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

using System;
using System.Collections.Generic;

namespace SixLabors.Fonts.Unicode {
  internal readonly struct BidiRun : IEquatable<BidiRun>
  {
      public BidiRun(BidiCharacterType direction, int level, int start, int length)
      {
          this.Direction = direction;
          this.Level = level;
          this.Start = start;
          this.Length = length;
      }

      public BidiCharacterType Direction { get; }

      public int Level { get; }

      public int Start { get; }

      public int Length { get; }

      public int End => this.Start + this.Length;

      public static bool operator ==(BidiRun left, BidiRun right) => left.Equals(right);

      public static bool operator !=(BidiRun left, BidiRun right) => !(left == right);

      public override string ToString() => $"{this.Start} - {this.End} - {this.Direction}";

      public static IEnumerable<BidiRun> CoalesceLevels(ReadOnlyArraySlice<sbyte> levels)
      {
          if (levels.Length == 0)
          {
              yield break;
          }

          int startRun = 0;
          sbyte runLevel = levels[0];
          BidiCharacterType direction;
          for (int i = 1; i < levels.Length; i++)
          {
              if (levels[i] == runLevel)
              {
                  continue;
              }

              // End of this run
              direction = (runLevel & 0x01) == 0 ? BidiCharacterType.LeftToRight : BidiCharacterType.RightToLeft;
              yield return new BidiRun(direction, runLevel, startRun, i - startRun);

              // Move to next run
              startRun = i;
              runLevel = levels[i];
          }

          direction = (runLevel & 0x01) == 0 ? BidiCharacterType.LeftToRight : BidiCharacterType.RightToLeft;
          yield return new BidiRun(direction, runLevel, startRun, levels.Length - startRun);
      }

      public override bool Equals(object? obj)
          => obj is BidiRun run && this.Equals(run);

      public bool Equals(BidiRun other)
          => this.Direction == other.Direction
          && this.Level == other.Level
          && this.Start == other.Start
          && this.Length == other.Length
          && this.End == other.End;

      public override int GetHashCode()
          => HashCode.Combine(this.Direction, this.Level, this.Start, this.Length, this.End);
  }
}