// Copyright (c) Alex Ellis 2017. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

// Package main provides the OpenFaaS Classic Watchdog. The Classic Watchdog is a HTTP
// shim for serverless functions providing health-checking, graceful shutdowns,
// timeouts and a consistent logging experience.
package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"path/filepath"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/openfaas/faas/watchdog/metrics"
	"github.com/openfaas/faas/watchdog/types"
)

var (
	acceptingConnections int32
)

func main() {
	var runHealthcheck bool
	var versionFlag bool

	flag.BoolVar(&versionFlag, "version", false, "Print the version and exit")
	flag.BoolVar(&runHealthcheck,
		"run-healthcheck",
		false,
		"Check for the a lock-file, when using an exec healthcheck. Exit 0 for present, non-zero when not found.")

	flag.Parse()

	if runHealthcheck {
		if lockFilePresent() {
			os.Exit(0)
		}

		fmt.Fprintf(os.Stderr, "unable to find lock file.\n")
		os.Exit(1)
	}

	printVersion()

	if versionFlag {
		return
	}

	atomic.StoreInt32(&acceptingConnections, 0)

	osEnv := types.OsEnv{}
	readConfig := ReadConfig{}
	config := readConfig.Read(osEnv)

	if len(config.faasProcess) == 0 {
		log.Panicln("Provide a valid process via fprocess environmental variable.")
		return
	}

	readTimeout := config.readTimeout
	writeTimeout := config.writeTimeout

	s := &http.Server{
		Addr:           fmt.Sprintf(":%d", config.port),
		ReadTimeout:    readTimeout,
		WriteTimeout:   writeTimeout,
		MaxHeaderBytes: 1 << 20, // Max header of 1MB
	}

	httpMetrics := metrics.NewHttp()

	log.Printf("Timeouts: read: %s, write: %s hard: %s.\n",
		readTimeout,
		writeTimeout,
		config.execTimeout)
	log.Printf("Listening on port: %d\n", config.port)

	http.HandleFunc("/_/health", makeHealthHandler())
	http.HandleFunc("/", metrics.InstrumentHandler(makeRequestHandler(&config), httpMetrics))

	metricsServer := metrics.MetricsServer{}
	metricsServer.Register(config.metricsPort)

	cancel := make(chan bool)

	go metricsServer.Serve(cancel)

	shutdownTimeout := config.writeTimeout
	listenUntilShutdown(shutdownTimeout, s, config.suppressLock)
}

func markUnhealthy() error {
	atomic.StoreInt32(&acceptingConnections, 0)

	path := filepath.Join(os.TempDir(), ".lock")
	log.Printf("Removing lock-file : %s\n", path)
	removeErr := os.Remove(path)
	return removeErr
}

// listenUntilShutdown will listen for HTTP requests until SIGTERM
// is sent at which point the code will wait `shutdownTimeout` before
// closing off connections and a futher `shutdownTimeout` before
// exiting
func listenUntilShutdown(shutdownTimeout time.Duration, s *http.Server, suppressLock bool) {

	idleConnsClosed := make(chan struct{})
	go func() {
		sig := make(chan os.Signal, 1)
		signal.Notify(sig, syscall.SIGTERM)

		<-sig

		log.Printf("SIGTERM received.. shutting down server in %s\n", shutdownTimeout.String())

		healthErr := markUnhealthy()

		if healthErr != nil {
			log.Printf("Unable to mark unhealthy during shutdown: %s\n", healthErr.Error())
		}

		<-time.Tick(shutdownTimeout)

		if err := s.Shutdown(context.Background()); err != nil {
			// Error from closing listeners, or context timeout:
			log.Printf("Error in Shutdown: %v", err)
		}

		log.Printf("No new connections allowed. Exiting in: %s\n", shutdownTimeout.String())

		<-time.Tick(shutdownTimeout)

		close(idleConnsClosed)
	}()

	// Run the HTTP server in a separate go-routine.
	go func() {
		if err := s.ListenAndServe(); err != http.ErrServerClosed {
			log.Printf("Error ListenAndServe: %v", err)
			close(idleConnsClosed)
		}
	}()

	if suppressLock == false {
		path, writeErr := createLockFile()

		if writeErr != nil {
			log.Panicf("Cannot write %s. To disable lock-file set env suppress_lock=true.\n Error: %s.\n", path, writeErr.Error())
		}
	} else {
		log.Println("Warning: \"suppress_lock\" is enabled. No automated health-checks will be in place for your function.")

		atomic.StoreInt32(&acceptingConnections, 1)
	}

	<-idleConnsClosed
}

func printVersion() {
	sha := "unknown"
	if len(GitCommit) > 0 {
		sha = GitCommit
	}

	log.Printf("Version: %v\tSHA: %v\n", BuildVersion(), sha)
}