/**
* Obtain a unique abbreviation (prefix) of an object SHA-1.
*
* <p>The returned abbreviation would expand back to the argument ObjectId when passed to {@link
* #resolve(AbbreviatedObjectId)}, assuming no new objects are added to this repository between
* calls.
*
* <p>The default implementation of this method abbreviates the id to the minimum length, then
* resolves it to see if there are multiple results. When multiple results are found, the length
* is extended by 1 and resolve is tried again.
*
* @param objectId object identity that needs to be abbreviated.
* @param len minimum length of the abbreviated string. Must be in the range [2, {@value
* Constants#OBJECT_ID_STRING_LENGTH}].
* @return SHA-1 abbreviation. If no matching objects exist in the repository, the abbreviation
* will match the minimum length.
* @throws IOException the object store cannot be read.
*/
public AbbreviatedObjectId abbreviate(AnyObjectId objectId, int len) throws IOException {
if (len == Constants.OBJECT_ID_STRING_LENGTH) return AbbreviatedObjectId.fromObjectId(objectId);
AbbreviatedObjectId abbrev = objectId.abbreviate(len);
Collection<ObjectId> matches = resolve(abbrev);
while (1 < matches.size() && len < Constants.OBJECT_ID_STRING_LENGTH) {
abbrev = objectId.abbreviate(++len);
List<ObjectId> n = new ArrayList<ObjectId>(8);
for (ObjectId candidate : matches) {
if (abbrev.prefixCompare(candidate) == 0) n.add(candidate);
}
if (1 < n.size()) matches = n;
else matches = resolve(abbrev);
}
return abbrev;
}
/**
* Tests if this ObjectId starts with the given abbreviation.
*
* @param abbr the abbreviation.
* @return true if this ObjectId begins with the abbreviation; else false.
*/
public boolean startsWith(final AbbreviatedObjectId abbr) {
return abbr.prefixCompare(this) == 0;
}
