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

using SixLabors.Fonts.Unicode;
using System.Collections.Generic;

namespace SixLabors.Fonts.Tables.AdvancedTypographic.Shapers {
  /// <summary>
  /// Abstract base class for all script shapers. Defines the shaping pipeline
  /// consisting of preprocessing, feature planning, postprocessing, and feature assignment stages.
  /// </summary>
  internal abstract class BaseShaper
  {
      /// <summary>
      /// Gets or sets the script classification for this shaper.
      /// </summary>
      public ScriptClass ScriptClass { get; protected set; }

      /// <summary>
      /// Gets or sets the mark zeroing mode that determines when mark advances are zeroed.
      /// </summary>
      public MarkZeroingMode MarkZeroingMode { get; protected set; }

      /// <summary>
      /// Assigns the features to each glyph within the collection.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="index">The zero-based index of the elements to assign.</param>
      /// <param name="count">The number of elements to assign.</param>
      public void Plan(IGlyphShapingCollection collection, int index, int count)
      {
          int collectionCount = collection.Count;

          this.PlanPreprocessingFeatures(collection, index, count);

          RecalculateCount(collection, ref collectionCount, ref count);

          this.PlanFeatures(collection, index, count);

          RecalculateCount(collection, ref collectionCount, ref count);

          this.PlanPostprocessingFeatures(collection, index, count);

          RecalculateCount(collection, ref collectionCount, ref count);

          this.AssignFeatures(collection, index, count);
      }

      /// <summary>
      /// Assigns the features to each glyph within the collection.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="index">The zero-based index of the elements to assign.</param>
      /// <param name="count">The number of elements to assign.</param>
      protected abstract void PlanFeatures(IGlyphShapingCollection collection, int index, int count);

      /// <summary>
      /// Assigns the preprocessing features to each glyph within the collection.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="index">The zero-based index of the elements to assign.</param>
      /// <param name="count">The number of elements to assign.</param>
      protected abstract void PlanPreprocessingFeatures(IGlyphShapingCollection collection, int index, int count);

      /// <summary>
      /// Assigns the postprocessing features to each glyph within the collection.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="index">The zero-based index of the elements to assign.</param>
      /// <param name="count">The number of elements to assign.</param>
      protected abstract void PlanPostprocessingFeatures(IGlyphShapingCollection collection, int index, int count);

      /// <summary>
      /// Assigns the shaper specific substitution features to each glyph within the collection.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="index">The zero-based index of the elements to assign.</param>
      /// <param name="count">The number of elements to assign.</param>
      protected abstract void AssignFeatures(IGlyphShapingCollection collection, int index, int count);

      /// <summary>
      /// Gets the ordered collection of shaping stages for this shaper.
      /// </summary>
      /// <returns>The shaping stages.</returns>
      public abstract IEnumerable<ShapingStage> GetShapingStages();

      /// <summary>
      /// Recalculates the count when the collection size changes during shaping.
      /// </summary>
      /// <param name="collection">The glyph shaping collection.</param>
      /// <param name="oldCount">The previous collection count, updated to the current count.</param>
      /// <param name="count">The element count, adjusted by the size delta.</param>
      private static void RecalculateCount(IGlyphShapingCollection collection, ref int oldCount, ref int count)
      {
          // If the collection has changed size we need to recalculate the count.
          int delta = collection.Count - oldCount;
          count += delta;
          oldCount += delta;
      }
  }
}