merkle-trie/src/main/kotlin/org/apache/tuweni/trie/ExtensionNode.kt

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.tuweni.trie

import org.apache.tuweni.bytes.Bytes
import org.apache.tuweni.bytes.Bytes32
import org.apache.tuweni.crypto.Hash.keccak256
import org.apache.tuweni.rlp.RLP
import java.lang.ref.WeakReference

internal class ExtensionNode<V>(
  private val path: Bytes,
  private val child: Node<V>,
  private val nodeFactory: NodeFactory<V>
) : Node<V> {
  @Volatile
  private var rlp: WeakReference<Bytes>? = null
  @Volatile
  private var hash: Bytes32? = null

  init {
    assert(path.size() > 0)
    assert(path.get(path.size() - 1) != CompactEncoding.LEAF_TERMINATOR) { "Extension path ends in a leaf terminator" }
  }

  override suspend fun accept(visitor: NodeVisitor<V>, path: Bytes): Node<V> = visitor.visit(this, path)

  override suspend fun path(): Bytes = path

  override suspend fun value(): V? = throw UnsupportedOperationException()

  fun child(): Node<V> = child

  override fun rlp(): Bytes {
    val prevEncoded = rlp?.get()
    if (prevEncoded != null) {
      return prevEncoded
    }
    val encoded = RLP.encodeList { writer ->
      writer.writeValue(CompactEncoding.encode(path))
      writer.writeRLP(child.rlpRef())
    }
    rlp = WeakReference(encoded)
    return encoded
  }

  override fun rlpRef(): Bytes {
    val rlp = rlp()
    return if (rlp.size() < 32) rlp else RLP.encodeValue(hash())
  }

  override fun hash(): Bytes32 {
    hash?.let { return it }
    val hashed = keccak256(rlp())
    hash = hashed
    return hashed
  }

  suspend fun replaceChild(updatedChild: Node<V>): Node<V> {
    // collapse this extension - if the child is a branch, it will create a new extension
    val childPath = updatedChild.path()
    return updatedChild.replacePath(Bytes.concatenate(path, childPath))
  }

  override suspend fun replacePath(path: Bytes): Node<V> {
    return if (path.size() == 0) child else nodeFactory.createExtension(path, child)
  }
}