Merge pull request #25 from gemstone/csv-extensions

Add extension methods for parsing CSV data

Author: StephenCWills

src/Gemstone/StringExtensions/StringExtensions.cs

@@ -2474,4 +2474,109 @@ public static string Interpolate(this string format, IEnumerable<KeyValuePair<st
 
         return string.Format(indexed, parameterValues);
     }
+
+    /// <summary>
+    /// Parses the string as a CSV document.
+    /// </summary>
+    /// <param name="csv">The string to be parsed</param>
+    /// <returns>An array of rows parsed as CSV data.</returns>
+    public static string[][] ParseAsCSV(this string csv)
+    {
+        using StringReader reader = new(csv);
+        List<string[]> rows = [];
+
+        while (true)
+        {
+            string[]? row = ReadCSVRow(reader);
+            if (row is null) break;
+            rows.Add(row);
+        }
+
+        return [.. rows];
+    }
+
+    /// <summary>
+    /// Reads characters from the text reader and returns a single row of CSV data.
+    /// </summary>
+    /// <param name="reader">The text reader providing the CSV data</param>
+    /// <returns>An array of fields in one row of CSV data or <c>null</c> if there is no more data available from the text reader.</returns>
+    public static string[]? ReadCSVRow(this TextReader reader)
+    {
+        List<string> fields = [];
+        int c = reader.Read();
+
+        if (EOF())
+            return null;
+
+        while (!EOF() && !EOL())
+        {
+            if (Matches('"'))
+                fields.Add(ReadQuoted());
+            else
+                fields.Add(ReadToComma());
+
+            if (Matches(','))
+            {
+                Advance();
+
+                // Edge case for when the last
+                // field in a row is empty
+                if (EOF() || EOL())
+                    fields.Add(string.Empty);
+            }
+        }
+
+        // Advance to the next line before returning
+        if (Matches('\r')) Advance();
+        if (Matches('\n')) Advance();
+        return [.. fields];
+
+        // Gets current character and advances to read the next character
+        char Advance() => (char)(c, c = reader.Read()).c;
+
+        bool Matches(char m) => c == m;
+        bool EOL() => Matches('\r') || Matches('\n');
+        bool EOF() => c == -1;
+
+        string ReadToComma()
+        {
+            StringBuilder token = new();
+
+            while (!EOF() && !EOL() && !Matches(','))
+                token.Append(Advance());
+
+            return token.ToString();
+        }
+
+        string ReadQuoted()
+        {
+            StringBuilder token = new();
+
+            // Skip past the opening quote
+            Advance();
+
+            while (true)
+            {
+                while (!EOF() && !Matches('"'))
+                    token.Append(Advance());
+
+                // Skip past the end quote
+                if (!EOF())
+                    Advance();
+
+                // Check if it's actually an end quote vs an escaped quote
+                if (Matches('"'))
+                    token.Append(Advance());
+                else
+                    break;
+            }
+
+            // Excel treats everything after the
+            // end quote as if it were not quoted
+            if (!EOF() && !EOL() && !Matches(','))
+                token.Append(ReadToComma());
+
+            return token.ToString();
+        }
+    }
 }