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

namespace SixLabors.Fonts.Tables.General {
  /// <summary>
  /// Represents the vertical header table, which contains information needed to lay out fonts
  /// whose characters are written vertically.
  /// <see href="https://learn.microsoft.com/en-us/typography/opentype/spec/vhea"/>
  /// </summary>
  internal sealed class VerticalHeadTable : Table
  {
      /// <summary>
      /// The table name identifier.
      /// </summary>
      internal const string TableName = "vhea";

      /// <summary>
      /// Initializes a new instance of the <see cref="VerticalHeadTable"/> class.
      /// </summary>
      /// <param name="ascender">The vertical typographic ascender.</param>
      /// <param name="descender">The vertical typographic descender.</param>
      /// <param name="lineGap">The vertical typographic line gap.</param>
      /// <param name="advanceHeightMax">The maximum advance height.</param>
      /// <param name="minTopSideBearing">The minimum top side bearing.</param>
      /// <param name="minBottomSideBearing">The minimum bottom side bearing.</param>
      /// <param name="yMaxExtent">The maximum y extent.</param>
      /// <param name="caretSlopeRise">The caret slope rise.</param>
      /// <param name="caretSlopeRun">The caret slope run.</param>
      /// <param name="caretOffset">The caret offset for slanted fonts.</param>
      /// <param name="numberOfVMetrics">The number of vertical metrics in the 'vmtx' table.</param>
      public VerticalHeadTable(
          short ascender,
          short descender,
          short lineGap,
          short advanceHeightMax,
          short minTopSideBearing,
          short minBottomSideBearing,
          short yMaxExtent,
          short caretSlopeRise,
          short caretSlopeRun,
          short caretOffset,
          ushort numberOfVMetrics)
      {
          this.Ascender = ascender;
          this.Descender = descender;
          this.LineGap = lineGap;
          this.AdvanceHeightMax = advanceHeightMax;
          this.MinTopSideBearing = minTopSideBearing;
          this.MinBottomSideBearing = minBottomSideBearing;
          this.YMaxExtent = yMaxExtent;
          this.CaretSlopeRise = caretSlopeRise;
          this.CaretSlopeRun = caretSlopeRun;
          this.CaretOffset = caretOffset;
          this.NumberOfVMetrics = numberOfVMetrics;
      }

      /// <summary>
      /// Gets the vertical typographic ascender.
      /// </summary>
      public short Ascender { get; }

      /// <summary>
      /// Gets the vertical typographic descender.
      /// </summary>
      public short Descender { get; }

      /// <summary>
      /// Gets the vertical typographic line gap.
      /// </summary>
      public short LineGap { get; }

      /// <summary>
      /// Gets the maximum advance height in font design units.
      /// </summary>
      public short AdvanceHeightMax { get; }

      /// <summary>
      /// Gets the minimum top side bearing in font design units.
      /// </summary>
      public short MinTopSideBearing { get; }

      /// <summary>
      /// Gets the minimum bottom side bearing in font design units.
      /// </summary>
      public short MinBottomSideBearing { get; }

      /// <summary>
      /// Gets the maximum y extent: minTopSideBearing + (yMin - yMax).
      /// </summary>
      public short YMaxExtent { get; }

      /// <summary>
      /// Gets the caret slope rise. A value of 0 for rise and 1 for run specifies a horizontal caret.
      /// </summary>
      public short CaretSlopeRise { get; }

      /// <summary>
      /// Gets the caret slope run. A value of 0 for non-slanted fonts.
      /// </summary>
      public short CaretSlopeRun { get; }

      /// <summary>
      /// Gets the caret offset for slanted fonts. Set to 0 for non-slanted fonts.
      /// </summary>
      public short CaretOffset { get; }

      /// <summary>
      /// Gets the number of vertical metrics in the 'vmtx' table.
      /// </summary>
      public ushort NumberOfVMetrics { get; }

      /// <summary>
      /// Loads the <see cref="VerticalHeadTable"/> from the specified font reader.
      /// </summary>
      /// <param name="fontReader">The font reader.</param>
      /// <returns>The <see cref="VerticalHeadTable"/>, or <see langword="null"/> if the table is not present.</returns>
      public static VerticalHeadTable? Load(FontReader fontReader)
      {
          if (!fontReader.TryGetReaderAtTablePosition(TableName, out BigEndianBinaryReader? binaryReader))
          {
              return null;
          }

          using (binaryReader)
          {
              return Load(binaryReader);
          }
      }

      /// <summary>
      /// Loads the <see cref="VerticalHeadTable"/> from the specified binary reader.
      /// </summary>
      /// <param name="reader">The big-endian binary reader.</param>
      /// <returns>The <see cref="VerticalHeadTable"/>.</returns>
      public static VerticalHeadTable Load(BigEndianBinaryReader reader)
      {
          // +---------+----------------------+----------------------------------------------------------------------+
          // | Type    | Name                 | Description                                                          |
          // +=========+======================+======================================================================+
          // | fixed32 | version              | Version number of the Vertical Header Table (0x00011000 for          |
          // |         |                      | the current version).                                                |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | vertTypoAscender     | The vertical typographic ascender for this font. It is the distance  |
          // |         |                      | in FUnits from the vertical center baseline to the right of the      |
          // |         |                      | design space. This will usually be set to half the horizontal        |
          // |         |                      | advance of full-width glyphs. For example, if the full width is      |
          // |         |                      | 1000 FUnits, this field will be set to 500.                          |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | vertTypoDescender    | The vertical typographic descender for this font. It is the          |
          // |         |                      | distance in FUnits from the vertical center baseline to the left of  |
          // |         |                      | the design space. This will usually be set to half the horizontal    |
          // |         |                      | advance of full-width glyphs. For example, if the full width is      |
          // |         |                      | 1000 FUnits, this field will be set to -500.                         |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | vertTypoLineGap      | The vertical typographic line gap for this font.                     |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | advanceHeightMax     | The maximum advance height measurement in FUnits found in            |
          // |         |                      | the font. This value must be consistent with the entries in the      |
          // |         |                      | vertical metrics table.                                              |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | minTopSideBearing    | The minimum top side bearing measurement in FUnits found in          |
          // |         |                      | the font, in FUnits. This value must be consistent with the          |
          // |         |                      | entries in the vertical metrics table.                               |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | minBottomSideBearing | The minimum bottom side bearing measurement in FUnits                |
          // |         |                      | found in the font, in FUnits. This value must be consistent with     |
          // |         |                      | the entries in the vertical metrics table.                           |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | yMaxExtent           | This is defined as the value of the minTopSideBearing field          |
          // |         |                      | added to the result of the value of the yMin field subtracted        |
          // |         |                      | from the value of the yMax field.                                    |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | caretSlopeRise       | The value of the caretSlopeRise field divided by the value of the    |
          // |         |                      | caretSlopeRun field determines the slope of the caret. A value       |
          // |         |                      | of 0 for the rise and a value of 1 for the run specifies a           |
          // |         |                      | horizontal caret. A value of 1 for the rise and a value of 0 for the |
          // |         |                      | run specifies a vertical caret. A value between 0 for the rise and   |
          // |         |                      | 1 for the run is desirable for fonts whose glyphs are oblique or     |
          // |         |                      | italic. For a vertical font, a horizontal caret is best.             |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | caretSlopeRun        | See the caretSlopeRise field. Value = 0 for non-slanted fonts.       |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | caretOffset          | The amount by which the highlight on a slanted glyph needs to        |
          // |         |                      | be shifted away from the glyph in order to produce the best          |
          // |         |                      | appearance. Set value equal to 0 for non-slanted fonts.              |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | reserved             | Set to 0.                                                            |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | reserved             | Set to 0.                                                            |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | reserved             | Set to 0.                                                            |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | reserved             | Set to 0.                                                            |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | int16   | metricDataFormat     | Set to 0.                                                            |
          // +---------+----------------------+----------------------------------------------------------------------+
          // | uint16  | numOfLongVerMetrics  | Number of advance heights in the Vertical Metrics table.             |
          // +---------+----------------------+----------------------------------------------------------------------+
          ushort majorVersion = reader.ReadUInt16();
          ushort minorVersion = reader.ReadUInt16();
          short vertTypoAscender = reader.ReadInt16();
          short vertTypoDescender = reader.ReadInt16();
          short vertTypoLineGap = reader.ReadInt16();
          short advanceHeightMax = reader.ReadInt16();
          short minTopSideBearing = reader.ReadInt16();
          short minBottomSideBearing = reader.ReadInt16();
          short yMaxExtent = reader.ReadInt16();
          short caretSlopeRise = reader.ReadInt16();
          short caretSlopeRun = reader.ReadInt16();
          short caretOffset = reader.ReadInt16();
          reader.ReadInt16(); // reserved
          reader.ReadInt16(); // reserved
          reader.ReadInt16(); // reserved
          reader.ReadInt16(); // reserved
          short metricDataFormat = reader.ReadInt16(); // 0

          if (metricDataFormat != 0)
          {
              throw new InvalidFontTableException($"Expected metricDataFormat = 0 found {metricDataFormat}", TableName);
          }

          ushort numOfLongVerMetrics = reader.ReadUInt16();

          return new VerticalHeadTable(
              vertTypoAscender,
              vertTypoDescender,
              vertTypoLineGap,
              advanceHeightMax,
              minTopSideBearing,
              minBottomSideBearing,
              yMaxExtent,
              caretSlopeRise,
              caretSlopeRun,
              caretOffset,
              numOfLongVerMetrics);
      }
  }
}