/**
 * @dev This only stores the hashed value of the leaf.
 * If you need to retrieve the detail data later, use a map to store them.
 */
function append(Tree storage tree, bytes memory data) public;

/**
 * @dev It returns the root value of the tree
 */
function getRoot(Tree storage tree) public view returns (bytes32);

/**
 * @dev It returns the size of the tree
 */
function getSize(Tree storage tree) public view returns (uint256);

/**
 * @dev It returns the hash value of a node for the given position. Note that the index starts from 1
 */
function getNode(Tree storage tree, uint256 index) public view returns (bytes32);

/**
 * @dev It returns a merkle proof for a leaf. Note that the index starts from 1
 */
function getMerkleProof(Tree storage tree, uint256 index) public view returns (
    bytes32 root,
    uint256 size,
    bytes32[] memory peakBagging,
    bytes32[] memory siblings
);

/** Pure functions */

/**
 * @dev It returns true when the given params verifies that the given value exists in the tree or reverts the transaction.
 */
function inclusionProof(
    bytes32 root,
    uint256 size,
    uint256 index,
    bytes memory value,
    bytes32[] memory peakBagging,
    bytes32[] memory siblings
) public pure returns (bool);

/**
 * @dev It returns the hash a parent node with hash(M | Left child | Right child)
 *      M is the index of the node
 */
function hashParent(uint256 index, bytes32 left, bytes32 right) public pure returns (bytes32);

/**
 * @dev it returns the hash of a leaf node with hash(M | DATA )
 *      M is the index of the node
 */
function hashLeaf(uint256 index, bytes memory data) public pure returns (bytes32);

/**
 * @dev It returns the height of the highest peak
 */
function mountainHeight(uint256 size) public pure returns (uint8);

/**
 * @dev It returns the height of the index
 */
function heightAt(uint256 index) public pure returns (uint8 height);

/**
 * @dev It returns whether the index is the leaf node or not
 */
function isLeaf(uint256 index) public pure returns (bool);

/**
 * @dev It returns the children when it is a parent node
 */
function getChildren(uint256 index) public pure returns (uint256 left, uint256 right);

/**
 * @dev It returns all peaks of the smallest merkle mountain range tree which includes
 *      the given index(size)
 */
function getPeaks(uint256 size) public pure returns (uint256[] memory peaks);