feat(tui): add SLA reporting view

Full-screen SLA report accessible via [s] from detail panel.
Computes uptime%, downtime, outage count, longest outage, MTTR,
and MTBF from state_changes table. Includes daily breakdown with
bar chart, switchable time periods (24h/7d/30d/90d), and
scrollable viewport. LATE/STALE treated as UP for SLA purposes.

internal/monitor/sla.go

@@ -0,0 +1,225 @@
+package monitor
+
+import (
+	"time"
+
+	"gitea.lerkolabs.com/lerkolabs/uptop/internal/models"
+)
+
+type SLAReport struct {
+	Window      time.Duration
+	UptimePct   float64
+	Downtime    time.Duration
+	OutageCount int
+	LongestOut  time.Duration
+	MTTR        time.Duration
+	MTBF        time.Duration
+}
+
+func ComputeSLA(changes []models.StateChange, currentStatus string, window time.Duration) SLAReport {
+	now := time.Now()
+	windowStart := now.Add(-window)
+
+	report := SLAReport{Window: window}
+
+	if len(changes) == 0 {
+		if isDown(currentStatus) {
+			report.UptimePct = 0
+			report.Downtime = window
+		} else {
+			report.UptimePct = 100
+		}
+		return report
+	}
+
+	// Sort changes chronologically (they come in DESC from DB).
+	sorted := make([]models.StateChange, len(changes))
+	copy(sorted, changes)
+	for i, j := 0, len(sorted)-1; i < j; i, j = i+1, j-1 {
+		sorted[i], sorted[j] = sorted[j], sorted[i]
+	}
+
+	// Determine status at window start: last transition before or at windowStart.
+	statusAtStart := "UP"
+	for i := len(sorted) - 1; i >= 0; i-- {
+		if !sorted[i].ChangedAt.After(windowStart) {
+			statusAtStart = sorted[i].ToStatus
+			break
+		}
+	}
+
+	var upTime, downTime time.Duration
+	var outages []time.Duration
+	cursor := windowStart
+	wasDown := isDown(statusAtStart)
+
+	if wasDown {
+		report.OutageCount = 1
+	}
+
+	var outageStart time.Time
+	if wasDown {
+		outageStart = windowStart
+	}
+
+	for _, sc := range sorted {
+		if sc.ChangedAt.Before(windowStart) {
+			continue
+		}
+		if sc.ChangedAt.After(now) {
+			break
+		}
+
+		seg := sc.ChangedAt.Sub(cursor)
+		if wasDown {
+			downTime += seg
+		} else {
+			upTime += seg
+		}
+
+		newDown := isDown(sc.ToStatus)
+		if !wasDown && newDown {
+			report.OutageCount++
+			outageStart = sc.ChangedAt
+		}
+		if wasDown && !newDown {
+			dur := sc.ChangedAt.Sub(outageStart)
+			outages = append(outages, dur)
+		}
+
+		wasDown = newDown
+		cursor = sc.ChangedAt
+	}
+
+	// Account for time from last change to now.
+	remaining := now.Sub(cursor)
+	if wasDown {
+		downTime += remaining
+		dur := now.Sub(outageStart)
+		outages = append(outages, dur)
+	} else {
+		upTime += remaining
+	}
+
+	total := upTime + downTime
+	if total > 0 {
+		report.UptimePct = float64(upTime) / float64(total) * 100
+	} else {
+		report.UptimePct = 100
+	}
+	report.Downtime = downTime
+
+	if len(outages) > 0 {
+		var totalOutage time.Duration
+		for _, d := range outages {
+			totalOutage += d
+			if d > report.LongestOut {
+				report.LongestOut = d
+			}
+		}
+		report.MTTR = totalOutage / time.Duration(len(outages))
+	}
+
+	if report.OutageCount > 0 && upTime > 0 {
+		report.MTBF = upTime / time.Duration(report.OutageCount)
+	}
+
+	return report
+}
+
+func ComputeDailyBreakdown(changes []models.StateChange, currentStatus string, days int) []DayReport {
+	now := time.Now()
+	reports := make([]DayReport, days)
+
+	for i := 0; i < days; i++ {
+		dayEnd := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location()).Add(-time.Duration(i) * 24 * time.Hour)
+		if i == 0 {
+			dayEnd = now
+		}
+		dayStart := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location()).Add(-time.Duration(i) * 24 * time.Hour)
+		if i > 0 {
+			dayEnd = dayStart.Add(24 * time.Hour)
+		}
+
+		windowChanges := filterChangesForWindow(changes, dayStart, dayEnd)
+
+		statusAtStart := inferStatusAt(changes, dayStart)
+		sla := computeSLAForWindow(windowChanges, statusAtStart, dayStart, dayEnd)
+
+		reports[i] = DayReport{
+			Date:      dayStart,
+			UptimePct: sla,
+		}
+	}
+
+	return reports
+}
+
+type DayReport struct {
+	Date      time.Time
+	UptimePct float64
+}
+
+func isDown(status string) bool {
+	return status == "DOWN" || status == "SSL EXP"
+}
+
+func filterChangesForWindow(changes []models.StateChange, start, end time.Time) []models.StateChange {
+	var filtered []models.StateChange
+	for _, sc := range changes {
+		if !sc.ChangedAt.Before(start) && sc.ChangedAt.Before(end) {
+			filtered = append(filtered, sc)
+		}
+	}
+	return filtered
+}
+
+func inferStatusAt(changes []models.StateChange, at time.Time) string {
+	// Changes come DESC from DB. Walk backwards to find last change before `at`.
+	for _, sc := range changes {
+		if !sc.ChangedAt.After(at) {
+			return sc.ToStatus
+		}
+	}
+	return "UP"
+}
+
+func computeSLAForWindow(changes []models.StateChange, statusAtStart string, start, end time.Time) float64 {
+	// Sort chronologically.
+	sorted := make([]models.StateChange, len(changes))
+	copy(sorted, changes)
+	for i, j := 0, len(sorted)-1; i < j; i, j = i+1, j-1 {
+		sorted[i], sorted[j] = sorted[j], sorted[i]
+	}
+
+	var upTime, downTime time.Duration
+	cursor := start
+	wasDown := isDown(statusAtStart)
+
+	for _, sc := range sorted {
+		if sc.ChangedAt.Before(start) || !sc.ChangedAt.Before(end) {
+			continue
+		}
+		seg := sc.ChangedAt.Sub(cursor)
+		if wasDown {
+			downTime += seg
+		} else {
+			upTime += seg
+		}
+		wasDown = isDown(sc.ToStatus)
+		cursor = sc.ChangedAt
+	}
+
+	remaining := end.Sub(cursor)
+	if wasDown {
+		downTime += remaining
+	} else {
+		upTime += remaining
+	}
+
+	total := upTime + downTime
+	if total <= 0 {
+		return 100
+	}
+	return float64(upTime) / float64(total) * 100
+}