3 files changed, 149 insertions, 0 deletions
diff --git a/strings/pad.ts b/strings/pad.ts
new file mode 100644
index 000000000..f74742cc1
--- /dev/null
+++ b/strings/pad.ts
@@ -0,0 +1,75 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+/** FillOption Object */
+export interface FillOption {
+  /** Char to fill in */
+  char: string;
+  /** Side to fill in */
+  side: "left" | "right";
+  /** If strict, output string can't be greater than strLen*/
+  strict?: boolean;
+  /** char/string used to specify the string has been truncated */
+  strictChar?: string;
+  /** Side of truncate */
+  strictSide?: "left" | "right";
+}
+
+/**
+ * Pad helper for strings.
+ * Input string is processed to output a string with a minimal length.
+ * If the parameter `strict` is set to true, the output string length
+ * is equal to the `strLen` parameter.
+ * Example:
+ *
+ *    pad("deno", 6, { char: "*", side: "left" }) // output : "**deno"
+ *    pad("deno", 6, { char: "*", side: "right"}) // output : "deno**"
+ *    pad("denosorusrex", 6 {
+ *      char: "*",
+ *      side: "left",
+ *      strict: true,
+ *      strictSide: "right",
+ *      strictChar: "..."
+ *    }) // output : "den..."
+ *
+ * @param input Input string
+ * @param strLen Output string lenght
+ * @param opts Configuration object
+ * @param [opts.char=" "] Character used to fill in
+ * @param [opts.side="left"] Side to fill in
+ * @param [opts.strict=false] Flag to truncate the string if length > strLen
+ * @param [opts.strictChar=""] Character to add if string is truncated
+ * @param [opts.strictSide="right"] Side to truncate
+ */
+export function pad(
+  input: string,
+  strLen: number,
+  opts: FillOption = {
+    char: " ",
+    strict: false,
+    side: "left",
+    strictChar: "",
+    strictSide: "right"
+  }
+): string {
+  let out = input;
+  const outL = out.length;
+  if (outL < strLen) {
+    if (opts.side === "left") {
+      out = out.padStart(strLen, opts.char);
+    } else {
+      out = out.padEnd(strLen, opts.char);
+    }
+  } else if (opts.strict && outL > strLen) {
+    let addChar = opts.strictChar ? opts.strictChar : "";
+    if (opts.strictSide === "left") {
+      let toDrop = outL - strLen;
+      if (opts.strictChar) {
+        toDrop += opts.strictChar.length;
+      }
+      out = `${addChar}${out.slice(toDrop, outL)}`;
+    } else {
+      out = `${out.substring(0, strLen - addChar.length)}${addChar}`;
+    }
+  }
+  return out;
+}
diff --git a/strings/pad_test.ts b/strings/pad_test.ts
new file mode 100644
index 000000000..43c80b36f
--- /dev/null
+++ b/strings/pad_test.ts
@@ -0,0 +1,73 @@
+import { test } from "../testing/mod.ts";
+import { assertEquals } from "../testing/asserts.ts";
+import { pad } from "./pad.ts";
+
+test(function padTest() {
+  const expected1 = "**deno";
+  const expected2 = "deno";
+  const expected3 = "deno**";
+  const expected4 = "denosorusrex";
+  const expected5 = "denosorus";
+  const expected6 = "sorusrex";
+  const expected7 = "den...";
+  const expected8 = "...rex";
+  assertEquals(pad("deno", 6, { char: "*", side: "left" }), expected1);
+  assertEquals(pad("deno", 4, { char: "*", side: "left" }), expected2);
+  assertEquals(pad("deno", 6, { char: "*", side: "right" }), expected3);
+  assertEquals(
+    pad("denosorusrex", 4, {
+      char: "*",
+      side: "right",
+      strict: false
+    }),
+    expected4
+  );
+  assertEquals(
+    pad("denosorusrex", 9, {
+      char: "*",
+      side: "left",
+      strict: true,
+      strictSide: "right"
+    }),
+    expected5
+  );
+  assertEquals(
+    pad("denosorusrex", 8, {
+      char: "*",
+      side: "left",
+      strict: true,
+      strictSide: "left"
+    }),
+    expected6
+  );
+  assertEquals(
+    pad("denosorusrex", 6, {
+      char: "*",
+      side: "left",
+      strict: true,
+      strictSide: "right",
+      strictChar: "..."
+    }),
+    expected7
+  );
+  assertEquals(
+    pad("denosorusrex", 6, {
+      char: "*",
+      side: "left",
+      strict: true,
+      strictSide: "left",
+      strictChar: "..."
+    }),
+    expected8
+  );
+  assertEquals(
+    pad("deno", 4, {
+      char: "*",
+      side: "left",
+      strict: true,
+      strictSide: "right",
+      strictChar: "..."
+    }),
+    expected2
+  );
+});
diff --git a/test.ts b/test.ts
index 9034631a6..ee449a971 100755
--- a/test.ts
+++ b/test.ts
@@ -28,6 +28,7 @@ import "./media_types/test.ts";
 import "./multipart/formfile_test.ts";
 import "./multipart/multipart_test.ts";
 import "./prettier/main_test.ts";
+import "./strings/pad_test.ts";
 import "./testing/test.ts";
 import "./textproto/test.ts";
 import "./ws/test.ts";