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use alloc::vec::Vec;
#[cfg(feature = "parallel")]
use rayon::prelude::{IntoParallelRefIterator, ParallelIterator};

/// A backend for Merkle trees. This defines raw `Data` from which the Merkle
/// tree is built from. It also defines the `Node` type and the hash function
/// used to build parent nodes from children nodes.
pub trait IsMerkleTreeBackend: Default {
    type Node: PartialEq + Eq + Clone + Sync + Send;
    type Data: Sync + Send;

    /// This function takes a single variable `Data` and converts it to a node.
    fn hash_data(leaf: &Self::Data) -> Self::Node;

    /// This function takes the list of data from which the Merkle
    /// tree will be built from and converts it to a list of leaf nodes.
    fn hash_leaves(unhashed_leaves: &[Self::Data]) -> Vec<Self::Node> {
        #[cfg(feature = "parallel")]
        let iter = unhashed_leaves.par_iter();
        #[cfg(not(feature = "parallel"))]
        let iter = unhashed_leaves.iter();

        iter.map(|leaf| Self::hash_data(leaf)).collect()
    }

    /// This function takes to children nodes and builds a new parent node.
    /// It will be used in the construction of the Merkle tree.
    fn hash_new_parent(child_1: &Self::Node, child_2: &Self::Node) -> Self::Node;
}