error handling (#16)

AlrikOlson · web-flow · commit 701a9e4c73fe · 2024-08-06T03:39:58.000Z
diff --git a/README.md b/README.md
@@ -59,6 +59,36 @@ var svg = wrapper.RenderDiagram(script);
 // You can save this to a file, display it in a web page, or process it further as needed
 ```
 
+## Error Handling
+
+The `RenderDiagram` method now returns a `RenderResult` object, which includes both the rendered SVG (if successful) and detailed error information (if rendering failed). Here's how you can use it:
+
+```csharp
+var wrapper = new D2Wrapper();
+string script = @"
+A -> B
+B ->  // This line has an error
+C -> D
+";
+
+var result = wrapper.RenderDiagram(script);
+
+if (result.IsSuccess)
+{
+    Console.WriteLine("Diagram rendered successfully:");
+    Console.WriteLine(result.Svg);
+}
+else
+{
+    Console.WriteLine("Error rendering diagram:");
+    Console.WriteLine($"Message: {result.Error.Message}");
+    if (result.Error.LineNumber.HasValue)
+    {
+        Console.WriteLine($"Line {result.Error.LineNumber}: {result.Error.LineContent}");
+    }
+}
+```
+
 Running the web demo:
 
 ```
diff --git a/README.nuget.md b/README.nuget.md
@@ -49,6 +49,36 @@ catch (Exception ex)
 }
 ```
 
+## Error Handling
+
+The `RenderDiagram` method now returns a `RenderResult` object, which includes both the rendered SVG (if successful) and detailed error information (if rendering failed). Here's how you can use it:
+
+```csharp
+var wrapper = new D2Wrapper();
+string script = @"
+A -> B
+B ->  // This line has an error
+C -> D
+";
+
+var result = wrapper.RenderDiagram(script);
+
+if (result.IsSuccess)
+{
+    Console.WriteLine("Diagram rendered successfully:");
+    Console.WriteLine(result.Svg);
+}
+else
+{
+    Console.WriteLine("Error rendering diagram:");
+    Console.WriteLine($"Message: {result.Error.Message}");
+    if (result.Error.LineNumber.HasValue)
+    {
+        Console.WriteLine($"Line {result.Error.LineNumber}: {result.Error.LineContent}");
+    }
+}
+```
+
 ## Features
 
 - Render D2 diagrams as SVG
diff --git a/examples/D2Sharp.Web/Program.cs b/examples/D2Sharp.Web/Program.cs
@@ -19,14 +19,29 @@
         return Results.BadRequest("Script is required");
     }
 
-    try
+    var result = d2Wrapper.RenderDiagram(request.Script);
+
+    if (result.IsSuccess)
     {
-        var svg = d2Wrapper.RenderDiagram(request.Script);
-        return Results.Content(svg, "image/svg+xml");
+        return Results.Content(result.Svg, "image/svg+xml");
     }
-    catch (Exception ex)
+    else
     {
-        return Results.BadRequest($"Error rendering diagram: {ex.Message}");
+        var highlightedParts = result.Error.GetHighlightedLineParts();
+        var errorResponse = new
+        {
+            message = result.Error.Message,
+            lineNumber = result.Error.LineNumber,
+            column = result.Error.Column,
+            lineContent = result.Error.LineContent,
+            highlightedLineParts = new
+            {
+                beforeError = highlightedParts.beforeError,
+                errorPart = highlightedParts.errorPart,
+                afterError = highlightedParts.afterError
+            }
+        };
+        return Results.BadRequest(errorResponse);
     }
 });
 
diff --git a/examples/D2Sharp.Web/wwwroot/index.html b/examples/D2Sharp.Web/wwwroot/index.html
@@ -8,12 +8,16 @@
         body { font-family: Arial, sans-serif; max-width: 800px; margin: 0 auto; padding: 20px; }
         textarea { width: 100%; height: 200px; }
         #result { margin-top: 20px; }
+        .error { color: red; }
+        .error-line { font-family: monospace; white-space: pre; background-color: #ffeeee; padding: 5px; border-radius: 3px; }
+        .error-highlight { background-color: #ff6666; color: white; font-weight: bold; }
     </style>
 </head>
 <body>
     <h1>D2Sharp Web Demo</h1>
     <textarea id="script" placeholder="Enter your D2 script here...">direction: right
-A -> B -> C</textarea>
+A -> B ->
+C -> D</textarea>
     <button onclick="renderDiagram()">Render Diagram</button>
     <div id="result"></div>
 
@@ -33,11 +37,16 @@ <h1>D2Sharp Web Demo</h1>
                     const svg = await response.text();
                     result.innerHTML = svg;
                 } else {
-                    const error = await response.text();
-                    result.textContent = `Error: ${error}`;
+                    const error = await response.json();
+                    let errorMessage = `<p class="error">Error: ${error.message}</p>`;
+                    if (error.lineNumber && error.column) {
+                        errorMessage += `<p class="error">At line ${error.lineNumber}, column ${error.column}:</p>`;
+                        errorMessage += `<div class="error-line">${error.highlightedLineParts.beforeError}<span class="error-highlight">${error.highlightedLineParts.errorPart}</span>${error.highlightedLineParts.afterError}</div>`;
+                    }
+                    result.innerHTML = errorMessage;
                 }
             } catch (error) {
-                result.textContent = `Error: ${error.message}`;
+                result.innerHTML = `<p class="error">Error: ${error.message}</p>`;
             }
         }
     </script>
diff --git a/src/D2Sharp/D2Wrapper.cs b/src/D2Sharp/D2Wrapper.cs
@@ -1,6 +1,7 @@
 ﻿using System.Runtime.InteropServices;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using System.Text.RegularExpressions;
 
 namespace D2Sharp;
 
@@ -19,9 +20,10 @@ public D2Wrapper(ILogger<D2Wrapper>? logger = null)
     [LibraryImport("d2wrapper", EntryPoint = "FreeDiagram")]
     private static partial void FreeDiagram(IntPtr ptr);
 
-    public string? RenderDiagram(string script)
+    public RenderResult RenderDiagram(string script)
     {
-        _logger.LogDebug("Calling RenderDiagram with script {Script}", script);
+        _logger.LogDebug("Calling RenderDiagram with script");
+
         IntPtr errorPtr;
         var svgPtr = RenderDiagramInternal(script, out errorPtr);
 
@@ -30,19 +32,87 @@ public D2Wrapper(ILogger<D2Wrapper>? logger = null)
             var errorMessage = Marshal.PtrToStringUTF8(errorPtr);
             FreeDiagram(errorPtr);
             _logger.LogError("Diagram rendering failed: {ErrorMessage}", errorMessage);
-            throw new Exception($"Diagram rendering failed: {errorMessage}");
+            return new RenderResult { Error = ParseError(errorMessage, script) };
         }
 
         if (svgPtr == IntPtr.Zero)
         {
             _logger.LogError("RenderDiagramInternal returned null pointer");
-            return null;
+            return new RenderResult { Error = new D2Error { Message = "Rendering failed with null result" } };
         }
 
         var svg = Marshal.PtrToStringUTF8(svgPtr);
         FreeDiagram(svgPtr);
 
-        _logger.LogDebug("Rendered diagram");
-        return svg;
+        _logger.LogDebug("Rendered diagram successfully");
+        return new RenderResult { Svg = svg };
+    }
+
+    private D2Error ParseError(string errorMessage, string script)
+    {
+        var error = new D2Error { Message = errorMessage };
+
+        // Match the format: "Compilation error: line:column: specific error message"
+        var match = Regex.Match(errorMessage, @"Compilation error: (\d+):(\d+): (.+)");
+        if (match.Success)
+        {
+            if (int.TryParse(match.Groups[1].Value, out int lineNumber))
+            {
+                error.LineNumber = lineNumber;
+                error.LineContent = GetLineContent(script, lineNumber);
+            }
+            if (int.TryParse(match.Groups[2].Value, out int column))
+            {
+                error.Column = column;
+            }
+            error.Message = match.Groups[3].Value.Trim();
+        }
+
+        return error;
+    }
+
+    private string GetLineContent(string script, int lineNumber)
+    {
+        var lines = script.Split('\n');
+        if (lineNumber > 0 && lineNumber <= lines.Length)
+        {
+            return lines[lineNumber - 1];
+        }
+        return string.Empty;
+    }
+}
+
+public class RenderResult
+{
+    public string? Svg { get; set; }
+    public D2Error? Error { get; set; }
+    public bool IsSuccess => Error == null;
+}
+
+public class D2Error
+{
+    public string Message { get; set; } = "";
+    public int? LineNumber { get; set; }
+    public int? Column { get; set; }
+    public string? LineContent { get; set; }
+
+    public (string beforeError, string errorPart, string afterError) GetHighlightedLineParts()
+    {
+        if (string.IsNullOrEmpty(LineContent) || !Column.HasValue || Column.Value <= 0)
+        {
+            return (LineContent ?? "", "", "");
+        }
+
+        int highlightIndex = Column.Value - 1;
+        if (highlightIndex >= LineContent.Length)
+        {
+            highlightIndex = LineContent.Length - 1;
+        }
+
+        string beforeError = LineContent.Substring(0, highlightIndex);
+        string errorPart = LineContent.Substring(highlightIndex, 1);
+        string afterError = highlightIndex + 1 < LineContent.Length ? LineContent.Substring(highlightIndex + 1) : "";
+
+        return (beforeError, errorPart, afterError);
     }
 }
