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

using System;
using System.Diagnostics;

namespace SixLabors.Fonts {
  /// <summary>
  /// Represents a single variation axis setting for a variable font,
  /// consisting of a four-character tag and a value.
  /// </summary>
  /// <remarks>
  /// Follows CSS <c>font-variation-settings</c> semantics.
  /// Values are clamped to the axis range defined in the font's <c>fvar</c> table.
  /// </remarks>
  [DebuggerDisplay("Tag: {Tag}, Value: {Value}")]
  public readonly struct FontVariation
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="FontVariation"/> struct.
      /// </summary>
      /// <param name="tag">The four-character axis tag (e.g. "wght", "wdth", "opsz").</param>
      /// <param name="value">The axis value in design-space units.</param>
      public FontVariation(string tag, float value)
      {
          Guard.NotNullOrWhiteSpace(tag, nameof(tag));
          if (tag.Length != 4)
          {
              throw new ArgumentException("Variation axis tag must be exactly 4 characters.", nameof(tag));
          }

          this.Tag = tag;
          this.Value = value;
      }

      /// <summary>
      /// Gets the four-character axis tag identifying the design variation.
      /// </summary>
      public string Tag { get; }

      /// <summary>
      /// Gets the axis value in design-space units.
      /// </summary>
      public float Value { get; }
  }
}