Improve cmdline argument parsing

Two related changes:
- Improve code readability of argument parsing
- Add extra error cases for arguments (elaborate on some errors, like
  the case of parsing the radix)

1 files changed, 32 insertions, 17 deletions

diff --git a/args.go b/args.go
index 3b2bbdd..fbb4cf0 100644
--- a/args.go
+++ b/args.go
@@ -50,30 +50,45 @@ func parseArgs() (args, error) {
 		return args{}, errors.New("You cannot use both -t and -c at the same time.")
 	} else if a.DigitMapOnly && (a.TotativeDigits || a.ExactMTCLarge) {
 		return args{}, errors.New("You cannot use both -d and -t or -m at the same time.")
+	} else if flag.NArg() < 1 {
+		return args{}, errors.New("Please provide an argument (radix to study).")
+	} else if flag.NArg() > 1 {
+		return args{}, errors.New("Too many arguments provided.")
+	}
+
+	radix, err := strconv.ParseUint(flag.Arg(0), 0, 0)
+	if err != nil {
+		return args{}, uintParsingError(flag.Arg(0), err)
+	} else if radix < 2 {
+		return args{}, errors.New("Cannot use 0 or 1 as radices.")
+	}
+
+	a.Radix = uint(radix)
+	return a, nil
+}
+
+// uintParsingError determines what error to show the user if radix parsing fails.
+// parsed is the radix string that was parsed and uintErr is the resulting error.
+func uintParsingError(parsed string, uintErr error) error {
+	_, floatErr := strconv.ParseFloat(parsed, 64)
+	if floatErr != nil {
+		return fmt.Errorf("Error parsing radix: %w", uintErr)
+	}
+
+	var parsingErr *strconv.NumError
+	if !errors.As(uintErr, &parsingErr) {
+		return fmt.Errorf("Error parsing radix: %w", uintErr)
+	} else if errors.Is(parsingErr.Err, strconv.ErrRange) {
+		return fmt.Errorf("Radix is too large.  Please use something smaller.")
 	} else {
-		if flag.NArg() == 1 {
-			if radix, err := strconv.ParseUint(flag.Arg(0), 0, 0); err == nil {
-				if radix > 1 {
-					a.Radix = uint(radix)
-					return a, nil
-				} else {
-					return args{}, errors.New("Radix must be an integer above 1.")
-				}
-			} else {
-				return args{}, fmt.Errorf(
-					"Argument must be an integer above 1 [%w].", err)
-			}
-		} else if flag.NArg() < 1 {
-			return args{}, errors.New("Please provide an argument (radix to study).")
-		} else {
-			return args{}, errors.New("Too many arguments provided.")
-		}
+		return fmt.Errorf("Radix must be an unsigned integer.")
 	}
 }
 
 func printHelp() {
 	fmt.Println("Get important information about a radix.")
 	fmt.Println("You must provide one argument, which is the radix to get information about.")
+	fmt.Println("The radix must be an unsigned integer above 1.")
 	fmt.Println("Usage: radix_info [flags...] <radix>")
 	fmt.Println("Options:")
 	flag.PrintDefaults()