/*
    * Copyright (C) 2016, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.internal.ketch;
  
  import static org.eclipse.jgit.internal.ketch.Proposal.State.ABORTED;
  import static org.eclipse.jgit.internal.ketch.Proposal.State.EXECUTED;
  import static org.eclipse.jgit.internal.ketch.Proposal.State.NEW;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.storage.reftree.Command;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.transport.PushCertificate;
  import org.eclipse.jgit.transport.ReceiveCommand;
  import org.eclipse.jgit.util.time.ProposedTimestamp;
  
  /**
   * A proposal to be applied in a Ketch system.
   * <p>
   * Pushing to a Ketch leader results in the leader making a proposal. The
   * proposal includes the list of reference updates. The leader attempts to send
   * the proposal to a quorum of replicas by pushing the proposal to a "staging"
   * area under the {@code refs/txn/stage/} namespace. If the proposal succeeds
   * then the changes are durable and the leader can commit the proposal.
   * <p>
   * Proposals are executed by
   * {@link org.eclipse.jgit.internal.ketch.KetchLeader#queueProposal(Proposal)},
   * which runs them asynchronously in the background. Proposals are thread-safe
   * futures allowing callers to {@link #await()} for results or be notified by
   * callback using {@link #addListener(Runnable)}.
   */
  public class Proposal {
  	/** Current state of the proposal. */
  	public enum State {
  		/** Proposal has not yet been given to a {@link KetchLeader}. */
  		NEW(false),
  
  		/**
  		 * Proposal was validated and has entered the queue, but a round
  		 * containing this proposal has not started yet.
  		 */
  		QUEUED(false),
  
  		/** Round containing the proposal has begun and is in progress. */
  		RUNNING(false),
  
  		/**
  		 * Proposal was executed through a round. Individual results from
  		 * {@link Proposal#getCommands()}, {@link Command#getResult()} explain
  		 * the success or failure outcome.
  		 */
  		EXECUTED(true),
  
  		/** Proposal was aborted and did not reach consensus. */
  		ABORTED(true);
  
  		private final boolean done;
  
  		private State(boolean done) {
  			this.done = done;
  		}
  
  		/** @return true if this is a terminal state. */
  		public boolean isDone() {
  			return done;
  		}
  	}
  
  	private final List<Command> commands;
  	private PersonIdent author;
  	private String message;
  	private PushCertificate pushCert;
  
  	private List<ProposedTimestamp> timestamps;
  	private final List<Runnable> listeners = new CopyOnWriteArrayList<>();
  	private final AtomicReference<State> state = new AtomicReference<>(NEW);
  
 	/**
 	 * Create a proposal from a list of Ketch commands.
 	 *
 	 * @param cmds
 	 *            prepared list of commands.
 	 */
 	public Proposal(List<Command> cmds) {
 		commands = Collections.unmodifiableList(new ArrayList<>(cmds));
 	}
 
 	/**
 	 * Create a proposal from a collection of received commands.
 	 *
 	 * @param rw
 	 *            walker to assist in preparing commands.
 	 * @param cmds
 	 *            list of pending commands.
 	 * @throws org.eclipse.jgit.errors.MissingObjectException
 	 *             newId of a command is not found locally.
 	 * @throws java.io.IOException
 	 *             local objects cannot be accessed.
 	 */
 	public Proposal(RevWalk rw, Collection<ReceiveCommand> cmds)
 			throws MissingObjectException, IOException {
 		commands = asCommandList(rw, cmds);
 	}
 
 	private static List<Command> asCommandList(RevWalk rw,
 			Collection<ReceiveCommand> cmds)
 					throws MissingObjectException, IOException {
 		List<Command> commands = new ArrayList<>(cmds.size());
 		for (ReceiveCommand cmd : cmds) {
 			commands.add(new Command(rw, cmd));
 		}
 		return Collections.unmodifiableList(commands);
 	}
 
 	/**
 	 * Get commands from this proposal.
 	 *
 	 * @return commands from this proposal.
 	 */
 	public Collection<Command> getCommands() {
 		return commands;
 	}
 
 	/**
 	 * Get optional author of the proposal.
 	 *
 	 * @return optional author of the proposal.
 	 */
 	@Nullable
 	public PersonIdent getAuthor() {
 		return author;
 	}
 
 	/**
 	 * Set the author for the proposal.
 	 *
 	 * @param who
 	 *            optional identity of the author of the proposal.
 	 * @return {@code this}
 	 */
 	public Proposal setAuthor(@Nullable PersonIdent who) {
 		author = who;
 		return this;
 	}
 
 	/**
 	 * Get optional message for the commit log of the RefTree.
 	 *
 	 * @return optional message for the commit log of the RefTree.
 	 */
 	@Nullable
 	public String getMessage() {
 		return message;
 	}
 
 	/**
 	 * Set the message to appear in the commit log of the RefTree.
 	 *
 	 * @param msg
 	 *            message text for the commit.
 	 * @return {@code this}
 	 */
 	public Proposal setMessage(@Nullable String msg) {
 		message = msg != null && !msg.isEmpty() ? msg : null;
 		return this;
 	}
 
 	/**
 	 * Get optional certificate signing the references.
 	 *
 	 * @return optional certificate signing the references.
 	 */
 	@Nullable
 	public PushCertificate getPushCertificate() {
 		return pushCert;
 	}
 
 	/**
 	 * Set the push certificate signing the references.
 	 *
 	 * @param cert
 	 *            certificate, may be null.
 	 * @return {@code this}
 	 */
 	public Proposal setPushCertificate(@Nullable PushCertificate cert) {
 		pushCert = cert;
 		return this;
 	}
 
 	/**
 	 * Get timestamps that Ketch must block for.
 	 *
 	 * @return timestamps that Ketch must block for. These may have been used as
 	 *         commit times inside the objects involved in the proposal.
 	 */
 	public List<ProposedTimestamp> getProposedTimestamps() {
 		if (timestamps != null) {
 			return timestamps;
 		}
 		return Collections.emptyList();
 	}
 
 	/**
 	 * Request the proposal to wait for the affected timestamps to resolve.
 	 *
 	 * @param ts
 	 *            a {@link org.eclipse.jgit.util.time.ProposedTimestamp} object.
 	 * @return {@code this}.
 	 */
 	public Proposal addProposedTimestamp(ProposedTimestamp ts) {
 		if (timestamps == null) {
 			timestamps = new ArrayList<>(4);
 		}
 		timestamps.add(ts);
 		return this;
 	}
 
 	/**
 	 * Add a callback to be invoked when the proposal is done.
 	 * <p>
 	 * A proposal is done when it has entered either
 	 * {@link org.eclipse.jgit.internal.ketch.Proposal.State#EXECUTED} or
 	 * {@link org.eclipse.jgit.internal.ketch.Proposal.State#ABORTED} state. If
 	 * the proposal is already done {@code callback.run()} is immediately
 	 * invoked on the caller's thread.
 	 *
 	 * @param callback
 	 *            method to run after the proposal is done. The callback may be
 	 *            run on a Ketch system thread and should be completed quickly.
 	 */
 	public void addListener(Runnable callback) {
 		boolean runNow = false;
 		synchronized (state) {
 			if (state.get().isDone()) {
 				runNow = true;
 			} else {
 				listeners.add(callback);
 			}
 		}
 		if (runNow) {
 			callback.run();
 		}
 	}
 
 	/** Set command result as OK. */
 	void success() {
 		for (Command c : commands) {
 			if (c.getResult() == NOT_ATTEMPTED) {
 				c.setResult(OK);
 			}
 		}
 		notifyState(EXECUTED);
 	}
 
 	/** Mark commands as "transaction aborted". */
 	void abort() {
 		Command.abort(commands, null);
 		notifyState(ABORTED);
 	}
 
 	/**
 	 * Read the current state of the proposal.
 	 *
 	 * @return read the current state of the proposal.
 	 */
 	public State getState() {
 		return state.get();
 	}
 
 	/**
 	 * Whether the proposal was attempted
 	 *
 	 * @return {@code true} if the proposal was attempted. A true value does not
 	 *         mean consensus was reached, only that the proposal was considered
 	 *         and will not be making any more progress beyond its current
 	 *         state.
 	 */
 	public boolean isDone() {
 		return state.get().isDone();
 	}
 
 	/**
 	 * Wait for the proposal to be attempted and {@link #isDone()} to be true.
 	 *
 	 * @throws java.lang.InterruptedException
 	 *             caller was interrupted before proposal executed.
 	 */
 	public void await() throws InterruptedException {
 		synchronized (state) {
 			while (!state.get().isDone()) {
 				state.wait();
 			}
 		}
 	}
 
 	/**
 	 * Wait for the proposal to be attempted and {@link #isDone()} to be true.
 	 *
 	 * @param wait
 	 *            how long to wait.
 	 * @param unit
 	 *            unit describing the wait time.
 	 * @return true if the proposal is done; false if the method timed out.
 	 * @throws java.lang.InterruptedException
 	 *             caller was interrupted before proposal executed.
 	 */
 	public boolean await(long wait, TimeUnit unit) throws InterruptedException {
 		synchronized (state) {
 			if (state.get().isDone()) {
 				return true;
 			}
 			state.wait(unit.toMillis(wait));
 			return state.get().isDone();
 		}
 	}
 
 	/**
 	 * Wait for the proposal to exit a state.
 	 *
 	 * @param notIn
 	 *            state the proposal should not be in to return.
 	 * @param wait
 	 *            how long to wait.
 	 * @param unit
 	 *            unit describing the wait time.
 	 * @return true if the proposal exited the state; false on time out.
 	 * @throws java.lang.InterruptedException
 	 *             caller was interrupted before proposal executed.
 	 */
 	public boolean awaitStateChange(State notIn, long wait, TimeUnit unit)
 			throws InterruptedException {
 		synchronized (state) {
 			if (state.get() != notIn) {
 				return true;
 			}
 			state.wait(unit.toMillis(wait));
 			return state.get() != notIn;
 		}
 	}
 
 	void notifyState(State s) {
 		synchronized (state) {
 			state.set(s);
 			state.notifyAll();
 		}
 		if (s.isDone()) {
 			for (Runnable callback : listeners) {
 				callback.run();
 			}
 			listeners.clear();
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		StringBuilder s = new StringBuilder();
 		s.append("Ketch Proposal {\n"); //$NON-NLS-1$
 		s.append("  ").append(state.get()).append('\n'); //$NON-NLS-1$
 		if (author != null) {
 			s.append("  author ").append(author).append('\n'); //$NON-NLS-1$
 		}
 		if (message != null) {
 			s.append("  message ").append(message).append('\n'); //$NON-NLS-1$
 		}
 		for (Command c : commands) {
 			s.append("  "); //$NON-NLS-1$
 			format(s, c.getOldRef(), "CREATE"); //$NON-NLS-1$
 			s.append(' ');
 			format(s, c.getNewRef(), "DELETE"); //$NON-NLS-1$
 			s.append(' ').append(c.getRefName());
 			if (c.getResult() != ReceiveCommand.Result.NOT_ATTEMPTED) {
 				s.append(' ').append(c.getResult()); // $NON-NLS-1$
 			}
 			s.append('\n');
 		}
 		s.append('}');
 		return s.toString();
 	}
 
 	private static void format(StringBuilder s, @Nullable Ref r, String n) {
 		if (r == null) {
 			s.append(n);
 		} else if (r.isSymbolic()) {
 			s.append(r.getTarget().getName());
 		} else {
 			ObjectId id = r.getObjectId();
 			if (id != null) {
 				s.append(id.abbreviate(8).name());
 			}
 		}
 	}
 }