// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using System.Globalization;
using System.Runtime.CompilerServices;

namespace SixLabors.Fonts.Unicode {
  /// <summary>
  /// Represents the Unicode joining properties of a given <see cref="CodePoint"/>.
  /// <see href="https://www.unicode.org/reports/tr44/#Joining_Type"/>
  /// <see href="https://www.unicode.org/reports/tr44/#Joining_Group"/>
  /// </summary>
  /// <remarks>
  /// This combines the Unicode <c>Joining_Type</c> and <c>Joining_Group</c>
  /// properties used by cursive shaping. Unlisted nonspacing marks, enclosing marks,
  /// and format controls follow the Unicode default joining behavior.
  /// </remarks>
  public readonly struct ArabicJoiningClass
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="ArabicJoiningClass"/> struct.
      /// </summary>
      /// <param name="codePoint">The codepoint.</param>
      public ArabicJoiningClass(CodePoint codePoint)
      {
          UnicodeCategory category = CodePoint.GetGeneralCategory(codePoint);
          uint value = UnicodeData.GetJoiningClass((uint)codePoint.Value);
          this.JoiningType = GetJoiningType(codePoint, value, category);
          this.JoiningGroup = (ArabicJoiningGroup)((value >> 16) & 0xFF);
      }

      /// <summary>
      /// Gets the Unicode joining type.
      /// </summary>
      public ArabicJoiningType JoiningType { get; }

      /// <summary>
      /// Gets the Unicode joining group.
      /// </summary>
      public ArabicJoiningGroup JoiningGroup { get; }

      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      private static ArabicJoiningType GetJoiningType(CodePoint codePoint, uint value, UnicodeCategory category)
      {
          var type = (ArabicJoiningType)(value & 0xFF);

          // All others not explicitly listed have joining type U
          if (type == ArabicJoiningType.NonJoining)
          {
              // 200C; ZERO WIDTH NON-JOINER; U; No_Joining_Group
              // 200D; ZERO WIDTH JOINER; C; No_Joining_Group
              // 202F; NARROW NO-BREAK SPACE; U; No_Joining_Group
              // 2066; LEFT-TO-RIGHT ISOLATE; U; No_Joining_Group
              // 2067; RIGHT-TO-LEFT ISOLATE; U; No_Joining_Group
              // 2068; FIRST STRONG ISOLATE; U; No_Joining_Group
              // 2069; POP DIRECTIONAL ISOLATE; U; No_Joining_Group
              if (codePoint.Value is 0x200C
                  or 0x200D
                  or 0x202F
                  or 0x2066
                  or 0x2067
                  or 0x2068
                  or 0x2069)
              {
                  return type;
              }

              // Those that are not explicitly listed and that are of General Category Mn, Me, or Cf have joining type T.
              if (category is UnicodeCategory.NonSpacingMark or UnicodeCategory.EnclosingMark or UnicodeCategory.Format)
              {
                  type = ArabicJoiningType.Transparent;
              }
          }

          return type;
      }
  }
}