One Phone Format for the SMS Gateway

One Phone Format for the SMS Gateway

The SMS gateway your company just signed up with accepts one number format only: E.164 — a +, the country calling code, then the subscriber number, digits only and at most 15 of them. The contact records hold whatever people typed over the years: (0)151 234-5678, +49 (151) 2345678, 0049151…, sometimes with an extension tacked on the end. Every message to a badly formatted number bounces, and the gateway bills the bounce. You are writing the normalizer that runs before every send.

Requirements

Create a codeunit named "Phone E164 Formatter" with one public procedure:

procedure ToE164(Raw: Text; DefaultCountryPrefix: Text): Text

Raw is the number as typed. DefaultCountryPrefix is the country calling code to assume for numbers entered in national format, always given with its leading + — for example +49 or +1. Pick object IDs in the 50100–50199 range, and reference other objects by name, never by ID.

Apply the rules in this order:

1. Trim, then cut the extension. Leading and trailing whitespace is ignored. If the remaining text contains the letter x (either case), it introduces an extension: the x and everything after it are discarded, so 0151 234 5678 x123 is the number 0151 234 5678.
2. A + belongs only at the start. After step 1, a + may appear only as the very first character. A + anywhere else — including a second one — makes the number invalid: raise the error Phone number %1 has a + that is not at the start., where %1 is Raw exactly as it was passed in.
3. No letters. If any letter a–z / A–Z remains after step 1, raise Phone number %1 contains letters.
4. Keep the digits and decide the shape. Every character that is not a digit 0–9 — spaces, parentheses, dashes, dots, slashes, the + itself — is dropped; what remains is the digit string. Then:
   • If the text from step 1 starts with +, the number is already international: the result is + followed by the digit string.
   • Otherwise, if the digit string starts with 00, that is the international dialling prefix: the result is + followed by the digit string without its first two zeros.
   • Otherwise the number is national: drop one leading 0 from the digit string if there is one (the national trunk prefix) and put DefaultCountryPrefix in front.
5. Length. Count the digits of the result — the country code counts, the dropped trunk 0 does not. If fewer than 8 or more than 15 remain, raise Phone number %1 has %2 digits, but an E.164 number has 8 to 15., where %2 is that count. Exactly 8 and exactly 15 digits are valid.

The result is always a + followed by digits and nothing else, so a number that is already in that form comes back unchanged.

Examples with DefaultCountryPrefix = +49:

• (0)151 234-5678 → +491512345678
• 030/123.456-78 → +493012345678
• +49 (151) 2345678 → +491512345678
• 0049 151 2345678 → +491512345678
• 0151 234 5678 x123 → +491512345678
• +491512345678 → +491512345678
• 49+151 2345678 → error: the + is not at the start
• 0151 234 ABCD → error: letters
• 01234 → error: after dropping the 0 and adding +49, only 6 digits remain

What the tests check

The grading tests call ToE164 with each input shape above and compare the result character for character: the national number with the trunk zero in parentheses and a dash, a national number written with a slash, a dot and a dash (030/123.456-78), the + form with parentheses and spaces, the 00 form, an extension after a lowercase and after an uppercase x, an input padded with spaces, a national number without a trunk zero (212 555 0123 with +1), and an already canonical number that must come back unchanged. The + and 00 inputs are passed with a different DefaultCountryPrefix than the number carries, so a solution that always prepends the default prefix fails; the national shape is also driven with a randomly generated prefix and subscriber number, so hardcoding +49 fails too. The error tests use a + in the middle, a doubled +, uppercase letters, lowercase letters, the empty input, and results of 6, 7 and 16 digits — they assert that an error is raised and that its text contains the message given above, spelled exactly, with Raw substituted for %1 and the count for %2. Raw is the input as typed: the 7-digit case is +49 12345 x7 with +49, so its message must quote the extension too, and the 7 must not count the extension's digit; the 6-digit case is 01234 with +49, where the count must include the country code and exclude the dropped trunk zero. Exactly 8 and exactly 15 digits must be accepted.

Learn More

• Text data type — the full toolbox for taking a string apart: StrPos, CopyStr, UpperCase and the rest.
• Text.DelChr(Text [, Text] [, Text]) method — removes a set of characters from a string; read the remarks on the Where and Which parameters twice.
• Text.Trim() method — strips the whitespace at both ends in one call.
• Dialog.Error(Text [, Any,...]) method — raising an error whose placeholders are filled from a label.