package beater

import (
	"sync"

	"github.com/elastic/beats/libbeat/publisher"
)

// ModuleRunner is a facade for a ModuleWrapper that provides a simple interface
// for starting and stopping a Module.
type ModuleRunner interface {
	// Start starts the Module. If Start is called more than once, only the
	// first will start the Module.
	Start()

	// Stop stops the Module and waits for module's MetricSets to exit. The
	// publisher.Client will be closed by Stop. If Stop is called more than
	// once, only the first stop the Module and wait for it to exit.
	Stop()
}

// NewModuleRunner returns a ModuleRunner facade. The events generated by
// the Module will be published to a new publisher.Client generated from the
// pubClientFactory.
func NewModuleRunner(pubClientFactory func() publisher.Client, mod *ModuleWrapper) ModuleRunner {
	return &moduleRunner{
		done:   make(chan struct{}),
		mod:    mod,
		client: pubClientFactory(),
	}
}

type moduleRunner struct {
	done      chan struct{}
	wg        sync.WaitGroup
	startOnce sync.Once
	stopOnce  sync.Once
	mod       *ModuleWrapper
	client    publisher.Client
}

func (mr *moduleRunner) Start() {
	mr.startOnce.Do(func() {
		output := mr.mod.Start(mr.done)
		mr.wg.Add(1)
		go func() {
			defer mr.wg.Done()
			PublishChannels(mr.client, output)
		}()
	})
}

func (mr *moduleRunner) Stop() {
	mr.stopOnce.Do(func() {
		close(mr.done)
		mr.client.Close()
		mr.wg.Wait()
	})
}