the old value and the new value are identical. No change was
  		 * necessary for an update. For delete the branch is removed.
  		 */
  		NO_CHANGE,
  
  		/**
  		 * The ref was created locally for an update, but ignored for delete.
  		 * <p>
  		 * The ref did not exist when the update started, but it was created
  		 * successfully with the new value.
  		 */
  		NEW,
  
  		/**
  		 * The ref had to be forcefully updated/deleted.
  		 * <p>
  		 * The ref already existed but its old value was not fully merged into
  		 * the new value. The configuration permitted a forced update to take
  		 * place, so ref now contains the new value. History associated with the
  		 * objects not merged may no longer be reachable.
  		 */
  		FORCED,
 
 		/**
 		 * The ref was updated/deleted in a fast-forward way.
 		 * <p>
 		 * The tracking ref already existed and its old value was fully merged
 		 * into the new value. No history was made unreachable.
 		 */
 		FAST_FORWARD,
 
 		/**
 		 * Not a fast-forward and not stored.
 		 * <p>
 		 * The tracking ref already existed but its old value was not fully
 		 * merged into the new value. The configuration did not allow a forced
 		 * update/delete to take place, so ref still contains the old value. No
 		 * previous history was lost.
 		 */
 		REJECTED,
 
 		/**
 		 * Rejected because trying to delete the current branch.
 		 * <p>
 		 * Has no meaning for update.
 		 */
 		REJECTED_CURRENT_BRANCH,
 
 		/**
 		 * The ref was probably not updated/deleted because of I/O error.
 		 * <p>
 		 * Unexpected I/O error occurred when writing new ref. Such error may
 		 * result in uncertain state, but most probably ref was not updated.
 		 * <p>
 		 * This kind of error doesn't include {@link #LOCK_FAILURE}, which is a
 		 * different case.
 		 */
 		IO_FAILURE,
 
 		/**
 		 * The ref was renamed from another name
 		 * <p>
 		 */
 		RENAMED
 	}
 
 	/** New value the caller wants this ref to have. */
 	private ObjectId newValue;
 
 	/** Does this specification ask for forced updated (rewind/reset)? */
 	private boolean force;
 
 	/** Identity to record action as within the reflog. */
 	private PersonIdent refLogIdent;
 
 	/** Message the caller wants included in the reflog. */
 	private String refLogMessage;
 
 	/** Should the Result value be appended to {@link #refLogMessage}. */
 	private boolean refLogIncludeResult;
 
 	/** Old value of the ref, obtained after we lock it. */
 	private ObjectId oldValue;
 
 	/** If non-null, the value {@link #oldValue} must have to continue. */
 	private ObjectId expValue;
 
 	/** Result of the update operation. */
 	private Result result = Result.NOT_ATTEMPTED;
 
 	private final Ref ref;
 
 	/**
 	 * Is this RefUpdate detaching a symbolic ref?
 	 *
 	 * We need this info since this.ref will normally be peeled of in case of
 	 * detaching a symbolic ref (HEAD for example).
 	 *
 	 * Without this flag we cannot decide whether the ref has to be updated or
 	 * not in case when it was a symbolic ref and the newValue == oldValue.
 	 */
 	private boolean detachingSymbolicRef;
 
 	private boolean checkConflicting = true;
 
 	/**
 	 * Construct a new update operation for the reference.
 	 * <p>
 	 * {@code ref.getObjectId()} will be used to seed {@link #getOldObjectId()},
 	 * which callers can use as part of their own update logic.
 	 *
 	 * @param ref
 	 *            the reference that will be updated by this operation.
 	 */
 	protected RefUpdate(final Ref ref) {
 		this.ref = ref;
 		oldValue = ref.getObjectId();
 		refLogMessage = ""; //$NON-NLS-1$
 	}
 
 	/** @return the reference database this update modifies. */
 	protected abstract RefDatabase getRefDatabase();
 
 	/** @return the repository storing the database's objects. */
 	protected abstract Repository getRepository();
 
 	/**
 	 * Try to acquire the lock on the reference.
 	 * <p>
 	 * If the locking was successful the implementor must set the current
 	 * identity value by calling {@link #setOldObjectId(ObjectId)}.
 	 *
 	 * @param deref
 	 *            true if the lock should be taken against the leaf level
 	 *            reference; false if it should be taken exactly against the
 	 *            current reference.
 	 * @return true if the lock was acquired and the reference is likely
 	 *         protected from concurrent modification; false if it failed.
 	 * @throws IOException
 	 *             the lock couldn't be taken due to an unexpected storage
 	 *             failure, and not because of a concurrent update.
 	 */
 	protected abstract boolean tryLock(boolean deref) throws IOException;
 
 	/** Releases the lock taken by {@link #tryLock} if it succeeded. */
 	protected abstract void unlock();
 
 	/**
 	 * @param desiredResult
 	 * @return {@code result}
 	 * @throws IOException
 	 */
 	protected abstract Result doUpdate(Result desiredResult) throws IOException;
 
 	/**
 	 * @param desiredResult
 	 * @return {@code result}
 	 * @throws IOException
 	 */
 	protected abstract Result doDelete(Result desiredResult) throws IOException;
 
 	/**
 	 * @param target
 	 * @return {@link Result#NEW} on success.
 	 * @throws IOException
 	 */
 	protected abstract Result doLink(String target) throws IOException;
 
 	/**
 	 * Get the name of the ref this update will operate on.
 	 *
 	 * @return name of underlying ref.
 	 */
 	public String getName() {
 		return getRef().getName();
 	}
 
 	/** @return the reference this update will create or modify. */
 	public Ref getRef() {
 		return ref;
 	}
 
 	/**
 	 * Get the new value the ref will be (or was) updated to.
 	 *
 	 * @return new value. Null if the caller has not configured it.
 	 */
 	public ObjectId getNewObjectId() {
 		return newValue;
 	}
 
 	/**
 	 * Tells this RefUpdate that it is actually detaching a symbolic ref.
 	 */
 	public void setDetachingSymbolicRef() {
 		detachingSymbolicRef = true;
 	}
 
 	/**
 	 * Set the new value the ref will update to.
 	 *
 	 * @param id
 	 *            the new value.
 	 */
 	public void setNewObjectId(final AnyObjectId id) {
 		newValue = id.copy();
 	}
 
 	/**
 	 * @return the expected value of the ref after the lock is taken, but before
 	 *         update occurs. Null to avoid the compare and swap test. Use
 	 *         {@link ObjectId#zeroId()} to indicate expectation of a
 	 *         non-existant ref.
 	 */
 	public ObjectId getExpectedOldObjectId() {
 		return expValue;
 	}
 
 	/**
 	 * @param id
 	 *            the expected value of the ref after the lock is taken, but
 	 *            before update occurs. Null to avoid the compare and swap test.
 	 *            Use {@link ObjectId#zeroId()} to indicate expectation of a
 	 *            non-existant ref.
 	 */
 	public void setExpectedOldObjectId(final AnyObjectId id) {
 		expValue = id != null ? id.toObjectId() : null;
 	}
 
 	/**
 	 * Check if this update wants to forcefully change the ref.
 	 *
 	 * @return true if this update should ignore merge tests.
 	 */
 	public boolean isForceUpdate() {
 		return force;
 	}
 
 	/**
 	 * Set if this update wants to forcefully change the ref.
 	 *
 	 * @param b
 	 *            true if this update should ignore merge tests.
 	 */
 	public void setForceUpdate(final boolean b) {
 		force = b;
 	}
 
 	/** @return identity of the user making the change in the reflog. */
 	public PersonIdent getRefLogIdent() {
 		return refLogIdent;
 	}
 
 	/**
 	 * Set the identity of the user appearing in the reflog.
 	 * <p>
 	 * The timestamp portion of the identity is ignored. A new identity with the
 	 * current timestamp will be created automatically when the update occurs
 	 * and the log record is written.
 	 *
 	 * @param pi
 	 *            identity of the user. If null the identity will be
 	 *            automatically determined based on the repository
 	 *            configuration.
 	 */
 	public void setRefLogIdent(final PersonIdent pi) {
 		refLogIdent = pi;
 	}
 
 	/**
 	 * Get the message to include in the reflog.
 	 *
 	 * @return message the caller wants to include in the reflog; null if the
 	 *         update should not be logged.
 	 */
 	public String getRefLogMessage() {
 		return refLogMessage;
 	}
 
 	/** @return {@code true} if the ref log message should show the result. */
 	protected boolean isRefLogIncludingResult() {
 		return refLogIncludeResult;
 	}
 
 	/**
 	 * Set the message to include in the reflog.
 	 *
 	 * @param msg
 	 *            the message to describe this change. It may be null if
 	 *            appendStatus is null in order not to append to the reflog
 	 * @param appendStatus
 	 *            true if the status of the ref change (fast-forward or
 	 *            forced-update) should be appended to the user supplied
 	 *            message.
 	 */
 	public void setRefLogMessage(final String msg, final boolean appendStatus) {
 		if (msg == null && !appendStatus)
 			disableRefLog();
 		else if (msg == null && appendStatus) {
 			refLogMessage = ""; //$NON-NLS-1$
 			refLogIncludeResult = true;
 		} else {
 			refLogMessage = msg;
 			refLogIncludeResult = appendStatus;
 		}
 	}
 
 	/** Don't record this update in the ref's associated reflog. */
 	public void disableRefLog() {
 		refLogMessage = null;
 		refLogIncludeResult = false;
 	}
 
 	/**
 	 * The old value of the ref, prior to the update being attempted.
 	 * <p>
 	 * This value may differ before and after the update method. Initially it is
 	 * populated with the value of the ref before the lock is taken, but the old
 	 * value may change if someone else modified the ref between the time we
 	 * last read it and when the ref was locked for update.
 	 *
 	 * @return the value of the ref prior to the update being attempted; null if
 	 *         the updated has not been attempted yet.
 	 */
 	public ObjectId getOldObjectId() {
 		return oldValue;
 	}
 
 	/**
 	 * Set the old value of the ref.
 	 *
 	 * @param old
 	 *            the old value.
 	 */
 	protected void setOldObjectId(ObjectId old) {
 		oldValue = old;
 	}
 
 	/**
 	 * Get the status of this update.
 	 * <p>
 	 * The same value that was previously returned from an update method.
 	 *
 	 * @return the status of the update.
 	 */
 	public Result getResult() {
 		return result;
 	}
 
 	private void requireCanDoUpdate() {
 		if (newValue == null)
 			throw new IllegalStateException(JGitText.get().aNewObjectIdIsRequired);
 	}
 
 	/**
 	 * Force the ref to take the new value.
 	 * <p>
 	 * This is just a convenient helper for setting the force flag, and as such
 	 * the merge test is performed.
 	 *
 	 * @return the result status of the update.
 	 * @throws IOException
 	 *             an unexpected IO error occurred while writing changes.
 	 */
 	public Result forceUpdate() throws IOException {
 		force = true;
 		return update();
 	}
 
 	/**
 	 * Gracefully update the ref to the new value.
 	 * <p>
 	 * Merge test will be performed according to {@link #isForceUpdate()}.
 	 * <p>
 	 * This is the same as:
 	 *
 	 * <pre>
 	 * return update(new RevWalk(getRepository()));
 	 * </pre>
 	 *
 	 * @return the result status of the update.
 	 * @throws IOException
 	 *             an unexpected IO error occurred while writing changes.
 	 */
 	public Result update() throws IOException {
 		try (RevWalk rw = new RevWalk(getRepository())) {
 			return update(rw);
 		}
 	}
 
 	/**
 	 * Gracefully update the ref to the new value.
 	 * <p>
 	 * Merge test will be performed according to {@link #isForceUpdate()}.
 	 *
 	 * @param walk
 	 *            a RevWalk instance this update command can borrow to perform
 	 *            the merge test. The walk will be reset to perform the test.
 	 * @return the result status of the update.
 	 * @throws IOException
 	 *             an unexpected IO error occurred while writing changes.
 	 */
 	public Result update(final RevWalk walk) throws IOException {
 		requireCanDoUpdate();
 		try {
 			return result = updateImpl(walk, new Store() {
 				@Override
 				Result execute(Result status) throws IOException {
 					if (status == Result.NO_CHANGE)
 						return status;
 					return doUpdate(status);
 				}
 			});
 		} catch (IOException x) {
 			result = Result.IO_FAILURE;
 			throw x;
 		}
 	}
 
 	/**
 	 * Delete the ref.
 	 * <p>
 	 * This is the same as:
 	 *
 	 * <pre>
 	 * return delete(new RevWalk(getRepository()));
 	 * </pre>
 	 *
 	 * @return the result status of the delete.
 	 * @throws IOException
 	 */
 	public Result delete() throws IOException {
 		try (RevWalk rw = new RevWalk(getRepository())) {
 			return delete(rw);
 		}
 	}
 
 	/**
 	 * Delete the ref.
 	 *
 	 * @param walk
 	 *            a RevWalk instance this delete command can borrow to perform
 	 *            the merge test. The walk will be reset to perform the test.
 	 * @return the result status of the delete.
 	 * @throws IOException
 	 */
 	public Result delete(final RevWalk walk) throws IOException {
 		final String myName = getRef().getLeaf().getName();
 		if (myName.startsWith(Constants.R_HEADS)) {
 			Ref head = getRefDatabase().getRef(Constants.HEAD);
 			while (head != null && head.isSymbolic()) {
 				head = head.getTarget();
 				if (myName.equals(head.getName()))
 					return result = Result.REJECTED_CURRENT_BRANCH;
 			}
 		}
 
 		try {
 			return result = updateImpl(walk, new Store() {
 				@Override
 				Result execute(Result status) throws IOException {
 					return doDelete(status);
 				}
 			});
 		} catch (IOException x) {
 			result = Result.IO_FAILURE;
 			throw x;
 		}
 	}
 
 	/**
 	 * Replace this reference with a symbolic reference to another reference.
 	 * <p>
 	 * This exact reference (not its traversed leaf) is replaced with a symbolic
 	 * reference to the requested name.
 	 *
 	 * @param target
 	 *            name of the new target for this reference. The new target name
 	 *            must be absolute, so it must begin with {@code refs/}.
 	 * @return {@link Result#NEW} or {@link Result#FORCED} on success.
 	 * @throws IOException
 	 */
 	public Result link(String target) throws IOException {
 		if (!target.startsWith(Constants.R_REFS))
 			throw new IllegalArgumentException(MessageFormat.format(JGitText.get().illegalArgumentNotA, Constants.R_REFS));
 		if (checkConflicting && getRefDatabase().isNameConflicting(getName()))
 			return Result.LOCK_FAILURE;
 		try {
 			if (!tryLock(false))
 				return Result.LOCK_FAILURE;
 
 			final Ref old = getRefDatabase().getRef(getName());
 			if (old != null && old.isSymbolic()) {
 				final Ref dst = old.getTarget();
 				if (target.equals(dst.getName()))
 					return result = Result.NO_CHANGE;
 			}
 
 			if (old != null && old.getObjectId() != null)
 				setOldObjectId(old.getObjectId());
 
 			final Ref dst = getRefDatabase().getRef(target);
 			if (dst != null && dst.getObjectId() != null)
 				setNewObjectId(dst.getObjectId());
 
 			return result = doLink(target);
 		} catch (IOException x) {
 			result = Result.IO_FAILURE;
 			throw x;
 		} finally {
 			unlock();
 		}
 	}
 
 	private Result updateImpl(final RevWalk walk, final Store store)
 			throws IOException {
 		RevObject newObj;
 		RevObject oldObj;
 
 		// don't make expensive conflict check if this is an existing Ref
 		if (oldValue == null && checkConflicting && getRefDatabase().isNameConflicting(getName()))
 			return Result.LOCK_FAILURE;
 		try {
 			if (!tryLock(true))
 				return Result.LOCK_FAILURE;
 			if (expValue != null) {
 				final ObjectId o;
 				o = oldValue != null ? oldValue : ObjectId.zeroId();
 				if (!AnyObjectId.equals(expValue, o))
 					return Result.LOCK_FAILURE;
 			}
 			if (oldValue == null)
 				return store.execute(Result.NEW);
 
 			newObj = safeParse(walk, newValue);
 			oldObj = safeParse(walk, oldValue);
 			if (newObj == oldObj && !detachingSymbolicRef)
 				return store.execute(Result.NO_CHANGE);
 
 			if (isForceUpdate())
 				return store.execute(Result.FORCED);
 
 			if (newObj instanceof RevCommit && oldObj instanceof RevCommit) {
 				if (walk.isMergedInto((RevCommit) oldObj, (RevCommit) newObj))
 					return store.execute(Result.FAST_FORWARD);
 			}
 
 			return Result.REJECTED;
 		} finally {
 			unlock();
 		}
 	}
 
 	/**
 	 * Enable/disable the check for conflicting ref names. By default conflicts
 	 * are checked explicitly.
 	 *
 	 * @param check
 	 * @since 3.0
 	 */
 	public void setCheckConflicting(boolean check) {
 		checkConflicting = check;
 	}
 
 	private static RevObject safeParse(final RevWalk rw, final AnyObjectId id)
 			throws IOException {
 		try {
 			return id != null ? rw.parseAny(id) : null;
 		} catch (MissingObjectException e) {
 			// We can expect some objects to be missing, like if we are
 			// trying to force a deletion of a branch and the object it
 			// points to has been pruned from the database due to freak
 			// corruption accidents (it happens with 'git new-work-dir').
 			//
 			return null;
 		}
 	}
 
 	/**
 	 * Handle the abstraction of storing a ref update. This is because both
 	 * updating and deleting of a ref have merge testing in common.
 	 */
 	private abstract class Store {
 		abstract Result execute(Result status) throws IOException;
 	}
 }