/// <summary>
/// Retreat to the start of the previous code point in the text, and return it (pre-decrement semantics). If the
/// index is not preceeded by a valid surrogate pair, the behavior is the same as <see cref="Previous()"/>. Otherwise
/// the iterator is decremented to the start of the surrogate pair, and the code point represented by the pair is
/// returned.
/// </summary>
/// <returns>The previous code point in the text, or <see cref="UForwardCharacterIterator.Done"/> if the new index is before the start of the text.</returns>
/// <stable>ICU 2.4</stable>
public virtual int PreviousCodePoint()
{
int ch1 = Previous();
if (UTF16.IsTrailSurrogate((char)ch1))
{
int ch2 = Previous();
if (UTF16.IsLeadSurrogate((char)ch2))
{
return(Character.ToCodePoint((char)ch2, (char)ch1));
}
else if (ch2 != Done)
{
// unmatched trail surrogate so back out
Next();
}
}
return(ch1);
}
