src

ordered_group.go (5928B)

---

 package middleware
 
 import "fmt"
 
 // RelativePosition provides specifying the relative position of a middleware
 // in an ordered group.
 type RelativePosition int
 
 // Relative position for middleware in steps.
 const (
 	After RelativePosition = iota
 	Before
 )
 
 type ider interface {
 	ID() string
 }
 
 // orderedIDs provides an ordered collection of items with relative ordering
 // by name.
 type orderedIDs struct {
 	order *relativeOrder
 	items map[string]ider
 }
 
 const baseOrderedItems = 5
 
 func newOrderedIDs() *orderedIDs {
 	return &orderedIDs{
 		order: newRelativeOrder(),
 		items: make(map[string]ider, baseOrderedItems),
 	}
 }
 
 // Add injects the item to the relative position of the item group. Returns an
 // error if the item already exists.
 func (g *orderedIDs) Add(m ider, pos RelativePosition) error {
 	id := m.ID()
 	if len(id) == 0 {
 		return fmt.Errorf("empty ID, ID must not be empty")
 	}
 
 	if err := g.order.Add(pos, id); err != nil {
 		return err
 	}
 
 	g.items[id] = m
 	return nil
 }
 
 // Insert injects the item relative to an existing item id. Returns an error if
 // the original item does not exist, or the item being added already exists.
 func (g *orderedIDs) Insert(m ider, relativeTo string, pos RelativePosition) error {
 	if len(m.ID()) == 0 {
 		return fmt.Errorf("insert ID must not be empty")
 	}
 	if len(relativeTo) == 0 {
 		return fmt.Errorf("relative to ID must not be empty")
 	}
 
 	if err := g.order.Insert(relativeTo, pos, m.ID()); err != nil {
 		return err
 	}
 
 	g.items[m.ID()] = m
 	return nil
 }
 
 // Get returns the ider identified by id. If ider is not present, returns false.
 func (g *orderedIDs) Get(id string) (ider, bool) {
 	v, ok := g.items[id]
 	return v, ok
 }
 
 // Swap removes the item by id, replacing it with the new item. Returns an error
 // if the original item doesn't exist.
 func (g *orderedIDs) Swap(id string, m ider) (ider, error) {
 	if len(id) == 0 {
 		return nil, fmt.Errorf("swap from ID must not be empty")
 	}
 
 	iderID := m.ID()
 	if len(iderID) == 0 {
 		return nil, fmt.Errorf("swap to ID must not be empty")
 	}
 
 	if err := g.order.Swap(id, iderID); err != nil {
 		return nil, err
 	}
 
 	removed := g.items[id]
 
 	delete(g.items, id)
 	g.items[iderID] = m
 
 	return removed, nil
 }
 
 // Remove removes the item by id. Returns an error if the item
 // doesn't exist.
 func (g *orderedIDs) Remove(id string) (ider, error) {
 	if len(id) == 0 {
 		return nil, fmt.Errorf("remove ID must not be empty")
 	}
 
 	if err := g.order.Remove(id); err != nil {
 		return nil, err
 	}
 
 	removed := g.items[id]
 	delete(g.items, id)
 	return removed, nil
 }
 
 func (g *orderedIDs) List() []string {
 	items := g.order.List()
 	order := make([]string, len(items))
 	copy(order, items)
 	return order
 }
 
 // Clear removes all entries and slots.
 func (g *orderedIDs) Clear() {
 	g.order.Clear()
 	g.items = map[string]ider{}
 }
 
 // GetOrder returns the item in the order it should be invoked in.
 func (g *orderedIDs) GetOrder() []interface{} {
 	order := g.order.List()
 	ordered := make([]interface{}, len(order))
 	for i := 0; i < len(order); i++ {
 		ordered[i] = g.items[order[i]]
 	}
 
 	return ordered
 }
 
 // relativeOrder provides ordering of item
 type relativeOrder struct {
 	order []string
 }
 
 func newRelativeOrder() *relativeOrder {
 	return &relativeOrder{
 		order: make([]string, 0, baseOrderedItems),
 	}
 }
 
 // Add inserts an item into the order relative to the position provided.
 func (s *relativeOrder) Add(pos RelativePosition, ids ...string) error {
 	if len(ids) == 0 {
 		return nil
 	}
 
 	for _, id := range ids {
 		if _, ok := s.has(id); ok {
 			return fmt.Errorf("already exists, %v", id)
 		}
 	}
 
 	switch pos {
 	case Before:
 		return s.insert(0, Before, ids...)
 
 	case After:
 		s.order = append(s.order, ids...)
 
 	default:
 		return fmt.Errorf("invalid position, %v", int(pos))
 	}
 
 	return nil
 }
 
 // Insert injects an item before or after the relative item. Returns
 // an error if the relative item does not exist.
 func (s *relativeOrder) Insert(relativeTo string, pos RelativePosition, ids ...string) error {
 	if len(ids) == 0 {
 		return nil
 	}
 
 	for _, id := range ids {
 		if _, ok := s.has(id); ok {
 			return fmt.Errorf("already exists, %v", id)
 		}
 	}
 
 	i, ok := s.has(relativeTo)
 	if !ok {
 		return fmt.Errorf("not found, %v", relativeTo)
 	}
 
 	return s.insert(i, pos, ids...)
 }
 
 // Swap will replace the item id with the to item. Returns an
 // error if the original item id does not exist. Allows swapping out an
 // item for another item with the same id.
 func (s *relativeOrder) Swap(id, to string) error {
 	i, ok := s.has(id)
 	if !ok {
 		return fmt.Errorf("not found, %v", id)
 	}
 
 	if _, ok = s.has(to); ok && id != to {
 		return fmt.Errorf("already exists, %v", to)
 	}
 
 	s.order[i] = to
 	return nil
 }
 
 func (s *relativeOrder) Remove(id string) error {
 	i, ok := s.has(id)
 	if !ok {
 		return fmt.Errorf("not found, %v", id)
 	}
 
 	s.order = append(s.order[:i], s.order[i+1:]...)
 	return nil
 }
 
 func (s *relativeOrder) List() []string {
 	return s.order
 }
 
 func (s *relativeOrder) Clear() {
 	s.order = s.order[0:0]
 }
 
 func (s *relativeOrder) insert(i int, pos RelativePosition, ids ...string) error {
 	switch pos {
 	case Before:
 		n := len(ids)
 		var src []string
 		if n <= cap(s.order)-len(s.order) {
 			s.order = s.order[:len(s.order)+n]
 			src = s.order
 		} else {
 			src = s.order
 			s.order = make([]string, len(s.order)+n)
 			copy(s.order[:i], src[:i]) // only when allocating a new slice do we need to copy the front half
 		}
 		copy(s.order[i+n:], src[i:])
 		copy(s.order[i:], ids)
 	case After:
 		if i == len(s.order)-1 || len(s.order) == 0 {
 			s.order = append(s.order, ids...)
 		} else {
 			s.order = append(s.order[:i+1], append(ids, s.order[i+1:]...)...)
 		}
 
 	default:
 		return fmt.Errorf("invalid position, %v", int(pos))
 	}
 
 	return nil
 }
 
 func (s *relativeOrder) has(id string) (i int, found bool) {
 	for i := 0; i < len(s.order); i++ {
 		if s.order[i] == id {
 			return i, true
 		}
 	}
 	return 0, false
 }