/*
Copyright 2021 The Caoyingjunz Authors.

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

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package signals

import (
	"context"
	"os"
	"os/signal"
	"syscall"
)

var (
	onlyOneSignalHandler = make(chan struct{})
	shutdownSignals      = []os.Signal{os.Interrupt, syscall.SIGTERM}
)

// SetupSignalHandler registered for SIGTERM and SIGINT. A context is returned
// which is cancelled on one of these signals. If a second signal is caught,
// the program is terminated with exit code 1.
func SetupSignalHandler() context.Context {
	close(onlyOneSignalHandler) // panics when called twice

	c := make(chan os.Signal, 2)
	ctx, cancel := context.WithCancel(context.Background())
	signal.Notify(c, shutdownSignals...)
	go func() {
		<-c
		cancel()
		<-c
		os.Exit(1) // second signal. Exit directly.
	}()

	return ctx
}
