/*
 * Copyright (C) 2021 Zilliqa
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
package mpt

import (
	"fmt"
)

func Verify(key []byte, proof *Database, rootHash []byte) (value []byte, err error) {
	key = keybytesToHex(key)
	wantHash := rootHash

	for i := 0; ; i++ {
		buf, _ := proof.Get(wantHash[:])
		if buf == nil {
			return nil, fmt.Errorf("proof node %d (hash %064x) missing", i, wantHash)
		}
		n, err := decodeNode(wantHash[:], buf)
		if err != nil {
			return nil, fmt.Errorf("bad proof node %d: %v", i, err)
		}
		keyrest, cld := get(n, key, true)
		switch cld := cld.(type) {
		case nil:
			// The trie doesn't contain the key.
			return nil, nil
		case hashNode:
			key = keyrest
			copy(wantHash[:], cld)
		case valueNode:
			return cld, nil
		}
	}
}
