// Copyright (C) MongoDB, Inc. 2017-present.
//
// 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

// Package event is a library for monitoring events from the MongoDB Go
// driver. Monitors can be set for commands sent to the MongoDB cluster,
// connection pool changes, or changes on the MongoDB cluster.
//
// Monitoring commands requires specifying a CommandMonitor when constructing
// a mongo.Client. A CommandMonitor can be set to monitor started, succeeded,
// and/or failed events. A CommandStartedEvent can be correlated to its matching
// CommandSucceededEvent or CommandFailedEvent through the RequestID field. For
// example, the following code collects the names of started events:
//
//	var commandStarted []string
//	cmdMonitor := &event.CommandMonitor{
//	  Started: func(_ context.Context, evt *event.CommandStartedEvent) {
//	    commandStarted = append(commandStarted, evt.CommandName)
//	  },
//	}
//	clientOpts := options.Client().ApplyURI("mongodb://localhost:27017").SetMonitor(cmdMonitor)
//	client, err := mongo.Connect(context.Background(), clientOpts)
//
// Monitoring the connection pool requires specifying a PoolMonitor when constructing
// a mongo.Client. The following code tracks the number of checked out connections:
//
//	var int connsCheckedOut
//	poolMonitor := &event.PoolMonitor{
//	  Event: func(evt *event.PoolEvent) {
//	    switch evt.Type {
//	    case event.GetSucceeded:
//	      connsCheckedOut++
//	    case event.ConnectionReturned:
//	      connsCheckedOut--
//	    }
//	  },
//	}
//	clientOpts := options.Client().ApplyURI("mongodb://localhost:27017").SetPoolMonitor(poolMonitor)
//	client, err := mongo.Connect(context.Background(), clientOpts)
//
// Monitoring server changes specifying a ServerMonitor object when constructing
// a mongo.Client. Different functions can be set on the ServerMonitor to
// monitor different kinds of events. See ServerMonitor for more details.
// The following code appends ServerHeartbeatStartedEvents to a slice:
//
//	   var heartbeatStarted []*event.ServerHeartbeatStartedEvent
//	   svrMonitor := &event.ServerMonitor{
//	     ServerHeartbeatStarted: func(e *event.ServerHeartbeatStartedEvent) {
//		      heartbeatStarted = append(heartbeatStarted, e)
//	     }
//	   }
//	   clientOpts := options.Client().ApplyURI("mongodb://localhost:27017").SetServerMonitor(svrMonitor)
//	   client, err := mongo.Connect(context.Background(), clientOpts)
package event