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

using System.Buffers;

namespace SixLabors.ImageSharp.Drawing.Processing.Backends {
  internal static partial class DefaultRasterizer
  {
      /// <summary>
      /// Contract implemented by retained line-block payloads.
      /// </summary>
      /// <typeparam name="TSelf">The concrete retained line-block type.</typeparam>
      internal interface ILineBlock<TSelf>
          where TSelf : class, ILineBlock<TSelf>
      {
          /// <summary>
          /// Gets the number of lines stored in a full block.
          /// </summary>
          public static abstract int LineCount { get; }

          /// <summary>
          /// Gets the next block in the retained chain.
          /// </summary>
          public TSelf? Next { get; }

          /// <summary>
          /// Rasterizes the leading <paramref name="count"/> lines from this block.
          /// </summary>
          /// <param name="count">The number of leading lines to rasterize from this block.</param>
          /// <param name="context">The mutable scan-conversion context to write into.</param>
          public void Rasterize(int count, ref Context context);
      }

      /// <summary>
      /// Retained tile-space bounds for one linearized geometry payload.
      /// </summary>
      internal readonly struct TileBounds
      {
          /// <summary>
          /// Initializes a new instance of the <see cref="TileBounds"/> struct.
          /// </summary>
          /// <param name="x">The tile-space left coordinate.</param>
          /// <param name="y">The tile-space top coordinate.</param>
          /// <param name="columnCount">The tile-space column count.</param>
          /// <param name="rowCount">The tile-space row count.</param>
          public TileBounds(int x, int y, int columnCount, int rowCount)
          {
              this.X = x;
              this.Y = y;
              this.ColumnCount = columnCount;
              this.RowCount = rowCount;
          }

          /// <summary>
          /// Gets the tile-space left coordinate.
          /// </summary>
          public int X { get; }

          /// <summary>
          /// Gets the tile-space top coordinate.
          /// </summary>
          public int Y { get; }

          /// <summary>
          /// Gets the tile-space column count.
          /// </summary>
          public int ColumnCount { get; }

          /// <summary>
          /// Gets the tile-space row count.
          /// </summary>
          public int RowCount { get; }
      }

      /// <summary>
      /// Holds the finalized retained raster payload for one line-block encoding.
      /// </summary>
      /// <typeparam name="TLineBlock">The concrete retained line-block type.</typeparam>
      internal sealed class LinearizedRasterData<TLineBlock>
          where TLineBlock : class, ILineBlock<TLineBlock>
      {
          /// <summary>
          /// Initializes a new instance of the <see cref="LinearizedRasterData{TLineBlock}"/> class.
          /// </summary>
          /// <param name="geometry">The source linear geometry.</param>
          /// <param name="bounds">The retained tile-space bounds.</param>
          /// <param name="lines">The retained line-block chain for each row band.</param>
          /// <param name="firstBlockLineCounts">The valid line count in each row's front block.</param>
          /// <param name="startCoverTable">The retained start-cover seeds for each row band.</param>
          public LinearizedRasterData(
              LinearGeometry geometry,
              TileBounds bounds,
              TLineBlock?[] lines,
              int[] firstBlockLineCounts,
              IMemoryOwner<int>?[] startCoverTable)
          {
              this.Geometry = geometry;
              this.Bounds = bounds;
              this.Lines = lines;
              this.FirstBlockLineCounts = firstBlockLineCounts;
              this.StartCoverTable = startCoverTable;
          }

          /// <summary>
          /// Gets the source linear geometry.
          /// </summary>
          public LinearGeometry Geometry { get; }

          /// <summary>
          /// Gets the retained tile-space bounds.
          /// </summary>
          public TileBounds Bounds { get; }

          /// <summary>
          /// Gets the retained line-block chain for each row band.
          /// </summary>
          public TLineBlock?[] Lines { get; }

          /// <summary>
          /// Gets the valid front-block line count for each row band.
          /// </summary>
          public int[] FirstBlockLineCounts { get; }

          /// <summary>
          /// Gets the retained start-cover seeds for each row band.
          /// </summary>
          public IMemoryOwner<int>?[] StartCoverTable { get; }

          /// <summary>
          /// Iterates the retained line blocks for one row band.
          /// </summary>
          /// <param name="rowIndex">The row band index to iterate.</param>
          /// <param name="context">The mutable scan-conversion context.</param>
          public void Iterate(int rowIndex, ref Context context)
          {
              int count = this.FirstBlockLineCounts[rowIndex];
              TLineBlock? lineBlock = this.Lines[rowIndex];
              while (lineBlock is not null)
              {
                  lineBlock.Rasterize(count, ref context);
                  lineBlock = lineBlock.Next;
                  count = TLineBlock.LineCount;
              }
          }
      }
  }
}