// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.1;

contract DynamicMetadata {
    // Mapping of token ID to another mapping that maps attribute names to their values.
    mapping(uint256 => mapping(string => string)) private tokenAttributes;
    // Mapping of token ID to a list of its attribute names.
    mapping(uint256 => string[]) private attributeNames;

    // Struct to represent an attribute with its name and value.
    struct Attribute {
        string name;
        string value;
    }

    // Event to notify that metadata for a specific token ID needs to be refreshed.
    event RefreshRequired(
        uint256 indexed ID,
        string attribute,
        string newValue
    );

    // Fetches the list of attribute names for a specific token ID.
    function getAttributeNames(
        uint256 tokenId
    ) public view returns (string[] memory) {
        return attributeNames[tokenId];
    }

    // Fetches the value of a specific attribute for a specific token ID.
    function getAttribute(
        uint256 tokenId,
        string memory attribute
    ) public view returns (string memory) {
        return tokenAttributes[tokenId][attribute];
    }

    // Fetches all attributes (name-value pairs) for a specific token ID.
    function getAttributes(
        uint256 tokenId
    ) public view returns (Attribute[] memory) {
        string[] memory names = attributeNames[tokenId];
        Attribute[] memory attributes = new Attribute[](names.length);
        for (uint i = 0; i < names.length; i++) {
            attributes[i] = Attribute(
                names[i],
                tokenAttributes[tokenId][names[i]]
            );
        }
        return attributes;
    }

    // Internal function to trigger a RefreshRequired event for a specific token ID.
    function _emitRefresh(
        uint256 ID,
        string memory attribute,
        string memory newValue
    ) internal {
        emit RefreshRequired(ID, attribute, newValue);
    }

    // Internal function to update or add a new attribute for a specific token ID.
    function _updateMetadata(
        uint256 ID,
        string memory attribute,
        string memory newValue
    ) internal {
        if (bytes(tokenAttributes[ID][attribute]).length == 0) {
            // If this attribute was not previously set for this token, add the attribute name to the list.
            attributeNames[ID].push(attribute);
        }
        _updateAttribute(ID, attribute, newValue);
    }

    // Private helper function to handle attribute-specific logic.
    function _updateAttribute(
        uint256 ID,
        string memory attribute,
        string memory newValue
    ) private {
        tokenAttributes[ID][attribute] = newValue;
        _emitRefresh(ID, attribute, newValue);
    }
}