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

using System.Collections.Generic;
using System.Linq;

namespace SixLabors.Fonts {
  /// <summary>
  /// Represents a shaped and line-broken block of text.
  /// </summary>
  internal sealed class TextBox
  {
      private readonly TextDirection textDirection;

      private float? scaledMaxAdvance;

      private float? minY;

      private int glyphLayoutCount;

      private bool hasGlyphLayoutCounts;

      /// <summary>
      /// Initializes a new instance of the <see cref="TextBox"/> class.
      /// </summary>
      /// <param name="textLines">The shaped, line-broken lines that make up this text box.</param>
      /// <param name="textDirection">The block-level text direction.</param>
      public TextBox(IReadOnlyList<TextLine> textLines, TextDirection textDirection)
      {
          this.TextLines = textLines;
          this.textDirection = textDirection;
      }

      /// <summary>
      /// Gets the shaped and line-broken lines that make up the text.
      /// </summary>
      public IReadOnlyList<TextLine> TextLines { get; }

      /// <summary>
      /// Returns the widest scaled line advance across all lines. The result is memoized.
      /// </summary>
      /// <returns>The widest scaled line advance.</returns>
      public float ScaledMaxAdvance()
          => this.scaledMaxAdvance ??= this.TextLines.Max(x => x.ScaledLineAdvance);

      /// <summary>
      /// Returns the smallest (most negative) scaled Y position encountered across all lines.
      /// Used to detect ink that extends above the typographic ascender (stacked marks in Tibetan etc.).
      /// The result is memoized.
      /// </summary>
      /// <returns>The smallest scaled Y position in the text box.</returns>
      public float ScaledMinY()
          => this.minY ??= this.TextLines.Min(x => x.ScaledMinY);

      /// <summary>
      /// Counts all glyph entries emitted from this text box. The result is memoized.
      /// </summary>
      /// <returns>The number of glyph entries that layout will emit.</returns>
      public int CountGlyphLayouts()
          => this.hasGlyphLayoutCounts ? this.glyphLayoutCount : this.CountGlyphLayoutsCore();

      /// <summary>
      /// Computes the glyph-layout count in one pass.
      /// </summary>
      /// <returns>The number of glyph entries that layout will emit.</returns>
      private int CountGlyphLayoutsCore()
      {
          int count = 0;
          for (int i = 0; i < this.TextLines.Count; i++)
          {
              count += this.TextLines[i].CountGlyphLayouts();
          }

          this.glyphLayoutCount = count;
          this.hasGlyphLayoutCounts = true;
          return count;
      }

      /// <summary>
      /// Returns the block-level text direction used for alignment calculations.
      /// </summary>
      /// <returns>The block-level text direction.</returns>
      public TextDirection TextDirection() => this.textDirection;
  }
}