// Copyright 2019 Google LLC. All Rights Reserved.
//
// Licensed 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 smt

import "github.com/google/trillian/merkle/smt/node"

// Hasher provides sparse Merkle tree hash functions.
type Hasher interface {
	// HashEmpty returns the hash of an empty subtree with the given root. Note
	// that the empty node ID indicates the root of the entire tree.
	HashEmpty(treeID int64, root node.ID) []byte
	// HashChildren returns the node hash based on its children node hashes.
	HashChildren(l, r []byte) []byte
}

// mapHasher is a wrapper around Hasher bound to a specific tree ID.
type mapHasher struct {
	mh     Hasher
	treeID int64
}

// bindHasher returns a mapHasher binding the given hasher to a tree ID.
func bindHasher(hasher Hasher, treeID int64) mapHasher {
	return mapHasher{mh: hasher, treeID: treeID}
}

// hashEmpty returns the hash of an empty subtree with the given root ID.
func (h mapHasher) hashEmpty(id node.ID) []byte {
	return h.mh.HashEmpty(h.treeID, id)
}