From 73ecc0defffe013a8b7ba43542b785012c1c09f9 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Tue, 7 Jul 2015 09:46:39 +0200
Subject: [PATCH] add crdt package with LWW set

---
 crdt/crdt.go | 190 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 190 insertions(+)
 create mode 100644 crdt/crdt.go

diff --git a/crdt/crdt.go b/crdt/crdt.go
new file mode 100644
index 00000000..f60d811b
--- /dev/null
+++ b/crdt/crdt.go
@@ -0,0 +1,190 @@
+package crdt
+
+import (
+	"errors"
+	"sync"
+
+	"github.com/prometheus/log"
+)
+
+var (
+	ErrNotFound = errors.New("not found")
+)
+
+type Elem struct {
+	Key   string
+	Score uint64
+	Value interface{}
+}
+
+type Set interface {
+	Get(key string) (*Elem, error)
+	List() ([]*Elem, error)
+
+	Add(key string, score uint64, v interface{}) error
+	Del(key string, score uint64) error
+}
+
+type Entity struct {
+	add uint64
+	del uint64
+	val interface{}
+}
+
+type LWW struct {
+	storage Storage
+}
+
+func NewLWW(storage Storage) Set {
+	return &LWW{
+		storage: storage,
+	}
+}
+
+func (lww *LWW) Add(key string, score uint64, val interface{}) error {
+	e, err := lww.storage.Get(key)
+	if err != nil && err != ErrNotFound {
+		return err
+	}
+	if err == ErrNotFound {
+		e = &Entity{0, 0, nil}
+	}
+
+	if e.add > score || e.del > score {
+		return nil
+	}
+
+	log.Infof("adding %s", val)
+
+	e.del = 0
+	e.add = score
+	e.val = val
+
+	return lww.storage.Set(key, e)
+}
+
+func (lww *LWW) Del(key string, score uint64) error {
+	e, err := lww.storage.Get(key)
+	if err != nil {
+		return err
+	}
+
+	if e.add > score || e.del > score {
+		return nil
+	}
+
+	e.del = score
+	e.add = 0
+	e.val = nil
+
+	return lww.storage.Set(key, e)
+}
+
+func (lww *LWW) Get(key string) (*Elem, error) {
+	e, err := lww.storage.Get(key)
+	if err != nil {
+		return nil, err
+	}
+	if e.del > e.add {
+		return nil, ErrNotFound
+	}
+
+	return &Elem{
+		Key:   key,
+		Score: e.add,
+		Value: e.val,
+	}, nil
+}
+
+func (lww *LWW) List() ([]*Elem, error) {
+	kval, err := lww.storage.All()
+	if err != nil {
+		return nil, err
+	}
+
+	var res []*Elem
+	for k, e := range kval {
+		if e.add <= e.del {
+			continue
+		}
+		res = append(res, &Elem{
+			Key:   k,
+			Score: e.add,
+			Value: e.val,
+		})
+	}
+
+	return res, nil
+}
+
+// Storage is an interface that holds values associated with
+// a key. This can be used to connect different storage backends
+// to a key set.
+type Storage interface {
+	Set(key string, e *Entity) error
+	Del(key string) error
+	Has(key string) (bool, error)
+	Get(key string) (*Entity, error)
+	All() (map[string]*Entity, error)
+}
+
+func NewMemStorage() Storage {
+	return &memStorage{
+		kval: map[string]*Entity{},
+	}
+}
+
+type memStorage struct {
+	kval map[string]*Entity
+	mtx  sync.RWMutex
+}
+
+func (s *memStorage) Set(key string, e *Entity) error {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	s.kval[key] = e
+	return nil
+}
+
+func (s *memStorage) Get(key string) (*Entity, error) {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	if v, ok := s.kval[key]; ok {
+		return v, nil
+	}
+	return nil, ErrNotFound
+}
+
+func (s *memStorage) Del(key string) error {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	if _, ok := s.kval[key]; !ok {
+		return ErrNotFound
+	}
+
+	delete(s.kval, key)
+	return nil
+}
+
+func (s *memStorage) Has(key string) (bool, error) {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	_, ok := s.kval[key]
+	return ok, nil
+}
+
+func (s *memStorage) All() (map[string]*Entity, error) {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	res := make(map[string]*Entity, len(s.kval))
+	for k, v := range s.kval {
+		res[k] = v
+	}
+
+	return res, nil
+}