1 files changed, 136 insertions, 0 deletions
diff --git a/internal/cli/duration.go b/internal/cli/duration.go
new file mode 100644
index 0000000..ee40562
--- /dev/null
+++ b/internal/cli/duration.go
@@ -0,0 +1,136 @@
+package cli
+
+import (
+	"fmt"
+	"math"
+	"strings"
+	"time"
+
+	"github.com/spf13/pflag"
+)
+
+// Per-component upper bounds. A cache-safety grace window is measured in days
+// to a few years; anything past these is a typo or an attempt to overflow the
+// cutoff arithmetic. They are chosen so cutoff = now.AddDate(-y,-m,-d) can never
+// overflow the int year addition or the int64 range of time.Time (representable
+// to ~year 292 billion), so the destructive cutoff can never silently wrap.
+const (
+	maxDurationYears  = 100000
+	maxDurationMonths = 100000 * 12
+	maxDurationDays   = 100000 * 366
+)
+
+var _ pflag.Value = (*duration)(nil)
+
+// duration is a calendar-aware grace window . It holds a tuple
+// (years, months, days) rather than a time.Duration.
+type duration struct {
+	years  int
+	months int
+	days   int
+}
+
+func registerDurationFlag(flags *pflag.FlagSet, v *duration, name string, def string, usage string) {
+	if err := v.Set(def); err != nil {
+		panic(fmt.Sprintf("invalid default for --%s: %v", name, err))
+	}
+	flags.Var(v, name, usage)
+}
+
+// Type implements the `pflags.Value` interface.
+func (d *duration) Type() string {
+	return "duration"
+}
+
+// String implements the `pflags.Value` interface.
+func (d *duration) String() string {
+	sb := &strings.Builder{}
+	if d.years != 0 {
+		fmt.Fprintf(sb, "%dy", d.years)
+	}
+	if d.months != 0 {
+		fmt.Fprintf(sb, "%dm", d.months)
+	}
+	if d.days != 0 {
+		fmt.Fprintf(sb, "%dd", d.days)
+	}
+
+	if sb.Len() == 0 {
+		return "0d"
+	}
+	return sb.String()
+}
+
+// Set parses a combinable value like "1y2m10d", "7d" or "30d". Each component is
+// a non-negative integer followed by one of the units y, m (month), d, and each
+// unit may appear at most once. An empty value or a value with no components is
+// rejected.
+//
+// Set implements the `pflags.Value` interface.
+func (d *duration) Set(raw string) error {
+	parsed := duration{}
+	seen := map[byte]bool{}
+	components := 0
+
+	for i := 0; i < len(raw); {
+		c := raw[i]
+		if c < '0' || c > '9' {
+			return usageError{fmt.Sprintf("invalid duration %q", raw)}
+		}
+
+		n := 0
+		for i < len(raw) && raw[i] >= '0' && raw[i] <= '9' {
+			digit := int(raw[i] - '0')
+			if n > (math.MaxInt-digit)/10 {
+				return usageError{fmt.Sprintf("invalid duration %q (out of range)", raw)}
+			}
+			n = n*10 + digit
+			i++
+		}
+		if i >= len(raw) {
+			return usageError{fmt.Sprintf("invalid duration %q (number %d has no unit)", raw, n)}
+		}
+
+		unit := raw[i]
+		if seen[unit] {
+			return usageError{fmt.Sprintf("invalid duration %q (unit %q repeated)", raw, string(unit))}
+		}
+		switch unit {
+		case 'y':
+			if n > maxDurationYears {
+				return usageError{fmt.Sprintf("invalid duration %q (years exceeds %d)", raw, maxDurationYears)}
+			}
+			parsed.years = n
+		case 'm':
+			if n > maxDurationMonths {
+				return usageError{fmt.Sprintf("invalid duration %q (months exceeds %d)", raw, maxDurationMonths)}
+			}
+			parsed.months = n
+		case 'd':
+			if n > maxDurationDays {
+				return usageError{fmt.Sprintf("invalid duration %q (days exceeds %d)", raw, maxDurationDays)}
+			}
+			parsed.days = n
+		default:
+			return usageError{fmt.Sprintf("invalid duration %q (unknown unit %q)", raw, string(unit))}
+		}
+		seen[unit] = true
+		components++
+		i++
+	}
+
+	if components == 0 {
+		return usageError{fmt.Sprintf("invalid duration %q", raw)}
+	}
+
+	*d = parsed
+	return nil
+}
+
+func (d duration) cutoff(tm time.Time) time.Time {
+	return tm.AddDate(-d.years, -d.months, -d.days)
+}
+
+func (d duration) isZero() bool {
+	return d.years == 0 && d.months == 0 && d.days == 0
+}