1 files changed, 37 insertions, 2 deletions

diff --git a/core/src/main/kotlin/model/properties/PropertyContainer.kt b/core/src/main/kotlin/model/properties/PropertyContainer.kt
index da351569..ed4b99de 100644
--- a/core/src/main/kotlin/model/properties/PropertyContainer.kt
+++ b/core/src/main/kotlin/model/properties/PropertyContainer.kt
@@ -1,13 +1,16 @@
 package org.jetbrains.dokka.model.properties
 
-class PropertyContainer<C : Any> private constructor(
+import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstance
+import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstanceOrNull
+
+class PropertyContainer<C : Any> internal constructor(
     @PublishedApi internal val map: Map<Property.Key<C, *>, Property<C>>
 ) {
     operator fun <D : C> plus(prop: Property<D>): PropertyContainer<D> =
         PropertyContainer(map + (prop.key to prop))
 
     // TODO: Add logic for caching calculated properties
-    inline operator fun <reified T: Any> get(key: Property.Key<C, T>): T? = when (val prop = map[key]) {
+    inline operator fun <reified T : Any> get(key: Property.Key<C, T>): T? = when (val prop = map[key]) {
         is T? -> prop
         else -> throw ClassCastException("Property for $key stored under not matching key type.")
     }
@@ -15,4 +18,36 @@ class PropertyContainer<C : Any> private constructor(
     companion object {
         val empty: PropertyContainer<Any> = PropertyContainer(emptyMap())
     }
+}
+
+interface WithExtraProperties<C : Any> {
+    val extra: PropertyContainer<C>
+
+    fun withNewExtras(newExtras: PropertyContainer<C>): C
+}
+
+fun <C> C.mergeExtras(left: C, right: C): C where C : Any, C : WithExtraProperties<C> {
+    val aggregatedExtras: List<List<Property<C>>> =
+        (left.extra.map.values + right.extra.map.values)
+            .groupBy { it.key }
+            .values
+            .map { it.distinct() }
+
+    val (unambiguous, toMerge) = aggregatedExtras.partition { it.size == 1 }
+
+    @Suppress("UNCHECKED_CAST")
+    val strategies: List<MergeStrategy<C>> = toMerge.map { (l, r) ->
+        (l.key as Property.Key<C, Property<C>>).mergeStrategyFor(l, r)
+    }
+
+    strategies.firstIsInstanceOrNull<MergeStrategy.Fail>()?.error?.invoke()
+
+    val replaces: List<Property<C>> = strategies.filterIsInstance<MergeStrategy.Replace<C>>().map { it.newProperty }
+
+    val needingFullMerge: List<(preMerged: C, left: C, right: C) -> C> =
+        strategies.filterIsInstance<MergeStrategy.Full<C>>().map { it.merger }
+
+    val newExtras = PropertyContainer((unambiguous.flatten() + replaces).associateBy { it.key })
+
+    return needingFullMerge.fold(withNewExtras(newExtras)) { acc, merger -> merger(acc, left, right) }
 }
\ No newline at end of file