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

namespace SixLabors.Fonts {
  /// <summary>
  /// Walks a <see cref="TextBlock"/> one laid-out line at a time.
  /// </summary>
  /// <remarks>
  /// Each produced line is positioned independently, without cumulative offsets from earlier or later lines.
  /// </remarks>
  public sealed class LineLayoutEnumerator
  {
      private readonly TextBlock textBlock;
      private readonly TextLineBreakEnumerator lineEnumerator;
      private readonly TextDirection textDirection;
      private readonly bool suppressLayout;
      private LineLayout? current;

      /// <summary>
      /// Initializes a new instance of the <see cref="LineLayoutEnumerator"/> class.
      /// </summary>
      /// <param name="textBlock">The prepared text block to enumerate.</param>
      internal LineLayoutEnumerator(TextBlock textBlock)
      {
          this.textBlock = textBlock;
          this.lineEnumerator = new(textBlock.LogicalLine, textBlock.Options);
          this.textDirection = TextLayout.GetTextDirection(textBlock.LogicalLine, textBlock.Options);
          this.suppressLayout = textBlock.Options.MaxLines == 0;
      }

      /// <summary>
      /// Gets the current line layout.
      /// </summary>
      public LineLayout Current => this.current!;

      /// <summary>
      /// Advances to the next line using the supplied wrapping length.
      /// </summary>
      /// <remarks>
      /// The wrapping length applies only to the line being produced by this call.
      /// </remarks>
      /// <param name="wrappingLength">The wrapping length in pixels. Use <c>-1</c> to disable wrapping.</param>
      /// <returns><see langword="true"/> when a line was produced.</returns>
      public bool MoveNext(float wrappingLength)
      {
          if (this.suppressLayout)
          {
              return false;
          }

          if (!this.lineEnumerator.MoveNext(wrappingLength))
          {
              return false;
          }

          // The walker lays out each produced line independently so callers can
          // place variable-width lines into custom columns, shapes, or virtualized
          // surfaces without inheriting block-level line offsets.
          this.current = this.textBlock.GetLineLayout(
              this.lineEnumerator.Current,
              wrappingLength,
              this.textDirection);

          return true;
      }
  }
}