/**
* Creates a <code>TagFilter</code> from the given {@link Collection} of tags and {@link
* FilteringStrategy} using the following rules:
*
* <ul>
* <li>If the {@link FilteringStrategy} is <code>null</code>, the {@link
* FilteringStrategy#getDefault() default} is used instead.
* <li>If the given {@link Collection} of tags is non-<code>null</code>, then a cleansed {@link
* Collection} of unique tags is created by only adding tags which are non-empty after being
* {@link Tag#cleanse(String) cleansed}.
* <li>If the {@link FilteringStrategy} is {@link FilteringStrategy#UNTAGGED}, then the given
* {@link Collection} of <code>tags</code> is ignored and a <code>TagFilter</code> is
* created with an empty {@link Collection} of tags.
* <li>If the {@link FilteringStrategy} is <i>not</i> {@link FilteringStrategy#UNTAGGED}, but
* the given cleansed {@link Collection} of <code>tags</code> is <code>null</code> or empty,
* then this method returns <code>null</code>.
* <li>If the {@link FilteringStrategy} is <i>not</i> {@link FilteringStrategy#UNTAGGED}, and
* the given {@link Collection} of <code>tags</code> is non-<code>null</code> and non-empty,
* then this method creates a <code>TagFilter</code> using the given unique, cleansed <code>
* tags</code> and {@link FilteringStrategy}.
* </ul>
*/
@Nullable
public static TagFilter create(
@Nullable final Collection<String> tags,
@Nullable final FilteringStrategy requestedFilteringStrategy) {
// make sure the filtering strategy is non-null, choosing the default if necessary
final FilteringStrategy filteringStrategy =
requestedFilteringStrategy == null
? FilteringStrategy.getDefault()
: requestedFilteringStrategy;
if (FilteringStrategy.UNTAGGED.equals(filteringStrategy)) {
// filter for untagged items
return new TagFilter(null, FilteringStrategy.UNTAGGED);
} else {
if (tags != null) {
final Set<String> cleansedTags = new HashSet<String>();
for (final String tag : tags) {
final String cleansedTag = Tag.cleanse(tag);
if (cleansedTag.length() > 0) {
cleansedTags.add(cleansedTag);
}
}
if (!cleansedTags.isEmpty()) {
return new TagFilter(cleansedTags, filteringStrategy);
}
}
}
return null;
}