ImageSharp/SixLabors.Fonts/Tables/General/Name/NameTable.cs

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

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using SixLabors.Fonts.Utilities;
using SixLabors.Fonts.WellKnownIds;

namespace SixLabors.Fonts.Tables.General.Name {
  /// <summary>
  /// Represents the OpenType 'name' table, which contains human-readable string names
  /// for features, font metadata, and other descriptive information.
  /// <see href="https://learn.microsoft.com/en-us/typography/opentype/spec/name"/>
  /// </summary>
  internal class NameTable : Table
  {
      /// <summary>
      /// The table tag name identifying the 'name' table.
      /// </summary>
      internal const string TableName = "name";

      /// <summary>
      /// The array of name records contained in this table.
      /// </summary>
      private readonly NameRecord[] names;

      /// <summary>
      /// Initializes a new instance of the <see cref="NameTable"/> class.
      /// </summary>
      /// <param name="names">The name records.</param>
      /// <param name="languages">The language tag strings (format 1 only).</param>
      internal NameTable(NameRecord[] names, string[] languages)
          => this.names = names;

      /// <summary>
      /// Gets the unique font identifier for the specified culture.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <returns>The unique font identifier string.</returns>
      public string Id(CultureInfo culture)
          => this.GetNameById(culture, KnownNameIds.UniqueFontID);

      /// <summary>
      /// Gets the full font name for the specified culture.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <returns>The full font name string.</returns>
      public string FontName(CultureInfo culture)
          => this.GetNameById(culture, KnownNameIds.FullFontName);

      /// <summary>
      /// Gets the font family name for the specified culture.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <returns>The font family name string.</returns>
      public string FontFamilyName(CultureInfo culture)
          => this.GetNameById(culture, KnownNameIds.FontFamilyName);

      /// <summary>
      /// Gets the font subfamily name (e.g., "Bold", "Italic") for the specified culture.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <returns>The font subfamily name string.</returns>
      public string FontSubFamilyName(CultureInfo culture)
          => this.GetNameById(culture, KnownNameIds.FontSubfamilyName);

      /// <summary>
      /// Gets the name string for the specified culture and name identifier.
      /// Falls back to US English (0x0409), then the first Windows platform record, then any record.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <param name="nameId">The name identifier to look up.</param>
      /// <returns>The name string, or <see cref="string.Empty"/> if not found.</returns>
      public string GetNameById(CultureInfo culture, KnownNameIds nameId)
      {
          int languageId = culture.LCID;
          NameRecord? usaVersion = null;
          NameRecord? firstWindows = null;
          NameRecord? first = null;
          foreach (NameRecord name in this.names)
          {
              if (name.NameID == nameId)
              {
                  // Get just the first one, just in case.
                  first ??= name;
                  if (name.Platform == PlatformIDs.Windows)
                  {
                      // If us not found return the first windows one.
                      firstWindows ??= name;
                      if (name.LanguageID == 0x0409)
                      {
                          // Grab the us version as its on next best match.
                          usaVersion ??= name;
                      }

                      if (name.LanguageID == languageId)
                      {
                          // Return the most exact first.
                          return name.Value;
                      }
                  }
              }
          }

          return usaVersion?.Value ??
                 firstWindows?.Value ??
                 first?.Value ??
                 string.Empty;
      }

      /// <summary>
      /// Gets the name string for the specified culture and raw name identifier.
      /// </summary>
      /// <param name="culture">The culture used to select the appropriate language-specific name.</param>
      /// <param name="nameId">The raw name identifier value to look up.</param>
      /// <returns>The name string, or <see cref="string.Empty"/> if not found.</returns>
      public string GetNameById(CultureInfo culture, ushort nameId)
          => this.GetNameById(culture, (KnownNameIds)nameId);

      /// <summary>
      /// Loads the <see cref="NameTable"/> from the specified font reader.
      /// </summary>
      /// <param name="fontReader">The font reader to read the table from.</param>
      /// <returns>The loaded <see cref="NameTable"/>.</returns>
      /// <exception cref="InvalidFontTableException">Thrown when the table is missing from the font.</exception>
      public static NameTable? Load(FontReader fontReader)
      {
          if (!fontReader.TryGetReaderAtTablePosition(TableName, out BigEndianBinaryReader? binaryReader))
          {
              throw new InvalidFontTableException($"Table '{TableName}' is missing", TableName);
          }

          using (binaryReader)
          {
              // Move to start of table.
              return Load(binaryReader);
          }
      }

      /// <summary>
      /// Loads the <see cref="NameTable"/> from the specified binary reader.
      /// </summary>
      /// <param name="reader">The binary reader positioned at the start of the name table data.</param>
      /// <returns>The loaded <see cref="NameTable"/>.</returns>
      public static NameTable Load(BigEndianBinaryReader reader)
      {
          var strings = new List<StringLoader>();
          ushort format = reader.ReadUInt16();
          ushort nameCount = reader.ReadUInt16();
          ushort stringOffset = reader.ReadUInt16();

          var names = new NameRecord[nameCount];

          for (int i = 0; i < nameCount; i++)
          {
              names[i] = NameRecord.Read(reader);
              StringLoader? sr = names[i].StringReader;
              if (sr is not null)
              {
                  strings.Add(sr);
              }
          }

          StringLoader[]? langs = Array.Empty<StringLoader>();
          if (format == 1)
          {
              // Format 1 adds language data.
              ushort langCount = reader.ReadUInt16();
              langs = new StringLoader[langCount];

              for (int i = 0; i < langCount; i++)
              {
                  langs[i] = StringLoader.Create(reader);
                  strings.Add(langs[i]);
              }
          }

          foreach (StringLoader readable in strings)
          {
              int readableStartOffset = stringOffset + readable.Offset;

              reader.Seek(readableStartOffset, SeekOrigin.Begin);

              readable.LoadValue(reader);
          }

          string[] langNames = langs?.Select(x => x.Value).ToArray() ?? Array.Empty<string>();

          return new NameTable(names, langNames);
      }
  }
}