mtredisalize: Do the actual change tracking, store them in a map and serialize them to JSON when flushing is triggered.

TODO: Implement the POST request to the remote host with this JSON document.

cmd/mtredisalize/changetracker.go

@@ -1,23 +1,27 @@
 package main
 
 import (
+	"encoding/json"
 	"log"
 	"sync"
 
 	"bitbucket.org/s_l_teichmann/mtredisalize/common"
 )
 
+type quantizedXZ struct {
+	X, Z int16
+}
+
 type ChangeTracker struct {
-	mutex sync.Mutex
+	changes map[quantizedXZ]bool
+	mutex   sync.Mutex
 }
 
 func NewChangeTracker() *ChangeTracker {
-	return &ChangeTracker{}
+	return &ChangeTracker{changes: make(map[quantizedXZ]bool)}
 }
 
 func (ct *ChangeTracker) BlockChanged(key []byte) {
-	ct.mutex.Lock()
-	defer ct.mutex.Unlock()
 	var err error
 	var coord common.Coord
 	if coord, err = common.DecodeStringBytesToCoord(key); err != nil {
@@ -25,9 +29,33 @@ func (ct *ChangeTracker) BlockChanged(key []byte) {
 		return
 	}
 	log.Printf("changed block: %v", coord)
+	ct.mutex.Lock()
+	ct.changes[quantizedXZ{X: coord.X / 16, Z: coord.Z / 16}] = true
+	ct.mutex.Unlock()
 }
 
 func (ct *ChangeTracker) FlushChanges(url string) (err error) {
 	log.Println("change flush triggered")
+	var oldChanges map[quantizedXZ]bool
+	ct.mutex.Lock()
+	oldChanges = ct.changes
+	ct.changes = make(map[quantizedXZ]bool)
+	ct.mutex.Unlock()
+	go func() {
+		changes := make([]quantizedXZ, len(oldChanges))
+		i := 0
+		for change, _ := range oldChanges {
+			changes[i] = change
+			i++
+		}
+		var err error
+		var encoded []byte
+		if encoded, err = json.Marshal(changes); err != nil {
+			log.Printf("WARN: encode changes to JSON failed: %s", err)
+			return
+		}
+		// TODO: implement http POST
+		_ = encoded
+	}()
 	return
 }