package localapi

import "time"

// normalizeBackupTiers resolves the tier list the Server serves.
//
// Contract (R-82), and the reason this is a named function rather than inline setup: the UNTARGETED
// local-API endpoints must keep behaving exactly as they did before multi-tier existed, forever.
// That property lives here.
//
//   - tiers == nil → synthesize ONE tier from the legacy (Backups, BackupCadence) pair and mark it
//     primary. This is the pre-R-82 shape; every existing caller and test hits this path.
//   - tiers supplied → keep order but hoist the primary to the front; if none is marked primary,
//     the FIRST becomes primary (a tier list with no primary would leave untargeted requests with
//     nothing to act on, which would silently stop backups).
//   - tiers with a nil Service are dropped: a tier with no runner cannot back anything up, and
//     advertising it would be an "applied and empty" tier — the exact fault R-82 exists to fix.
func normalizeBackupTiers(tiers []BackupTier, legacy BackupService, cadence time.Duration) []BackupTier {
	usable := make([]BackupTier, 0, len(tiers))
	for _, t := range tiers {
		if t.Service == nil || t.TargetID == "" {
			continue
		}
		if t.Cadence <= 0 {
			t.Cadence = cadence
		}
		if t.WaitTimeout <= 0 {
			t.WaitTimeout = 2 * time.Hour
		}
		usable = append(usable, t)
	}
	if len(usable) == 0 {
		if legacy == nil {
			return nil
		}
		return []BackupTier{{TargetID: "", Cadence: cadence, WaitTimeout: 2 * time.Hour, Primary: true, Service: legacy}}
	}
	primary := -1
	for i, t := range usable {
		if t.Primary {
			primary = i
			break
		}
	}
	if primary < 0 {
		primary = 0
	}
	out := make([]BackupTier, 0, len(usable))
	usable[primary].Primary = true
	out = append(out, usable[primary])
	for i, t := range usable {
		if i == primary {
			continue
		}
		t.Primary = false
		out = append(out, t)
	}
	return out
}