From 90a92c4121f49d3d631dcf1df2af9be088c17eea Mon Sep 17 00:00:00 2001
From: Alexander Nozik <altavir@gmail.com>
Date: Sun, 1 Aug 2021 20:27:43 +0300
Subject: [PATCH] Don't serialize empty metas

---
 .../space/kscience/dataforge/meta/JsonMeta.kt | 27 +++++++++++--------
 .../space/kscience/dataforge/meta/Meta.kt     |  5 ++--
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
index 60320d7d..12f64762 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
@@ -32,17 +32,22 @@ private fun Meta.toJsonWithIndex(descriptor: MetaDescriptor?, index: String?): J
 } else {
     val pairs: MutableList<Pair<String, JsonElement>> = items.entries.groupBy {
         it.key.body
-    }.mapTo(ArrayList()) { (body, list) ->
+    }.mapNotNullTo(ArrayList()) { (body, list) ->
         val childDescriptor = descriptor?.children?.get(body)
         if (list.size == 1) {
             val (token, element) = list.first()
-            val child: JsonElement = element.toJsonWithIndex(childDescriptor, token.index)
-            body to child
+            //do not add empty element
+            if (!element.isEmpty()) {
+                val child: JsonElement = element.toJsonWithIndex(childDescriptor, token.index)
+                body to child
+            } else null
         } else {
-            val elements: List<JsonElement> = list.sortedBy { it.key.index }.mapIndexed { index, entry ->
-                //Use index if it is not equal to the item order
-                val actualIndex = if (index.toString() != entry.key.index) entry.key.index else null
-                entry.value.toJsonWithIndex(childDescriptor, actualIndex)
+            val elements: List<JsonElement> = list.sortedBy { it.key.index }.mapIndexedNotNull { index, entry ->
+                if (!entry.value.isEmpty()) {
+                    //Use index if it is not equal to the item order
+                    val actualIndex = if (index.toString() != entry.key.index) entry.key.index else null
+                    entry.value.toJsonWithIndex(childDescriptor, actualIndex)
+                } else null
             }
             body to JsonArray(elements)
         }
@@ -55,15 +60,15 @@ private fun Meta.toJsonWithIndex(descriptor: MetaDescriptor?, index: String?): J
 
     //Add value if needed
     if (value != null) {
-        pairs += Meta.VALUE_KEY to value!!.toJson(null)
+        pairs += Meta.VALUE_KEY to value!!.toJson(descriptor)
     }
 
     JsonObject(pairs.toMap())
 }
 
 public fun Meta.toJson(descriptor: MetaDescriptor? = null): JsonObject {
-    val element =  toJsonWithIndex(descriptor, null)
-    return if(element is JsonObject){
+    val element = toJsonWithIndex(descriptor, null)
+    return if (element is JsonObject) {
         element
     } else {
         buildJsonObject {
@@ -96,7 +101,7 @@ public fun JsonElement.toValueOrNull(descriptor: MetaDescriptor?): Value? = when
     is JsonPrimitive -> toValue(descriptor)
     is JsonObject -> get(Meta.VALUE_KEY)?.toValueOrNull(descriptor)
     is JsonArray -> {
-        if(isEmpty()) ListValue.EMPTY else {
+        if (isEmpty()) ListValue.EMPTY else {
             val values = map { it.toValueOrNull(descriptor) }
             values.map { it ?: return null }.asValue()
         }
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Meta.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Meta.kt
index 45723682..21f9e5e3 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Meta.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Meta.kt
@@ -34,7 +34,7 @@ public interface Meta : MetaRepr, MetaProvider {
     public val value: Value?
     public val items: Map<NameToken, Meta>
 
-    override fun getMeta(name: Name): Meta?{
+    override fun getMeta(name: Name): Meta? {
         tailrec fun Meta.find(name: Name): Meta? = if (name.isEmpty()) {
             this
         } else {
@@ -197,7 +197,8 @@ public fun Meta.nodeSequence(): Sequence<Pair<Name, Meta>> = sequence {
 
 public operator fun Meta.iterator(): Iterator<Pair<Name, Meta>> = nodeSequence().iterator()
 
-public fun Meta.isEmpty(): Boolean = this === Meta.EMPTY || (value == null && items.isEmpty())
+public fun Meta.isEmpty(): Boolean = this === Meta.EMPTY
+        || (value == null && (items.isEmpty() || items.values.all { it.isEmpty() }))
 
 
 /* Get operations*/