/*
    * Copyright (C) 2008, Google Inc.
    * 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.dircache;
  
  import static org.eclipse.jgit.lib.FileMode.TYPE_TREE;
  import static org.eclipse.jgit.util.Paths.compareSameName;
  
  import java.io.IOException;
  
  import org.eclipse.jgit.errors.DirCacheNameConflictException;
  
  /**
   * Generic update/editing support for {@link DirCache}.
   * <p>
   * The different update strategies extend this class to provide their own unique
   * services to applications.
   */
  abstract class BaseDirCacheEditor {
  	/** The cache instance this editor updates during {@link #finish()}. */
  	protected DirCache cache;
  
  	/**
  	 * Entry table this builder will eventually replace into {@link #cache}.
  	 * <p>
  	 * Use {@link #fastAdd(DirCacheEntry)} or {@link #fastKeep(int, int)} to
  	 * make additions to this table. The table is automatically expanded if it
  	 * is too small for a new addition.
  	 * <p>
  	 * Typically the entries in here are sorted by their path names, just like
  	 * they are in the DirCache instance.
  	 */
  	protected DirCacheEntry[] entries;
  
  	/** Total number of valid entries in {@link #entries}. */
  	protected int entryCnt;
  
  	/**
  	 * Construct a new editor.
  	 *
  	 * @param dc
  	 *            the cache this editor will eventually update.
  	 * @param ecnt
  	 *            estimated number of entries the editor will have upon
  	 *            completion. This sizes the initial entry table.
  	 */
  	protected BaseDirCacheEditor(DirCache dc, int ecnt) {
  		cache = dc;
  		entries = new DirCacheEntry[ecnt];
  	}
  
  	/**
  	 * Get the {@code DirCache}
  	 *
  	 * @return the cache we will update on {@link #finish()}.
  	 */
  	public DirCache getDirCache() {
  		return cache;
  	}
  
  	/**
  	 * Append one entry into the resulting entry list.
  	 * <p>
  	 * The entry is placed at the end of the entry list. The caller is
  	 * responsible for making sure the final table is correctly sorted.
  	 * <p>
  	 * The {@link #entries} table is automatically expanded if there is
  	 * insufficient space for the new addition.
  	 *
  	 * @param newEntry
  	 *            the new entry to add.
  	 */
  	protected void fastAdd(DirCacheEntry newEntry) {
  		if (entries.length == entryCnt) {
  			final DirCacheEntryheEntry.html#DirCacheEntry">DirCacheEntry[] n = new DirCacheEntry[(entryCnt + 16) * 3 / 2];
  			System.arraycopy(entries, 0, n, 0, entryCnt);
  			entries = n;
  		}
  		entries[entryCnt++] = newEntry;
  	}
  
  	/**
  	 * Add a range of existing entries from the destination cache.
  	 * <p>
  	 * The entries are placed at the end of the entry list, preserving their
  	 * current order. The caller is responsible for making sure the final table
  	 * is correctly sorted.
  	 * <p>
  	 * This method copies from the destination cache, which has not yet been
  	 * updated with this editor's new table. So all offsets into the destination
  	 * cache are not affected by any updates that may be currently taking place
 	 * in this editor.
 	 * <p>
 	 * The {@link #entries} table is automatically expanded if there is
 	 * insufficient space for the new additions.
 	 *
 	 * @param pos
 	 *            first entry to copy from the destination cache.
 	 * @param cnt
 	 *            number of entries to copy.
 	 */
 	protected void fastKeep(int pos, int cnt) {
 		if (entryCnt + cnt > entries.length) {
 			final int m1 = (entryCnt + 16) * 3 / 2;
 			final int m2 = entryCnt + cnt;
 			final DirCacheEntryheEntry.html#DirCacheEntry">DirCacheEntry[] n = new DirCacheEntry[Math.max(m1, m2)];
 			System.arraycopy(entries, 0, n, 0, entryCnt);
 			entries = n;
 		}
 
 		cache.toArray(pos, entries, entryCnt, cnt);
 		entryCnt += cnt;
 	}
 
 	/**
 	 * Finish this builder and update the destination
 	 * {@link org.eclipse.jgit.dircache.DirCache}.
 	 * <p>
 	 * When this method completes this builder instance is no longer usable by
 	 * the calling application. A new builder must be created to make additional
 	 * changes to the index entries.
 	 * <p>
 	 * After completion the DirCache returned by {@link #getDirCache()} will
 	 * contain all modifications.
 	 * <p>
 	 * <i>Note to implementors:</i> Make sure {@link #entries} is fully sorted
 	 * then invoke {@link #replace()} to update the DirCache with the new table.
 	 */
 	public abstract void finish();
 
 	/**
 	 * Update the DirCache with the contents of {@link #entries}.
 	 * <p>
 	 * This method should be invoked only during an implementation of
 	 * {@link #finish()}, and only after {@link #entries} is sorted.
 	 */
 	protected void replace() {
 		checkNameConflicts();
 		if (entryCnt < entries.length / 2) {
 			final DirCacheEntryheEntry.html#DirCacheEntry">DirCacheEntry[] n = new DirCacheEntry[entryCnt];
 			System.arraycopy(entries, 0, n, 0, entryCnt);
 			entries = n;
 		}
 		cache.replace(entries, entryCnt);
 	}
 
 	private void checkNameConflicts() {
 		int end = entryCnt - 1;
 		for (int eIdx = 0; eIdx < end; eIdx++) {
 			DirCacheEntry e = entries[eIdx];
 			if (e.getStage() != 0) {
 				continue;
 			}
 
 			byte[] ePath = e.path;
 			int prefixLen = lastSlash(ePath) + 1;
 
 			for (int nIdx = eIdx + 1; nIdx < entryCnt; nIdx++) {
 				DirCacheEntry n = entries[nIdx];
 				if (n.getStage() != 0) {
 					continue;
 				}
 
 				byte[] nPath = n.path;
 				if (!startsWith(ePath, nPath, prefixLen)) {
 					// Different prefix; this entry is in another directory.
 					break;
 				}
 
 				int s = nextSlash(nPath, prefixLen);
 				int m = s < nPath.length ? TYPE_TREE : n.getRawMode();
 				int cmp = compareSameName(
 						ePath, prefixLen, ePath.length,
 						nPath, prefixLen, s, m);
 				if (cmp < 0) {
 					break;
 				} else if (cmp == 0) {
 					throw new DirCacheNameConflictException(
 							e.getPathString(),
 							n.getPathString());
 				}
 			}
 		}
 	}
 
 	private static int lastSlash(byte[] path) {
 		for (int i = path.length - 1; i >= 0; i--) {
 			if (path[i] == '/') {
 				return i;
 			}
 		}
 		return -1;
 	}
 
 	private static int nextSlash(byte[] b, int p) {
 		final int n = b.length;
 		for (; p < n; p++) {
 			if (b[p] == '/') {
 				return p;
 			}
 		}
 		return n;
 	}
 
 	private static boolean startsWith(byte[] a, byte[] b, int n) {
 		if (b.length < n) {
 			return false;
 		}
 		for (n--; n >= 0; n--) {
 			if (a[n] != b[n]) {
 				return false;
 			}
 		}
 		return true;
 	}
 
 	/**
 	 * Finish, write, commit this change, and release the index lock.
 	 * <p>
 	 * If this method fails (returns false) the lock is still released.
 	 * <p>
 	 * This is a utility method for applications as the finish-write-commit
 	 * pattern is very common after using a builder to update entries.
 	 *
 	 * @return true if the commit was successful and the file contains the new
 	 *         data; false if the commit failed and the file remains with the
 	 *         old data.
 	 * @throws java.lang.IllegalStateException
 	 *             the lock is not held.
 	 * @throws java.io.IOException
 	 *             the output file could not be created. The caller no longer
 	 *             holds the lock.
 	 */
 	public boolean commit() throws IOException {
 		finish();
 		cache.write();
 		return cache.commit();
 	}
 }