/*
 * Minio Cloud Storage, (C) 2016 Minio, Inc.
 *
 * 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 cmd

import (
	"os"
	"os/exec"
	"syscall"
)

// Represents a type of an exit func which will be invoked upon service signal.
type onExitFunc func(err error)

// Represents a type for all the the callback functions invoked upon service signal.
type cleanupOnExitFunc func() error

// Type of service signals currently supported.
type serviceSignal int

const (
	serviceStatus  = iota // Gets status about the service.
	serviceRestart        // Restarts the service.
	serviceStop           // Stops the server.
	// Add new service requests here.
)

// Global service signal channel.
var globalServiceSignalCh chan serviceSignal

// Global service done channel.
var globalServiceDoneCh chan struct{}

// Initialize service mutex once.
func init() {
	globalServiceDoneCh = make(chan struct{}, 1)
	globalServiceSignalCh = make(chan serviceSignal, 1)
}

// restartProcess starts a new process passing it the active fd's. It
// doesn't fork, but starts a new process using the same environment and
// arguments as when it was originally started. This allows for a newly
// deployed binary to be started. It returns the pid of the newly started
// process when successful.
func restartProcess() error {
	// Use the original binary location. This works with symlinks such that if
	// the file it points to has been changed we will use the updated symlink.
	argv0, err := exec.LookPath(os.Args[0])
	if err != nil {
		return err
	}

	// Pass on the environment and replace the old count key with the new one.
	cmd := exec.Command(argv0, os.Args[1:]...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	return cmd.Start()
}

// Handles all serviceSignal and execute service functions.
func (m *ServerMux) handleServiceSignals() error {
	// Custom exit function
	runExitFn := func(err error) {
		// If global profiler is set stop before we exit.
		if globalProfiler != nil {
			globalProfiler.Stop()
		}

		// Call user supplied user exit function
		fatalIf(err, "Unable to gracefully complete service operation.")

		// We are usually done here, close global service done channel.
		globalServiceDoneCh <- struct{}{}
	}

	// Start listening on service signal. Monitor signals.
	trapCh := signalTrap(os.Interrupt, syscall.SIGTERM)
	for {
		select {
		case <-trapCh:
			// Initiate graceful stop.
			globalServiceSignalCh <- serviceStop
		case signal := <-globalServiceSignalCh:
			switch signal {
			case serviceStatus:
				/// We don't do anything for this.
			case serviceRestart:
				if err := m.Close(); err != nil {
					errorIf(err, "Unable to close server gracefully")
				}
				if err := restartProcess(); err != nil {
					errorIf(err, "Unable to restart the server.")
				}
				runExitFn(nil)
			case serviceStop:
				if err := m.Close(); err != nil {
					errorIf(err, "Unable to close server gracefully")
				}
				objAPI := newObjectLayerFn()
				if objAPI == nil {
					// Server not initialized yet, exit happily.
					runExitFn(nil)
				}
				runExitFn(objAPI.Shutdown())
			}
		}
	}
}