Offer archive expiry choices on the target forms, show plain units (closes #396)

Adding or editing a database target now offers the archive expiry
choices of the new webhook page (never, 1h, 12h, 24h, 30d, 90d, 365d)
in place of a text field. The list is defined once, in
internal/handlers/archive_expiry.go, and all three forms render it. The
edit form starts on the expiry it shows: the stored one, or the
submitted one after a refused save. One that is not among the choices
is listed first as its own entry, so saving unchanged keeps it. The
target list shows the expiry in plain units, such as "30 days" or
"12 hours", or "never".

Model: opus-5-5

internal/delivery/target_config_view.go

@@ -1,9 +1,9 @@
 package delivery
 
 import (
-	"encoding/json"
 	"fmt"
 	"strconv"
+	"time"
 
 	"sneak.berlin/go/webhooker/internal/database"
 )
@@ -197,37 +197,61 @@ func maxRetriesField(t *database.Target) ConfigField {
 	}
 }
 
-// databaseConfigFields describes an archive target. Its
-// configuration is optional, and an absent or empty expiry
-// means the archive is kept forever. An expiry that is set
-// but not a valid duration is reported as unavailable rather
-// than echoed back.
+// databaseConfigFields describes an archive target by its
+// expiry in plain units, such as "30 days", or "never" when
+// the archive is kept forever. An expiry that is set but not
+// a valid duration is reported as unavailable rather than
+// echoed back.
 func databaseConfigFields(configJSON string) []ConfigField {
-	expiry := archiveExpiryNever
+	expiry, err := parseArchiveExpiry(configJSON)
+	if err != nil {
+		return unavailableConfigFields()
+	}
 
-	if configJSON != "" {
-		var cfg databaseTargetConfig
-
-		err := json.Unmarshal([]byte(configJSON), &cfg)
-		if err != nil {
-			return unavailableConfigFields()
-		}
-
-		if cfg.Expiry != "" {
-			if ValidateArchiveExpiry(cfg.Expiry) != nil {
-				return unavailableConfigFields()
-			}
-
-			expiry = cfg.Expiry
-		}
+	value := archiveExpiryNever
+	if expiry > 0 {
+		value = plainDuration(expiry)
 	}
 
 	return []ConfigField{{
 		Label: "Archive Expiry",
-		Value: expiry,
+		Value: value,
 	}}
 }
 
+// plainDuration writes a positive duration as a count of the
+// largest whole unit it divides into: "30 days", "12 hours",
+// "1 minute". A duration with a fraction of a second is
+// written as Go writes it.
+func plainDuration(d time.Duration) string {
+	const day = 24 * time.Hour
+
+	units := []struct {
+		size time.Duration
+		name string
+	}{
+		{day, "day"},
+		{time.Hour, "hour"},
+		{time.Minute, "minute"},
+		{time.Second, "second"},
+	}
+
+	for _, unit := range units {
+		if d%unit.size != 0 {
+			continue
+		}
+
+		count := int64(d / unit.size)
+		if count == 1 {
+			return "1 " + unit.name
+		}
+
+		return fmt.Sprintf("%d %ss", count, unit.name)
+	}
+
+	return d.String()
+}
+
 // MaskedWebhookURL returns the Slack webhook URL reduced to
 // its scheme and host, with the path, query and any userinfo
 // elided. The path segments are the credential, so none of