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EventTrigger...EventTrigger.sol

pragma solidity ^0.6.0;

contract ItemManager{
    
    enum ItemState {CREATED, PAID, DELIVERED}
    
    struct ItemArray{
        string _itemName;
        uint _itemPrice;
        ItemState _state;
    }
    
    mapping(uint => ItemArray) items;
    
    uint itemIndex;
    event createItem(uint _itemIndex, string  _itemName, ItemState _state);
    function create(string memory _itemName, uint _price) public{
        items[itemIndex]._itemName = _itemName;
        items[itemIndex]._itemPrice = _price;
        items[itemIndex]._state = ItemState.CREATED;
        
        emit createItem(itemIndex, items[itemIndex]._itemName, items[itemIndex]._state);
        itemIndex++;
    }
    
    
    event payItem(uint _itemIndex, string  _itemName, ItemState _state);
    function pay(uint _itemIndex) payable public{
        require(items[_itemIndex]._state == ItemState.CREATED, "The Item is on process");
        require(items[_itemIndex]._itemPrice == msg.value, "Not enough amount");
        
        items[_itemIndex]._state = ItemState.PAID;
        emit payItem(_itemIndex, items[_itemIndex]._itemName,  items[_itemIndex]._state);
        
    }
    
    event deliverItem(uint _itemIndex, string  _itemName, ItemState _state);
    function deliver(uint _itemIndex) public{
        require(items[_itemIndex]._state == ItemState.PAID, "This item has not been paid");
        
        items[_itemIndex]._state = ItemState.DELIVERED;
        emit deliverItem(_itemIndex, items[_itemIndex]._itemName, items[_itemIndex]._state);
    }
    
}