From 30a4181ceebb5bcee13e62a6539d8253af8a536e Mon Sep 17 00:00:00 2001
From: tacosontitan <contact@tacosontitan.com>
Date: Mon, 25 Nov 2024 22:32:00 -0600
Subject: [PATCH] Add support for capturing comments in JSON.

---
 src/Pasper.Json/Parsing/JsonLexer.cs          | 33 +++++++++++++++++++
 .../Parsing/JsonLexer/TryGetNextToken.cs      | 13 ++++++++
 2 files changed, 46 insertions(+)

diff --git a/src/Pasper.Json/Parsing/JsonLexer.cs b/src/Pasper.Json/Parsing/JsonLexer.cs
index cda82c6..7f5c74a 100644
--- a/src/Pasper.Json/Parsing/JsonLexer.cs
+++ b/src/Pasper.Json/Parsing/JsonLexer.cs
@@ -71,6 +71,9 @@ private bool TryGetNextToken([NotNullWhen(true)] out IToken? token)
         if (TryGetStringToken(out token))
             return true;
 
+        if (TryGetSingleLineCommentToken(out token))
+            return true;
+
         throw new UnexpectedTokenException(_lineNumber, _columnNumber, currentCharacter.ToString());
     }
 
@@ -129,4 +132,34 @@ private bool TryGetStringToken([NotNullWhen(true)] out IToken? token)
         _currentIndex = endIndex + 1;
         return true;
     }
+
+    private bool TryGetSingleLineCommentToken([NotNullWhen(true)] out IToken? token)
+    {
+        if (json[_currentIndex] != '/')
+        {
+            token = null;
+            return false;
+        }
+        
+        var nextToken = json[_currentIndex + 1];
+        if (nextToken is not '/')
+        {
+            token = null;
+            return false;
+        }
+        
+        // Single line comments can technically be placed on the final line of the specified
+        // input. The lexer accounts for this by assuming that if no line breaks are detected
+        // after the start of a comment, that the comment goes to the end of the input.
+        var startIndex = _currentIndex + 2;
+        var endIndex = json.IndexOf('\n', startIndex);
+        if (endIndex == -1)
+            endIndex = json.Length;
+        
+        var value = json.Substring(startIndex, endIndex - startIndex);
+        token = new CommentToken(value.Trim());
+        _currentIndex = endIndex + 1;
+        _columnNumber += value.Length + 2;
+        return true;
+    }
 }
\ No newline at end of file
diff --git a/test/Pasper.Json.Tests/Parsing/JsonLexer/TryGetNextToken.cs b/test/Pasper.Json.Tests/Parsing/JsonLexer/TryGetNextToken.cs
index 3d417b9..0f45dfe 100644
--- a/test/Pasper.Json.Tests/Parsing/JsonLexer/TryGetNextToken.cs
+++ b/test/Pasper.Json.Tests/Parsing/JsonLexer/TryGetNextToken.cs
@@ -44,4 +44,17 @@ public void TryGetNextToken_EndObjectDetected_ReturnsTrue()
         Assert.NotNull(lexer.Current);
         Assert.IsType<EndObjectToken>(lexer.Current);
     }
+
+    [Fact]
+    public void TryGetNextToken_CommentDetected_ReturnsTrue()
+    {
+        const string comment = "this is a comment";
+        const string testJson = $"// {comment}";
+        var lexer = new JsonLexer(testJson);
+        var tokenAvailable = lexer.MoveNext();
+        Assert.True(tokenAvailable);
+        Assert.NotNull(lexer.Current);
+        Assert.IsType<CommentToken>(lexer.Current);
+        Assert.Equal(comment, lexer.Current.Value);
+    }
 }
\ No newline at end of file