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    * 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
    *
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  package org.eclipse.jgit.util;
  
  import java.util.AbstractMap;
  import java.util.AbstractSet;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Set;
  
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.RefComparator;
  
  /**
   * Specialized Map to present a {@code RefDatabase} namespace.
   * <p>
   * Although not declared as a {@link java.util.SortedMap}, iterators from this
   * map's projections always return references in {@link RefComparator} ordering.
   * The map's internal representation is a sorted array of {@link Ref} objects,
   * which means lookup and replacement is O(log N), while insertion and removal
   * can be as expensive as O(N + log N) while the list expands or contracts.
   * Since this is not a general map implementation, all entries must be keyed by
   * the reference name.
   * <p>
   * This class is really intended as a helper for {@code RefDatabase}, which
   * needs to perform a merge-join of three sorted {@link RefList}s in order to
   * present the unified namespace of the packed-refs file, the loose refs/
   * directory tree, and the resolved form of any symbolic references.
   */
  public class RefMap extends AbstractMap<String, Ref> {
  	/**
  	 * Prefix denoting the reference subspace this map contains.
  	 * <p>
  	 * All reference names in this map must start with this prefix. If the
  	 * prefix is not the empty string, it must end with a '/'.
  	 */
  	private final String prefix;
  
  	/** Immutable collection of the packed references at construction time. */
  	private RefList<Ref> packed;
  
  	/**
  	 * Immutable collection of the loose references at construction time.
  	 * <p>
  	 * If an entry appears here and in {@link #packed}, this entry must take
  	 * precedence, as its more current. Symbolic references in this collection
  	 * are typically unresolved, so they only tell us who their target is, but
  	 * not the current value of the target.
  	 */
  	private RefList<Ref> loose;
  
  	/**
  	 * Immutable collection of resolved symbolic references.
  	 * <p>
  	 * This collection contains only the symbolic references we were able to
 	 * resolve at map construction time. Other loose references must be read
 	 * from {@link #loose}. Every entry in this list must be matched by an entry
 	 * in {@code loose}, otherwise it might be omitted by the map.
 	 */
 	private RefList<Ref> resolved;
 
 	private int size;
 
 	private boolean sizeIsValid;
 
 	private Set<Entry<String, Ref>> entrySet;
 
 	/** Construct an empty map with a small initial capacity. */
 	public RefMap() {
 		prefix = ""; //$NON-NLS-1$
 		packed = RefList.emptyList();
 		loose = RefList.emptyList();
 		resolved = RefList.emptyList();
 	}
 
 	/**
 	 * Construct a map to merge 3 collections together.
 	 *
 	 * @param prefix
 	 *            prefix used to slice the lists down. Only references whose
 	 *            names start with this prefix will appear to reside in the map.
 	 *            Must not be null, use {@code ""} (the empty string) to select
 	 *            all list items.
 	 * @param packed
 	 *            items from the packed reference list, this is the last list
 	 *            searched.
 	 * @param loose
 	 *            items from the loose reference list, this list overrides
 	 *            {@code packed} if a name appears in both.
 	 * @param resolved
 	 *            resolved symbolic references. This list overrides the prior
 	 *            list {@code loose}, if an item appears in both. Items in this
 	 *            list <b>must</b> also appear in {@code loose}.
 	 */
 	@SuppressWarnings("unchecked")
 	public RefMap(String prefix, RefList<? extends Ref> packed,
 			RefList<? extends Ref> loose, RefList<? extends Ref> resolved) {
 		this.prefix = prefix;
 		this.packed = (RefList<Ref>) packed;
 		this.loose = (RefList<Ref>) loose;
 		this.resolved = (RefList<Ref>) resolved;
 	}
 
 	@Override
 	public boolean containsKey(Object name) {
 		return get(name) != null;
 	}
 
 	@Override
 	public Ref get(Object key) {
 		String name = toRefName((String) key);
 		Ref ref = resolved.get(name);
 		if (ref == null)
 			ref = loose.get(name);
 		if (ref == null)
 			ref = packed.get(name);
 		return ref;
 	}
 
 	@Override
 	public Ref put(final String keyName, Ref value) {
 		String name = toRefName(keyName);
 
 		if (!name.equals(value.getName()))
 			throw new IllegalArgumentException();
 
 		if (!resolved.isEmpty()) {
 			// Collapse the resolved list into the loose list so we
 			// can discard it and stop joining the two together.
 			for (Ref ref : resolved)
 				loose = loose.put(ref);
 			resolved = RefList.emptyList();
 		}
 
 		int idx = loose.find(name);
 		if (0 <= idx) {
 			Ref prior = loose.get(name);
 			loose = loose.set(idx, value);
 			return prior;
 		} else {
 			Ref prior = get(keyName);
 			loose = loose.add(idx, value);
 			sizeIsValid = false;
 			return prior;
 		}
 	}
 
 	@Override
 	public Ref remove(Object key) {
 		String name = toRefName((String) key);
 		Ref res = null;
 		int idx;
 		if (0 <= (idx = packed.find(name))) {
 			res = packed.get(name);
 			packed = packed.remove(idx);
 			sizeIsValid = false;
 		}
 		if (0 <= (idx = loose.find(name))) {
 			res = loose.get(name);
 			loose = loose.remove(idx);
 			sizeIsValid = false;
 		}
 		if (0 <= (idx = resolved.find(name))) {
 			res = resolved.get(name);
 			resolved = resolved.remove(idx);
 			sizeIsValid = false;
 		}
 		return res;
 	}
 
 	@Override
 	public boolean isEmpty() {
 		return entrySet().isEmpty();
 	}
 
 	@Override
 	public Set<Entry<String, Ref>> entrySet() {
 		if (entrySet == null) {
 			entrySet = new AbstractSet<Entry<String, Ref>>() {
 				@Override
 				public Iterator<Entry<String, Ref>> iterator() {
 					return new SetIterator();
 				}
 
 				@Override
 				public int size() {
 					if (!sizeIsValid) {
 						size = 0;
 						Iterator<?> i = entrySet().iterator();
 						for (; i.hasNext(); i.next())
 							size++;
 						sizeIsValid = true;
 					}
 					return size;
 				}
 
 				@Override
 				public boolean isEmpty() {
 					if (sizeIsValid)
 						return 0 == size;
 					return !iterator().hasNext();
 				}
 
 				@Override
 				public void clear() {
 					packed = RefList.emptyList();
 					loose = RefList.emptyList();
 					resolved = RefList.emptyList();
 					size = 0;
 					sizeIsValid = true;
 				}
 			};
 		}
 		return entrySet;
 	}
 
 	@Override
 	public String toString() {
 		StringBuilder r = new StringBuilder();
 		boolean first = true;
 		r.append('[');
 		for (Ref ref : values()) {
 			if (first)
 				first = false;
 			else
 				r.append(", "); //$NON-NLS-1$
 			r.append(ref);
 		}
 		r.append(']');
 		return r.toString();
 	}
 
 	private String toRefName(String name) {
 		if (0 < prefix.length())
 			name = prefix + name;
 		return name;
 	}
 
 	private String toMapKey(Ref ref) {
 		String name = ref.getName();
 		if (0 < prefix.length())
 			name = name.substring(prefix.length());
 		return name;
 	}
 
 	private class SetIterator implements Iterator<Entry<String, Ref>> {
 		private int packedIdx;
 
 		private int looseIdx;
 
 		private int resolvedIdx;
 
 		private Entry<String, Ref> next;
 
 		SetIterator() {
 			if (0 < prefix.length()) {
 				packedIdx = -(packed.find(prefix) + 1);
 				looseIdx = -(loose.find(prefix) + 1);
 				resolvedIdx = -(resolved.find(prefix) + 1);
 			}
 		}
 
 		public boolean hasNext() {
 			if (next == null)
 				next = peek();
 			return next != null;
 		}
 
 		public Entry<String, Ref> next() {
 			if (hasNext()) {
 				Entry<String, Ref> r = next;
 				next = peek();
 				return r;
 			}
 			throw new NoSuchElementException();
 		}
 
 		public Entry<String, Ref> peek() {
 			if (packedIdx < packed.size() && looseIdx < loose.size()) {
 				Ref p = packed.get(packedIdx);
 				Ref l = loose.get(looseIdx);
 				int cmp = RefComparator.compareTo(p, l);
 				if (cmp < 0) {
 					packedIdx++;
 					return toEntry(p);
 				}
 
 				if (cmp == 0)
 					packedIdx++;
 				looseIdx++;
 				return toEntry(resolveLoose(l));
 			}
 
 			if (looseIdx < loose.size())
 				return toEntry(resolveLoose(loose.get(looseIdx++)));
 			if (packedIdx < packed.size())
 				return toEntry(packed.get(packedIdx++));
 			return null;
 		}
 
 		private Ref resolveLoose(final Ref l) {
 			if (resolvedIdx < resolved.size()) {
 				Ref r = resolved.get(resolvedIdx);
 				int cmp = RefComparator.compareTo(l, r);
 				if (cmp == 0) {
 					resolvedIdx++;
 					return r;
 				} else if (cmp > 0) {
 					// WTF, we have a symbolic entry but no match
 					// in the loose collection. That's an error.
 					throw new IllegalStateException();
 				}
 			}
 			return l;
 		}
 
 		private Ent toEntry(Ref p) {
 			if (p.getName().startsWith(prefix))
 				return new Ent(p);
 			packedIdx = packed.size();
 			looseIdx = loose.size();
 			resolvedIdx = resolved.size();
 			return null;
 		}
 
 		public void remove() {
 			throw new UnsupportedOperationException();
 		}
 	}
 
 	private class Ent implements Entry<String, Ref> {
 		private Ref ref;
 
 		Ent(Ref ref) {
 			this.ref = ref;
 		}
 
 		public String getKey() {
 			return toMapKey(ref);
 		}
 
 		public Ref getValue() {
 			return ref;
 		}
 
 		public Ref setValue(Ref value) {
 			Ref prior = put(getKey(), value);
 			ref = value;
 			return prior;
 		}
 
 		@Override
 		public int hashCode() {
 			return getKey().hashCode();
 		}
 
 		@Override
 		public boolean equals(Object obj) {
 			if (obj instanceof Map.Entry) {
 				final Object key = ((Map.Entry) obj).getKey();
 				final Object val = ((Map.Entry) obj).getValue();
 				if (key instanceof String && val instanceof Ref) {
 					final Ref r = (Ref) val;
 					if (r.getName().equals(ref.getName())) {
 						final ObjectId a = r.getObjectId();
 						final ObjectId b = ref.getObjectId();
 						if (a != null && b != null && AnyObjectId.equals(a, b))
 							return true;
 					}
 				}
 			}
 			return false;
 		}
 
 		@Override
 		public String toString() {
 			return ref.toString();
 		}
 	}
 }