ordering: fix the semantics of Less()

This tries to address a semantic glitch in Less() to actually do a "less
than" operation on strings and timestamps.  It does not change the
actual behaviour of the endpoints that support "orderby". The sorted
results will be the same as before.

graph/pkg/service/v0/drives.go

@@ -791,7 +791,7 @@ func sortSpaces(req *godata.GoDataRequest, spaces []*libregraph.Drive) ([]*libre
 		return nil, fmt.Errorf("we do not support <%s> as a order parameter", req.Query.OrderBy.OrderByItems[0].Field.Value)
 	}
 
-	if req.Query.OrderBy.OrderByItems[0].Order == "asc" {
+	if req.Query.OrderBy.OrderByItems[0].Order == "desc" {
 		sorter = sort.Reverse(sorter)
 	}
 	sort.Sort(sorter)

graph/pkg/service/v0/groups.go

@@ -352,7 +352,7 @@ func sortGroups(req *godata.GoDataRequest, groups []*libregraph.Group) ([]*libre
 		return nil, fmt.Errorf("we do not support <%s> as a order parameter", req.Query.OrderBy.OrderByItems[0].Field.Value)
 	}
 
-	if req.Query.OrderBy.OrderByItems[0].Order == "asc" {
+	if req.Query.OrderBy.OrderByItems[0].Order == "desc" {
 		sorter = sort.Reverse(sorter)
 	}
 	sort.Sort(sorter)

graph/pkg/service/v0/ordering.go

@@ -24,7 +24,7 @@ type spacesByLastModifiedDateTime struct {
 // Less reports whether the element with index i
 // must sort before the element with index j.
 func (s spacesByName) Less(i, j int) bool {
-	return strings.ToLower(*s.spacesSlice[i].Name) > strings.ToLower(*s.spacesSlice[j].Name)
+	return strings.ToLower(*s.spacesSlice[i].Name) < strings.ToLower(*s.spacesSlice[j].Name)
 }
 
 // Less reports whether the element with index i
@@ -32,18 +32,18 @@ func (s spacesByName) Less(i, j int) bool {
 func (s spacesByLastModifiedDateTime) Less(i, j int) bool {
 	// compare the items when both dates are set
 	if s.spacesSlice[i].LastModifiedDateTime != nil && s.spacesSlice[j].LastModifiedDateTime != nil {
-		return s.spacesSlice[i].LastModifiedDateTime.After(*s.spacesSlice[j].LastModifiedDateTime)
+		return s.spacesSlice[i].LastModifiedDateTime.Before(*s.spacesSlice[j].LastModifiedDateTime)
 	}
-	// move left item down if it has no value
+	// an item without a timestamp is considered "less than" an item with a timestamp
 	if s.spacesSlice[i].LastModifiedDateTime == nil && s.spacesSlice[j].LastModifiedDateTime != nil {
-		return false
-	}
-	// move right item down if it has no value
-	if s.spacesSlice[i].LastModifiedDateTime != nil && s.spacesSlice[j].LastModifiedDateTime == nil {
 		return true
 	}
+	// an item without a timestamp is considered "less than" an item with a timestamp
+	if s.spacesSlice[i].LastModifiedDateTime != nil && s.spacesSlice[j].LastModifiedDateTime == nil {
+		return false
+	}
 	// fallback to name if no dateTime is set on both items
-	return strings.ToLower(*s.spacesSlice[i].Name) > strings.ToLower(*s.spacesSlice[j].Name)
+	return strings.ToLower(*s.spacesSlice[i].Name) < strings.ToLower(*s.spacesSlice[j].Name)
 }
 
 type userSlice []*libregraph.User
@@ -69,19 +69,19 @@ type usersByOnPremisesSamAccountName struct {
 // Less reports whether the element with index i
 // must sort before the element with index j.
 func (u usersByDisplayName) Less(i, j int) bool {
-	return strings.ToLower(u.userSlice[i].GetDisplayName()) > strings.ToLower(u.userSlice[j].GetDisplayName())
+	return strings.ToLower(u.userSlice[i].GetDisplayName()) < strings.ToLower(u.userSlice[j].GetDisplayName())
 }
 
 // Less reports whether the element with index i
 // must sort before the element with index j.
 func (u usersByMail) Less(i, j int) bool {
-	return strings.ToLower(u.userSlice[i].GetMail()) > strings.ToLower(u.userSlice[j].GetMail())
+	return strings.ToLower(u.userSlice[i].GetMail()) < strings.ToLower(u.userSlice[j].GetMail())
 }
 
 // Less reports whether the element with index i
 // must sort before the element with index j.
 func (u usersByOnPremisesSamAccountName) Less(i, j int) bool {
-	return strings.ToLower(u.userSlice[i].GetOnPremisesSamAccountName()) > strings.ToLower(u.userSlice[j].GetOnPremisesSamAccountName())
+	return strings.ToLower(u.userSlice[i].GetOnPremisesSamAccountName()) < strings.ToLower(u.userSlice[j].GetOnPremisesSamAccountName())
 }
 
 type groupSlice []*libregraph.Group
@@ -99,5 +99,5 @@ type groupsByDisplayName struct {
 // Less reports whether the element with index i
 // must sort before the element with index j.
 func (g groupsByDisplayName) Less(i, j int) bool {
-	return strings.ToLower(g.groupSlice[i].GetDisplayName()) > strings.ToLower(g.groupSlice[j].GetDisplayName())
+	return strings.ToLower(g.groupSlice[i].GetDisplayName()) < strings.ToLower(g.groupSlice[j].GetDisplayName())
 }

graph/pkg/service/v0/users.go

@@ -272,7 +272,7 @@ func sortUsers(req *godata.GoDataRequest, users []*libregraph.User) ([]*libregra
 		return nil, fmt.Errorf("we do not support <%s> as a order parameter", req.Query.OrderBy.OrderByItems[0].Field.Value)
 	}
 
-	if req.Query.OrderBy.OrderByItems[0].Order == "asc" {
+	if req.Query.OrderBy.OrderByItems[0].Order == "desc" {
 		sorter = sort.Reverse(sorter)
 	}
 	sort.Sort(sorter)