--# https://theweeklychallenge.org/blog/perl-weekly-challenge-347/
--[[

Task 2: Format Phone Number

Submitted by: [45]Mohammad Sajid Anwar
     __________________________________________________________________

   You are given a phone number as a string containing digits, space and
   dash only.

   Write a script to format the given phone number using the below rules:
1. Removing all spaces and dashes
2. Grouping digits into blocks of length 3 from left to right
3. Handling the final digits (4 or fewer) specially:
   - 2 digits: one block of length 2
   - 3 digits: one block of length 3
   - 4 digits: two blocks of length 2
4. Joining all blocks with dashes

Example 1

Input: $phone = "1-23-45-6"
Output: "123-456"

Example 2

Input: $phone = "1234"
Output: "12-34"

Example 3

Input: $phone = "12 345-6789"
Output: "123-456-789"

Example 4

Input: $phone = "123 4567"
Output: "123-45-67"

Example 5

Input: $phone = "123 456-78"
Output: "123-456-78"
     __________________________________________________________________

   Last date to submit the solution 23:59 (UK Time) Sunday 16th November
   2025.
     __________________________________________________________________

SO WHAT DO YOU THINK ?
--]]
--# solution by pokgopun@gmail.com

function fpn(phone)
	local dgt = {}
	for v in string.gmatch(phone,"%d") do
		table.insert(dgt,v)
	end
	local l = #dgt
	local i = 4
	while i <= l do
		if i == l then
			i = i - 1
		end
		dgt[i] = "-"..dgt[i]
		i = i + 3
	end
	return table.concat(dgt,"")
end

local lu = require("luaunit")

function TestFpn()
	for inpt, otpt in pairs({
		["1-23-45-6"]= "123-456",
		["1234"]= "12-34",
		["12 345-6789"]= "123-456-789",
		["123 4567"] = "123-45-67",
		["123 456-78"] = "123-456-78"}) do
		lu.assertEquals(fpn(inpt), otpt)
	end
end

lu.run()