Counter contract

contracts/Counter.sol

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+// SPDX-License-Identifier: GPL-3.0
+pragma solidity 0.6.12;
+pragma experimental ABIEncoderV2;
+
+/**
+  @title A simple, example contract for incrementing a counter.
+  @author Tim Clancy
+
+  We use this contract to test out our centralized chain.
+*/
+contract Counter {
+
+  /// A version number for this contract's interface.
+  uint256 public version = 1;
+
+  /// The current value of the counter.
+  uint256 public value;
+
+  /// A mapping of addresses to the last value they incremented to.
+  mapping (address => uint256) public increments;
+
+  /// An event to track the counter incrementing.
+  event Increment(address incrementer, uint256 oldValue, uint256 newValue);
+
+  /**
+    Construct a new Counter with a starting initial value.
+
+    @param _initialValue The initial value of the Counter.
+  */
+  constructor(uint256 _initialValue) public {
+    value = _initialValue;
+  }
+
+  /**
+    Returns the last value incremented to by a given address.
+
+    @param _incrementer The address to check.
+    @return the last value incremented to by an address.
+  */
+  function getIncrementFor(address _incrementer) external view returns (uint256) {
+    return increments[_incrementer];
+  }
+
+  /**
+    Allow a user to increment this counter.
+  */
+  function increment() external {
+    uint256 oldValue = value;
+    value = value + 1;
+    increments[msg.sender] = value;
+    emit Increment(msg.sender, oldValue, value);
+  }
+}