From a6cfd2d694461e82cf4751f3189e589058fce626 Mon Sep 17 00:00:00 2001
From: Hadrien Croubois <hc@iex.ec>
Date: Sat, 12 Oct 2019 08:29:35 +0200
Subject: [PATCH] adding an indexing contract:

Build sets of tokens indexed by the corresponding events. Allows to
build an onchain, trustless, list of token that belong to an event.
Needed for auditable/trustless loterry
---
 eth/contracts/PoapIndex.sol | 65 ++++++++++++++++++++++++++
 eth/contracts/Set.sol       | 91 +++++++++++++++++++++++++++++++++++++
 2 files changed, 156 insertions(+)
 create mode 100644 eth/contracts/PoapIndex.sol
 create mode 100644 eth/contracts/Set.sol

diff --git a/eth/contracts/PoapIndex.sol b/eth/contracts/PoapIndex.sol
new file mode 100644
index 00000000..dafc0001
--- /dev/null
+++ b/eth/contracts/PoapIndex.sol
@@ -0,0 +1,65 @@
+/* Copyright 2019 Hadrien Croubois
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+pragma solidity ^0.5.0;
+
+import "./Poap.sol";
+import "./Set.sol";
+
+contract PoapIndex
+{
+	using Set for Set.set;
+
+	// Poap token address
+	Poap public poap;
+
+	// event to tokens
+	mapping(uint256 => Set.set) private m_tokensEvent;
+
+	event TokenAdded(uint256 indexed tokenId, uint256 indexed eventId);
+
+	constructor(Poap _poap)
+	public
+	{
+		poap = _poap;
+	}
+
+	function addToken(uint256 _tokenId) external
+	{
+		_addToken(_tokenId);
+	}
+
+	function addTokens(uint256[] calldata _tokenIds) external
+	{
+		for (uint256 i = 0; i < _tokenIds.length; ++i)
+		{
+			_addToken(_tokenIds[i]);
+		}
+	}
+
+	function _addToken(uint256 _tokenId) internal
+	{
+		uint256 eventId = poap.tokenEvent(_tokenId);
+		if (eventId != 0 && m_tokensEvent[eventId].add(_tokenId))
+		{
+			emit TokenAdded(_tokenId, eventId);
+		}
+	}
+
+	function viewTokens(uint256 _eventId) external view returns (uint256[] memory)
+	{
+		return m_tokensEvent[_eventId].content();
+	}
+}
diff --git a/eth/contracts/Set.sol b/eth/contracts/Set.sol
new file mode 100644
index 00000000..79ac1e38
--- /dev/null
+++ b/eth/contracts/Set.sol
@@ -0,0 +1,91 @@
+/* Copyright 2019 Hadrien Croubois
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+pragma solidity ^0.5.0;
+
+library Set
+{
+	struct set
+	{
+		uint256[] members;
+		mapping(uint256 => uint256) indexes;
+	}
+
+	function length(set storage _list)
+	internal view returns (uint256)
+	{
+		return _list.members.length;
+	}
+
+	function at(set storage _list, uint256 _index)
+	internal view returns (uint256)
+	{
+		return _list.members[_index - 1];
+	}
+
+	function indexOf(set storage _list, uint256 _value)
+	internal view returns (uint256)
+	{
+		return _list.indexes[_value];
+	}
+
+	function contains(set storage _list, uint256 _value)
+	internal view returns (bool)
+	{
+		return indexOf(_list, _value) != 0;
+	}
+
+	function content(set storage _list)
+	internal view returns (uint256[] memory)
+	{
+		return _list.members;
+	}
+
+	function add(set storage _list, uint256 _value)
+	internal returns (bool)
+	{
+		if (contains(_list, _value))
+		{
+			return false;
+		}
+		_list.indexes[_value] = _list.members.push(_value);
+		return true;
+	}
+
+	function remove(set storage _list, uint256 _value)
+	internal returns (bool)
+	{
+		if (!contains(_list, _value))
+		{
+			return false;
+		}
+
+		uint256 i    = indexOf(_list, _value);
+		uint256 last = length(_list);
+
+		if (i != last)
+		{
+			uint256 swapValue = _list.members[last - 1];
+			_list.members[i - 1] = swapValue;
+			_list.indexes[swapValue] = i;
+		}
+
+		delete _list.indexes[_value];
+		--_list.members.length;
+
+		return true;
+	}
+
+}