/// <summary>
/// Check if a position in a code point buffer is a grapheme cluster boundary
/// </summary>
/// <param name="codePoints">The code points</param>
/// <param name="position">The position to check</param>
/// <returns></returns>
public static bool IsBoundary(Slice <int> codePoints, int position)
{
if (codePoints.Length == 0)
{
return(false);
}
// Get the grapheme cluster class of the character on each side
var a = position <= 0 ? GraphemeClusterClass.SOT : UnicodeClasses.GraphemeClusterClass(codePoints[position - 1]);
var b = position < codePoints.Length ? UnicodeClasses.GraphemeClusterClass(codePoints[position]) : GraphemeClusterClass.EOT;
// Rule 11 - Special handling for ZWJ in extended pictograph
if (a == GraphemeClusterClass.ZWJ)
{
var i = position - 2;
while (i >= 0 && UnicodeClasses.GraphemeClusterClass(codePoints[i]) == GraphemeClusterClass.Extend)
{
i--;
}
if (i >= 0 && UnicodeClasses.GraphemeClusterClass(codePoints[i]) == GraphemeClusterClass.ExtPict)
{
a = GraphemeClusterClass.ExtPictZwg;
}
}
// Special handling for regional indicator
// Rule 12 and 13
if (a == GraphemeClusterClass.Regional_Indicator)
{
// Count how many
int count = 0;
for (int i = position - 1; i > 0; i--)
{
if (UnicodeClasses.GraphemeClusterClass(codePoints[i - 1]) != GraphemeClusterClass.Regional_Indicator)
{
break;
}
count++;
}
// If odd, switch from RI to Any
if ((count % 2) != 0)
{
a = GraphemeClusterClass.Any;
}
}
return(pairTable[(int)b][(int)a] != 0);
}