Refactor of from_finalized_snapshot()

from_finalized_snapshot_refactor.rs

    pub fn from_finalized_snapshot(
        finalized_branch: &[H256],
        deposits: usize,
        level: usize,
    ) -> Result<Self, MerkleTreeError> {
        if let Some(hash) = finalized_branch.get(0) {
            if deposits == (0x1 << level) {
                return Ok(MerkleTree::Finalized(*hash));
            }
            if level == 0 {
                return Err(InvalidSnapshot::EndOfTree.into());
            }
        } else {
            // finalized_branch is empty
            return if deposits == 0 {
                Ok(MerkleTree::Zero(level))
            } else {
                Err(InvalidSnapshot::EmptyBranchWithNonZeroDeposits(deposits).into())
            };
        }

        let left_subtree = 0x1 << (level - 1);
        return if deposits <= left_subtree {
            let left = MerkleTree::from_finalized_snapshot(finalized_branch, deposits, level - 1)?;
            let right = MerkleTree::Zero(level - 1);
            let hash = H256::from_slice(&hash32_concat(
                left.hash().as_bytes(),
                right.hash().as_bytes(),
            ));
            Ok(MerkleTree::Node(hash, Box::new(left), Box::new(right)))
        } else if let Some((left_hash, right_branch)) = finalized_branch.split_first() {
            let left = MerkleTree::Finalized(*left_hash);
            let right = MerkleTree::from_finalized_snapshot(
                right_branch,
                deposits - left_subtree,
                level - 1,
            )?;
            let hash = H256::from_slice(&hash32_concat(
                left.hash().as_bytes(),
                right.hash().as_bytes(),
            ));
            Ok(MerkleTree::Node(hash, Box::new(left), Box::new(right)))
        } else {
            // Execution should never get here
            Err(MerkleTreeError::PleaseNotifyTheDevs)
        }
    }