|
| 1 | +package main |
| 2 | + |
| 3 | +import ( |
| 4 | + _ "embed" |
| 5 | + "fmt" |
| 6 | + "os" |
| 7 | + "strings" |
| 8 | + |
| 9 | + "github.com/spf13/pflag" |
| 10 | +) |
| 11 | + |
| 12 | +var ( |
| 13 | + BUILDER = "unknown" |
| 14 | + COMMIT = "(local)" |
| 15 | + LASTMOD = "(local)" |
| 16 | + VERSION = "internal" |
| 17 | +) |
| 18 | + |
| 19 | +//go:embed README.md |
| 20 | +var helpText string |
| 21 | + |
| 22 | +func allDigits(s string) bool { |
| 23 | + if s == "" { |
| 24 | + return false |
| 25 | + } |
| 26 | + for _, r := range s { |
| 27 | + if r < '0' || r > '9' { |
| 28 | + return false |
| 29 | + } |
| 30 | + } |
| 31 | + return true |
| 32 | +} |
| 33 | + |
| 34 | +func luhnCheckDigit(withoutCheckDigit string) (byte, error) { |
| 35 | + if withoutCheckDigit == "" { |
| 36 | + return 0, fmt.Errorf("input is empty") |
| 37 | + } |
| 38 | + if !allDigits(withoutCheckDigit) { |
| 39 | + return 0, fmt.Errorf("input contains non-digit characters") |
| 40 | + } |
| 41 | + |
| 42 | + sum := 0 |
| 43 | + double := true |
| 44 | + for i := len(withoutCheckDigit) - 1; i >= 0; i-- { |
| 45 | + d := int(withoutCheckDigit[i] - '0') |
| 46 | + if double { |
| 47 | + d *= 2 |
| 48 | + if d > 9 { |
| 49 | + d -= 9 |
| 50 | + } |
| 51 | + } |
| 52 | + sum += d |
| 53 | + double = !double |
| 54 | + } |
| 55 | + |
| 56 | + check := (10 - (sum % 10)) % 10 |
| 57 | + return byte('0' + check), nil |
| 58 | +} |
| 59 | + |
| 60 | +func luhnValid(number string) bool { |
| 61 | + if len(number) < 2 || !allDigits(number) { |
| 62 | + return false |
| 63 | + } |
| 64 | + cd, err := luhnCheckDigit(number[:len(number)-1]) |
| 65 | + if err != nil { |
| 66 | + return false |
| 67 | + } |
| 68 | + return number[len(number)-1] == cd |
| 69 | +} |
| 70 | + |
| 71 | +func correctedLuhn(number string) (string, error) { |
| 72 | + if len(number) < 2 { |
| 73 | + return "", fmt.Errorf("number must have at least 2 digits") |
| 74 | + } |
| 75 | + if !allDigits(number) { |
| 76 | + return "", fmt.Errorf("number must contain only digits") |
| 77 | + } |
| 78 | + cd, err := luhnCheckDigit(number[:len(number)-1]) |
| 79 | + if err != nil { |
| 80 | + return "", err |
| 81 | + } |
| 82 | + return number[:len(number)-1] + string(cd), nil |
| 83 | +} |
| 84 | + |
| 85 | +func main() { |
| 86 | + var noErrorLevel = pflag.Bool("no-error-level", false, "Do not return non-zero exit code when Luhn check fails") |
| 87 | + var verbose = pflag.Bool("verbose", false, "If check fails, print corrected number with fixed last digit") |
| 88 | + var quiet = pflag.Bool("quiet", false, "Do not print PASS/FAIL") |
| 89 | + |
| 90 | + var help = pflag.BoolP("help", "h", false, "Show help message") |
| 91 | + var version = pflag.Bool("version", false, "Print version information") |
| 92 | + |
| 93 | + pflag.Parse() |
| 94 | + |
| 95 | + if *version { |
| 96 | + fmt.Fprintf(os.Stdout, "luhncheck version %s (built by %s on %s, commit %s)\n", VERSION, BUILDER, LASTMOD, COMMIT) |
| 97 | + return |
| 98 | + } |
| 99 | + |
| 100 | + if *help { |
| 101 | + fmt.Printf("Usage: luhncheck [options] <number>\n\n") |
| 102 | + fmt.Printf("Options:\n") |
| 103 | + pflag.PrintDefaults() |
| 104 | + fmt.Printf("%s\n", helpText) |
| 105 | + return |
| 106 | + } |
| 107 | + |
| 108 | + args := pflag.Args() |
| 109 | + if len(args) == 0 { |
| 110 | + fmt.Fprintf(os.Stderr, "ERROR: missing number argument\n") |
| 111 | + os.Exit(1) |
| 112 | + } |
| 113 | + if len(args) > 1 { |
| 114 | + fmt.Fprintf(os.Stderr, "WARNING: ignoring extra arguments (count=%d)\n", len(args)-1) |
| 115 | + } |
| 116 | + |
| 117 | + number := strings.TrimSpace(args[0]) |
| 118 | + if len(number) < 2 { |
| 119 | + fmt.Fprintf(os.Stderr, "ERROR: number must have at least 2 digits\n") |
| 120 | + os.Exit(1) |
| 121 | + } |
| 122 | + if !allDigits(number) { |
| 123 | + fmt.Fprintf(os.Stderr, "ERROR: number must contain only digits\n") |
| 124 | + os.Exit(1) |
| 125 | + } |
| 126 | + |
| 127 | + valid := luhnValid(number) |
| 128 | + if !*quiet { |
| 129 | + if valid { |
| 130 | + fmt.Fprint(os.Stdout, "PASS") |
| 131 | + } else { |
| 132 | + fmt.Fprint(os.Stdout, "FAIL") |
| 133 | + } |
| 134 | + } |
| 135 | + |
| 136 | + if !valid && *verbose { |
| 137 | + fixed, err := correctedLuhn(number) |
| 138 | + if err == nil { |
| 139 | + if !*quiet { |
| 140 | + fmt.Fprintln(os.Stdout) |
| 141 | + } |
| 142 | + fmt.Fprintf(os.Stdout, "Fixed: %s", fixed) |
| 143 | + } |
| 144 | + } |
| 145 | + |
| 146 | + if valid || *noErrorLevel { |
| 147 | + return |
| 148 | + } |
| 149 | + os.Exit(1) |
| 150 | +} |
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