// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package cli contains the cmd/tailscale CLI code in a package that can be included
// in other wrapper binaries such as the Mac and Windows clients.
package cli

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net"
	"os"
	"os/signal"
	"runtime"
	"strings"
	"syscall"
	"text/tabwriter"

	"github.com/peterbourgon/ff/v2/ffcli"
	"tailscale.com/ipn"
	"tailscale.com/paths"
	"tailscale.com/safesocket"
)

// ActLikeCLI reports whether a GUI application should act like the
// CLI based on os.Args, GOOS, the context the process is running in
// (pty, parent PID), etc.
func ActLikeCLI() bool {
	if len(os.Args) < 2 {
		return false
	}
	switch os.Args[1] {
	case "up", "down", "status", "netcheck", "ping", "version",
		"debug",
		"-V", "--version", "-h", "--help":
		return true
	}
	return false
}

// Run runs the CLI. The args do not include the binary name.
func Run(args []string) error {
	if len(args) == 1 && (args[0] == "-V" || args[0] == "--version") {
		args = []string{"version"}
	}

	rootfs := flag.NewFlagSet("tailscale", flag.ExitOnError)
	rootfs.StringVar(&rootArgs.socket, "socket", paths.DefaultTailscaledSocket(), "path to tailscaled's unix socket")

	rootCmd := &ffcli.Command{
		Name:       "tailscale",
		ShortUsage: "tailscale [flags] <subcommand> [command flags]",
		ShortHelp:  "The easiest, most secure way to use WireGuard.",
		LongHelp: strings.TrimSpace(`
For help on subcommands, add --help after: "tailscale status --help".

This CLI is still under active development. Commands and flags will
change in the future.
`),
		Subcommands: []*ffcli.Command{
			upCmd,
			downCmd,
			netcheckCmd,
			ipCmd,
			statusCmd,
			pingCmd,
			versionCmd,
		},
		FlagSet:   rootfs,
		Exec:      func(context.Context, []string) error { return flag.ErrHelp },
		UsageFunc: usageFunc,
	}
	for _, c := range rootCmd.Subcommands {
		c.UsageFunc = usageFunc
	}

	// Don't advertise the debug command, but it exists.
	if strSliceContains(args, "debug") {
		rootCmd.Subcommands = append(rootCmd.Subcommands, debugCmd)
	}

	if err := rootCmd.Parse(args); err != nil {
		return err
	}

	err := rootCmd.Run(context.Background())
	if err == flag.ErrHelp {
		return nil
	}
	return err
}

func fatalf(format string, a ...interface{}) {
	log.SetFlags(0)
	log.Fatalf(format, a...)
}

var rootArgs struct {
	socket string
}

func connect(ctx context.Context) (net.Conn, *ipn.BackendClient, context.Context, context.CancelFunc) {
	c, err := safesocket.Connect(rootArgs.socket, 41112)
	if err != nil {
		if runtime.GOOS != "windows" && rootArgs.socket == "" {
			fatalf("--socket cannot be empty")
		}
		fatalf("Failed to connect to tailscaled. (safesocket.Connect: %v)\n", err)
	}
	clientToServer := func(b []byte) {
		ipn.WriteMsg(c, b)
	}

	ctx, cancel := context.WithCancel(ctx)

	go func() {
		interrupt := make(chan os.Signal, 1)
		signal.Notify(interrupt, syscall.SIGINT, syscall.SIGTERM)
		<-interrupt
		c.Close()
		cancel()
	}()

	bc := ipn.NewBackendClient(log.Printf, clientToServer)
	return c, bc, ctx, cancel
}

// pump receives backend messages on conn and pushes them into bc.
func pump(ctx context.Context, bc *ipn.BackendClient, conn net.Conn) {
	defer conn.Close()
	for ctx.Err() == nil {
		msg, err := ipn.ReadMsg(conn)
		if err != nil {
			if ctx.Err() != nil {
				return
			}
			log.Printf("ReadMsg: %v\n", err)
			break
		}
		bc.GotNotifyMsg(msg)
	}
}

func strSliceContains(ss []string, s string) bool {
	for _, v := range ss {
		if v == s {
			return true
		}
	}
	return false
}

func usageFunc(c *ffcli.Command) string {
	var b strings.Builder

	fmt.Fprintf(&b, "USAGE\n")
	if c.ShortUsage != "" {
		fmt.Fprintf(&b, "  %s\n", c.ShortUsage)
	} else {
		fmt.Fprintf(&b, "  %s\n", c.Name)
	}
	fmt.Fprintf(&b, "\n")

	if c.LongHelp != "" {
		fmt.Fprintf(&b, "%s\n\n", c.LongHelp)
	}

	if len(c.Subcommands) > 0 {
		fmt.Fprintf(&b, "SUBCOMMANDS\n")
		tw := tabwriter.NewWriter(&b, 0, 2, 2, ' ', 0)
		for _, subcommand := range c.Subcommands {
			fmt.Fprintf(tw, "  %s\t%s\n", subcommand.Name, subcommand.ShortHelp)
		}
		tw.Flush()
		fmt.Fprintf(&b, "\n")
	}

	if countFlags(c.FlagSet) > 0 {
		fmt.Fprintf(&b, "FLAGS\n")
		tw := tabwriter.NewWriter(&b, 0, 2, 2, ' ', 0)
		c.FlagSet.VisitAll(func(f *flag.Flag) {
			var s string
			name, usage := flag.UnquoteUsage(f)
			if isBoolFlag(f) {
				s = fmt.Sprintf("  --%s, --%s=false", f.Name, f.Name)
			} else {
				s = fmt.Sprintf("  --%s", f.Name) // Two spaces before --; see next two comments.
				if len(name) > 0 {
					s += " " + name
				}
			}
			// Four spaces before the tab triggers good alignment
			// for both 4- and 8-space tab stops.
			s += "\n    \t"
			s += strings.ReplaceAll(usage, "\n", "\n    \t")

			if f.DefValue != "" {
				s += fmt.Sprintf(" (default %s)", f.DefValue)
			}

			fmt.Fprintln(&b, s)
		})
		tw.Flush()
		fmt.Fprintf(&b, "\n")
	}

	return strings.TrimSpace(b.String())
}

func isBoolFlag(f *flag.Flag) bool {
	bf, ok := f.Value.(interface {
		IsBoolFlag() bool
	})
	return ok && bf.IsBoolFlag()
}

func countFlags(fs *flag.FlagSet) (n int) {
	fs.VisitAll(func(*flag.Flag) { n++ })
	return n
}