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

using System;
using System.Numerics;
using SixLabors.Fonts.Rendering;

namespace SixLabors.Fonts {
  /// <summary>
  /// Represents one laid-out line from a <see cref="TextBlock"/>.
  /// </summary>
  public sealed class LineLayout
  {
      private readonly TextBox textBox;
      private readonly TextOptions options;
      private readonly float wrappingLength;
      private readonly int lineIndex;
      private readonly LayoutMode layoutMode;
      private readonly ReadOnlyMemory<GraphemeMetrics> graphemeMetrics;
      private readonly ReadOnlyMemory<WordMetrics> wordMetrics;
      private GlyphMetrics[]? glyphMetrics;

      internal LineLayout(
          TextBox textBox,
          TextOptions options,
          float wrappingLength,
          int lineIndex,
          in LineMetrics metrics,
          ReadOnlyMemory<GraphemeMetrics> graphemeMetrics,
          ReadOnlyMemory<WordMetrics> wordMetrics)
      {
          this.textBox = textBox;
          this.options = options;
          this.wrappingLength = wrappingLength;
          this.lineIndex = lineIndex;
          this.layoutMode = options.LayoutMode;
          this.LineMetrics = metrics;
          this.graphemeMetrics = graphemeMetrics;
          this.wordMetrics = wordMetrics;
      }

      /// <summary>
      /// Gets the measured line metrics.
      /// </summary>
      public LineMetrics LineMetrics { get; }

      /// <summary>
      /// Gets the grapheme metrics entries for this line in final layout order.
      /// </summary>
      public ReadOnlySpan<GraphemeMetrics> GraphemeMetrics => this.graphemeMetrics.Span;

      /// <summary>
      /// Hit tests the supplied point against this line's grapheme advance bounds.
      /// </summary>
      /// <param name="point">The point in pixel units.</param>
      /// <returns>The hit-tested grapheme position.</returns>
      public TextHit HitTest(Vector2 point)
          => TextInteraction.HitTestLine(this.lineIndex, this.GraphemeMetrics, point, this.layoutMode);

      /// <summary>
      /// Gets the caret position for the supplied hit.
      /// </summary>
      /// <param name="hit">The hit-tested grapheme position.</param>
      /// <returns>The caret position in pixel units.</returns>
      public CaretPosition GetCaretPosition(TextHit hit)
          => TextInteraction.GetCaretPositionLine(
              this.lineIndex,
              this.LineMetrics,
              this.GraphemeMetrics,
              hit.GraphemeInsertionIndex,
              this.layoutMode);

      /// <summary>
      /// Gets an absolute caret position in the laid-out line.
      /// </summary>
      /// <param name="placement">The absolute caret placement.</param>
      /// <returns>The caret position in pixel units.</returns>
      public CaretPosition GetCaret(CaretPlacement placement)
          => TextInteraction.GetCaretLine(
              this.lineIndex,
              this.LineMetrics,
              this.GraphemeMetrics,
              placement,
              this.layoutMode,
              this.textBox.TextDirection());

      /// <summary>
      /// Moves the supplied caret by the requested operation within this line.
      /// </summary>
      /// <param name="caret">The current caret position.</param>
      /// <param name="movement">The movement operation.</param>
      /// <returns>The moved caret position in pixel units.</returns>
      public CaretPosition MoveCaret(CaretPosition caret, CaretMovement movement)
          => TextInteraction.MoveCaretLine(
              this.lineIndex,
              this.LineMetrics,
              this.GraphemeMetrics,
              this.wordMetrics.Span,
              caret,
              movement,
              this.layoutMode,
              this.textBox.TextDirection());

      /// <summary>
      /// Gets the word metrics for the word-boundary segment containing the supplied hit-tested grapheme position.
      /// </summary>
      /// <param name="hit">The hit-tested grapheme position.</param>
      /// <returns>The word metrics containing the hit grapheme.</returns>
      public WordMetrics GetWordMetrics(TextHit hit)
          => TextInteraction.GetWordMetrics(this.wordMetrics.Span, hit.GraphemeIndex);

      /// <summary>
      /// Gets the word metrics for the word-boundary segment containing the supplied caret position.
      /// </summary>
      /// <param name="caret">The caret position.</param>
      /// <returns>The word metrics containing the caret's grapheme insertion index.</returns>
      public WordMetrics GetWordMetrics(CaretPosition caret)
          => TextInteraction.GetWordMetrics(this.wordMetrics.Span, caret.GraphemeIndex);

      /// <summary>
      /// Gets selection bounds between two hit-tested grapheme positions.
      /// </summary>
      /// <param name="anchor">The fixed selection endpoint.</param>
      /// <param name="focus">The active selection endpoint.</param>
      /// <returns>A read-only memory region containing the selection bounds in visual order and pixel units.</returns>
      public ReadOnlyMemory<FontRectangle> GetSelectionBounds(TextHit anchor, TextHit focus)
          => TextInteraction.GetSelectionBoundsLine(
              this.LineMetrics,
              this.GraphemeMetrics,
              anchor.GraphemeInsertionIndex,
              focus.GraphemeInsertionIndex,
              this.layoutMode);

      /// <summary>
      /// Gets selection bounds between two caret positions.
      /// </summary>
      /// <param name="anchor">The fixed selection endpoint.</param>
      /// <param name="focus">The active selection endpoint.</param>
      /// <returns>A read-only memory region containing the selection bounds in visual order and pixel units.</returns>
      public ReadOnlyMemory<FontRectangle> GetSelectionBounds(CaretPosition anchor, CaretPosition focus)
          => TextInteraction.GetSelectionBoundsLine(
              this.LineMetrics,
              this.GraphemeMetrics,
              anchor.GraphemeIndex,
              focus.GraphemeIndex,
              this.layoutMode);

      /// <summary>
      /// Gets line-local selection bounds for the supplied grapheme metrics.
      /// </summary>
      /// <param name="metrics">The grapheme metrics to select.</param>
      /// <returns>A read-only memory region containing the selection bounds in visual order and pixel units.</returns>
      public ReadOnlyMemory<FontRectangle> GetSelectionBounds(GraphemeMetrics metrics)
          => TextInteraction.GetSelectionBoundsLine(
              this.LineMetrics,
              metrics,
              this.layoutMode);

      /// <summary>
      /// Gets line-local selection bounds for the supplied word metrics.
      /// </summary>
      /// <param name="metrics">The word metrics to select.</param>
      /// <returns>A read-only memory region containing the selection bounds in visual order and pixel units.</returns>
      public ReadOnlyMemory<FontRectangle> GetSelectionBounds(WordMetrics metrics)
          => TextInteraction.GetSelectionBoundsLine(
              this.LineMetrics,
              this.GraphemeMetrics,
              metrics.GraphemeStart,
              metrics.GraphemeEnd,
              this.layoutMode);

      /// <inheritdoc cref="TextBlock.GetGlyphMetrics(float)"/>
      public ReadOnlyMemory<GlyphMetrics> GetGlyphMetrics()
          => this.glyphMetrics ??= TextBlock.GetGlyphMetricsArray(
              this.textBox,
              this.options,
              this.wrappingLength,
              this.lineIndex);

      /// <summary>
      /// Renders this line to the supplied glyph renderer.
      /// </summary>
      /// <param name="renderer">The target renderer.</param>
      public void RenderTo(IGlyphRenderer renderer)
      {
          FontRectangle bounds = FontRectangle.Empty;
          ReadOnlySpan<GlyphMetrics> glyphMetrics = this.GetGlyphMetrics().Span;

          for (int i = 0; i < glyphMetrics.Length; i++)
          {
              bounds = i == 0
                  ? glyphMetrics[i].Bounds
                  : FontRectangle.Union(bounds, glyphMetrics[i].Bounds);
          }

          TextBlock.RenderTo(
              renderer,
              this.textBox,
              this.options,
              this.wrappingLength,
              bounds,
              this.lineIndex);
      }
  }
}