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/handlers/archive_expiry.go

@@ -10,10 +10,10 @@ const (
 	tmplKeyArchiveExpiryChoices = "ArchiveExpiryChoices"
 )
 
-// archiveExpiryChoice is one entry of a database target's archive
-// expiry select: the expiry stored, the label shown, and whether the
-// select starts on it.
-type archiveExpiryChoice struct {
+// archiveChoice is one entry of a database target's archive expiry
+// or archive rotation select: the value stored, the label shown, and
+// whether the select starts on it.
+type archiveChoice struct {
 	Value    string
 	Label    string
 	Selected bool
@@ -21,8 +21,8 @@ type archiveExpiryChoice struct {
 
 // archiveExpiryChoices lists the archive expiries offered by the new
 // webhook page, the add target form and the target edit form.
-func archiveExpiryChoices() []archiveExpiryChoice {
-	return []archiveExpiryChoice{
+func archiveExpiryChoices() []archiveChoice {
+	return []archiveChoice{
 		{Value: archiveExpiryNever, Label: archiveExpiryNever},
 		{Value: "1h", Label: "1h"},
 		{Value: "12h", Label: "12h"},
@@ -37,7 +37,7 @@ func archiveExpiryChoices() []archiveExpiryChoice {
 // empty expiry selects never. An expiry that is not one of the
 // choices comes first as its own selected entry, so saving the form
 // unchanged keeps it.
-func archiveExpiryOptions(expiry string) []archiveExpiryChoice {
+func archiveExpiryOptions(expiry string) []archiveChoice {
 	if expiry == "" {
 		expiry = archiveExpiryNever
 	}
@@ -52,7 +52,7 @@ func archiveExpiryOptions(expiry string) []archiveExpiryChoice {
 		}
 	}
 
-	own := archiveExpiryChoice{Value: expiry, Label: expiry, Selected: true}
+	own := archiveChoice{Value: expiry, Label: expiry, Selected: true}
 
-	return append([]archiveExpiryChoice{own}, options...)
+	return append([]archiveChoice{own}, options...)
 }