Show a database target's archive file, size and last write in the target list (closes #397)

Each database target's row on the webhook page names its archive
file, as delivery.ArchivePath finds it, and shows its size on disk and
when it was last written, or "not created yet" when there is no file.
The figures come from the metadata of the file and its -wal only: the
size is the two together, and the last write the later of their
modification times, since a write lands in the -wal first.

Model: opus-5-5

internal/handlers/target_list.go

@@ -0,0 +1,90 @@
+package handlers
+
+import (
+	"errors"
+	"io/fs"
+	"path/filepath"
+	"time"
+
+	"github.com/dustin/go-humanize"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+)
+
+// TargetRowView is one row of the target list on a webhook's page.
+type TargetRowView struct {
+	delivery.TargetView
+
+	// Archive is a database target's archive file, and nil for a target
+	// of any other type.
+	Archive *ArchiveFileView
+}
+
+// ArchiveFileView is what a database target's row shows about its
+// archive file.
+type ArchiveFileView struct {
+	Name string
+
+	// Note stands in for the size and the last write when there are
+	// none to show, and is empty when there are.
+	Note string
+
+	// Size is the size on disk. Written is how long ago the file was
+	// last written, and WrittenUTC the full time the page shows on
+	// hover.
+	Size       string
+	Written    string
+	WrittenUTC string
+}
+
+// targetRows projects a webhook's targets for the target list on its
+// page.
+func (h *Handlers) targetRows(
+	webhook *database.Webhook, targets []database.Target,
+) []TargetRowView {
+	views := delivery.NewTargetViews(targets)
+	rows := make([]TargetRowView, len(views))
+
+	// NewTargetViews returns one view per target, in order.
+	for i := range views {
+		rows[i].TargetView = views[i]
+
+		if targets[i].Type == database.TargetTypeDatabase {
+			rows[i].Archive = h.archiveFileView(webhook, &targets[i])
+		}
+	}
+
+	return rows
+}
+
+// archiveFileView describes a database target's archive file from the
+// file's metadata alone; the archive is never opened. The file is found
+// by the name the archive writer uses, so it follows a rename of the
+// webhook or the target.
+func (h *Handlers) archiveFileView(
+	webhook *database.Webhook, target *database.Target,
+) *ArchiveFileView {
+	path := delivery.ArchivePath(h.dbMgr, webhook, target)
+	view := &ArchiveFileView{Name: filepath.Base(path)}
+
+	file, err := delivery.StatArchive(path)
+
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		view.Note = "not created yet"
+	case err != nil:
+		h.log.Error(
+			"failed to read archive file metadata",
+			"target_id", target.ID,
+			"error", err,
+		)
+
+		view.Note = "could not be read"
+	default:
+		view.Size = humanize.Bytes(uint64(file.Size)) //nolint:gosec // never negative
+		view.Written = humanize.Time(file.Written)
+		view.WrittenUTC = file.Written.UTC().Format(time.DateTime) + " UTC"
+	}
+
+	return view
+}