// File: @openzeppelin/contracts/utils/math/Math.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (utils/math/Math.sol)

pragma solidity ^0.8.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    enum Rounding {
        Down, // Toward negative infinity
        Up, // Toward infinity
        Zero // Toward zero
    }

    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a > b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow.
        return (a & b) + (a ^ b) / 2;
    }

    /**
     * @dev Returns the ceiling of the division of two numbers.
     *
     * This differs from standard division with `/` in that it rounds up instead
     * of rounding down.
     */
    function ceilDiv(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b - 1) / b can overflow on addition, so we distribute.
        return a == 0 ? 0 : (a - 1) / b + 1;
    }

    /**
     * @notice Calculates floor(x * y / denominator) with full precision. Throws if result overflows a uint256 or denominator == 0
     * @dev Original credit to Remco Bloemen under MIT license (https://xn--2-umb.com/21/muldiv)
     * with further edits by Uniswap Labs also under MIT license.
     */
    function mulDiv(uint256 x, uint256 y, uint256 denominator) internal pure returns (uint256 result) {
        unchecked {
            // 512-bit multiply [prod1 prod0] = x * y. Compute the product mod 2^256 and mod 2^256 - 1, then use
            // use the Chinese Remainder Theorem to reconstruct the 512 bit result. The result is stored in two 256
            // variables such that product = prod1 * 2^256 + prod0.
            uint256 prod0; // Least significant 256 bits of the product
            uint256 prod1; // Most significant 256 bits of the product
            assembly {
                let mm := mulmod(x, y, not(0))
                prod0 := mul(x, y)
                prod1 := sub(sub(mm, prod0), lt(mm, prod0))
            }

            // Handle non-overflow cases, 256 by 256 division.
            if (prod1 == 0) {
                // Solidity will revert if denominator == 0, unlike the div opcode on its own.
                // The surrounding unchecked block does not change this fact.
                // See https://docs.soliditylang.org/en/latest/control-structures.html#checked-or-unchecked-arithmetic.
                return prod0 / denominator;
            }

            // Make sure the result is less than 2^256. Also prevents denominator == 0.
            require(denominator > prod1, "Math: mulDiv overflow");

            ///////////////////////////////////////////////
            // 512 by 256 division.
            ///////////////////////////////////////////////

            // Make division exact by subtracting the remainder from [prod1 prod0].
            uint256 remainder;
            assembly {
                // Compute remainder using mulmod.
                remainder := mulmod(x, y, denominator)

                // Subtract 256 bit number from 512 bit number.
                prod1 := sub(prod1, gt(remainder, prod0))
                prod0 := sub(prod0, remainder)
            }

            // Factor powers of two out of denominator and compute largest power of two divisor of denominator. Always >= 1.
            // See https://cs.stackexchange.com/q/138556/92363.

            // Does not overflow because the denominator cannot be zero at this stage in the function.
            uint256 twos = denominator & (~denominator + 1);
            assembly {
                // Divide denominator by twos.
                denominator := div(denominator, twos)

                // Divide [prod1 prod0] by twos.
                prod0 := div(prod0, twos)

                // Flip twos such that it is 2^256 / twos. If twos is zero, then it becomes one.
                twos := add(div(sub(0, twos), twos), 1)
            }

            // Shift in bits from prod1 into prod0.
            prod0 |= prod1 * twos;

            // Invert denominator mod 2^256. Now that denominator is an odd number, it has an inverse modulo 2^256 such
            // that denominator * inv = 1 mod 2^256. Compute the inverse by starting with a seed that is correct for
            // four bits. That is, denominator * inv = 1 mod 2^4.
            uint256 inverse = (3 * denominator) ^ 2;

            // Use the Newton-Raphson iteration to improve the precision. Thanks to Hensel's lifting lemma, this also works
            // in modular arithmetic, doubling the correct bits in each step.
            inverse *= 2 - denominator * inverse; // inverse mod 2^8
            inverse *= 2 - denominator * inverse; // inverse mod 2^16
            inverse *= 2 - denominator * inverse; // inverse mod 2^32
            inverse *= 2 - denominator * inverse; // inverse mod 2^64
            inverse *= 2 - denominator * inverse; // inverse mod 2^128
            inverse *= 2 - denominator * inverse; // inverse mod 2^256

            // Because the division is now exact we can divide by multiplying with the modular inverse of denominator.
            // This will give us the correct result modulo 2^256. Since the preconditions guarantee that the outcome is
            // less than 2^256, this is the final result. We don't need to compute the high bits of the result and prod1
            // is no longer required.
            result = prod0 * inverse;
            return result;
        }
    }

    /**
     * @notice Calculates x * y / denominator with full precision, following the selected rounding direction.
     */
    function mulDiv(uint256 x, uint256 y, uint256 denominator, Rounding rounding) internal pure returns (uint256) {
        uint256 result = mulDiv(x, y, denominator);
        if (rounding == Rounding.Up && mulmod(x, y, denominator) > 0) {
            result += 1;
        }
        return result;
    }

    /**
     * @dev Returns the square root of a number. If the number is not a perfect square, the value is rounded down.
     *
     * Inspired by Henry S. Warren, Jr.'s "Hacker's Delight" (Chapter 11).
     */
    function sqrt(uint256 a) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        // For our first guess, we get the biggest power of 2 which is smaller than the square root of the target.
        //
        // We know that the "msb" (most significant bit) of our target number `a` is a power of 2 such that we have
        // `msb(a) <= a < 2*msb(a)`. This value can be written `msb(a)=2**k` with `k=log2(a)`.
        //
        // This can be rewritten `2**log2(a) <= a < 2**(log2(a) + 1)`
        // → `sqrt(2**k) <= sqrt(a) < sqrt(2**(k+1))`
        // → `2**(k/2) <= sqrt(a) < 2**((k+1)/2) <= 2**(k/2 + 1)`
        //
        // Consequently, `2**(log2(a) / 2)` is a good first approximation of `sqrt(a)` with at least 1 correct bit.
        uint256 result = 1 << (log2(a) >> 1);

        // At this point `result` is an estimation with one bit of precision. We know the true value is a uint128,
        // since it is the square root of a uint256. Newton's method converges quadratically (precision doubles at
        // every iteration). We thus need at most 7 iteration to turn our partial result with one bit of precision
        // into the expected uint128 result.
        unchecked {
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            return min(result, a / result);
        }
    }

    /**
     * @notice Calculates sqrt(a), following the selected rounding direction.
     */
    function sqrt(uint256 a, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = sqrt(a);
            return result + (rounding == Rounding.Up && result * result < a ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 2, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 128;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 64;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 32;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 16;
            }
            if (value >> 8 > 0) {
                value >>= 8;
                result += 8;
            }
            if (value >> 4 > 0) {
                value >>= 4;
                result += 4;
            }
            if (value >> 2 > 0) {
                value >>= 2;
                result += 2;
            }
            if (value >> 1 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 2, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log2(value);
            return result + (rounding == Rounding.Up && 1 << result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 10, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >= 10 ** 64) {
                value /= 10 ** 64;
                result += 64;
            }
            if (value >= 10 ** 32) {
                value /= 10 ** 32;
                result += 32;
            }
            if (value >= 10 ** 16) {
                value /= 10 ** 16;
                result += 16;
            }
            if (value >= 10 ** 8) {
                value /= 10 ** 8;
                result += 8;
            }
            if (value >= 10 ** 4) {
                value /= 10 ** 4;
                result += 4;
            }
            if (value >= 10 ** 2) {
                value /= 10 ** 2;
                result += 2;
            }
            if (value >= 10 ** 1) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log10(value);
            return result + (rounding == Rounding.Up && 10 ** result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 256, rounded down, of a positive value.
     * Returns 0 if given 0.
     *
     * Adding one to the result gives the number of pairs of hex symbols needed to represent `value` as a hex string.
     */
    function log256(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 16;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 8;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 4;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 2;
            }
            if (value >> 8 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 256, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log256(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log256(value);
            return result + (rounding == Rounding.Up && 1 << (result << 3) < value ? 1 : 0);
        }
    }
}

// File: @openzeppelin/contracts/utils/math/SignedMath.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (utils/math/SignedMath.sol)

pragma solidity ^0.8.0;

/**
 * @dev Standard signed math utilities missing in the Solidity language.
 */
library SignedMath {
    /**
     * @dev Returns the largest of two signed numbers.
     */
    function max(int256 a, int256 b) internal pure returns (int256) {
        return a > b ? a : b;
    }

    /**
     * @dev Returns the smallest of two signed numbers.
     */
    function min(int256 a, int256 b) internal pure returns (int256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two signed numbers without overflow.
     * The result is rounded towards zero.
     */
    function average(int256 a, int256 b) internal pure returns (int256) {
        // Formula from the book "Hacker's Delight"
        int256 x = (a & b) + ((a ^ b) >> 1);
        return x + (int256(uint256(x) >> 255) & (a ^ b));
    }

    /**
     * @dev Returns the absolute unsigned value of a signed value.
     */
    function abs(int256 n) internal pure returns (uint256) {
        unchecked {
            // must be unchecked in order to support `n = type(int256).min`
            return uint256(n >= 0 ? n : -n);
        }
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (utils/Strings.sol)

pragma solidity ^0.8.0;

import "./math/Math.sol";
import "./math/SignedMath.sol";

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _SYMBOLS = "0123456789abcdef";
    uint8 private constant _ADDRESS_LENGTH = 20;

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        unchecked {
            uint256 length = Math.log10(value) + 1;
            string memory buffer = new string(length);
            uint256 ptr;
            /// @solidity memory-safe-assembly
            assembly {
                ptr := add(buffer, add(32, length))
            }
            while (true) {
                ptr--;
                /// @solidity memory-safe-assembly
                assembly {
                    mstore8(ptr, byte(mod(value, 10), _SYMBOLS))
                }
                value /= 10;
                if (value == 0) break;
            }
            return buffer;
        }
    }

    /**
     * @dev Converts a `int256` to its ASCII `string` decimal representation.
     */
    function toString(int256 value) internal pure returns (string memory) {
        return string(abi.encodePacked(value < 0 ? "-" : "", toString(SignedMath.abs(value))));
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        unchecked {
            return toHexString(value, Math.log256(value) + 1);
        }
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }

    /**
     * @dev Converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation.
     */
    function toHexString(address addr) internal pure returns (string memory) {
        return toHexString(uint256(uint160(addr)), _ADDRESS_LENGTH);
    }

    /**
     * @dev Returns true if the two strings are equal.
     */
    function equal(string memory a, string memory b) internal pure returns (bool) {
        return keccak256(bytes(a)) == keccak256(bytes(b));
    }
}

// File: contracts/LiveTeach.sol



pragma solidity ^0.8.12;

import {Strings} from "@openzeppelin/contracts/utils/Strings.sol";

interface ILANDRegistry {
    function encodeTokenId(int x, int y) external pure returns (uint256);

    function decodeTokenId(uint value) external pure returns (int, int);

    function isApprovedForAll(
        address assetHolder,
        address operator
    ) external view returns (bool);

    function isAuthorized(
        address operator,
        uint256 assetId
    ) external view returns (bool);
}

contract LiveTeach {
    uint256 private latestClassroomId;

    address private owner;

    constructor() {
        owner = msg.sender;
        latestClassroomId = 1;
        roleMap.classroomAdmin.roleName = "CLASSROOM_ADMIN";
        roleMap.teacher.roleName = "TEACHER";
    }

    // id generators, start at one so we can determine unassigned.
    function getNewClassroomId() private returns (uint256) {
        return latestClassroomId++;
    }

    // structs
    struct Land {
        uint256 id;
        address classroomAdminId;
        uint256 classroomId;
    }

    struct ClassroomAdmin {
        address walletAddress;
        uint256[] landIds;
        int[][] landCoordinates; // not persisted
        uint256[] classroomIds;
        address[] teacherIds;
    }

    struct Classroom {
        uint256 id;
        string name;
        uint256[] landIds;
        int[][] landCoordinates; // not persisted
        address classroomAdminId;
        address[] teacherIds;
        string guid;
        string configUrl;
    }

    struct Teacher {
        address walletAddress;
        uint256[] classroomIds;
        address[] classroomAdminIds;
    }

    struct RoleDetail {
        string roleName;
        address[] addressArray;
        mapping(address => bool) boolMapping;
    }

    struct RoleMap {
        RoleDetail classroomAdmin;
        RoleDetail teacher;
    }

    struct RegisteredIds {
        uint256[] landsRegisteredToClassroomAdmin;
        mapping(uint256 => bool) landsRegisteredToClassroomAdminBool;
        uint256[] classroom;
        mapping(uint256 => bool) classroomBool;
        uint256[] landsRegisteredToClassroom;
        mapping(uint256 => bool) landsRegisteredToClassroomBool;
        mapping(string => uint256) guidToClassroom;
    }

    // id to object mappings
    struct IdsToObjects {
        mapping(uint256 => Land) land;
        mapping(address => ClassroomAdmin) classroomAdmin;
        mapping(uint256 => Classroom) classroom;
        mapping(address => Teacher) teacher;
    }

    struct RoleResult {
        // bool student;
        bool teacher;
        bool classroomAdmin;
        // bool landOperator;
    }

    // Error messages
    string public constant ERR_OBJECT_ACCESS =
        "Object doesn't exist or you don't have access to it.";
    string public constant ERR_ROLE_ASSIGNED =
        "Provided wallet already has role: ";
    string public constant ERR_OBJECT_EXISTS = "Provided id invalid.";
    string public constant ERR_ACCESS_DENIED =
        "Provided wallet lacks appropriate role.";

    RegisteredIds private registeredIds;
    RoleMap private roleMap;
    IdsToObjects private idsToObjects;

    ILANDRegistry public landRegistry;

     // OWNER ONLY METHODS

    function allLands() public view onlyOwner returns (uint256[] memory) {
        return registeredIds.landsRegisteredToClassroomAdmin;
    }

    function allClassrooms() public view onlyOwner returns (uint256[] memory) {
        return registeredIds.classroom;
    }

    function allTeachers() public view onlyOwner returns (address[] memory) {
        return roleMap.teacher.addressArray;
    }

    function setLANDRegistry(address _registry) public onlyOwner {
        require(_isContract(_registry), "LAND registry not a contract");
        landRegistry = ILANDRegistry(_registry);
    }

    // PUBLIC UTILITY
    function getRoles() public view returns (RoleResult memory) {
        return
            RoleResult({
                // student: hasRole(STUDENT, msg.sender),
                teacher: hasRole(roleMap.teacher, msg.sender),
                classroomAdmin: hasRole(roleMap.classroomAdmin, msg.sender)
                // landOperator: hasRole(LAND_OPERATOR, msg.sender)
            });
    }

    function getCoordinatesFromLandIds(
        uint256[] memory landIds
    ) public view returns (int[][] memory) {
        int[][] memory rtn = new int[][](landIds.length);
        for (uint256 i = 0; i < landIds.length; i++) {
            (int x, int y) = landRegistry.decodeTokenId(landIds[i]);
            rtn[i] = new int[](2);
            rtn[i][0] = x;
            rtn[i][1] = y;
        }
        return rtn;
    }

    function getLandIdsFromCoordinates(
        int[][] memory coordinatePairs
    ) public view returns (uint256[] memory) {
        uint256[] memory landIds = new uint256[](coordinatePairs.length);
        for (uint256 i = 0; i < coordinatePairs.length; i++) {
            landIds[i] = landRegistry.encodeTokenId(
                coordinatePairs[i][0],
                coordinatePairs[i][1]
            );
        }
        return landIds;
    }

    // CLASSROOM ADMIN
    // create

    function isCallerLandOperator(
        uint256[] memory assetIds
    ) private view returns (bool) {
        for (uint256 i = 0; i < assetIds.length; i++) {
            if (!landRegistry.isAuthorized(msg.sender, assetIds[i])) {
                return false;
            }
        }
        return true;
    }

    function createClassroomAdmin(
        address _walletAddress,
        uint256[] memory _landIds
    ) public {
        require(
            isCallerLandOperator(_landIds),
            "You don't have access to this land"
        );
        require(
            !hasRole(roleMap.classroomAdmin, _walletAddress),
            string.concat(ERR_ROLE_ASSIGNED, roleMap.classroomAdmin.roleName)
        );
        registerClassroomAdmin(_walletAddress, _landIds);
    }

    // read
    function getClassroomAdmins()
        public
        view
        returns (ClassroomAdmin[] memory)
    {
        address[] memory registeredClassroomAdminIds = roleMap
            .classroomAdmin
            .addressArray;
        ClassroomAdmin[] memory rtn = new ClassroomAdmin[](
            registeredClassroomAdminIds.length
        );
        for (uint256 i = 0; i < registeredClassroomAdminIds.length; i++) {
            rtn[i] = idsToObjects.classroomAdmin[
                registeredClassroomAdminIds[i]
            ];
            rtn[i].landCoordinates = getCoordinatesFromLandIds(rtn[i].landIds);
        }
        return rtn;
    }

    function getClassroomAdmin(
        address _walletAddress
    ) public view returns (ClassroomAdmin memory) {
        ClassroomAdmin memory rtn = idsToObjects.classroomAdmin[_walletAddress];
        rtn.landCoordinates = getCoordinatesFromLandIds(rtn.landIds);
        return rtn;
    }

    // delete

    function deleteClassroomAdmin(address _walletAddress) public {
        // check caller is entitled to land TODO
        require(
            hasRole(roleMap.classroomAdmin, _walletAddress),
            ERR_ACCESS_DENIED
        );
        // remove existing mappings
        ClassroomAdmin memory classroomAdmin = idsToObjects.classroomAdmin[
            _walletAddress
        ];

        for (uint256 i = 0; i < classroomAdmin.landIds.length; i++) {
            unregisterLandFromClassroomAdmin(classroomAdmin.landIds[i]);
        }

        // delete classrooms
        for (uint256 i = 0; i < classroomAdmin.classroomIds.length; i++) {
            unregisterClassroom(classroomAdmin.classroomIds[i]);
        }

        delete idsToObjects.classroomAdmin[_walletAddress];
        toggleRole(_walletAddress, roleMap.classroomAdmin, false);
    }

    // CLASSROOM
    // create

    function createClassroomLandIds(
        string memory _name,
        uint256[] memory _landIds,
        string memory guid
    ) public onlyRole(roleMap.classroomAdmin) {
        bool landIdsSuitable = true;
        for (uint256 i = 0; i < _landIds.length; i++) {
            uint256 landId = _landIds[i];
            // do the land ids exist?
            if (!registeredIds.landsRegisteredToClassroomAdminBool[landId]) {
                landIdsSuitable = false;
                break;
            }
            Land memory land = idsToObjects.land[landId];
            // are they yours?
            if (msg.sender != land.classroomAdminId) {
                landIdsSuitable = false;
                break;
            }
        }

        require(landIdsSuitable, ERR_OBJECT_EXISTS);
        registerClassroom(
            getNewClassroomId(),
            _name,
            _landIds,
            msg.sender,
            guid
        );
    }

    function createClassroomCoordinates(
        string memory _name,
        int[][] memory coordinatePairs,
        string memory guid
    ) public onlyRole(roleMap.classroomAdmin) {
        uint256[] memory landIds = new uint256[](coordinatePairs.length);
        for (uint256 i = 0; i < coordinatePairs.length; i++) {
            landIds[i] = landRegistry.encodeTokenId(
                coordinatePairs[i][0],
                coordinatePairs[i][1]
            );
        }
        createClassroomLandIds(_name, landIds, guid);
    }

    // read
    function getClassrooms()
        public
        view
        onlyRole(roleMap.classroomAdmin)
        returns (Classroom[] memory)
    {
        uint256[] memory classroomIds = idsToObjects
            .classroomAdmin[msg.sender]
            .classroomIds;
        Classroom[] memory rtn = new Classroom[](classroomIds.length);
        for (uint256 i = 0; i < classroomIds.length; i++) {
            rtn[i] = idsToObjects.classroom[classroomIds[i]];
            rtn[i].landCoordinates = getCoordinatesFromLandIds(rtn[i].landIds);
        }
        return rtn;
    }

    function getClassroom(uint256 id) public view returns (Classroom memory) {
        // check you're entitled to view this classroom
        // either the owning classroom admin
        // or a teacher assigned to this classroom

        require(registeredIds.classroomBool[id], ERR_OBJECT_ACCESS);
        Classroom memory rtn = idsToObjects.classroom[id];
        bool entitledToViewClassroom = false;

        if (hasRole(roleMap.teacher, msg.sender)) {
            for (uint256 i = 0; i < rtn.teacherIds.length; i++) {
                if (msg.sender == rtn.teacherIds[i]) {
                    entitledToViewClassroom = true;
                    break;
                }
            }
        } else if (hasRole(roleMap.classroomAdmin, msg.sender)) {
            entitledToViewClassroom = walletOwnsClassroom(msg.sender, id);
        }
        require(entitledToViewClassroom, ERR_OBJECT_ACCESS);
        rtn.landCoordinates = getCoordinatesFromLandIds(rtn.landIds);
        return rtn;
    }

    // delete
    function deleteClassroom(
        uint256 id
    ) public onlyRole(roleMap.classroomAdmin) {
        // check you're entitled to this classroom
        require(walletOwnsClassroom(msg.sender, id), ERR_OBJECT_ACCESS);
        unregisterClassroom(id);
    }

    // TEACHER
    function createTeacher(
        address walletAddress,
        uint256[] memory classroomIds
    ) public onlyRole(roleMap.classroomAdmin) {
        // check classroom ids belong to this
        // classroom admin
        bool classroomIdsSuitable = true;

        for (uint256 i = 0; i < classroomIds.length; i++) {
            uint256 classroomId = classroomIds[i];
            // do the classroom ids exist?
            if (!registeredIds.classroomBool[classroomId]) {
                classroomIdsSuitable = false;
                break;
            }
            Classroom memory classroom = idsToObjects.classroom[classroomId];
            // are they yours?
            if (msg.sender != classroom.classroomAdminId) {
                classroomIdsSuitable = false;
                break;
            }
        }

        require(classroomIdsSuitable, ERR_OBJECT_EXISTS);
        registerTeacher(walletAddress, classroomIds);
    }

    // read
    function getTeachers()
        public
        view
        onlyRole(roleMap.classroomAdmin)
        returns (Teacher[] memory)
    {
        address[] memory teacherIds = idsToObjects
            .classroomAdmin[msg.sender]
            .teacherIds;
        Teacher[] memory rtn = new Teacher[](teacherIds.length);
        for (uint256 i = 0; i < teacherIds.length; i++) {
            rtn[i] = idsToObjects.teacher[teacherIds[i]];
        }
        return rtn;
    }

    function getTeacher(address id) public view returns (Teacher memory) {
        require(hasRole(roleMap.teacher, id), ERR_OBJECT_ACCESS);
        Teacher memory rtn = idsToObjects.teacher[id];
        bool entitledToViewTeacher = false;

        if (hasRole(roleMap.teacher, msg.sender)) {
            // teacher trying to view self
            if (msg.sender == id) {
                entitledToViewTeacher = true;
            }
        } else if (hasRole(roleMap.classroomAdmin, msg.sender)) {
            // classroom admin trying to view teacher
            entitledToViewTeacher = walletOwnsTeacher(msg.sender, id);
        }
        require(entitledToViewTeacher, ERR_OBJECT_ACCESS);
        return rtn;
    }

    // delete
    function deleteTeacher(address id) public onlyRole(roleMap.classroomAdmin) {
        require(walletOwnsTeacher(msg.sender, id), ERR_OBJECT_ACCESS);
        unregisterTeacher(id);
    }

    // EXTERNAL CALLS
    // TODO: Move these calls to external contract
    // function getClassroomConfigUrl(
    //     string memory classroomGuid
    // ) public view onlyRole(roleMap.teacher) returns (string memory) {
    //     uint256 classroomId = registeredIds.guidToClassroom[classroomGuid];

    //     require(
    //         arrayContainsUint(
    //             idsToObjects.teacher[msg.sender].classroomIds,
    //             classroomId
    //         ),
    //         ERR_OBJECT_ACCESS
    //     );
    //     Classroom memory classroom = idsToObjects.classroom[classroomId];
    //     if (Strings.equal(classroom.configUrl, "")) {
    //         return "Config url not yet set for this classroom";
    //     } else {
    //         return classroom.configUrl;
    //     }
    // }

    // function setClassroomConfigUrl(
    //     string memory classroomGuid,
    //     string memory url
    // ) public onlyRole(roleMap.teacher) {
    //     uint256 classroomId = registeredIds.guidToClassroom[classroomGuid];
    //     require(
    //         arrayContainsUint(
    //             idsToObjects.teacher[msg.sender].classroomIds,
    //             classroomId
    //         ),
    //         ERR_OBJECT_ACCESS
    //     );
    //     Classroom storage classroom = idsToObjects.classroom[classroomId];
    //     classroom.configUrl = url;
    // }

    function getClassroomGuid(
        int x,
        int y
    ) public view returns (string memory) {
        // does the teacher have access to this classroom from the supplied coordinates?
        Teacher memory teacher = idsToObjects.teacher[msg.sender];
        uint256 callingLandId = landRegistry.encodeTokenId(x, y);
        bool teacherCanUseLand = false;
        string memory _classroomGuid;
        for (uint256 i = 0; i < teacher.classroomIds.length; i++) {
            Classroom memory currentClassroom = idsToObjects.classroom[
                teacher.classroomIds[i]
            ];
            for (uint256 j = 0; j < currentClassroom.landIds.length; j++) {
                uint256 currentLandId = currentClassroom.landIds[j];
                if (callingLandId == currentLandId) {
                    teacherCanUseLand = true;
                    _classroomGuid = currentClassroom.guid;
                    break;
                }
            }
            if (teacherCanUseLand) {
                break;
            }
        }
        require(
            teacherCanUseLand,
            string.concat(
                "You ",
                Strings.toHexString(uint160(msg.sender)),
                " are not authorised to use this classroom."
            )
        );

        return _classroomGuid;
    }

    // private
    // land
    function walletOwnsClassroom(
        address walletId,
        uint256 _classroomId
    ) private view returns (bool) {
        return
            idsToObjects.classroom[_classroomId].classroomAdminId == walletId;
    }

    function walletOwnsTeacher(
        address walletId,
        address _teacherId
    ) private view returns (bool) {
        return
            arrayContainsAddress(
                idsToObjects.teacher[_teacherId].classroomAdminIds,
                walletId
            );
    }

    function unregisterLandFromClassroomAdmin(uint256 landId) private {
        delete idsToObjects.land[landId];
        removeUintFromArrayMaintainOrder(
            registeredIds.landsRegisteredToClassroomAdmin,
            landId
        );
        delete registeredIds.landsRegisteredToClassroomAdminBool[landId];
    }

    function registerLandToClassroom(
        uint256 landId,
        uint256 _classroomId
    ) private {
        idsToObjects.land[landId].classroomId = _classroomId;
        registeredIds.landsRegisteredToClassroom.push(landId);
        registeredIds.landsRegisteredToClassroomBool[landId] = true;
    }

    function unregisterLandFromClassroom(uint256 landId) private {
        idsToObjects.land[landId].classroomId = 0;
        removeUintFromArrayMaintainOrder(
            registeredIds.landsRegisteredToClassroom,
            landId
        );
        delete registeredIds.landsRegisteredToClassroomBool[landId];
    }

    // classroomAdmin
    function registerClassroomAdmin(
        address _walletAddress,
        uint256[] memory landIds
    ) private {
        uint256[] memory emptyUintList;
        address[] memory emptyAddressList;
        int[][] memory _landCoordinates;

        // register land ids
        for (uint256 i = 0; i < landIds.length; i++) {
            uint256 landId = landIds[i];
            idsToObjects.land[landId] = Land({
                id: landId,
                classroomAdminId: _walletAddress,
                classroomId: 0
            });

            registeredIds.landsRegisteredToClassroomAdmin.push(landId);
            registeredIds.landsRegisteredToClassroomAdminBool[landId] = true;
        }

        idsToObjects.classroomAdmin[_walletAddress] = ClassroomAdmin({
            walletAddress: _walletAddress,
            landIds: landIds,
            landCoordinates: _landCoordinates,
            classroomIds: emptyUintList,
            teacherIds: emptyAddressList
        });
        toggleRole(_walletAddress, roleMap.classroomAdmin, true);
    }

    function registerClassroom(
        uint256 _id,
        string memory _name,
        uint256[] memory _landIds,
        address _classroomAdminId,
        string memory _guid
    ) private {
        address[] memory emptyAddressList;
        int[][] memory emptyIntList;

        idsToObjects.classroom[_id] = Classroom({
            id: _id,
            name: _name,
            landIds: _landIds,
            landCoordinates: emptyIntList,
            classroomAdminId: _classroomAdminId,
            teacherIds: emptyAddressList,
            guid: _guid,
            configUrl: ""
        });
        registeredIds.classroom.push(_id);
        registeredIds.classroomBool[_id] = true;
        registeredIds.guidToClassroom[_guid] = _id;
        for (uint256 i = 0; i < _landIds.length; i++) {
            registerLandToClassroom(_landIds[i], _id);
        }
        idsToObjects.classroomAdmin[_classroomAdminId].classroomIds.push(_id);
    }

    function unregisterClassroom(uint256 _id) private {
        Classroom memory classroom = idsToObjects.classroom[_id];
        uint256[] memory _landIds = classroom.landIds;
        removeUintFromArrayMaintainOrder(registeredIds.classroom, _id);

        delete registeredIds.classroomBool[_id];
        if (Strings.equal(classroom.guid, "")) {
            delete registeredIds.guidToClassroom[classroom.guid];
        }
        for (uint256 i = 0; i < _landIds.length; i++) {
            unregisterLandFromClassroom(_landIds[i]);
        }
        removeUintFromArrayMaintainOrder(
            idsToObjects
                .classroomAdmin[classroom.classroomAdminId]
                .classroomIds,
            _id
        );

        // delete orphaned teachers
        for (uint256 i = 0; i < classroom.teacherIds.length; i++) {
            Teacher memory teacher = idsToObjects.teacher[
                classroom.teacherIds[i]
            ];
            if (teacher.classroomIds.length == 1) {
                unregisterTeacher(teacher.walletAddress);
            } else {
                // remove this classroom from the teacher
                uint256[] memory newClassroomIds = new uint256[](
                    teacher.classroomIds.length - 1
                );
                // build the new array
                // skip the classroom to be removed
                uint256 keyCounter = 0;
                for (uint256 j = 0; j < teacher.classroomIds.length; j++) {
                    if (teacher.classroomIds[j] != _id) {
                        newClassroomIds[j] = teacher.classroomIds[keyCounter];
                        keyCounter++;
                    }
                }

                unregisterTeacher(teacher.walletAddress);
                registerTeacher(teacher.walletAddress, newClassroomIds);
            }
        }

        delete idsToObjects.classroom[_id];
    }

    function registerTeacher(
        address _walletAddress,
        uint256[] memory _classroomIds
    ) private {
        // they could already be registered by another classroom admin
        // in which case we need to update them
        if (hasRole(roleMap.teacher, _walletAddress)) {
            // they are already registered with another CA
            idsToObjects.teacher[_walletAddress].classroomAdminIds.push(
                msg.sender
            );
        } else {
            address[] memory classroomAdminsWallets = new address[](1);
            classroomAdminsWallets[0] = msg.sender;
            idsToObjects.teacher[_walletAddress] = Teacher({
                walletAddress: _walletAddress,
                classroomIds: _classroomIds,
                classroomAdminIds: classroomAdminsWallets
            });
            toggleRole(_walletAddress, roleMap.teacher, true);
        }
        // associate with classrooms
        for (uint256 i = 0; i < _classroomIds.length; i++) {
            idsToObjects.classroom[_classroomIds[i]].teacherIds.push(
                _walletAddress
            );
        }
        idsToObjects.classroomAdmin[msg.sender].teacherIds.push(_walletAddress);
    }

    function unregisterTeacher(address _walletAddress) private {
        Teacher memory teacher = idsToObjects.teacher[_walletAddress];
        uint256 classroomAdminCount = teacher.classroomAdminIds.length;

        removeAddressFromArrayMaintainOrder(
            idsToObjects.classroomAdmin[msg.sender].teacherIds,
            _walletAddress
        );
        removeAddressFromArrayMaintainOrder(
            idsToObjects.teacher[_walletAddress].classroomAdminIds,
            msg.sender
        );

        if (classroomAdminCount == 1) {
            toggleRole(_walletAddress, roleMap.teacher, false);
            for (uint256 i = 0; i < teacher.classroomIds.length; i++) {
                removeAddressFromArrayMaintainOrder(
                    idsToObjects.classroom[teacher.classroomIds[i]].teacherIds,
                    _walletAddress
                );
            }
            delete idsToObjects.teacher[_walletAddress];
        }
    }

    // PRIVATE UTILITY
    function removeAddressFromArrayMaintainOrder(
        address[] storage arr,
        address val
    ) private {
        for (uint256 i = 0; i < arr.length; i++) {
            if (val == arr[i]) {
                arr[i] = arr[arr.length - 1];
                arr.pop();
                break;
            }
        }
    }

    function removeUintFromArrayMaintainOrder(
        uint256[] storage arr,
        uint256 val
    ) private {
        for (uint256 i = 0; i < arr.length; i++) {
            if (val == arr[i]) {
                arr[i] = arr[arr.length - 1];
                arr.pop();
                break;
            }
        }
    }

    function arrayContainsUint(
        uint256[] memory arr,
        uint256 val
    ) private pure returns (bool) {
        for (uint256 i = 0; i < arr.length; i++) {
            if (arr[i] == val) {
                return true;
            }
        }
        return false;
    }

    function arrayContainsAddress(
        address[] memory arr,
        address val
    ) private pure returns (bool) {
        for (uint256 i = 0; i < arr.length; i++) {
            if (arr[i] == val) {
                return true;
            }
        }
        return false;
    }

    function removeClassroomFromArrayMaintainOrder(
        Classroom[] storage arr,
        uint256 _classroomId
    ) private {
        for (uint256 i = 0; i < arr.length; i++) {
            if (_classroomId == arr[i].id) {
                arr[i] = arr[arr.length - 1];
                arr.pop();
                break;
            }
        }
    }

    function _isContract(address addr) internal view returns (bool) {
        uint size;
        assembly {
            size := extcodesize(addr)
        }
        return size > 0;
    }

    // ROLES

    /*
     *    Grant or revoke role based on grant flag
     */
    function toggleRole(
        address beneficiary,
        RoleDetail storage roleDetail,
        bool grant
    ) private {
        if (grant) {
            roleDetail.addressArray.push(beneficiary);
            roleDetail.boolMapping[beneficiary] = true;
        } else {
            removeAddressFromArrayMaintainOrder(
                roleDetail.addressArray,
                beneficiary
            );
            delete roleDetail.boolMapping[beneficiary];
        }
    }

    function hasRole(
        RoleDetail storage roleDetail,
        address user
    ) internal view returns (bool) {
        return roleDetail.boolMapping[user];
    }

    modifier onlyRole(RoleDetail storage roleDetail) {
        require(
            hasRole(roleDetail, msg.sender),
            string.concat(
                "You ",
                Strings.toHexString(uint160(msg.sender)),
                " lack the appropriate role to call this function: ",
                roleDetail.roleName
            )
        );
        _;
    }

    modifier onlyOwner() {
        require(
            msg.sender == owner,
            "Only the contract owner can call this function"
        );
        _;
    }
}