fix: generate dummy items for missing types in historic summary data

models/summary.go

@@ -13,6 +13,8 @@ const (
 	SummaryMachine  uint8 = 4
 )
 
+const UnknownSummaryKey = "unknown"
+
 type Summary struct {
 	ID               uint           `json:"-" gorm:"primary_key"`
 	UserID           string         `json:"user_id" gorm:"not null; index:idx_time_summary_user"`
@@ -45,3 +47,55 @@ type SummaryViewModel struct {
 	Success        string
 	ApiKey         string
 }
+
+/* Augments the summary in a way that at least one item is present for every type.
+If a summary has zero items for a given type, but one or more for any of the other types,
+the total summary duration can be derived from those and inserted as a dummy-item with key "unknown"
+for the missing type.
+For instance, the machine type was introduced post hoc. Accordingly, no "machine"-information is present in
+the data for old heartbeats and summaries. If a user has two years of data without machine information and
+one day with such, a "machine"-chart plotted from that data will reference a way smaller absolute total amount
+of time than the other ones.
+To avoid having to modify persisted data retrospectively, i.e. inserting a dummy SummaryItem for the new type,
+such is generated dynamically here, considering the "machine" for all old heartbeats "unknown".
+*/
+func (s *Summary) FillUnknown() {
+	types := []uint8{SummaryProject, SummaryLanguage, SummaryEditor, SummaryOS, SummaryMachine}
+	missingTypes := make([]uint8, 0)
+	typeItems := map[uint8]*[]*SummaryItem{
+		SummaryProject:  &s.Projects,
+		SummaryLanguage: &s.Languages,
+		SummaryEditor:   &s.Editors,
+		SummaryOS:       &s.OperatingSystems,
+		SummaryMachine:  &s.Machines,
+	}
+	var somePresentType uint8
+
+	for _, t := range types {
+		if len(*typeItems[t]) == 0 {
+			missingTypes = append(missingTypes, t)
+		} else {
+			somePresentType = t
+		}
+	}
+
+	// can't proceed if entire summary is empty
+	if len(missingTypes) == len(types) {
+		return
+	}
+
+	// calculate total duration from any of the present sets of items
+	var timeSum time.Duration
+	for _, item := range *typeItems[somePresentType] {
+		timeSum += item.Total
+	}
+
+	// construct dummy item for all missing types
+	for _, t := range missingTypes {
+		*typeItems[t] = append(*typeItems[t], &SummaryItem{
+			Type:  t,
+			Key:   UnknownSummaryKey,
+			Total: timeSum,
+		})
+	}
+}