Added Contract for managing group / public chat suscriptions

contracts/communication/GroupAccess.sol

@@ -0,0 +1,87 @@
+pragma solidity ^0.4.24;
+
+import "../token/ERC20Token.sol";
+import "../common/MessageSigned.sol";
+
+
+contract GroupSuscription is MessageSigned {
+
+    struct SuscriptionData {
+        uint256 amount;
+        uint256 recurrency;
+        uint256 amountHeld;
+        bool requiresPayment;
+    }
+
+    mapping(bytes32 => uint) private suscriptions;
+    mapping(bytes32 => address) private groupOwnership;
+    mapping(bytes32 => SuscriptionData) private groupSuscriptionInfo;
+
+    event GroupSetup(bytes groupKey, bytes32 groupId);
+    
+    ERC20Token public token;
+    
+    constructor(ERC20Token _token) public {
+        token = _token;
+    }
+    
+    function registerGroup(bytes _groupKey, 
+                           uint256 _amount, 
+                           uint256 _recurrency, 
+                           uint256  _amountHeld, 
+                           bool _requiresPayment) public {
+        bytes32 groupId = keccak256(abi.encodePacked(address(this), msg.sender, _groupKey));
+        groupOwnership[groupId] = msg.sender;
+        groupSuscriptionInfo[groupId] = SuscriptionData(_amount, _recurrency, _amountHeld, _requiresPayment);
+        emit GroupSetup(_groupKey, groupId);
+    }
+
+    function getSuscriptionInfo(bytes32 groupId) public view 
+        returns (uint256 amount, uint256 recurrency, uint256 amountHeld bool requiresPayment) 
+    {
+        SuscriptionData memory susc = groupSuscriptionInfo[groupId];
+        return (susc.amount, susc.recurrency, susc.amountHeld, susc.requiresPayment);
+    }
+
+    function canParticipate(bytes32 _groupId) public view
+        returns (bool)
+    {
+        bytes32 suscriptionHash = getSuscriptionHash(_groupId);
+        
+        SuscriptionData memory susc = groupSuscriptionInfo[_groupId];
+        if(token.balanceOf(msg.sender) < susc.amountHeld){
+            return false;
+        }
+
+        return suscriptions[suscriptionHash] > block.timestamp;
+    }
+
+    function suscribe(bytes32 _groupId) public {
+        SuscriptionData memory susc = groupSuscriptionInfo[_groupId];
+        bytes32 suscriptionHash = getSuscriptionHash(_groupId);
+
+        if(susc.requiresPayment){
+            require(token.transferFrom(msg.sender, groupOwnership[_groupId], susc.amount));
+        }
+
+        if(susc.amountHeld > 0)
+            require(token.balanceOf(msg.sender) >= susc.amountHeld);
+
+        suscriptions[suscriptionHash] = now + susc.recurrency;
+    }
+
+    function getSuscriptionHash(bytes32 _groupId) 
+        public 
+        view 
+        returns (bytes32) {
+        return keccak256(
+            abi.encodePacked(
+                address(this),
+                msg.sender,
+                bytes4(keccak256("suscribe(bytes32)")),
+                _groupId
+            )
+        );
+    }
+
+}