some dest encoding refactoring

modules/game/src/main/Event.scala

@@ -157,7 +157,7 @@ object Event {
     def newJson(moves: Map[Pos, List[Pos]]) =
       if (moves.isEmpty) JsNull
       else {
-        val sb = new java.lang.StringBuilder(64)
+        val sb = new java.lang.StringBuilder(128)
         var first = true
         moves foreach {
           case (orig, dests) =>

modules/socket/src/main/AnaDests.scala

@@ -5,7 +5,7 @@ import play.api.libs.json._
 import chess.format.FEN
 import chess.opening._
 import chess.variant.Variant
-import lila.tree.Node.openingWriter
+import lila.tree.Node.{ openingWriter, destString }
 
 case class AnaDests(
     variant: Variant,
@@ -21,11 +21,7 @@ case class AnaDests(
     if (isInitial) AnaDests.initialDests
     else {
       val sit = chess.Game(variant.some, fen.value.some).situation
-      sit.playable(false) ?? {
-        sit.destinations map {
-          case (orig, dests) => s"${orig.piotr}${dests.map(_.piotr).mkString}"
-        } mkString " "
-      }
+      sit.playable(false) ?? destString(sit.destinations)
     }
 
   lazy val opening = Variant.openingSensibleVariants(variant) ?? {

modules/tree/src/main/tree.scala

@@ -264,11 +264,7 @@ object Node {
         .add("glyphs", glyphs.nonEmpty)
         .add("shapes", if (shapes.list.nonEmpty) Some(shapes.list) else None)
         .add("opening", opening)
-        .add("dests", dests.map {
-          _.map {
-            case (orig, dests) => s"${orig.piotr}${dests.map(_.piotr).mkString}"
-          }.mkString(" ")
-        })
+        .add("dests", dests)
         .add("drops", drops.map { drops =>
           JsString(drops.map(_.key).mkString)
         })
@@ -284,6 +280,23 @@ object Node {
     }
   }
 
+  def destString(dests: Map[Pos, List[Pos]]): String = {
+    val sb = new java.lang.StringBuilder(64)
+    var first = true
+    dests foreach {
+      case (orig, dests) =>
+        if (first) first = false
+        else sb append " "
+        sb append orig.piotr
+        dests foreach { sb append _.piotr }
+    }
+    sb.toString
+  }
+
+  implicit val destsJsonWriter: Writes[Map[Pos, List[Pos]]] = Writes { dests =>
+    JsString(destString(dests))
+  }
+
   implicit val defaultNodeJsonWriter: Writes[Node] =
     makeNodeJsonWriter(alwaysChildren = true)
 

ui/chess/src/main.ts

@@ -23,7 +23,7 @@ export function readDests(lines?: string): Dests | null {
   if (typeof lines === 'undefined') return null;
   const dests: Dests = {};
   if (lines) lines.split(' ').forEach(line => {
-    dests[piotr[line[0]]] = line.split('').slice(1).map(c => piotr[c] as Key)
+    dests[piotr[line[0]]] = line.slice(1).split('').map(c => piotr[c] as Key)
   });
   return dests;
 }