/*
    * Copyright (C) 2008-2009, Google Inc.
    * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> 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.revwalk;
  
  import java.io.IOException;
  import java.text.MessageFormat;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.revwalk.filter.AndRevFilter;
  import org.eclipse.jgit.revwalk.filter.RevFilter;
  import org.eclipse.jgit.treewalk.filter.TreeFilter;
  
  /**
   * Initial RevWalk generator that bootstraps a new walk.
   * <p>
   * Initially RevWalk starts with this generator as its chosen implementation.
   * The first request for a RevCommit from the RevWalk instance calls to our
   * {@link #next()} method, and we replace ourselves with the best Generator
   * implementation available based upon the current RevWalk configuration.
   */
  class StartGenerator extends Generator {
  	private final RevWalk walker;
  
  	StartGenerator(RevWalk w) {
  		super(w.isFirstParent());
  		walker = w;
  	}
  
  	@Override
  	int outputType() {
  		return 0;
  	}
  
  	@Override
  	RevCommit next() throws MissingObjectException,
  			IncorrectObjectTypeException, IOException {
  		Generator g;
  
  		final RevWalk w = walker;
  		RevFilter rf = w.getRevFilter();
  		final TreeFilter tf = w.getTreeFilter();
  		AbstractRevQueue q = walker.queue;
  
  		if (rf == RevFilter.MERGE_BASE) {
  			// Computing for merge bases is a special case and does not
  			// use the bulk of the generator pipeline.
  			//
  			if (tf != TreeFilter.ALL) {
  				throw new IllegalStateException(MessageFormat.format(
  						JGitText.get().cannotCombineTreeFilterWithRevFilter, tf, rf));
  			}
  			if (w.isFirstParent()) {
  				throw new IllegalStateException(
  						JGitText.get().cannotFindMergeBaseUsingFirstParent);
  			}
  
  			final MergeBaseGeneratorerator.html#MergeBaseGenerator">MergeBaseGenerator mbg = new MergeBaseGenerator(w);
  			walker.pending = mbg;
  			walker.queue = AbstractRevQueue.EMPTY_QUEUE;
  			mbg.init(q);
  			return mbg.next();
  		}
  
  		final boolean uninteresting = q.anybodyHasFlag(RevWalk.UNINTERESTING);
  		boolean boundary = walker.hasRevSort(RevSort.BOUNDARY);
  
  		if (!boundary && walker instanceof ObjectWalk) {
  			// The object walker requires boundary support to color
  			// trees and blobs at the boundary uninteresting so it
  			// does not produce those in the result.
  			//
  			boundary = true;
  		}
  		if (boundary && !uninteresting) {
  			// If we were not fed uninteresting commits we will never
  			// construct a boundary. There is no reason to include the
  			// extra overhead associated with that in our pipeline.
  			//
  			boundary = false;
  		}
  
  		final DateRevQueue pending;
  		int pendingOutputType = 0;
  		if (q instanceof DateRevQueue)
  			pending = (DateRevQueue)q;
  		else
  			pending = new DateRevQueue(q);
 		if (tf != TreeFilter.ALL) {
 			int rewriteFlag;
 			if (w.getRewriteParents()) {
 				pendingOutputType |= HAS_REWRITE | NEEDS_REWRITE;
 				rewriteFlag = RevWalk.REWRITE;
 			} else
 				rewriteFlag = 0;
 			rf = AndRevFilter.create(new TreeRevFilter(w, tf, rewriteFlag), rf);
 		}
 
 		walker.queue = q;
 
 		if (walker instanceof DepthWalk) {
 			DepthWalk dw = (DepthWalk) walker;
 			g = new DepthGenerator(dw, pending);
 		} else {
 			g = new PendingGenerator(w, pending, rf, pendingOutputType);
 
 			if (walker.hasRevSort(RevSort.BOUNDARY)) {
 				// Because the boundary generator may produce uninteresting
 				// commits we cannot allow the pending generator to dispose
 				// of them early.
 				//
 				((PendingGenerator) g).canDispose = false;
 			}
 		}
 
 		if ((g.outputType() & NEEDS_REWRITE) != 0) {
 			// Correction for an upstream NEEDS_REWRITE is to buffer
 			// fully and then apply a rewrite generator that can
 			// pull through the rewrite chain and produce a dense
 			// output graph.
 			//
 			g = new FIFORevQueue(g);
 			g = new RewriteGenerator(g);
 		}
 
 		if (walker.hasRevSort(RevSort.TOPO)
 				&& walker.hasRevSort(RevSort.TOPO_KEEP_BRANCH_TOGETHER)) {
 			throw new IllegalStateException(JGitText
 					.get().cannotCombineTopoSortWithTopoKeepBranchTogetherSort);
 		}
 
 		if (walker.hasRevSort(RevSort.TOPO)
 				&& (g.outputType() & SORT_TOPO) == 0) {
 			g = new TopoSortGenerator(g);
 		} else if (walker.hasRevSort(RevSort.TOPO_KEEP_BRANCH_TOGETHER)
 				&& (g.outputType() & SORT_TOPO) == 0) {
 			g = new TopoNonIntermixSortGenerator(g);
 		}
 		if (walker.hasRevSort(RevSort.REVERSE))
 			g = new LIFORevQueue(g);
 		if (boundary)
 			g = new BoundaryGenerator(w, g);
 		else if (uninteresting) {
 			// Try to protect ourselves from uninteresting commits producing
 			// due to clock skew in the commit time stamps. Delay such that
 			// we have a chance at coloring enough of the graph correctly,
 			// and then strip any UNINTERESTING nodes that may have leaked
 			// through early.
 			//
 			if (pending.peek() != null)
 				g = new DelayRevQueue(g);
 			g = new FixUninterestingGenerator(g);
 		}
 
 		w.pending = g;
 		return g.next();
 	}
 }