reverses bill customer account number id into bill customer account number.

accountno.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"

	"github.com/google/uuid"
)

/*

This reads a line by line input of customer account ids until EOF, and finds the related customer numbers by brute force.

Example : `echo 8b0bc34b-ba28-59bf-a87a-6e923e395069 | go run accountno.go`

*/

var (
	accountNSUUID = uuid.NewSHA1(uuid.UUID{}, []byte("customer")) // "customer" is for compatibility reasons
)

func main() {
	if err := run(); err != nil {
		log.Fatal(err)
	}
}

func run() error {

	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		wanted, err := uuid.Parse(scanner.Text())
		if err != nil {
			return err
		}
		for i := 1; i <= 9999999; i++ {
			no := fmt.Sprintf("%07d", i)
			u := uuid.NewSHA1(accountNSUUID, []byte(no))
			if wanted == u {
				fmt.Printf("account id %s relates to account number %s\n", wanted, no)
			}
		}
	}
	if err := scanner.Err(); err != nil {
		return err
	}
	return nil
}