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

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

      /// <summary>
      /// Initializes a new instance of the <see cref="HorizontalHeadTable"/> class.
      /// </summary>
      /// <param name="ascender">The typographic ascender.</param>
      /// <param name="descender">The typographic descender.</param>
      /// <param name="lineGap">The typographic line gap.</param>
      /// <param name="advanceWidthMax">The maximum advance width in font design units.</param>
      /// <param name="minLeftSideBearing">The minimum left side bearing.</param>
      /// <param name="minRightSideBearing">The minimum right side bearing.</param>
      /// <param name="xMaxExtent">The maximum x extent: max(lsb + (xMax - xMin)).</param>
      /// <param name="caretSlopeRise">The caret slope rise used to calculate the slope of the caret.</param>
      /// <param name="caretSlopeRun">The caret slope run used to calculate the slope of the caret.</param>
      /// <param name="caretOffset">The caret offset for slanted fonts.</param>
      /// <param name="numberOfHMetrics">The number of horizontal metrics in the 'hmtx' table.</param>
      public HorizontalHeadTable(
          short ascender,
          short descender,
          short lineGap,
          ushort advanceWidthMax,
          short minLeftSideBearing,
          short minRightSideBearing,
          short xMaxExtent,
          short caretSlopeRise,
          short caretSlopeRun,
          short caretOffset,
          ushort numberOfHMetrics)
      {
          this.Ascender = ascender;
          this.Descender = descender;
          this.LineGap = lineGap;
          this.AdvanceWidthMax = advanceWidthMax;
          this.MinLeftSideBearing = minLeftSideBearing;
          this.MinRightSideBearing = minRightSideBearing;
          this.XMaxExtent = xMaxExtent;
          this.CaretSlopeRise = caretSlopeRise;
          this.CaretSlopeRun = caretSlopeRun;
          this.CaretOffset = caretOffset;
          this.NumberOfHMetrics = numberOfHMetrics;
      }

      /// <summary>
      /// Gets the maximum advance width, in font design units.
      /// </summary>
      public ushort AdvanceWidthMax { get; }

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

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

      /// <summary>
      /// Gets the caret slope rise. Set to 1 for a vertical caret.
      /// </summary>
      public short CaretSlopeRise { get; }

      /// <summary>
      /// Gets the caret slope run. Set to 0 for a vertical caret.
      /// </summary>
      public short CaretSlopeRun { get; }

      /// <summary>
      /// Gets the typographic descender distance from the baseline (typically negative).
      /// </summary>
      public short Descender { get; }

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

      /// <summary>
      /// Gets the minimum left side bearing value.
      /// </summary>
      public short MinLeftSideBearing { get; }

      /// <summary>
      /// Gets the minimum right side bearing value.
      /// </summary>
      public short MinRightSideBearing { get; }

      /// <summary>
      /// Gets the number of horizontal metrics in the 'hmtx' table.
      /// </summary>
      public ushort NumberOfHMetrics { get; }

      /// <summary>
      /// Gets the maximum x extent: max(lsb + (xMax - xMin)).
      /// </summary>
      public short XMaxExtent { get; }

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

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

      /// <summary>
      /// Loads the <see cref="HorizontalHeadTable"/> from the specified binary reader.
      /// </summary>
      /// <param name="reader">The big-endian binary reader.</param>
      /// <returns>The <see cref="HorizontalHeadTable"/>.</returns>
      public static HorizontalHeadTable Load(BigEndianBinaryReader reader)
      {
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | Type   | Name                | Description                                                                     |
          // +========+=====================+=================================================================================+
          // | Fixed  | version             | 0x00010000 (1.0)                                                                |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | ascent              | Distance from baseline of highest ascender                                      |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | descent             | Distance from baseline of lowest descender                                      |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | lineGap             | typographic line gap                                                            |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | uFWord | advanceWidthMax     | must be consistent with horizontal metrics                                      |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | minLeftSideBearing  | must be consistent with horizontal metrics                                      |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | minRightSideBearing | must be consistent with horizontal metrics                                      |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | xMaxExtent          | max(lsb + (xMax-xMin))                                                          |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | caretSlopeRise      | used to calculate the slope of the caret (rise/run) set to 1 for vertical caret |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | caretSlopeRun       | 0 for vertical                                                                  |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | FWord  | caretOffset         | set value to 0 for non-slanted fonts                                            |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | reserved            | set value to 0                                                                  |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | reserved            | set value to 0                                                                  |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | reserved            | set value to 0                                                                  |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | reserved            | set value to 0                                                                  |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | int16  | metricDataFormat    | 0 for current format                                                            |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          // | uint16 | numOfLongHorMetrics | number of advance widths in metrics table                                       |
          // +--------+---------------------+---------------------------------------------------------------------------------+
          ushort majorVersion = reader.ReadUInt16();
          ushort minorVersion = reader.ReadUInt16();
          short ascender = reader.ReadFWORD();
          short descender = reader.ReadFWORD();
          short lineGap = reader.ReadFWORD();
          ushort advanceWidthMax = reader.ReadUFWORD();
          short minLeftSideBearing = reader.ReadFWORD();
          short minRightSideBearing = reader.ReadFWORD();
          short xMaxExtent = reader.ReadFWORD();
          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 numberOfHMetrics = reader.ReadUInt16();

          return new HorizontalHeadTable(
              ascender,
              descender,
              lineGap,
              advanceWidthMax,
              minLeftSideBearing,
              minRightSideBearing,
              xMaxExtent,
              caretSlopeRise,
              caretSlopeRun,
              caretOffset,
              numberOfHMetrics);
      }
  }
}