feat(LibEventRange): add LibEventRange

src/LibEventRange.sol

@@ -0,0 +1,42 @@
+//SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+struct EventRange {
+  // uint40 is enough to represent the timestamp until year 36812
+  uint40 startedAt;
+  uint40 endedAt;
+  /// @dev Reserved space for future upgrades
+  uint176 __reserved;
+}
+
+using LibEventRange for EventRange global;
+
+library LibEventRange {
+  /**
+   * @dev Checks whether the event range is valid.
+   */
+  function valid(EventRange memory range) internal pure returns (bool) {
+    return range.startedAt <= range.endedAt;
+  }
+
+  /**
+   * @dev Returns whether the current range is not yet started.
+   */
+  function isNotYetStarted(EventRange memory range) internal view returns (bool) {
+    return block.timestamp < range.startedAt;
+  }
+
+  /**
+   * @dev Returns whether the current range is ended or not.
+   */
+  function isEnded(EventRange memory range) internal view returns (bool) {
+    return range.endedAt <= block.timestamp;
+  }
+
+  /**
+   * @dev Returns whether the current block is in period.
+   */
+  function isInPeriod(EventRange memory range) internal view returns (bool) {
+    return range.startedAt <= block.timestamp && block.timestamp < range.endedAt;
+  }
+}