# Fluffy
# Copyright (c) 2024 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.

{.push raises: [].}

import results, eth/common, ../../common/common_utils, ./state_content, ./state_utils

export results, state_content

proc hashEquals(value: TrieNode | Bytecode, expectedHash: KeccakHash): bool {.inline.} =
  keccakHash(value.asSeq()) == expectedHash

proc isValidNextNode(
    thisNodeRlp: Rlp, rlpIdx: int, nextNode: TrieNode
): bool {.raises: RlpError.} =
  let hashOrShortRlp = thisNodeRlp.listElem(rlpIdx)
  if hashOrShortRlp.isEmpty():
    return false

  let nextHash =
    if hashOrShortRlp.isList():
      # is a short node
      rlpHash(hashOrShortRlp)
    else:
      let hash = hashOrShortRlp.toBytes()
      if hash.len() != 32:
        return false
      KeccakHash.fromBytes(hash)

  nextNode.hashEquals(nextHash)

# TODO: Refactor this function to improve maintainability
proc validateTrieProof*(
    expectedRootHash: Opt[KeccakHash],
    path: Nibbles,
    proof: TrieProof,
    allowKeyEndInPathForLeafs = false,
): Result[void, string] =
  if proof.len() == 0:
    return err("proof is empty")

  # TODO: Remove this once the hive tests support passing in state roots from the history network
  if expectedRootHash.isSome():
    if not proof[0].hashEquals(expectedRootHash.get()):
      return err("hash of proof root node doesn't match the expected root hash")

  let nibbles = path.unpackNibbles()
  if nibbles.len() == 0:
    if proof.len() == 1:
      return ok() # root node case, already validated above
    else:
      return err("empty path, only one node expected in proof")

  var nibbleIdx = 0
  for proofIdx, p in proof:
    let
      thisNodeRlp = rlpFromBytes(p.asSeq())
      remainingNibbles = nibbles.len() - nibbleIdx
      isLastNode = proofIdx == proof.high

    if remainingNibbles == 0:
      if isLastNode:
        break
      else:
        return err("proof has more nodes then expected for given path")

    try:
      case thisNodeRlp.listLen()
      of 2:
        let nodePrefixRlp = thisNodeRlp.listElem(0)
        if nodePrefixRlp.isEmpty():
          return err("node prefix is empty")

        let (prefix, isLeaf, prefixNibbles) = decodePrefix(nodePrefixRlp)
        if prefix >= 4:
          return err("invalid prefix in node")

        if not isLastNode or (isLeaf and allowKeyEndInPathForLeafs):
          let unpackedPrefix = prefixNibbles.unpackNibbles()
          if remainingNibbles < unpackedPrefix.len():
            return err("not enough nibbles to validate node prefix")

          let nibbleEndIdx = nibbleIdx + unpackedPrefix.len()
          if nibbles[nibbleIdx ..< nibbleEndIdx] != unpackedPrefix:
            return err("nibbles don't match node prefix")
          nibbleIdx += unpackedPrefix.len()

        if not isLastNode:
          if isLeaf:
            return err("leaf node must be last node in the proof")
          else: # is extension node
            if not isValidNextNode(thisNodeRlp, 1, proof[proofIdx + 1]):
              return
                err("hash of next node doesn't match the expected extension node hash")
      of 17:
        if not isLastNode:
          let nextNibble = nibbles[nibbleIdx]
          if nextNibble >= 16:
            return err("invalid next nibble for branch node")

          if not isValidNextNode(thisNodeRlp, nextNibble.int, proof[proofIdx + 1]):
            return err("hash of next node doesn't match the expected branch node hash")

          inc nibbleIdx
      else:
        return err("invalid rlp node, expected 2 or 17 elements")
    except RlpError as e:
      return err(e.msg)

  if nibbleIdx < nibbles.len():
    err("path contains more nibbles than expected for proof")
  else:
    ok()

proc validateRetrieval*(
    key: AccountTrieNodeKey, value: AccountTrieNodeRetrieval
): Result[void, string] =
  if value.node.hashEquals(key.nodeHash):
    ok()
  else:
    err("hash of account trie node doesn't match the expected node hash")

proc validateRetrieval*(
    key: ContractTrieNodeKey, value: ContractTrieNodeRetrieval
): Result[void, string] =
  if value.node.hashEquals(key.nodeHash):
    ok()
  else:
    err("hash of contract trie node doesn't match the expected node hash")

proc validateRetrieval*(
    key: ContractCodeKey, value: ContractCodeRetrieval
): Result[void, string] =
  if value.code.hashEquals(key.codeHash):
    ok()
  else:
    err("hash of bytecode doesn't match the expected code hash")

proc validateOffer*(
    trustedStateRoot: Opt[KeccakHash],
    key: AccountTrieNodeKey,
    offer: AccountTrieNodeOffer,
): Result[void, string] =
  ?validateTrieProof(trustedStateRoot, key.path, offer.proof)

  validateRetrieval(key, offer.toRetrievalValue())

proc validateOffer*(
    trustedStateRoot: Opt[KeccakHash],
    key: ContractTrieNodeKey,
    offer: ContractTrieNodeOffer,
): Result[void, string] =
  ?validateTrieProof(
    trustedStateRoot,
    key.address.toPath(),
    offer.accountProof,
    allowKeyEndInPathForLeafs = true,
  )

  let account = ?offer.accountProof.toAccount()

  ?validateTrieProof(Opt.some(account.storageRoot), key.path, offer.storageProof)

  validateRetrieval(key, offer.toRetrievalValue())

proc validateOffer*(
    trustedStateRoot: Opt[KeccakHash], key: ContractCodeKey, offer: ContractCodeOffer
): Result[void, string] =
  ?validateTrieProof(
    trustedStateRoot,
    key.address.toPath(),
    offer.accountProof,
    allowKeyEndInPathForLeafs = true,
  )

  let account = ?offer.accountProof.toAccount()
  if not offer.code.hashEquals(account.codeHash):
    return err("hash of bytecode doesn't match the code hash in the account proof")

  validateRetrieval(key, offer.toRetrievalValue())