ImageSharp/SixLabors.Fonts/SystemFontCollection.cs

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

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;

namespace SixLabors.Fonts {
  /// <summary>
  /// Provides a collection of fonts.
  /// </summary>
  internal sealed class SystemFontCollection : IReadOnlySystemFontCollection, IReadOnlyFontMetricsCollection
  {
      private readonly FontCollection collection;
      private readonly IReadOnlyCollection<string> searchDirectories;

      /// <summary>
      /// Gets the default set of locations we probe for System Fonts.
      /// </summary>
      private static readonly IReadOnlyCollection<string> StandardFontLocations;

      static SystemFontCollection()
      {
          if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
          {
              StandardFontLocations = new[]
              {
                  @"%SYSTEMROOT%\Fonts",
                  @"%APPDATA%\Microsoft\Windows\Fonts",
                  @"%LOCALAPPDATA%\Microsoft\Windows\Fonts",
              };
          }
          else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
          {
              StandardFontLocations = new[]
              {
                  "%HOME%/.fonts/",
                  "%HOME%/.local/share/fonts/",
                  "/usr/local/share/fonts/",
                  "/usr/share/fonts/",
              };
          }
          else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
          {
              StandardFontLocations = new[]
              {
                  // As documented on "Mac OS X: Font locations and their purposes"
                  // https://web.archive.org/web/20191015122508/https://support.apple.com/en-us/HT201722
                  "%HOME%/Library/Fonts/",
                  "/Library/Fonts/",
                  "/System/Library/Fonts/",
                  "/Network/Library/Fonts/",
              };
          }
          else if (RuntimeInformation.IsOSPlatform(OSPlatform.Create("Android")))
          {
              StandardFontLocations = new[]
              {
                  "/system/fonts/"
              };
          }
          else
          {
              StandardFontLocations = Array.Empty<string>();
          }
      }

      public SystemFontCollection()
      {
          IEnumerable<string> paths;
          Native.MacSystemFontsEnumerator? nativeEnumerator = null;

          bool forceDirectoryEnumeration = AppContext.TryGetSwitch("Switch.SixLabors.Fonts.DoNotUseNativeSystemFontsEnumeration", out bool isEnabled) && isEnabled;
          if (!forceDirectoryEnumeration && RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
          {
              nativeEnumerator = new Native.MacSystemFontsEnumerator();

              // The CTFontManagerCopyAvailableFontURLs method might return duplicate paths, hence the call to Distinct()
              paths = nativeEnumerator.Distinct();

              this.searchDirectories = Array.Empty<string>();
          }
          else
          {
              string[] expanded = [.. StandardFontLocations.Select(Environment.ExpandEnvironmentVariables)];
              string[] existingDirectories = [.. expanded.Where(x => Directory.Exists(x))];

              // We do this to provide a consistent experience with case sensitive file systems.
              paths = existingDirectories
                  .SelectMany(x => Directory.EnumerateFiles(x, "*.*", SearchOption.AllDirectories))
                  .Where(x => Path.GetExtension(x).Equals(".ttf", StringComparison.OrdinalIgnoreCase)
                              || Path.GetExtension(x).Equals(".ttc", StringComparison.OrdinalIgnoreCase)
                              || Path.GetExtension(x).Equals(".otf", StringComparison.OrdinalIgnoreCase));

              this.searchDirectories = existingDirectories;
          }

          this.collection = CreateSystemFontCollection(paths, this.searchDirectories);

          nativeEnumerator?.Dispose();
      }

      /// <inheritdoc/>
      public IEnumerable<FontFamily> Families => this.collection.Families;

      /// <inheritdoc/>
      public IEnumerable<string> SearchDirectories => this.searchDirectories;

      /// <inheritdoc/>
      public FontFamily Get(string name) => this.GetByCulture(name, CultureInfo.InvariantCulture);

      /// <inheritdoc/>
      public bool TryGet(string name, out FontFamily family)
          => this.collection.TryGet(name, out family);

      /// <inheritdoc/>
      public IEnumerable<FontFamily> GetByCulture(CultureInfo culture)
          => this.collection.GetByCulture(culture);

      /// <inheritdoc/>
      public FontFamily GetByCulture(string name, CultureInfo culture)
          => this.collection.GetByCulture(name, culture);

      /// <inheritdoc/>
      public bool TryGetByCulture(string name, CultureInfo culture, out FontFamily family)
          => this.collection.TryGetByCulture(name, culture, out family);

      /// <inheritdoc/>
      bool IReadOnlyFontMetricsCollection.TryGetMetrics(string name, CultureInfo culture, FontStyle style, [NotNullWhen(true)] out FontMetrics? metrics)
          => ((IReadOnlyFontMetricsCollection)this.collection).TryGetMetrics(name, culture, style, out metrics);

      /// <inheritdoc/>
      IEnumerable<FontMetrics> IReadOnlyFontMetricsCollection.GetAllMetrics(string name, CultureInfo culture)
          => ((IReadOnlyFontMetricsCollection)this.collection).GetAllMetrics(name, culture);

      /// <inheritdoc/>
      ReadOnlyMemory<FontStyle> IReadOnlyFontMetricsCollection.GetAllStyles(string name, CultureInfo culture)
          => ((IReadOnlyFontMetricsCollection)this.collection).GetAllStyles(name, culture);

      /// <inheritdoc/>
      IEnumerator<FontMetrics> IReadOnlyFontMetricsCollection.GetEnumerator()
          => ((IReadOnlyFontMetricsCollection)this.collection).GetEnumerator();

      private static FontCollection CreateSystemFontCollection(IEnumerable<string> paths, IReadOnlyCollection<string> searchDirectories)
      {
          FontCollection collection = new(searchDirectories);

          foreach (string path in paths)
          {
              try
              {
                  if (path.EndsWith(".ttc", StringComparison.OrdinalIgnoreCase))
                  {
                      _ = collection.AddCollection(path);
                  }
                  else
                  {
                      _ = collection.Add(path);
                  }
              }
              catch
              {
                  // We swallow exceptions installing system fonts as we hold no guarantees about permissions etc.
              }
          }

          return collection;
      }
  }
}