Added change.Timeline, added change submissions to channel mutations, made all change submissions spin off a goroutine

model/change/change.go

@@ -2,6 +2,7 @@ package change
 
 import (
 	"log"
+	"sync"
 	"time"
 
 	"git.aiterp.net/rpdata/api/model/counter"
@@ -30,8 +31,13 @@ var PublicModels = []string{
 	"Post",
 }
 
+var submitMutex sync.Mutex
+
 // Submit submits a change to the history.
 func Submit(model, op, author, objectID string, data interface{}) (Change, error) {
+	submitMutex.Lock()
+	defer submitMutex.Unlock()
+
 	index, err := counter.Next("auto_increment", "Change")
 	if err != nil {
 		return Change{}, err
@@ -47,6 +53,8 @@ func Submit(model, op, author, objectID string, data interface{}) (Change, error
 		Data:     data,
 	}
 
+	Timeline.push(change)
+
 	err = collection.Insert(&change)
 	if err != nil {
 		return Change{}, err
@@ -55,6 +63,28 @@ func Submit(model, op, author, objectID string, data interface{}) (Change, error
 	return change, err
 }
 
+// FindID gets a change by ID
+func FindID(id int) (Change, error) {
+	change := Change{}
+	err := collection.FindId(id).One(&change)
+	if err != nil {
+		return Change{}, err
+	}
+
+	return change, nil
+}
+
+// List gets all changes in ascending order
+func List() ([]Change, error) {
+	changes := make([]Change, 0, 64)
+	err := collection.Find(nil).Sort("_id").All(&changes)
+	if err != nil {
+		return nil, err
+	}
+
+	return changes, nil
+}
+
 func init() {
 	store.HandleInit(func(db *mgo.Database) {
 		collection = db.C("common.history")

model/change/timeline.go

@@ -0,0 +1,118 @@
+package change
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	"github.com/globalsign/mgo"
+)
+
+// ErrInvalidIndex is returned when a timeline subscriber tries to get a value
+// with a negative id
+var ErrInvalidIndex = errors.New("change.timeline: Invalid ID")
+
+// ErrWaitRequired is returned when a timeline subscriber requests an entry that
+// has not yet been pushed
+var ErrWaitRequired = errors.New("change.timeline: Waiting required")
+
+// ErrExpired is returned when a timeline subscriber requests a change that happened
+// too long ago for it to be in the database.
+var ErrExpired = errors.New("change.timeline: Change has expired")
+
+type timeline struct {
+	mutex      sync.Mutex
+	firstIndex int64
+	currentID  int64
+	cache      []Change
+	notifyCh   chan struct{}
+}
+
+func (timeline *timeline) Get(ctx context.Context, id int64) (Change, error) {
+	change, err := timeline.get(id, false)
+	if err == ErrWaitRequired {
+		if err := timeline.wait(ctx); err != nil {
+			return Change{}, err
+		}
+
+		return timeline.get(id, true)
+	} else if err == mgo.ErrNotFound {
+		return Change{}, ErrExpired
+	}
+
+	return change, nil
+}
+
+func (timeline *timeline) push(change Change) {
+	timeline.mutex.Lock()
+	timeline.cache = append(timeline.cache, change)
+	if len(timeline.cache) > 128 {
+		copy(timeline.cache, timeline.cache[32:])
+		timeline.cache = timeline.cache[:len(timeline.cache)-32]
+	}
+
+	// Only update the currentID if this is more recent than the existing ones
+	if int64(change.ID) > timeline.currentID {
+		timeline.currentID = int64(change.ID)
+	}
+
+	if timeline.notifyCh != nil {
+		close(timeline.notifyCh)
+		timeline.notifyCh = nil
+	}
+	timeline.mutex.Unlock()
+}
+
+func (timeline *timeline) get(id int64, hasWaited bool) (Change, error) {
+	if id < 0 {
+		return Change{}, ErrInvalidIndex
+	}
+
+	timeline.mutex.Lock()
+	if !hasWaited && id > timeline.currentID {
+		timeline.mutex.Unlock()
+		return Change{}, ErrWaitRequired
+	}
+
+	for _, change := range timeline.cache {
+		if change.ID == int(id) {
+			timeline.mutex.Unlock()
+			return change, nil
+		}
+	}
+	timeline.mutex.Unlock()
+
+	return FindID(int(id))
+}
+
+func (timeline *timeline) wait(ctx context.Context) error {
+	timeline.mutex.Lock()
+	if timeline.notifyCh == nil {
+		timeline.notifyCh = make(chan struct{})
+	}
+
+	ch := timeline.notifyCh
+	timeline.mutex.Unlock()
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-ch:
+		return nil
+	}
+}
+
+// Timeline has operations for subscribing to changes in real time
+var Timeline = &timeline{}
+
+// InitializeTimeline fills in the timeline with existing entries
+func InitializeTimeline() {
+	changes, err := List()
+	if err != nil {
+		return
+	}
+
+	for _, change := range changes {
+		Timeline.push(change)
+	}
+}