Permutate punctuation (dots) for test email name

make_test_gmails.go

package main

/*
Got the idea from https://learn.lytics.com/understanding/product-docs/lytics-javascript-tag/testing-and-verification#testing-audiences

Given an input of "test", makes:

    t.e.s.t.@gmail.com
    t.e.s.t@gmail.com
    t.e.st.@gmail.com
    t.e.st@gmail.com
    t.es.t.@gmail.com
    t.es.t@gmail.com
    t.est.@gmail.com
    t.est@gmail.com
    te.s.t.@gmail.com
    te.s.t@gmail.com
    te.st.@gmail.com
    te.st@gmail.com
    tes.t.@gmail.com
    tes.t@gmail.com
    test.@gmail.com
    test@gmail.com

This list gets exponentially big--7 letters in the name = 128 versions of the
name--so make sure to redirect to a file (I picked a CSV extension so
the list can be loaded and tracked in Excel):

    ./make_test_gmails test > test_gmails.csv
*/

import (
	"fmt"
	"os"
	"strings"
)

func permutatePuncs(s string, _len int, puncs []string) []string {
	if len(s) == _len {
		puncs = append(puncs, s)
		return puncs
	}

	puncs = permutatePuncs(s+".", _len, puncs)
	// Encode a space (" ") as a place-holder for "not-punctuated", e.g.,
	//   ['.. .', '. . ', ' . .']
	puncs = permutatePuncs(s+" ", _len, puncs)

	return puncs
}

func main() {
	name := os.Args[1]
	_len := len(name)
	puncSets := permutatePuncs("", _len, make([]string, 0))

	letters := strings.Split(name, "")
	punctuatedNames := make([]string, 0)

	for _, puncSet := range puncSets {
		puncFields := strings.Split(puncSet, "")

		puncNameFields := make([]string, 0)
		for i := 0; i < _len; i++ {
			puncLetter := strings.TrimSpace(letters[i] + puncFields[i])
			puncNameFields = append(puncNameFields, puncLetter)
		}
		punctuatedNames = append(
			punctuatedNames, strings.Join(puncNameFields, "")+"@gmail.com")
	}

	for _, punctuatedName := range punctuatedNames {
		fmt.Println(punctuatedName)
	}

}