// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import 'poseidon-solidity/PoseidonT3.sol';

// only allow arity 2, variable height

struct ReusableTreeData {
    uint256 depth;
    uint256 root;
    uint256 numberOfLeaves;
    // store as 0-2**depth first level
    // 2**depth - 2**(depth-1) as second level
    // 2**(depth-1) - 2**(depth - 2) as third level
    // etc
    mapping(uint256 => uint256) elements;
}

// TODO: update doc
/// @title ReusableMerkleTree
library ReusableMerkleTree {
    uint8 internal constant MAX_DEPTH = 32;
    uint256 internal constant SNARK_SCALAR_FIELD =
        21888242871839275222246405745257275088548364400416034343698204186575808495617;

    uint256 public constant Z_0 = 0;
    uint256 public constant Z_1 =
        14744269619966411208579211824598458697587494354926760081771325075741142829156;
    uint256 public constant Z_2 =
        7423237065226347324353380772367382631490014989348495481811164164159255474657;
    uint256 public constant Z_3 =
        11286972368698509976183087595462810875513684078608517520839298933882497716792;
    uint256 public constant Z_4 =
        3607627140608796879659380071776844901612302623152076817094415224584923813162;
    uint256 public constant Z_5 =
        19712377064642672829441595136074946683621277828620209496774504837737984048981;
    uint256 public constant Z_6 =
        20775607673010627194014556968476266066927294572720319469184847051418138353016;
    uint256 public constant Z_7 =
        3396914609616007258851405644437304192397291162432396347162513310381425243293;
    uint256 public constant Z_8 =
        21551820661461729022865262380882070649935529853313286572328683688269863701601;
    uint256 public constant Z_9 =
        6573136701248752079028194407151022595060682063033565181951145966236778420039;
    uint256 public constant Z_10 =
        12413880268183407374852357075976609371175688755676981206018884971008854919922;
    uint256 public constant Z_11 =
        14271763308400718165336499097156975241954733520325982997864342600795471836726;
    uint256 public constant Z_12 =
        20066985985293572387227381049700832219069292839614107140851619262827735677018;
    uint256 public constant Z_13 =
        9394776414966240069580838672673694685292165040808226440647796406499139370960;
    uint256 public constant Z_14 =
        11331146992410411304059858900317123658895005918277453009197229807340014528524;
    uint256 public constant Z_15 =
        15819538789928229930262697811477882737253464456578333862691129291651619515538;
    uint256 public constant Z_16 =
        19217088683336594659449020493828377907203207941212636669271704950158751593251;
    uint256 public constant Z_17 =
        21035245323335827719745544373081896983162834604456827698288649288827293579666;
    uint256 public constant Z_18 =
        6939770416153240137322503476966641397417391950902474480970945462551409848591;
    uint256 public constant Z_19 =
        10941962436777715901943463195175331263348098796018438960955633645115732864202;
    uint256 public constant Z_20 =
        15019797232609675441998260052101280400536945603062888308240081994073687793470;
    uint256 public constant Z_21 =
        11702828337982203149177882813338547876343922920234831094975924378932809409969;
    uint256 public constant Z_22 =
        11217067736778784455593535811108456786943573747466706329920902520905755780395;
    uint256 public constant Z_23 =
        16072238744996205792852194127671441602062027943016727953216607508365787157389;
    uint256 public constant Z_24 =
        17681057402012993898104192736393849603097507831571622013521167331642182653248;
    uint256 public constant Z_25 =
        21694045479371014653083846597424257852691458318143380497809004364947786214945;
    uint256 public constant Z_26 =
        8163447297445169709687354538480474434591144168767135863541048304198280615192;
    uint256 public constant Z_27 =
        14081762237856300239452543304351251708585712948734528663957353575674639038357;
    uint256 public constant Z_28 =
        16619959921569409661790279042024627172199214148318086837362003702249041851090;
    uint256 public constant Z_29 =
        7022159125197495734384997711896547675021391130223237843255817587255104160365;
    uint256 public constant Z_30 =
        4114686047564160449611603615418567457008101555090703535405891656262658644463;
    uint256 public constant Z_31 =
        12549363297364877722388257367377629555213421373705596078299904496781819142130;
    uint256 public constant Z_32 =
        21443572485391568159800782191812935835534334817699172242223315142338162256601;

    function defaultZero(uint256 index) public pure returns (uint256) {
        if (index == 0) return Z_0;
        if (index == 1) return Z_1;
        if (index == 2) return Z_2;
        if (index == 3) return Z_3;
        if (index == 4) return Z_4;
        if (index == 5) return Z_5;
        if (index == 6) return Z_6;
        if (index == 7) return Z_7;
        if (index == 8) return Z_8;
        if (index == 9) return Z_9;
        if (index == 10) return Z_10;
        if (index == 11) return Z_11;
        if (index == 12) return Z_12;
        if (index == 13) return Z_13;
        if (index == 14) return Z_14;
        if (index == 15) return Z_15;
        if (index == 16) return Z_16;
        if (index == 17) return Z_17;
        if (index == 18) return Z_18;
        if (index == 19) return Z_19;
        if (index == 20) return Z_20;
        if (index == 21) return Z_21;
        if (index == 22) return Z_22;
        if (index == 23) return Z_23;
        if (index == 24) return Z_24;
        if (index == 25) return Z_25;
        if (index == 26) return Z_26;
        if (index == 27) return Z_27;
        if (index == 28) return Z_28;
        if (index == 29) return Z_29;
        if (index == 30) return Z_30;
        if (index == 31) return Z_31;
        if (index == 32) return Z_32;
        revert('ReusableMerkleTree: defaultZero bad index');
    }

    function init(ReusableTreeData storage self, uint256 depth) public {
        require(
            depth > 0 && depth <= MAX_DEPTH,
            'ReusableMerkleTree: tree depth must be between 1 and 32'
        );

        self.depth = depth;
        self.root = defaultZero(depth);
    }

    function reset(ReusableTreeData storage self) public {
        self.numberOfLeaves = 0;
        self.root = defaultZero(self.depth);
    }

    function indexForElement(
        uint256 level,
        uint256 index,
        uint256 depth
    ) public pure returns (uint256) {
        uint256 _index = index;
        for (uint8 x = 0; x < level; x++) {
            _index += 2 ** (depth - x);
        }
        return _index;
    }

    function insert(
        ReusableTreeData storage self,
        uint256 leaf
    ) public returns (uint256) {
        uint256 depth = self.depth;

        require(
            leaf < SNARK_SCALAR_FIELD,
            'ReusableMerkleTree: leaf must be < SNARK_SCALAR_FIELD'
        );
        require(
            self.numberOfLeaves < 2 ** depth - 1,
            'ReusableMerkleTree: tree is full'
        );

        uint256 index = self.numberOfLeaves;

        uint256 hash = leaf;

        for (uint8 i = 0; i < depth; ) {
            self.elements[indexForElement(i, index, depth)] = hash;

            uint256[2] memory siblings;
            if (index & 1 == 0) {
                // it's a left sibling
                siblings = [hash, defaultZero(i)];
            } else {
                // it's a right sibling
                uint256 elementIndex = indexForElement(i, index - 1, depth);
                siblings = [self.elements[elementIndex], hash];
            }

            hash = PoseidonT3.hash(siblings);

            index >>= 1;

            unchecked {
                ++i;
            }
        }

        self.root = hash;
        self.numberOfLeaves += 1;
        return hash;
    }

    function update(
        ReusableTreeData storage self,
        uint256 newLeaf,
        uint256 leafIndex
    ) public returns (uint256) {
        uint256 depth = self.depth;
        uint256 leafCount = self.numberOfLeaves;

        require(
            newLeaf < SNARK_SCALAR_FIELD,
            'ReusableMerkleTree: leaf must be < SNARK_SCALAR_FIELD'
        );
        require(leafIndex < leafCount, 'ReusableMerkleTree: invalid index');

        uint256 hash = newLeaf;

        for (uint8 i = 0; i < depth; ) {
            self.elements[indexForElement(i, leafIndex, depth)] = hash;
            uint256[2] memory siblings;
            if (leafIndex & 1 == 0) {
                // it's a left sibling
                bool isLatest = leafIndex >= ((leafCount - 1) >> i);
                siblings = [
                    hash,
                    isLatest
                        ? defaultZero(i)
                        : self.elements[
                            indexForElement(i, leafIndex + 1, depth)
                        ]
                ];
            } else {
                // it's a right sibling
                uint256 elementIndex = indexForElement(i, leafIndex - 1, depth);
                siblings = [self.elements[elementIndex], hash];
            }

            hash = PoseidonT3.hash(siblings);

            leafIndex >>= 1;

            unchecked {
                ++i;
            }
        }
        self.root = hash;
        return hash;
    }
}