// Package coremain contains the functions for starting CoreDNS.
package coremain

import (
	"errors"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"runtime"
	"strconv"
	"strings"

	"github.com/coredns/coredns/core/dnsserver"
	clog "github.com/coredns/coredns/plugin/pkg/log"

	"github.com/mholt/caddy"
)

func init() {
	caddy.DefaultConfigFile = "Corefile"
	caddy.Quiet = true // don't show init stuff from caddy
	setVersion()

	flag.StringVar(&conf, "conf", "", "Corefile to load (default \""+caddy.DefaultConfigFile+"\")")
	flag.StringVar(&cpu, "cpu", "100%", "CPU cap")
	flag.BoolVar(&plugins, "plugins", false, "List installed plugins")
	flag.StringVar(&caddy.PidFile, "pidfile", "", "Path to write pid file")
	flag.BoolVar(&version, "version", false, "Show version")
	flag.BoolVar(&dnsserver.Quiet, "quiet", false, "Quiet mode (no initialization output)")

	caddy.RegisterCaddyfileLoader("flag", caddy.LoaderFunc(confLoader))
	caddy.SetDefaultCaddyfileLoader("default", caddy.LoaderFunc(defaultLoader))

	caddy.AppName = coreName
	caddy.AppVersion = CoreVersion
}

// Run is CoreDNS's main() function.
func Run() {
	caddy.TrapSignals()

	// Reset flag.CommandLine to get rid of unwanted flags for instance from glog (used in kubernetes).
	// And read the ones we want to keep.
	flag.VisitAll(func(f *flag.Flag) {
		if _, ok := flagsBlacklist[f.Name]; ok {
			return
		}
		flagsToKeep = append(flagsToKeep, f)
	})

	flag.CommandLine = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
	for _, f := range flagsToKeep {
		flag.Var(f.Value, f.Name, f.Usage)
	}

	flag.Parse()

	if len(flag.Args()) > 0 {
		mustLogFatal(fmt.Errorf("extra command line arguments: %s", flag.Args()))
	}

	log.SetOutput(os.Stdout)
	log.SetFlags(log.LstdFlags)

	if version {
		showVersion()
		os.Exit(0)
	}
	if plugins {
		fmt.Println(caddy.DescribePlugins())
		os.Exit(0)
	}

	// Set CPU cap
	if err := setCPU(cpu); err != nil {
		mustLogFatal(err)
	}

	// Get Corefile input
	corefile, err := caddy.LoadCaddyfile(serverType)
	if err != nil {
		mustLogFatal(err)
	}

	// Start your engines
	instance, err := caddy.Start(corefile)
	if err != nil {
		mustLogFatal(err)
	}

	logVersion()
	if !dnsserver.Quiet {
		showVersion()
	}

	// Execute instantiation events
	caddy.EmitEvent(caddy.InstanceStartupEvent, instance)

	// Twiddle your thumbs
	instance.Wait()
}

// mustLogFatal wraps log.Fatal() in a way that ensures the
// output is always printed to stderr so the user can see it
// if the user is still there, even if the process log was not
// enabled. If this process is an upgrade, however, and the user
// might not be there anymore, this just logs to the process
// log and exits.
func mustLogFatal(args ...interface{}) {
	if !caddy.IsUpgrade() {
		log.SetOutput(os.Stderr)
	}
	log.Fatal(args...)
}

// confLoader loads the Caddyfile using the -conf flag.
func confLoader(serverType string) (caddy.Input, error) {
	if conf == "" {
		return nil, nil
	}

	if conf == "stdin" {
		return caddy.CaddyfileFromPipe(os.Stdin, serverType)
	}

	contents, err := ioutil.ReadFile(conf)
	if err != nil {
		return nil, err
	}
	return caddy.CaddyfileInput{
		Contents:       contents,
		Filepath:       conf,
		ServerTypeName: serverType,
	}, nil
}

// defaultLoader loads the Corefile from the current working directory.
func defaultLoader(serverType string) (caddy.Input, error) {
	contents, err := ioutil.ReadFile(caddy.DefaultConfigFile)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	return caddy.CaddyfileInput{
		Contents:       contents,
		Filepath:       caddy.DefaultConfigFile,
		ServerTypeName: serverType,
	}, nil
}

// logVersion logs the version that is starting.
func logVersion() {
	clog.Info(versionString())
	clog.Info(releaseString())
}

// showVersion prints the version that is starting.
func showVersion() {
	fmt.Print(versionString())
	fmt.Print(releaseString())
	if devBuild && gitShortStat != "" {
		fmt.Printf("%s\n%s\n", gitShortStat, gitFilesModified)
	}
}

// versionString returns the CoreDNS version as a string.
func versionString() string {
	return fmt.Sprintf("%s-%s\n", caddy.AppName, caddy.AppVersion)
}

// releaseString returns the release information related to CoreDNS version:
// <OS>/<ARCH>, <go version>, <commit>
// e.g.,
// linux/amd64, go1.8.3, a6d2d7b5
func releaseString() string {
	return fmt.Sprintf("%s/%s, %s, %s\n", runtime.GOOS, runtime.GOARCH, runtime.Version(), GitCommit)
}

// setVersion figures out the version information
// based on variables set by -ldflags.
func setVersion() {
	// A development build is one that's not at a tag or has uncommitted changes
	devBuild = gitTag == "" || gitShortStat != ""

	// Only set the appVersion if -ldflags was used
	if gitNearestTag != "" || gitTag != "" {
		if devBuild && gitNearestTag != "" {
			appVersion = fmt.Sprintf("%s (+%s %s)",
				strings.TrimPrefix(gitNearestTag, "v"), GitCommit, buildDate)
		} else if gitTag != "" {
			appVersion = strings.TrimPrefix(gitTag, "v")
		}
	}
}

// setCPU parses string cpu and sets GOMAXPROCS
// according to its value. It accepts either
// a number (e.g. 3) or a percent (e.g. 50%).
func setCPU(cpu string) error {
	var numCPU int

	availCPU := runtime.NumCPU()

	if strings.HasSuffix(cpu, "%") {
		// Percent
		var percent float32
		pctStr := cpu[:len(cpu)-1]
		pctInt, err := strconv.Atoi(pctStr)
		if err != nil || pctInt < 1 || pctInt > 100 {
			return errors.New("invalid CPU value: percentage must be between 1-100")
		}
		percent = float32(pctInt) / 100
		numCPU = int(float32(availCPU) * percent)
	} else {
		// Number
		num, err := strconv.Atoi(cpu)
		if err != nil || num < 1 {
			return errors.New("invalid CPU value: provide a number or percent greater than 0")
		}
		numCPU = num
	}

	if numCPU > availCPU {
		numCPU = availCPU
	}

	runtime.GOMAXPROCS(numCPU)
	return nil
}

// Flags that control program flow or startup
var (
	conf    string
	cpu     string
	logfile bool
	version bool
	plugins bool
)

// Build information obtained with the help of -ldflags
var (
	appVersion = "(untracked dev build)" // inferred at startup
	devBuild   = true                    // inferred at startup

	buildDate        string // date -u
	gitTag           string // git describe --exact-match HEAD 2> /dev/null
	gitNearestTag    string // git describe --abbrev=0 --tags HEAD
	gitShortStat     string // git diff-index --shortstat
	gitFilesModified string // git diff-index --name-only HEAD

	// Gitcommit contains the commit where we built CoreDNS from.
	GitCommit string
)

// flagsBlacklist removes flags with these names from our flagset.
var flagsBlacklist = map[string]bool{
	"logtostderr":      true,
	"alsologtostderr":  true,
	"v":                true,
	"stderrthreshold":  true,
	"vmodule":          true,
	"log_backtrace_at": true,
	"log_dir":          true,
}

var flagsToKeep []*flag.Flag
