/**
* Returns the description of the {@code number}. This method distinguishes the case of an invalid
* prefix and a prefix for which the name is not available in the current language. If the
* description is not available in the current language an empty string is returned. If no
* description was found for the provided number, null is returned.
*
* @param number the phone number to look up
* @return the description of the number
*/
String lookup(long number) {
int numOfEntries = phonePrefixMapStorage.getNumOfEntries();
if (numOfEntries == 0) {
return null;
}
long phonePrefix = number;
int currentIndex = numOfEntries - 1;
SortedSet<Integer> currentSetOfLengths = phonePrefixMapStorage.getPossibleLengths();
while (currentSetOfLengths.size() > 0) {
Integer possibleLength = currentSetOfLengths.last();
String phonePrefixStr = String.valueOf(phonePrefix);
if (phonePrefixStr.length() > possibleLength) {
phonePrefix = Long.parseLong(phonePrefixStr.substring(0, possibleLength));
}
currentIndex = binarySearch(0, currentIndex, phonePrefix);
if (currentIndex < 0) {
return null;
}
int currentPrefix = phonePrefixMapStorage.getPrefix(currentIndex);
if (phonePrefix == currentPrefix) {
return phonePrefixMapStorage.getDescription(currentIndex);
}
currentSetOfLengths = currentSetOfLengths.headSet(possibleLength);
}
return null;
}
/**
* Does a binary search for {@code value} in the provided array from {@code start} to {@code end}
* (inclusive). Returns the position if {@code value} is found; otherwise, returns the position
* which has the largest value that is less than {@code value}. This means if {@code value} is the
* smallest, -1 will be returned.
*/
private int binarySearch(int start, int end, long value) {
int current = 0;
while (start <= end) {
current = (start + end) >>> 1;
int currentValue = phonePrefixMapStorage.getPrefix(current);
if (currentValue == value) {
return current;
} else if (currentValue > value) {
current--;
end = current;
} else {
start = current + 1;
}
}
return current;
}
