Handle cases where the source language is not present in BingTranslator

src/GTranslate/Models/BingTranslationResultModel.cs

@@ -14,7 +14,4 @@ internal sealed class BingTranslationResultModel
 
     [JsonPropertyName("inputTransliteration")]
     public string? InputTransliteration { get; set; }
-
-    [MemberNotNullWhen(true, nameof(DetectedLanguage), nameof(Translations))]
-    public bool HasTranslations => DetectedLanguage is not null && Translations is not null;
 }

src/GTranslate/Results/BingTranslationResult.cs

@@ -1,4 +1,5 @@
 using GTranslate.Translators;
+using System;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 
@@ -10,7 +11,7 @@ namespace GTranslate.Results;
 public class BingTranslationResult : ITranslationResult<Language>, ITranslationResult
 {
     internal BingTranslationResult(string translation, string source, Language targetLanguage,
-        Language sourceLanguage, string? transliteration, string? sourceTransliteration, string? script, float score)
+        Language? sourceLanguage, string? transliteration, string? sourceTransliteration, string? script, float score)
     {
         Translation = translation;
         Source = source;
@@ -34,8 +35,9 @@ internal BingTranslationResult(string translation, string source, Language targe
     /// <inheritdoc/>
     public Language TargetLanguage { get; }
 
-    /// <inheritdoc/>
-    public Language SourceLanguage { get; }
+    /// <inheritdoc cref="ITranslationResult{TLanguage}.SourceLanguage"/>
+    /// <remarks>This property returns <see langword="null"/> when the translator can't determine the source language.</remarks>
+    public Language? SourceLanguage { get; }
 
     /// <summary>
     /// Gets the transliteration of the result (<see cref="Translation"/>).
@@ -62,12 +64,16 @@ internal BingTranslationResult(string translation, string source, Language targe
 
     /// <inheritdoc />
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    ILanguage ITranslationResult<ILanguage>.SourceLanguage => SourceLanguage;
+    Language ITranslationResult<Language>.SourceLanguage => SourceLanguage ?? throw new NotSupportedException("The source language is not available for this result.");
+
+    /// <inheritdoc />
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    ILanguage ITranslationResult<ILanguage>.SourceLanguage => SourceLanguage ?? throw new NotSupportedException("The source language is not available for this result.");
 
     /// <inheritdoc />
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
     ILanguage ITranslationResult<ILanguage>.TargetLanguage => TargetLanguage;
 
     /// <inheritdoc/>
-    public override string ToString() => $"{nameof(Translation)}: '{Translation}', {nameof(TargetLanguage)}: '{TargetLanguage.Name} ({TargetLanguage.ISO6391})', {nameof(SourceLanguage)}: '{SourceLanguage.Name} ({SourceLanguage.ISO6391})', {nameof(Service)}: {Service}";
+    public override string ToString() => $"{nameof(Translation)}: '{Translation}', {nameof(TargetLanguage)}: '{TargetLanguage.Name} ({TargetLanguage.ISO6391})', {nameof(SourceLanguage)}: '{SourceLanguage?.Name ?? "Unknown"} ({SourceLanguage?.ISO6391 ?? "N/A"})', {nameof(Service)}: {Service}";
 }

src/GTranslate/Results/BingTransliterationResult.cs

@@ -1,4 +1,5 @@
 using GTranslate.Translators;
+using System;
 using System.Diagnostics;
 
 namespace GTranslate.Results;
@@ -8,7 +9,8 @@ namespace GTranslate.Results;
 /// </summary>
 public class BingTransliterationResult : ITransliterationResult<Language>, ITransliterationResult
 {
-    internal BingTransliterationResult(string transliteration, string? sourceTransliteration, string source, Language targetLanguage, Language sourceLanguage, string script)
+    internal BingTransliterationResult(string transliteration, string? sourceTransliteration,
+        string source, Language targetLanguage, Language? sourceLanguage, string script)
     {
         Transliteration = transliteration;
         SourceTransliteration = sourceTransliteration;
@@ -35,8 +37,9 @@ internal BingTransliterationResult(string transliteration, string? sourceTransli
     /// <inheritdoc/>
     public Language TargetLanguage { get; }
 
-    /// <inheritdoc/>
-    public Language SourceLanguage { get; }
+    /// <inheritdoc cref="ITransliterationResult{TLanguage}.SourceLanguage"/>
+    /// <remarks>This property returns <see langword="null"/> when the translator can't determine the source language.</remarks>
+    public Language? SourceLanguage { get; }
 
     /// <summary>
     /// Gets the language script.
@@ -45,12 +48,16 @@ internal BingTransliterationResult(string transliteration, string? sourceTransli
 
     /// <inheritdoc />
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    ILanguage ITransliterationResult<ILanguage>.SourceLanguage => SourceLanguage;
+    Language ITransliterationResult<Language>.SourceLanguage => SourceLanguage ?? throw new NotSupportedException("The source language is not available for this result.");
+
+    /// <inheritdoc />
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    ILanguage ITransliterationResult<ILanguage>.SourceLanguage => SourceLanguage ?? throw new NotSupportedException("The source language is not available for this result.");
 
     /// <inheritdoc />
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
     ILanguage ITransliterationResult<ILanguage>.TargetLanguage => TargetLanguage;
 
     /// <inheritdoc/>
-    public override string ToString() => $"{nameof(Transliteration)}: '{Transliteration}', {nameof(TargetLanguage)}: '{TargetLanguage.Name} ({TargetLanguage.ISO6391})', {nameof(SourceLanguage)}: '{SourceLanguage.Name} ({SourceLanguage.ISO6391})', {nameof(Service)}: {Service}";
+    public override string ToString() => $"{nameof(Transliteration)}: '{Transliteration}', {nameof(TargetLanguage)}: '{TargetLanguage.Name} ({TargetLanguage.ISO6391})', {nameof(SourceLanguage)}: '{SourceLanguage?.Name ?? "Unknown"} ({SourceLanguage?.ISO6391 ?? "N/A"})', {nameof(Service)}: {Service}";
 }

src/GTranslate/Translators/BingTranslator.cs

@@ -120,17 +120,18 @@ public async Task<BingTranslationResult> TranslateAsync(string text, ILanguage t
         var results = document.Deserialize(BingTranslationResultModelContext.Default.BingTranslationResultModelArray)!;
         var result = results[0];
 
-        if (!result.HasTranslations)
+        if (result.Translations is null)
         {
             throw new TranslatorException("Received an invalid response from the API.");
         }
 
         var translation = result.Translations[0];
         var transliteration = translation.Transliteration?.Text;
         var sourceTransliteration = results.ElementAtOrDefault(1)?.InputTransliteration;
+        var sourceLanguage = result.DetectedLanguage?.Language ?? fromLanguage?.ISO6391;
 
-        return new BingTranslationResult(translation.Text, text, Language.GetLanguage(translation.To), Language.GetLanguage(result.DetectedLanguage.Language),
-            transliteration, sourceTransliteration, translation.Transliteration?.Script, result.DetectedLanguage.Score ?? 0);
+        return new BingTranslationResult(translation.Text, text, Language.GetLanguage(translation.To), sourceLanguage is null ? null : Language.GetLanguage(sourceLanguage),
+            transliteration, sourceTransliteration, translation.Transliteration?.Script, result.DetectedLanguage?.Score ?? 0);
     }
 
     /// <summary>
@@ -191,7 +192,7 @@ public async Task<Language> DetectLanguageAsync(string text)
         TranslatorGuards.MaxTextLength(text, MaxTextLength);
 
         var result = await TranslateAsync(text, "en").ConfigureAwait(false);
-        return result.SourceLanguage;
+        return result.SourceLanguage ?? throw new TranslatorException("Unable to detect the language of text.");
     }
 
     /// <summary>