package watcher

import (
	golog "log"
	"os"

	"github.com/owncloud/ocis/ocis/pkg/runtime/log"
	"github.com/owncloud/ocis/ocis/pkg/runtime/process"
	"github.com/rs/zerolog"
)

// Watcher watches a process and sends messages using channels.
type Watcher struct {
	log zerolog.Logger
}

// NewWatcher initializes a watcher.
func NewWatcher() Watcher {
	return Watcher{
		log: log.NewLogger(log.WithPretty(true)),
	}
}

// Follow a process until it dies. If restart is enabled, a new fork of the original process will be automatically spawned.
func (w *Watcher) Follow(pe process.ProcEntry, followerChan chan process.ProcEntry, restart bool) {
	state := make(chan *os.ProcessState, 1)

	w.log.Debug().Str("package", "watcher").Msgf("watching %v", pe.Extension)
	go func() {
		ps, err := watch(pe.Pid)
		if err != nil {
			golog.Fatal(err)
		}

		state <- ps
	}()

	go func() {
		status := <-state
		w.log.Info().Str("package", "watcher").Msgf("%v exited with: %v", pe.Extension, status)
		if restart {
			followerChan <- pe
		}
	}()
}

// watch a process by its pid. This operation blocks.
func watch(pid int) (*os.ProcessState, error) {
	p, err := os.FindProcess(pid)
	if err != nil {
		return nil, err
	}

	return p.Wait()
}