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/progress.go

@@ -0,0 +1,56 @@
+package session
+
+import (
+	"github.com/containrrr/watchtower/pkg/types"
+)
+
+// Progress contains the current session container status
+type Progress map[types.ContainerID]*ContainerStatus
+
+// UpdateFromContainer sets various status fields from their corresponding container equivalents
+func UpdateFromContainer(cont types.Container, newImage types.ImageID, state State) *ContainerStatus {
+	return &ContainerStatus{
+		containerID:   cont.ID(),
+		containerName: cont.Name(),
+		imageName:     cont.ImageName(),
+		oldImage:      cont.SafeImageID(),
+		newImage:      newImage,
+		state:         state,
+	}
+}
+
+// AddSkipped adds a container to the Progress with the state set as skipped
+func (m Progress) AddSkipped(cont types.Container, err error) {
+	update := UpdateFromContainer(cont, cont.SafeImageID(), SkippedState)
+	update.error = err
+	m.Add(update)
+}
+
+// AddScanned adds a container to the Progress with the state set as scanned
+func (m Progress) AddScanned(cont types.Container, newImage types.ImageID) {
+	m.Add(UpdateFromContainer(cont, newImage, ScannedState))
+}
+
+// UpdateFailed updates the containers passed, setting their state as failed with the supplied error
+func (m Progress) UpdateFailed(failures map[types.ContainerID]error) {
+	for id, err := range failures {
+		update := m[id]
+		update.error = err
+		update.state = FailedState
+	}
+}
+
+// Add a container to the map using container ID as the key
+func (m Progress) Add(update *ContainerStatus) {
+	m[update.containerID] = update
+}
+
+// MarkForUpdate marks the container identified by containerID for update
+func (m Progress) MarkForUpdate(containerID types.ContainerID) {
+	m[containerID].state = UpdatedState
+}
+
+// Report creates a new Report from a Progress instance
+func (m Progress) Report() types.Report {
+	return NewReport(m)
+}