/*
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>,
    * Copyright (C) 2010, Christian Halstrick <christian.halstrick@sap.com>
    * Copyright (C) 2014, Konrad Kügler 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.revplot;
  
  import java.text.MessageFormat;
  import java.util.BitSet;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.TreeSet;
  
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.revwalk.RevCommitList;
  import org.eclipse.jgit.revwalk.RevWalk;
  
  /**
   * An ordered list of {@link org.eclipse.jgit.revplot.PlotCommit} subclasses.
   * <p>
   * Commits are allocated into lanes as they enter the list, based upon their
   * connections between descendant (child) commits and ancestor (parent) commits.
   * <p>
   * The source of the list must be a {@link org.eclipse.jgit.revplot.PlotWalk}
   * and {@link #fillTo(int)} must be used to populate the list.
   *
   * @param <L>
   *            type of lane used by the application.
   */
  public class PlotCommitList<L extends PlotLane> extends
  		RevCommitList<PlotCommit<L>> {
  	static final int MAX_LENGTH = 25;
  
  	private int positionsAllocated;
  
  	private final TreeSet<Integer> freePositions = new TreeSet<>();
  
  	private final HashSet<PlotLane> activeLanes = new HashSet<>(32);
  
  	/** number of (child) commits on a lane */
  	private final HashMap<PlotLane, Integer> laneLength = new HashMap<>(
  			32);
  
  	/** {@inheritDoc} */
  	@Override
  	public void clear() {
  		super.clear();
  		positionsAllocated = 0;
  		freePositions.clear();
  		activeLanes.clear();
  		laneLength.clear();
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public void source(RevWalk w) {
  		if (!(w instanceof PlotWalk))
  			throw new ClassCastException(MessageFormat.format(JGitText.get().classCastNotA, PlotWalk.class.getName()));
  		super.source(w);
  	}
  
  	/**
  	 * Find the set of lanes passing through a commit's row.
  	 * <p>
  	 * Lanes passing through a commit are lanes that the commit is not directly
  	 * on, but that need to travel through this commit to connect a descendant
  	 * (child) commit to an ancestor (parent) commit. Typically these lanes will
  	 * be drawn as lines in the passed commit's box, and the passed commit won't
  	 * appear to be connected to those lines.
  	 * <p>
  	 * This method modifies the passed collection by adding the lanes in any
  	 * order.
  	 *
  	 * @param currCommit
  	 *            the commit the caller needs to get the lanes from.
  	 * @param result
  	 *            collection to add the passing lanes into.
  	 */
  	@SuppressWarnings("unchecked")
  	public void findPassingThrough(final PlotCommit<L> currCommit,
  			final Collection<L> result) {
  		for (PlotLane p : currCommit.passingLanes)
  			result.add((L) p);
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	protected void enter(int index, PlotCommit<L> currCommit) {
  		setupChildren(currCommit);
  
  		final int nChildren = currCommit.getChildCount();
 		if (nChildren == 0) {
 			currCommit.lane = nextFreeLane();
 		} else if (nChildren == 1
 				&& currCommit.children[0].getParentCount() < 2) {
 			// Only one child, child has only us as their parent.
 			// Stay in the same lane as the child.
 
 			@SuppressWarnings("unchecked")
 			final PlotCommit<L> c = currCommit.children[0];
 			currCommit.lane = c.lane;
 			Integer len = laneLength.get(currCommit.lane);
 			len = len != null ? Integer.valueOf(len.intValue() + 1)
 					: Integer.valueOf(0);
 			laneLength.put(currCommit.lane, len);
 		} else {
 			// More than one child, or our child is a merge.
 
 			// We look for the child lane the current commit should continue.
 			// Candidate lanes for this are those with children, that have the
 			// current commit as their first parent.
 			// There can be multiple candidate lanes. In that case the longest
 			// lane is chosen, as this is usually the lane representing the
 			// branch the commit actually was made on.
 
 			// When there are no candidate lanes (i.e. the current commit has
 			// only children whose non-first parent it is) we place the current
 			// commit on a new lane.
 
 			// The lane the current commit will be placed on:
 			PlotLane reservedLane = null;
 			PlotCommit childOnReservedLane = null;
 			int lengthOfReservedLane = -1;
 
 			for (int i = 0; i < nChildren; i++) {
 				@SuppressWarnings("unchecked")
 				final PlotCommit<L> c = currCommit.children[i];
 				if (c.getParent(0) == currCommit) {
 					Integer len = laneLength.get(c.lane);
 					// we may be the first parent for multiple lines of
 					// development, try to continue the longest one
 					if (len.intValue() > lengthOfReservedLane) {
 						reservedLane = c.lane;
 						childOnReservedLane = c;
 						lengthOfReservedLane = len.intValue();
 					}
 				}
 			}
 
 			if (reservedLane != null) {
 				currCommit.lane = reservedLane;
 				laneLength.put(reservedLane,
 						Integer.valueOf(lengthOfReservedLane + 1));
 				handleBlockedLanes(index, currCommit, childOnReservedLane);
 			} else {
 				currCommit.lane = nextFreeLane();
 				handleBlockedLanes(index, currCommit, null);
 			}
 
 			// close lanes of children, if there are no first parents that might
 			// want to continue the child lanes
 			for (int i = 0; i < nChildren; i++) {
 				final PlotCommit c = currCommit.children[i];
 				PlotCommit firstParent = (PlotCommit) c.getParent(0);
 				if (firstParent.lane != null && firstParent.lane != c.lane)
 					closeLane(c.lane);
 			}
 		}
 
 		continueActiveLanes(currCommit);
 		if (currCommit.getParentCount() == 0)
 			closeLane(currCommit.lane);
 	}
 
 	private void continueActiveLanes(PlotCommit currCommit) {
 		for (PlotLane lane : activeLanes)
 			if (lane != currCommit.lane)
 				currCommit.addPassingLane(lane);
 	}
 
 	/**
 	 * Sets up fork and merge information in the involved PlotCommits.
 	 * Recognizes and handles blockades that involve forking or merging arcs.
 	 *
 	 * @param index
 	 *            the index of <code>currCommit</code> in the list
 	 * @param currCommit
 	 * @param childOnLane
 	 *            the direct child on the same lane as <code>currCommit</code>,
 	 *            may be null if <code>currCommit</code> is the first commit on
 	 *            the lane
 	 */
 	private void handleBlockedLanes(final int index, final PlotCommit currCommit,
 			final PlotCommit childOnLane) {
 		for (PlotCommit child : currCommit.children) {
 			if (child == childOnLane)
 				continue; // simple continuations of lanes are handled by
 							// continueActiveLanes() calls in enter()
 
 			// Is the child a merge or is it forking off?
 			boolean childIsMerge = child.getParent(0) != currCommit;
 			if (childIsMerge) {
 				PlotLane laneToUse = currCommit.lane;
 				laneToUse = handleMerge(index, currCommit, childOnLane, child,
 						laneToUse);
 				child.addMergingLane(laneToUse);
 			} else {
 				// We want to draw a forking arc in the child's lane.
 				// As an active lane, the child lane already continues
 				// (unblocked) up to this commit, we only need to mark it as
 				// forking off from the current commit.
 				PlotLane laneToUse = child.lane;
 				currCommit.addForkingOffLane(laneToUse);
 			}
 		}
 	}
 
 	// Handles the case where currCommit is a non-first parent of the child
 	private PlotLane handleMerge(final int index, final PlotCommit currCommit,
 			final PlotCommit./../org/eclipse/jgit/revplot/PlotCommit.html#PlotCommit">PlotCommit childOnLane, PlotCommit child, PlotLane laneToUse) {
 
 		// find all blocked positions between currCommit and this child
 
 		int childIndex = index; // useless initialization, should
 								// always be set in the loop below
 		BitSet blockedPositions = new BitSet();
 		for (int r = index - 1; r >= 0; r--) {
 			final PlotCommit rObj = get(r);
 			if (rObj == child) {
 				childIndex = r;
 				break;
 			}
 			addBlockedPosition(blockedPositions, rObj);
 		}
 
 		// handle blockades
 
 		if (blockedPositions.get(laneToUse.getPosition())) {
 			// We want to draw a merging arc in our lane to the child,
 			// which is on another lane, but our lane is blocked.
 
 			// Check if childOnLane is beetween commit and the child we
 			// are currently processing
 			boolean needDetour = false;
 			if (childOnLane != null) {
 				for (int r = index - 1; r > childIndex; r--) {
 					final PlotCommit rObj = get(r);
 					if (rObj == childOnLane) {
 						needDetour = true;
 						break;
 					}
 				}
 			}
 
 			if (needDetour) {
 				// It is childOnLane which is blocking us. Repositioning
 				// our lane would not help, because this repositions the
 				// child too, keeping the blockade.
 				// Instead, we create a "detour lane" which gets us
 				// around the blockade. That lane has no commits on it.
 				laneToUse = nextFreeLane(blockedPositions);
 				currCommit.addForkingOffLane(laneToUse);
 				closeLane(laneToUse);
 			} else {
 				// The blockade is (only) due to other (already closed)
 				// lanes at the current lane's position. In this case we
 				// reposition the current lane.
 				// We are the first commit on this lane, because
 				// otherwise the child commit on this lane would have
 				// kept other lanes from blocking us. Since we are the
 				// first commit, we can freely reposition.
 				int newPos = getFreePosition(blockedPositions);
 				freePositions.add(Integer.valueOf(laneToUse
 						.getPosition()));
 				laneToUse.position = newPos;
 			}
 		}
 
 		// Actually connect currCommit to the merge child
 		drawLaneToChild(index, child, laneToUse);
 		return laneToUse;
 	}
 
 	/**
 	 * Connects the commit at commitIndex to the child, using the given lane.
 	 * All blockades on the lane must be resolved before calling this method.
 	 *
 	 * @param commitIndex
 	 * @param child
 	 * @param laneToContinue
 	 */
 	private void drawLaneToChild(final int commitIndex, PlotCommit child,
 			PlotLane laneToContinue) {
 		for (int r = commitIndex - 1; r >= 0; r--) {
 			final PlotCommit rObj = get(r);
 			if (rObj == child)
 				break;
 			if (rObj != null)
 				rObj.addPassingLane(laneToContinue);
 		}
 	}
 
 	private static void addBlockedPosition(BitSet blockedPositions,
 			final PlotCommit rObj) {
 		if (rObj != null) {
 			PlotLane lane = rObj.getLane();
 			// Positions may be blocked by a commit on a lane.
 			if (lane != null)
 				blockedPositions.set(lane.getPosition());
 			// Positions may also be blocked by forking off and merging lanes.
 			// We don't consider passing lanes, because every passing lane forks
 			// off and merges at it ends.
 			for (PlotLane l : rObj.forkingOffLanes)
 				blockedPositions.set(l.getPosition());
 			for (PlotLane l : rObj.mergingLanes)
 				blockedPositions.set(l.getPosition());
 		}
 	}
 
 	@SuppressWarnings("unchecked")
 	private void closeLane(PlotLane lane) {
 		if (activeLanes.remove(lane)) {
 			recycleLane((L) lane);
 			laneLength.remove(lane);
 			freePositions.add(Integer.valueOf(lane.getPosition()));
 		}
 	}
 
 	private void setupChildren(PlotCommit<L> currCommit) {
 		final int nParents = currCommit.getParentCount();
 		for (int i = 0; i < nParents; i++)
 			((PlotCommit) currCommit.getParent(i)).addChild(currCommit);
 	}
 
 	private PlotLane nextFreeLane() {
 		return nextFreeLane(null);
 	}
 
 	private PlotLane nextFreeLane(BitSet blockedPositions) {
 		final PlotLane p = createLane();
 		p.position = getFreePosition(blockedPositions);
 		activeLanes.add(p);
 		laneLength.put(p, Integer.valueOf(1));
 		return p;
 	}
 
 	/**
 	 * @param blockedPositions
 	 *            may be null
 	 * @return a free lane position
 	 */
 	private int getFreePosition(BitSet blockedPositions) {
 		if (freePositions.isEmpty())
 			return positionsAllocated++;
 
 		if (blockedPositions != null) {
 			for (Integer pos : freePositions)
 				if (!blockedPositions.get(pos.intValue())) {
 					freePositions.remove(pos);
 					return pos.intValue();
 				}
 			return positionsAllocated++;
 		}
 		final Integer min = freePositions.first();
 		freePositions.remove(min);
 		return min.intValue();
 	}
 
 	/**
 	 * Create a new {@link PlotLane} appropriate for this particular
 	 * {@link PlotCommitList}.
 	 *
 	 * @return a new {@link PlotLane} appropriate for this particular
 	 *         {@link PlotCommitList}.
 	 */
 	@SuppressWarnings("unchecked")
 	protected L createLane() {
 		return (L) new PlotLane();
 	}
 
 	/**
 	 * Return colors and other reusable information to the plotter when a lane
 	 * is no longer needed.
 	 *
 	 * @param lane
 	 *            a lane
 	 */
 	protected void recycleLane(L lane) {
 		// Nothing.
 	}
 }