feat PadLines: added "Mode" argument

- Added "Mode" argument to the Pad Lines operation.
- Added "Fixed Count" mode. Mimics original behaviour, fixed number of characters added to the string.
- Added "Target Length" mode. Adds padding characters in order to reach a certain length.
- Modified Pad lines implementation to use join rather than slice for final result

src/core/operations/PadLines.mjs

@@ -19,6 +19,7 @@ class PadLines extends Operation {
 
         this.name = "Pad lines";
         this.module = "Default";
+        this.description = "Add the specified character to the beginning or end of each line. Operation modes for padding length are either fixed or target line length."
         this.description = "Add the specified number of the specified character to the beginning or end of each line";
         this.inputType = "string";
         this.outputType = "string";
@@ -37,6 +38,11 @@ class PadLines extends Operation {
                 "name": "Character",
                 "type": "binaryShortString",
                 "value": " "
+            },
+            {
+                "name": "Mode",
+                "type": "option",
+                "value": ["Fixed Count", "Target Length"]
             }
         ];
     }
@@ -47,22 +53,23 @@ class PadLines extends Operation {
      * @returns {string}
      */
     run(input, args) {
-        const [position, len, chr] = args,
+        const [position, len, chr, mode] = args,
             lines = input.split("\n");
         let output = "",
             i = 0;
 
-        if (position === "Start") {
+        for (let i = 0; i < lines.length; i++) {
-            for (i = 0; i < lines.length; i++) {
+            let line = lines[i];
-                output += lines[i].padStart(lines[i].length+len, chr) + "\n";
+            let targetLength = mode == "Fixed Count" ? line.length + len : len;
-            }
+
-        } else if (position === "End") {
+            if (position === "Start") {
-            for (i = 0; i < lines.length; i++) {
+                lines[i] = line.padStart(targetLength, chr);
-                output += lines[i].padEnd(lines[i].length+len, chr) + "\n";
+            } else if (position === "End") {
+                lines[i] = line.padEnd(targetLength, chr);
             }
         }
 
-        return output.slice(0, output.length-1);
+        return lines.join('\n');
     }
 
 }

tests/operations/tests/PadLines.mjs

@@ -0,0 +1,67 @@
+/**
+ * Pad Lines tests.
+ *
+ * @author oliver-mitchell [oliver@polymerlabs.dev]
+ *
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Can pad Lines adds the specified number of characters to the start.",
+        input: "ABCD\nEF",
+        expectedOutput: `--ABCD\n--EF`,
+        recipeConfig: [
+            {
+                op: "Pad Lines",
+                args: ["Start", 2, "-", "Fixed Count"], // [Position, Length, Character, Mode]
+            },
+        ],
+    },
+    {
+        name: "Can pad lines adds the specified number of characters to the start.",
+        input: "ABCD\nEF",
+        expectedOutput: `--ABCD\n--EF`,
+        recipeConfig: [
+            {
+                op: "Pad Lines",
+                args: ["Start", 2, "-", "Fixed Count"], // [Position, Length, Character, Mode]
+            },
+        ],
+    },
+    {
+        name: "Can pad lines adds the specified number of characters to the end.",
+        input: "ABCD\nEF",
+        expectedOutput: `ABCD--\nEF--`,
+        recipeConfig: [
+            {
+                op: "Pad Lines",
+                args: ["End", 2, "-", "Fixed Count"], // [Position, Length, Character, Mode]
+            },
+        ],
+    },
+    {
+        name: "Can pad lines with enough characters to the start in target length mode.",
+        input: "ABCD\nEF",
+        expectedOutput: `------ABCD\n--------EF`,
+        recipeConfig: [
+            {
+                op: "Pad Lines",
+                args: ["Start", 10, "-", "Target Length"], // [Position, Length, Character, Mode]
+            },
+        ],
+    },
+    {
+        name: "Can pad lines with enough characters to the end in target length mode.",
+        input: "ABCD\nEF",
+        expectedOutput: `ABCD------\nEF--------`,
+        recipeConfig: [
+            {
+                op: "Pad Lines",
+                args: ["End", 10, "-", "Target Length"], // [Position, Length, Character, Mode]
+            },
+        ],
+    },
+]);