cmd/amazon-cloudwatch-agent-target-allocator/watcher/file.go

// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

package watcher

import (
	"context"
	"path/filepath"

	"github.com/fsnotify/fsnotify"
	"github.com/go-logr/logr"
	promconfig "github.com/prometheus/prometheus/config"

	"github.com/aws/amazon-cloudwatch-agent-operator/cmd/amazon-cloudwatch-agent-target-allocator/config"
)

var _ Watcher = &FileWatcher{}

type FileWatcher struct {
	logger         logr.Logger
	configFilePath string
	watcher        *fsnotify.Watcher
	closer         chan bool
}

func NewFileWatcher(logger logr.Logger, configFilePath string) (*FileWatcher, error) {
	fileWatcher, err := fsnotify.NewWatcher()
	if err != nil {
		logger.Error(err, "Can't start the watcher")
		return &FileWatcher{}, err
	}

	return &FileWatcher{
		logger:         logger,
		configFilePath: configFilePath,
		watcher:        fileWatcher,
		closer:         make(chan bool),
	}, nil
}

func (f *FileWatcher) LoadConfig(_ context.Context) (*promconfig.Config, error) {
	cfg := config.CreateDefaultConfig()
	err := config.LoadFromFile(f.configFilePath, &cfg)
	if err != nil {
		f.logger.Error(err, "Unable to load configuration")
		return nil, err
	}
	return cfg.PromConfig, nil
}

func (f *FileWatcher) Watch(upstreamEvents chan Event, upstreamErrors chan error) error {
	err := f.watcher.Add(filepath.Dir(f.configFilePath))
	if err != nil {
		return err
	}

	for {
		select {
		case <-f.closer:
			return nil
		case fileEvent := <-f.watcher.Events:
			// Using Op.Has as per this doc - https://github.com/fsnotify/fsnotify/blob/9342b6df577910c6eac718dc62845d8c95f8548b/fsnotify.go#L30
			if fileEvent.Op.Has(fsnotify.Create) || fileEvent.Op.Has(fsnotify.Write) {
				f.logger.Info("File change detected", "event", fileEvent.Op.String())
				upstreamEvents <- Event{
					Source:  EventSourceConfigMap,
					Watcher: Watcher(f),
				}
			}
		case err := <-f.watcher.Errors:
			upstreamErrors <- err
		}
	}
}

func (f *FileWatcher) Close() error {
	f.closer <- true
	return f.watcher.Close()
}