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

using System;

namespace SixLabors.Fonts.Tables.AdvancedTypographic.Variations {
  /// <summary>
  /// Implements reading the font variations table `VVAR`.
  /// The VVAR table is used in variable fonts to provide variations for vertical glyph metrics values.
  /// This can be used to provide variation data for advance heights in the 'vmtx' table.
  /// <see href="https://docs.microsoft.com/en-gb/typography/opentype/spec/vvar"/>
  /// </summary>
  internal class VVarTable : Table
  {
      /// <summary>
      /// The table name identifier for the VVAR table.
      /// </summary>
      internal const string TableName = "VVAR";

      /// <summary>
      /// Initializes a new instance of the <see cref="VVarTable"/> class.
      /// </summary>
      /// <param name="itemVariationStore">The item variation store containing delta data.</param>
      /// <param name="advanceWidthMapping">The optional delta-set index mapping for advance heights.</param>
      /// <param name="tsbMapping">The optional delta-set index mapping for top side bearings.</param>
      /// <param name="bsbMapping">The optional delta-set index mapping for bottom side bearings.</param>
      /// <param name="vOrgMapping">The optional delta-set index mapping for vertical origin Y coordinates.</param>
      public VVarTable(
          ItemVariationStore itemVariationStore,
          DeltaSetIndexMap[]? advanceWidthMapping,
          DeltaSetIndexMap[]? tsbMapping,
          DeltaSetIndexMap[]? bsbMapping,
          DeltaSetIndexMap[]? vOrgMapping)
      {
          this.ItemVariationStore = itemVariationStore;
          this.AdvanceWidthMapping = advanceWidthMapping;
          this.TsbMapping = tsbMapping;
          this.BsbMapping = bsbMapping;
          this.VOrgMapping = vOrgMapping;
      }

      /// <summary>
      /// Gets the item variation store containing the variation delta data.
      /// </summary>
      public ItemVariationStore ItemVariationStore { get; }

      /// <summary>
      /// Gets the optional delta-set index mapping for advance heights.
      /// </summary>
      public DeltaSetIndexMap[]? AdvanceWidthMapping { get; }

      /// <summary>
      /// Gets the optional delta-set index mapping for top side bearings.
      /// </summary>
      public DeltaSetIndexMap[]? TsbMapping { get; }

      /// <summary>
      /// Gets the optional delta-set index mapping for bottom side bearings.
      /// </summary>
      public DeltaSetIndexMap[]? BsbMapping { get; }

      /// <summary>
      /// Gets the optional delta-set index mapping for Y coordinates of vertical origins.
      /// </summary>
      public DeltaSetIndexMap[]? VOrgMapping { get; }

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

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

      /// <summary>
      /// Loads the VVAR table from the specified binary reader.
      /// </summary>
      /// <param name="reader">The big-endian binary reader positioned at the start of the VVAR table.</param>
      /// <returns>The <see cref="VVarTable"/>.</returns>
      public static VVarTable Load(BigEndianBinaryReader reader)
      {
          // Horizontal metrics variations table
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Type                     | Name                                   | Description                                                             |
          // +==========================+========================================+=========================================================================+
          // | uint16                   | majorVersion                           | Major version number of the font variations table — set to 1.           |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | uint16                   | minorVersion                           | Minor version number of the font variations table — set to 0.           |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Offset32                 | itemVariationStoreOffset               | Offset in bytes from the start of this table to the                     |
          // |                          |                                        | item variation store table.                                             |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Offset32                 | advanceHeightMappingOffset             | Offset in bytes from the start of this table to the delta-set index     |
          // |                          |                                        | mapping for advance heights (may be NULL).                              |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Offset32                 | tsbMappingOffset                       | Offset in bytes from the start of this table to the delta-set index     |
          // |                          |                                        | mapping for top side bearings (may be NULL).                            |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Offset32                 | bsbMappingOffset                       | Offset in bytes from the start of this table to the delta-set index     |
          // |                          |                                        | mapping for bottom side bearings (may be NULL).                         |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          // | Offset32                 | vOrgMappingOffset                      | Offset in bytes from the start of this table to the delta-set index     |
          // |                          |                                        | mapping for Y coordinates of vertical origins (may be NULL).            |
          // +--------------------------+----------------------------------------+-------------------------------------------------------------------------+
          ushort major = reader.ReadUInt16();
          ushort minor = reader.ReadUInt16();
          uint itemVariationStoreOffset = reader.ReadOffset32();
          uint advanceHeightMappingOffset = reader.ReadOffset32();
          uint tsbMappingOffset = reader.ReadOffset32();
          uint bsbMappingOffset = reader.ReadOffset32();
          uint vOrgMappingOffset = reader.ReadOffset32();

          if (major != 1)
          {
              throw new NotSupportedException("Only version 1 of hvar table is supported");
          }

          ItemVariationStore itemVariationStore = ItemVariationStore.Load(reader, itemVariationStoreOffset);

          DeltaSetIndexMap[]? advanceHeightMapping = DeltaSetIndexMap.Load(reader, advanceHeightMappingOffset);
          DeltaSetIndexMap[]? tsbMapping = DeltaSetIndexMap.Load(reader, tsbMappingOffset);
          DeltaSetIndexMap[]? bsbMapping = DeltaSetIndexMap.Load(reader, bsbMappingOffset);
          DeltaSetIndexMap[]? vOrgMapping = DeltaSetIndexMap.Load(reader, vOrgMappingOffset);

          return new VVarTable(itemVariationStore, advanceHeightMapping, tsbMapping, bsbMapping, vOrgMapping);
      }
  }
}