checkpoint: column repositioning implementation

internal/board/board.go

@@ -11,6 +11,7 @@ import (
 	bolt "go.etcd.io/bbolt"
 )
 
+// Board is probably the heart of Pelican.
 type Board struct {
 	db *bolt.DB
 }
@@ -90,9 +91,7 @@ func (b *Board) StatusList() ([]Status, error) {
 	return statuses, nil
 }
 
-// Status returns a single status from the db.
-// TODO: Add a test case that handles when a status does not exist.
-// Or use in delete status case.
+// Status returns a single status from the database.
 func (b *Board) Status(statusID int) (Status, error) {
 	data, err := db.Read(b.db, db.StatusBucket, statusID)
 	if err != nil {
@@ -116,6 +115,7 @@ func (b *Board) Status(statusID int) (Status, error) {
 	return status, nil
 }
 
+// StatusArgs is an argument type for creating or updating statuses.
 type StatusArgs struct {
 	Name     string
 	Position int
@@ -198,21 +198,44 @@ func (b *Board) DeleteStatus(statusID int) error {
 		return fmt.Errorf("unable to delete the status from the database; %w", err)
 	}
 
-	if err := b.normaliseStatusesPositionValues(); err != nil {
+	if err := b.normaliseStatusesPositionValuesFromDatabase(); err != nil {
 		return fmt.Errorf("unable to normalise the statuses position values; %w", err)
 	}
 
 	return nil
 }
 
-// normaliseStatusesPositionValues retrieves the ordered list of statuses from the database and sets
-// each status' positional value based on its position in the list.
-func (b *Board) normaliseStatusesPositionValues() error {
+// RepositionStatus re-positions a status on the Kanban board.
+func (b *Board) RepositionStatus(currentPosition, targetPosition int) error {
 	statuses, err := b.StatusList()
 	if err != nil {
 		return fmt.Errorf("unable to get the list of statuses; %w", err)
 	}
 
+	statuses = moveAndShuffle(statuses, currentPosition, targetPosition)
+
+	if err := b.normaliseStatusesPositionValues(statuses); err != nil {
+		return fmt.Errorf("unable to normalise the statuses position values; %w", err)
+	}
+
+	return nil
+}
+
+// normaliseStatusesPositionValuesFromDatabase retrieves the ordered list of statuses from the database and sets
+// each status' positional value based on its position in the list before saving the updates to the database.
+func (b *Board) normaliseStatusesPositionValuesFromDatabase() error {
+	statuses, err := b.StatusList()
+	if err != nil {
+		return fmt.Errorf("unable to get the list of statuses; %w", err)
+	}
+
+	return b.normaliseStatusesPositionValues(statuses)
+}
+
+// normaliseStatusesPositionValues takes a list of statuses and sets
+// each status' positional value based on its position in the list before
+// saving the updates to the database.
+func (b *Board) normaliseStatusesPositionValues(statuses []Status) error {
 	for i, status := range statuses {
 		updateArgs := UpdateStatusArgs{
 			StatusID: status.ID,
@@ -230,6 +253,7 @@ func (b *Board) normaliseStatusesPositionValues() error {
 	return nil
 }
 
+// MoveToStatusArgs is an argument type for moving a card between statuses.
 type MoveToStatusArgs struct {
 	CardID          int
 	CurrentStatusID int
@@ -260,6 +284,7 @@ func (b *Board) MoveToStatus(args MoveToStatusArgs) error {
 	return nil
 }
 
+// CardArgs is an argument type for creating or updating cards.
 type CardArgs struct {
 	NewTitle       string
 	NewDescription string
@@ -360,6 +385,7 @@ func (b *Board) CardList(ids []int) ([]Card, error) {
 	return cards, nil
 }
 
+// UpdateCardArgs is an argument type for updating a card.
 type UpdateCardArgs struct {
 	CardID int
 	CardArgs
@@ -387,6 +413,7 @@ func (b *Board) UpdateCard(args UpdateCardArgs) error {
 	return nil
 }
 
+// DeleteCardArgs is an argument type for deleting a card.
 type DeleteCardArgs struct {
 	CardID   int
 	StatusID int

internal/board/shuffle.go

@@ -0,0 +1,49 @@
+package board
+
+type shuffleDirection int
+
+const (
+	forwards shuffleDirection = iota
+	backwards
+)
+
+// moveAndShuffle creates a new list where the element specified at the index of the current
+// position is moved to the index of the target position. Elements within the range of the
+// old and new positions will then shuffle forwards or backwards in the list depending on the
+// direction of the move.
+// This is currently used to move specified columns forwards or backwards on the Kanban board.
+// When a column changes position the other columns shuffle forward or backwards as required.
+func moveAndShuffle(input []Status, currentPosition, targetPosition int) []Status {
+	var shuffle shuffleDirection
+
+	if targetPosition < currentPosition {
+		// affected elements will need to shuffle backwards if the focused
+		// element moves towards the beginning of the list...
+		shuffle = backwards
+	} else {
+		// ...or else the elements need to shuffle forwards if the focused
+		// element moves towards the end of the list.
+		shuffle = forwards
+	}
+
+	output := make([]Status, len(input))
+
+	for ind := range input {
+		switch {
+		case (shuffle == backwards) && (ind < targetPosition || ind > currentPosition):
+			output[ind] = input[ind]
+		case (shuffle == backwards) && (ind == currentPosition):
+			output[targetPosition] = input[ind]
+		case (shuffle == backwards):
+			output[ind+1] = input[ind]
+		case (shuffle == forwards) && (ind < currentPosition || ind > targetPosition):
+			output[ind] = input[ind]
+		case (shuffle == forwards) && (ind == currentPosition):
+			output[targetPosition] = input[ind]
+		case (shuffle == forwards):
+			output[ind-1] = input[ind]
+		}
+	}
+
+	return output
+}