Rotate a database target's archive monthly, daily or hourly (closes #379)

A database target's rotation setting (none, monthly, daily or hourly) puts the UTC period of each event's receive time in its archive file name, so each file holds exactly its period's events. It is on the new webhook page and both target forms, and shown in the target list. Renames move every one of a target's files and move them all back if one fails. The sweep prunes one file at a time under the target's lock and deletes a rotated file it leaves empty. Download opens one file at a time, oldest period first, finding each again under the target's current name. The target list names the current file and totals all of them.

Model: opus-5-5

internal/delivery/target_config_edit.go

@@ -41,6 +41,8 @@ type TargetConfigForm struct {
 	Timeout string
 	// Expiry is the database (archive) target's row expiry.
 	Expiry string
+	// Rotation is the database (archive) target's rotation.
+	Rotation string
 }
 
 // NewTargetConfigForm parses a target's stored configuration into
@@ -85,11 +87,13 @@ func NewTargetConfigForm(
 	}
 }
 
-// databaseConfigForm parses an archive target's optional expiry.
-// An absent, empty or never expiry yields an empty expiry, on which
-// the edit form starts at never; saving it unchanged stores never,
-// which means the same as an empty expiry. An expiry that is set
-// but not a valid duration is an error, not a blank field.
+// databaseConfigForm parses an archive target's optional expiry and
+// rotation. An absent, empty or never expiry yields an empty expiry,
+// on which the edit form starts at never; saving it unchanged stores
+// never, which means the same as an empty expiry. An absent rotation
+// is empty too, and the form starts at none. An expiry that is set
+// but not a valid duration, or a rotation that is not one of the
+// four, is an error, not a blank field.
 func databaseConfigForm(
 	configJSON string,
 ) (TargetConfigForm, error) {
@@ -106,8 +110,15 @@ func databaseConfigForm(
 		)
 	}
 
+	err = ValidateArchiveRotation(cfg.Rotation)
+	if err != nil {
+		return TargetConfigForm{}, err
+	}
+
+	form := TargetConfigForm{Rotation: cfg.Rotation}
+
 	if cfg.Expiry == "" || cfg.Expiry == archiveExpiryNever {
-		return TargetConfigForm{}, nil
+		return form, nil
 	}
 
 	err = ValidateArchiveExpiry(cfg.Expiry)
@@ -115,5 +126,7 @@ func databaseConfigForm(
 		return TargetConfigForm{}, err
 	}
 
-	return TargetConfigForm{Expiry: cfg.Expiry}, nil
+	form.Expiry = cfg.Expiry
+
+	return form, nil
 }