Session report collection and report templates (#981)

* wip: notification stats

* make report notifications optional

* linting/documentation fixes

* linting/documentation fixes

* merge types.Container and container.Interface

* smaller naming/format fixes

* use typed image/container IDs

* simplify notifier and update tests

* add missed doc comments

* lint fixes

* remove unused constructors

* rename old/new current/latest

pkg/session/report.go

@@ -0,0 +1,90 @@
+package session
+
+import (
+	"github.com/containrrr/watchtower/pkg/types"
+	"sort"
+)
+
+type report struct {
+	scanned []types.ContainerReport
+	updated []types.ContainerReport
+	failed  []types.ContainerReport
+	skipped []types.ContainerReport
+	stale   []types.ContainerReport
+	fresh   []types.ContainerReport
+}
+
+func (r *report) Scanned() []types.ContainerReport {
+	return r.scanned
+}
+func (r *report) Updated() []types.ContainerReport {
+	return r.updated
+}
+func (r *report) Failed() []types.ContainerReport {
+	return r.failed
+}
+func (r *report) Skipped() []types.ContainerReport {
+	return r.skipped
+}
+func (r *report) Stale() []types.ContainerReport {
+	return r.stale
+}
+func (r *report) Fresh() []types.ContainerReport {
+	return r.fresh
+}
+
+// NewReport creates a types.Report from the supplied Progress
+func NewReport(progress Progress) types.Report {
+	report := &report{
+		scanned: []types.ContainerReport{},
+		updated: []types.ContainerReport{},
+		failed:  []types.ContainerReport{},
+		skipped: []types.ContainerReport{},
+		stale:   []types.ContainerReport{},
+		fresh:   []types.ContainerReport{},
+	}
+
+	for _, update := range progress {
+		if update.state == SkippedState {
+			report.skipped = append(report.skipped, update)
+			continue
+		}
+
+		report.scanned = append(report.scanned, update)
+		if update.newImage == update.oldImage {
+			update.state = FreshState
+			report.fresh = append(report.fresh, update)
+			continue
+		}
+
+		switch update.state {
+		case UpdatedState:
+			report.updated = append(report.updated, update)
+		case FailedState:
+			report.failed = append(report.failed, update)
+		default:
+			update.state = StaleState
+			report.stale = append(report.stale, update)
+		}
+	}
+
+	sort.Sort(sortableContainers(report.scanned))
+	sort.Sort(sortableContainers(report.updated))
+	sort.Sort(sortableContainers(report.failed))
+	sort.Sort(sortableContainers(report.skipped))
+	sort.Sort(sortableContainers(report.stale))
+	sort.Sort(sortableContainers(report.fresh))
+
+	return report
+}
+
+type sortableContainers []types.ContainerReport
+
+// Len implements sort.Interface.Len
+func (s sortableContainers) Len() int { return len(s) }
+
+// Less implements sort.Interface.Less
+func (s sortableContainers) Less(i, j int) bool { return s[i].ID() < s[j].ID() }
+
+// Swap implements sort.Interface.Swap
+func (s sortableContainers) Swap(i, j int) { s[i], s[j] = s[j], s[i] }