function extractBehaviourFeatures(actions) {
  if (!actions || actions.length < 2) return null;

  const actionCounts = {};
  const idleThreshold = 5000;
  const windowSize = 5;
  const intervals = [];
  const sequenceBuffer = [];
  let totalInterval = 0;
  let minInterval = Infinity;
  let maxInterval = -Infinity;
  let idleTimeCount = 0;
  let idleTimeTotal = 0;
  let lastTimestamp = actions[0].timestamp;
  let prevAction = actions[0].opcode;
  let sequenceMap = {};

  for (let i = 1; i < actions.length; i++) {
    const current = actions[i];
    const interval = current.timestamp - lastTimestamp;
    lastTimestamp = current.timestamp;

    intervals.push(interval);

    totalInterval += interval;
    minInterval = Math.min(minInterval, interval);
    maxInterval = Math.max(maxInterval, interval);

    actionCounts[current.opcode] = (actionCounts[current.opcode] || 0) + 1;

    if (interval > idleThreshold) {
      idleTimeCount++;
      idleTimeTotal += interval;
    };

    sequenceBuffer.push(current.opcode);
    if (sequenceBuffer.length === windowSize) {
      const key = sequenceBuffer.join(",");
      sequenceMap[key] = (sequenceMap[key] || 0) + 1;

      sequenceBuffer.shift();
    };

    prevAction = current.opcode;
  };

  const meanInterval = totalInterval / intervals.length;
  const stdDevInterval = Math.sqrt(intervals.reduce((sum, val) => sum + (val - meanInterval) ** 2, 0) / intervals.length);

  const uniqueActionsCount = Object.keys(actionCounts).length;
  const idleTimeRatio = idleTimeCount / (actions.length - 1);
  const maxSequenceRepeats = Math.max(...Object.values(sequenceMap)) || 0;

  const totalActions = actions.length;
  let entropy = 0;

  for (const count of Object.values(actionCounts)) {
    const p = count / totalActions;
    entropy -= p * Math.log2(p);
  };

  return {
    timestamp: new Date(),
    timestampStart: null,
    meanInterval,
    stdDevInterval,
    minInterval,
    maxInterval,
    uniqueActionsCount,
    actionEntropy: entropy,
    maxSequenceRepeats,
    idleTimeRatio
  };
};

module.exports = extractBehaviourFeatures;