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

using System;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace SixLabors.Fonts {
  /// <summary>
  /// Provides access to the color details for the current glyph.
  /// </summary>
  public readonly partial struct GlyphColor : IEquatable<GlyphColor>
  {
      internal GlyphColor(byte red, byte green, byte blue, byte alpha)
      {
          this.R = red;
          this.G = green;
          this.B = blue;
          this.A = alpha;
      }

      /// <summary>
      /// Gets the red component
      /// </summary>
      public readonly byte R { get; }

      /// <summary>
      /// Gets the green component
      /// </summary>
      public readonly byte G { get; }

      /// <summary>
      /// Gets the blue component
      /// </summary>
      public readonly byte B { get; }

      /// <summary>
      /// Gets the alpha component
      /// </summary>
      public readonly byte A { get; }

      /// <summary>
      /// Compares two <see cref="GlyphColor"/> objects for equality.
      /// </summary>
      /// <param name="left">
      /// The <see cref="GlyphColor"/> on the left side of the operand.
      /// </param>
      /// <param name="right">
      /// The <see cref="GlyphColor"/> on the right side of the operand.
      /// </param>
      /// <returns>
      /// True if the current left is equal to the <paramref name="right"/> parameter; otherwise, false.
      /// </returns>
      public static bool operator ==(GlyphColor left, GlyphColor right)
          => left.Equals(right);

      /// <summary>
      /// Compares two <see cref="GlyphColor"/> objects for inequality.
      /// </summary>
      /// <param name="left">
      /// The <see cref="GlyphColor"/> on the left side of the operand.
      /// </param>
      /// <param name="right">
      /// The <see cref="GlyphColor"/> on the right side of the operand.
      /// </param>
      /// <returns>
      /// True if the current left is unequal to the <paramref name="right"/> parameter; otherwise, false.
      /// </returns>
      public static bool operator !=(GlyphColor left, GlyphColor right)
          => !left.Equals(right);

      /// <inheritdoc/>
      public override bool Equals(object? obj)
          => obj is GlyphColor p && this.Equals(p);

      /// <summary>
      /// Compares the <see cref="GlyphColor"/> for equality to this color.
      /// </summary>
      /// <param name="other">
      /// The other <see cref="GlyphColor"/> to compare to.
      /// </param>
      /// <returns>
      /// True if the current color is equal to the <paramref name="other"/> parameter; otherwise, false.
      /// </returns>
      public bool Equals(GlyphColor other)
          => other.R == this.R
          && other.G == this.G
          && other.B == this.B
          && other.A == this.A;

      /// <inheritdoc/>
      public override int GetHashCode()
          => HashCode.Combine(
              this.R,
              this.G,
              this.B,
              this.A);

      /// <summary>
      /// Gets the hexadecimal string representation of the color instance in the format RRGGBBAA.
      /// </summary>
      /// <param name="value">
      /// The hexadecimal representation of the combined color components.
      /// </param>
      /// <param name="result">
      /// When this method returns, contains the <see cref="GlyphColor"/> equivalent of the hexadecimal input.
      /// </param>
      /// <returns>
      /// <see langword="true"/> if the parsing was successful; otherwise, <see langword="false"/>.
      /// </returns>
      public static bool TryParseHex(string? value, [NotNullWhen(true)] out GlyphColor result)
      {
          result = default;

          if (string.IsNullOrWhiteSpace(value))
          {
              return false;
          }

          ReadOnlySpan<char> hex = value.AsSpan();

          if (hex[0] != '#')
          {
              return false;
          }

          hex = hex[1..];

          byte a = 255, r, g, b;

          switch (hex.Length)
          {
              case 8:
                  if (!TryParseByte(hex[0], hex[1], out r) ||
                      !TryParseByte(hex[2], hex[3], out g) ||
                      !TryParseByte(hex[4], hex[5], out b) ||
                      !TryParseByte(hex[6], hex[7], out a))
                  {
                      return false;
                  }

                  break;

              case 6:
                  if (!TryParseByte(hex[0], hex[1], out r) ||
                      !TryParseByte(hex[2], hex[3], out g) ||
                      !TryParseByte(hex[4], hex[5], out b))
                  {
                      return false;
                  }

                  break;

              case 4:
                  if (!TryExpand(hex[0], out r) ||
                      !TryExpand(hex[1], out g) ||
                      !TryExpand(hex[2], out b) ||
                      !TryExpand(hex[3], out a))
                  {
                      return false;
                  }

                  break;

              case 3:
                  if (!TryExpand(hex[0], out r) ||
                      !TryExpand(hex[1], out g) ||
                      !TryExpand(hex[2], out b))
                  {
                      return false;
                  }

                  break;

              default:
                  return false;
          }

          result = new GlyphColor(r, g, b, a);
          return true;
      }

      /// <summary>
      /// Attempts to parse the specified name into a corresponding named glyph color.
      /// </summary>
      /// <param name="name">The name of the glyph color to parse.</param>
      /// <param name="result">
      /// When this method returns, contains the parsed <see cref="GlyphColor"/> value if the parse operation succeeded;
      /// otherwise, contains the default value.
      /// </param>
      /// <returns>
      /// <see langword="true"/> if the parsing was successful; otherwise, <see langword="false"/>.
      /// </returns>
      public static bool TryParseNamed(string? name, [NotNullWhen(true)] out GlyphColor result)
      {
          result = default;
          if (string.IsNullOrWhiteSpace(name))
          {
              return false;
          }

          return NamedGlyphColorsLookupLazy.Value.TryGetValue(name, out result);
      }

      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      private static bool TryParseByte(char hi, char lo, out byte value)
      {
          if (TryConvertHexCharToByte(hi, out byte high) && TryConvertHexCharToByte(lo, out byte low))
          {
              value = (byte)((high << 4) | low);
              return true;
          }

          value = 0;
          return false;
      }

      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      private static bool TryExpand(char c, out byte value)
      {
          if (TryConvertHexCharToByte(c, out byte nibble))
          {
              value = (byte)((nibble << 4) | nibble);
              return true;
          }

          value = 0;
          return false;
      }

      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      private static bool TryConvertHexCharToByte(char c, out byte value)
      {
          if ((uint)(c - '0') <= 9)
          {
              value = (byte)(c - '0');
              return true;
          }

          char lower = (char)(c | 0x20); // Normalize to lowercase

          if ((uint)(lower - 'a') <= 5)
          {
              value = (byte)(lower - 'a' + 10);
              return true;
          }

          value = 0;
          return false;
      }
  }
}