using System;
using System.Collections.Generic;
using System.Text;
using Topten.RichTextKit.Utils;

namespace Topten.RichTextKit
{
    static class GraphemeClusterAlgorithm
    {
        /// <summary>
        /// Given a sequence of code points, return its grapheme cluster boundaries
        /// </summary>
        /// <param name="codePoints">The code points</param>
        /// <returns>An enumerable of grapheme cluster boundaries</returns>
        public static IEnumerable<int> GetBoundaries(Slice<int> codePoints)
        {
            for (int i = 0; i <= codePoints.Length; i++)
            {
                if (IsBoundary(codePoints, i))
                    yield return i;
            }
        }

        /// <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;
        }

        static byte[][] pairTable= new byte[][]
        {
//                          Any   CR   LF   Control   Extend   Regional_Indicator   Prepend   SpacingMark   L   V   T   LV   LVT   ExtPict   ZWJ   SOT   EOT   ExtPictZwg
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // Any   
            new byte[] {    1,    1,   1,   1,        1,       1,                   1,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // CR   
            new byte[] {    1,    0,   1,   1,        1,       1,                   1,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // LF   
            new byte[] {    1,    1,   1,   1,        1,       1,                   1,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // Control   
            new byte[] {    0,    1,   1,   1,        0,       0,                   0,        0,            0,  0,  0,  0,   0,    0,        0,    1,    1,    0,     },    // Extend   
            new byte[] {    1,    1,   1,   1,        1,       0,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // Regional_Indicator   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // Prepend   
            new byte[] {    0,    1,   1,   1,        0,       0,                   0,        0,            0,  0,  0,  0,   0,    0,        0,    1,    1,    0,     },    // SpacingMark   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            0,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // L   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            0,  0,  1,  0,   1,    1,        1,    1,    1,    1,     },    // V   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  0,  0,  0,   0,    1,        1,    1,    1,    1,     },    // T   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            0,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // LV   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            0,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // LVT   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    0,     },    // ExtPict   
            new byte[] {    0,    1,   1,   1,        0,       0,                   0,        0,            0,  0,  0,  0,   0,    0,        0,    1,    1,    0,     },    // ZWJ   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // SOT   
            new byte[] {    1,    1,   1,   1,        1,       1,                   1,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // EOT   
            new byte[] {    1,    1,   1,   1,        1,       1,                   0,        1,            1,  1,  1,  1,   1,    1,        1,    1,    1,    1,     },    // ExtPictZwg   
        };
    }
}