From decc5b95e03cc732b8e1a074bafef37a5cb3726d Mon Sep 17 00:00:00 2001
From: Jakub Polak <jakub.polak.vz@gmail.com>
Date: Sat, 27 Jan 2024 23:06:18 +0100
Subject: [PATCH] Add ATIN (U.S. Adoption Taxpayer Identification Number).

---
 lib/us/atin.ml       | 18 ++++++++++++++++++
 lib/us/atin.mli      | 22 ++++++++++++++++++++++
 lib/us/dune          |  4 ++++
 test/us/dune         |  4 ++++
 test/us/test_atin.ml | 24 ++++++++++++++++++++++++
 5 files changed, 72 insertions(+)
 create mode 100644 lib/us/atin.ml
 create mode 100644 lib/us/atin.mli
 create mode 100644 lib/us/dune
 create mode 100644 test/us/dune
 create mode 100644 test/us/test_atin.ml

diff --git a/lib/us/atin.ml b/lib/us/atin.ml
new file mode 100644
index 0000000..dd9e14b
--- /dev/null
+++ b/lib/us/atin.ml
@@ -0,0 +1,18 @@
+exception Invalid_format
+
+let atin_re = Str.regexp "^9\\([0-9][0-9]\\)-93-\\([0-9][0-9][0-9][0-9]\\)$"
+
+let validate number =
+  if Str.string_match atin_re number 0 then number else raise Invalid_format
+
+let is_valid number =
+  try
+    ignore (validate number);
+    true
+  with Failure _ -> false
+
+let format_number number =
+  if String.length number = 9 then
+    String.sub number 0 3 ^ "-" ^ String.sub number 3 2 ^ "-"
+    ^ String.sub number 5 4
+  else number
diff --git a/lib/us/atin.mli b/lib/us/atin.mli
new file mode 100644
index 0000000..3dfff82
--- /dev/null
+++ b/lib/us/atin.mli
@@ -0,0 +1,22 @@
+(*
+ATIN (U.S. Adoption Taxpayer Identification Number).
+
+An Adoption Taxpayer Identification Number (ATIN) is a temporary
+nine-digit number issued by the United States IRS for a child for whom the
+adopting parents cannot obtain a Social Security Number.
+*)
+
+exception Invalid_format
+
+val atin_re : Str.regexp
+(** Regular expression for matching ATINs *)
+
+val validate : string -> string
+(** Check if the number is a valid ATIN.
+    This checks the length and formatting if it is present. *)
+
+val is_valid : string -> bool
+(** Check if the number is a valid ATIN. *)
+
+val format_number : string -> string
+(** Reformat the number to the standard presentation format. *)
diff --git a/lib/us/dune b/lib/us/dune
new file mode 100644
index 0000000..784f967
--- /dev/null
+++ b/lib/us/dune
@@ -0,0 +1,4 @@
+(library
+ (name us)
+ (modules atin)
+ (libraries tools))
diff --git a/test/us/dune b/test/us/dune
new file mode 100644
index 0000000..49c8cb3
--- /dev/null
+++ b/test/us/dune
@@ -0,0 +1,4 @@
+(test
+ (name test_atin)
+ (libraries alcotest us)
+ (modules test_atin))
diff --git a/test/us/test_atin.ml b/test/us/test_atin.ml
new file mode 100644
index 0000000..5d5b53b
--- /dev/null
+++ b/test/us/test_atin.ml
@@ -0,0 +1,24 @@
+let test_validate () =
+  let input = "900-93-0000" in
+  let expected_result = "900-93-0000" in
+  let result = Us.Atin.validate input in
+  Alcotest.(check string) "test_validate" expected_result result
+
+let test_is_valid () =
+  let input = "900-93-0000" in
+  let expected_result = true in
+  let result = Us.Atin.is_valid input in
+  Alcotest.(check bool) "test_is_valid" expected_result result
+
+let test_is_not_valid () =
+  Alcotest.check_raises "Invalid Length" Us.Atin.Invalid_format (fun () ->
+      ignore (Us.Atin.is_valid "123"))
+
+let suite =
+  [
+    ("test_validate", `Quick, test_validate)
+  ; ("test_is_valid", `Quick, test_is_valid)
+  ; ("test_is_not_valid", `Quick, test_is_not_valid)
+  ]
+
+let () = Alcotest.run "ATIN" [ ("suite", suite) ]