// The mbf program is a frontend for [hakurei.app/internal/rosa].
//
// This program is not covered by the compatibility promise. The command line
// interface, available packages and their behaviour, and even the on-disk
// format, may change at any time.
//
// # Name
//
// The name mbf stands for maiden's best friend, as a tribute to the DOOM source
// port of [the same name]. This name is a placeholder and is subject to change.
//
// [the same name]: https://www.doomwiki.org/wiki/MBF
package main

import (
	"context"
	"crypto/sha512"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"os/signal"
	"path/filepath"
	"runtime"
	"strconv"
	"sync"
	"sync/atomic"
	"syscall"
	"time"
	"unique"

	"hakurei.app/check"
	"hakurei.app/command"
	"hakurei.app/container"
	"hakurei.app/container/seccomp"
	"hakurei.app/container/std"
	"hakurei.app/ext"
	"hakurei.app/fhs"
	"hakurei.app/internal/pkg"
	"hakurei.app/internal/rosa"
	"hakurei.app/message"
)

func main() {
	container.TryArgv0(nil)

	log.SetFlags(0)
	log.SetPrefix("mbf: ")
	msg := message.New(log.Default())

	if os.Geteuid() == 0 {
		log.Fatal("this program must not run as root")
	}

	ctx, stop := signal.NotifyContext(context.Background(),
		syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP)
	defer stop()

	var cm cache
	defer func() {
		cm.Close()

		if r := recover(); r != nil {
			fmt.Println(r)
			log.Fatal("consider scrubbing the on-disk cache")
		}
	}()

	var (
		flagQuiet bool

		addr net.UnixAddr
	)
	c := command.New(os.Stderr, log.Printf, "mbf", func([]string) error {
		msg.SwapVerbose(!flagQuiet)
		cm.ctx, cm.msg = ctx, msg
		cm.base = os.ExpandEnv(cm.base)

		addr.Net = "unix"
		addr.Name = os.ExpandEnv(addr.Name)
		if addr.Name == "" {
			addr.Name = "daemon"
		}

		return nil
	}).Flag(
		&flagQuiet,
		"q", command.BoolFlag(false),
		"Do not print cure messages",
	).Flag(
		&cm.cures,
		"cures", command.IntFlag(0),
		"Maximum number of dependencies to cure at any given time",
	).Flag(
		&cm.jobs,
		"jobs", command.IntFlag(0),
		"Preferred number of jobs to run, when applicable",
	).Flag(
		&cm.base,
		"d", command.StringFlag("$MBF_CACHE_DIR"),
		"Directory to store cured artifacts",
	).Flag(
		&cm.idle,
		"sched-idle", command.BoolFlag(false),
		"Set SCHED_IDLE scheduling policy",
	).Flag(
		&cm.hostAbstract,
		"host-abstract", command.BoolFlag(
			os.Getenv("MBF_HOST_ABSTRACT") != "",
		),
		"Do not restrict networked cure containers from connecting to host "+
			"abstract UNIX sockets",
	).Flag(
		&addr.Name,
		"socket", command.StringFlag("$MBF_DAEMON_SOCKET"),
		"Pathname of socket to bind to",
	)

	c.NewCommand(
		"checksum", "Compute checksum of data read from standard input",
		func([]string) error {
			go func() { <-ctx.Done(); os.Exit(1) }()
			h := sha512.New384()
			if _, err := io.Copy(h, os.Stdin); err != nil {
				return err
			}
			log.Println(pkg.Encode(pkg.Checksum(h.Sum(nil))))
			return nil
		},
	)

	{
		var flagShifts int
		c.NewCommand(
			"scrub", "Examine the on-disk cache for errors",
			func(args []string) error {
				if len(args) > 0 {
					return errors.New("scrub expects no arguments")
				}
				if flagShifts < 0 || flagShifts > 31 {
					flagShifts = 12
				}
				return cm.Do(func(cache *pkg.Cache) error {
					return cache.Scrub(runtime.NumCPU() << flagShifts)
				})
			},
		).Flag(
			&flagShifts,
			"shift", command.IntFlag(12),
			"Scrub parallelism size exponent, to the power of 2",
		)
	}

	{
		var (
			flagStatus bool
			flagReport string
		)
		c.NewCommand(
			"info",
			"Display out-of-band metadata of an artifact",
			func(args []string) (err error) {
				return commandInfo(&cm, args, os.Stdout, flagStatus, flagReport)
			},
		).Flag(
			&flagStatus,
			"status", command.BoolFlag(false),
			"Display cure status if available",
		).Flag(
			&flagReport,
			"report", command.StringFlag(""),
			"Load cure status from this report file instead of cache",
		)
	}

	c.NewCommand(
		"report",
		"Generate an artifact cure report for the current cache",
		func(args []string) (err error) {
			var w *os.File
			switch len(args) {
			case 0:
				w = os.Stdout

			case 1:
				if w, err = os.OpenFile(
					args[0],
					os.O_CREATE|os.O_EXCL|syscall.O_WRONLY,
					0400,
				); err != nil {
					return
				}
				defer func() {
					closeErr := w.Close()
					if err == nil {
						err = closeErr
					}
				}()

			default:
				return errors.New("report requires 1 argument")
			}

			if ext.Isatty(int(w.Fd())) {
				return errors.New("output appears to be a terminal")
			}
			return cm.Do(func(cache *pkg.Cache) error {
				return rosa.WriteReport(msg, w, cache)
			})
		},
	)

	{
		var flagJobs int
		c.NewCommand("updates", command.UsageInternal, func([]string) error {
			var (
				errsMu sync.Mutex
				errs   []error

				n atomic.Uint64
			)

			w := make(chan rosa.PArtifact)
			var wg sync.WaitGroup
			for range max(flagJobs, 1) {
				wg.Go(func() {
					for p := range w {
						meta := rosa.GetMetadata(p)
						if meta.ID == 0 {
							continue
						}

						v, err := meta.GetVersions(ctx)
						if err != nil {
							errsMu.Lock()
							errs = append(errs, err)
							errsMu.Unlock()
							continue
						}

						if current, latest :=
							rosa.Std.Version(p),
							meta.GetLatest(v); current != latest {

							n.Add(1)
							log.Printf("%s %s < %s", meta.Name, current, latest)
							continue
						}

						msg.Verbosef("%s is up to date", meta.Name)
					}
				})
			}

		done:
			for i := range rosa.PresetEnd {
				select {
				case w <- rosa.PArtifact(i):
					break
				case <-ctx.Done():
					break done
				}
			}
			close(w)
			wg.Wait()

			if v := n.Load(); v > 0 {
				errs = append(errs, errors.New(strconv.Itoa(int(v))+
					" package(s) are out of date"))
			}
			return errors.Join(errs...)
		}).Flag(
			&flagJobs,
			"j", command.IntFlag(32),
			"Maximum number of simultaneous connections",
		)
	}

	c.NewCommand(
		"daemon",
		"Service artifact IR with Rosa OS extensions",
		func(args []string) error {
			ul, err := net.ListenUnix("unix", &addr)
			if err != nil {
				return err
			}
			log.Printf("listening on pathname socket at %s", addr.Name)
			return serve(ctx, log.Default(), &cm, ul)
		},
	)

	{
		var (
			flagGentoo   string
			flagChecksum string

			flagStage0 bool
		)
		c.NewCommand(
			"stage3",
			"Check for toolchain 3-stage non-determinism",
			func(args []string) (err error) {
				t := rosa.Std
				if flagGentoo != "" {
					t -= 3 // magic number to discourage misuse

					var checksum pkg.Checksum
					if len(flagChecksum) != 0 {
						if err = pkg.Decode(&checksum, flagChecksum); err != nil {
							return
						}
					}
					rosa.SetGentooStage3(flagGentoo, checksum)
				}

				var (
					pathname *check.Absolute
					checksum [2]unique.Handle[pkg.Checksum]
				)

				if err = cm.Do(func(cache *pkg.Cache) (err error) {
					pathname, _, err = cache.Cure(
						(t - 2).Load(rosa.Clang),
					)
					return
				}); err != nil {
					return
				}
				log.Println("stage1:", pathname)

				if err = cm.Do(func(cache *pkg.Cache) (err error) {
					pathname, checksum[0], err = cache.Cure(
						(t - 1).Load(rosa.Clang),
					)
					return
				}); err != nil {
					return
				}
				log.Println("stage2:", pathname)
				if err = cm.Do(func(cache *pkg.Cache) (err error) {
					pathname, checksum[1], err = cache.Cure(
						t.Load(rosa.Clang),
					)
					return
				}); err != nil {
					return
				}
				log.Println("stage3:", pathname)

				if checksum[0] != checksum[1] {
					err = &pkg.ChecksumMismatchError{
						Got:  checksum[0].Value(),
						Want: checksum[1].Value(),
					}
				} else {
					log.Println(
						"stage2 is identical to stage3",
						"("+pkg.Encode(checksum[0].Value())+")",
					)
				}

				if flagStage0 {
					if err = cm.Do(func(cache *pkg.Cache) (err error) {
						pathname, _, err = cache.Cure(
							t.Load(rosa.Stage0),
						)
						return
					}); err != nil {
						return
					}
					log.Println(pathname)
				}

				return
			},
		).Flag(
			&flagGentoo,
			"gentoo", command.StringFlag(""),
			"Bootstrap from a Gentoo stage3 tarball",
		).Flag(
			&flagChecksum,
			"checksum", command.StringFlag(""),
			"Checksum of Gentoo stage3 tarball",
		).Flag(
			&flagStage0,
			"stage0", command.BoolFlag(false),
			"Create bootstrap stage0 tarball",
		)
	}

	{
		var (
			flagDump   string
			flagEnter  bool
			flagExport string
			flagRemote bool
		)
		c.NewCommand(
			"cure",
			"Cure the named artifact and show its path",
			func(args []string) error {
				if len(args) != 1 {
					return errors.New("cure requires 1 argument")
				}
				p, ok := rosa.ResolveName(args[0])
				if !ok {
					return fmt.Errorf("unknown artifact %q", args[0])
				}

				switch {
				default:
					var pathname *check.Absolute
					err := cm.Do(func(cache *pkg.Cache) (err error) {
						pathname, _, err = cache.Cure(rosa.Std.Load(p))
						return
					})
					if err != nil {
						return err
					}
					log.Println(pathname)

					if flagExport != "" {
						msg.Verbosef("exporting %s to %s...", args[0], flagExport)

						var f *os.File
						if f, err = os.OpenFile(
							flagExport,
							os.O_WRONLY|os.O_CREATE|os.O_EXCL,
							0400,
						); err != nil {
							return err
						} else if _, err = pkg.Flatten(
							os.DirFS(pathname.String()),
							".",
							f,
						); err != nil {
							_ = f.Close()
							return err
						} else if err = f.Close(); err != nil {
							return err
						}
					}

					return nil

				case flagDump != "":
					f, err := os.OpenFile(
						flagDump,
						os.O_WRONLY|os.O_CREATE|os.O_EXCL,
						0644,
					)
					if err != nil {
						return err
					}

					if err = pkg.NewIR().EncodeAll(f, rosa.Std.Load(p)); err != nil {
						_ = f.Close()
						return err
					}

					return f.Close()

				case flagEnter:
					return cm.Do(func(cache *pkg.Cache) error {
						return cache.EnterExec(
							ctx,
							rosa.Std.Load(p),
							true, os.Stdin, os.Stdout, os.Stderr,
							rosa.AbsSystem.Append("bin", "mksh"),
							"sh",
						)
					})

				case flagRemote:
					pathname, err := cureRemote(ctx, &addr, rosa.Std.Load(p))
					if err == nil {
						log.Println(pathname)
					}
					return err
				}
			},
		).Flag(
			&flagDump,
			"dump", command.StringFlag(""),
			"Write IR to specified pathname and terminate",
		).Flag(
			&flagExport,
			"export", command.StringFlag(""),
			"Export cured artifact to specified pathname",
		).Flag(
			&flagEnter,
			"enter", command.BoolFlag(false),
			"Enter cure container with an interactive shell",
		).Flag(
			&flagRemote,
			"daemon", command.BoolFlag(false),
			"Cure artifact on the daemon",
		)
	}

	{
		var (
			flagNet     bool
			flagSession bool

			flagWithToolchain bool
		)
		c.NewCommand(
			"shell",
			"Interactive shell in the specified Rosa OS environment",
			func(args []string) error {
				presets := make([]rosa.PArtifact, len(args)+3)
				for i, arg := range args {
					p, ok := rosa.ResolveName(arg)
					if !ok {
						return fmt.Errorf("unknown artifact %q", arg)
					}
					presets[i] = p
				}

				base := rosa.Clang
				if !flagWithToolchain {
					base = rosa.Musl
				}
				presets = append(presets,
					base,
					rosa.Mksh,
					rosa.Toybox,
				)

				root := make(pkg.Collect, 0, 6+len(args))
				root = rosa.Std.AppendPresets(root, presets...)

				if err := cm.Do(func(cache *pkg.Cache) error {
					_, _, err := cache.Cure(&root)
					return err
				}); err == nil {
					return errors.New("unreachable")
				} else if !pkg.IsCollected(err) {
					return err
				}

				type cureRes struct {
					pathname *check.Absolute
					checksum unique.Handle[pkg.Checksum]
				}
				cured := make(map[pkg.Artifact]cureRes)
				for _, a := range root {
					if err := cm.Do(func(cache *pkg.Cache) error {
						pathname, checksum, err := cache.Cure(a)
						if err == nil {
							cured[a] = cureRes{pathname, checksum}
						}
						return err
					}); err != nil {
						return err
					}
				}

				// explicitly open for direct error-free use from this point
				if cm.c == nil {
					if err := cm.open(); err != nil {
						return err
					}
				}

				layers := pkg.PromoteLayers(root, func(a pkg.Artifact) (
					*check.Absolute,
					unique.Handle[pkg.Checksum],
				) {
					res := cured[a]
					return res.pathname, res.checksum
				}, func(i int, d pkg.Artifact) {
					r := pkg.Encode(cm.c.Ident(d).Value())
					if s, ok := d.(fmt.Stringer); ok {
						if name := s.String(); name != "" {
							r += "-" + name
						}
					}
					msg.Verbosef("promoted layer %d as %s", i, r)
				})

				z := container.New(ctx, msg)
				z.WaitDelay = 3 * time.Second
				z.SeccompPresets = pkg.SeccompPresets
				z.SeccompFlags |= seccomp.AllowMultiarch
				z.ParentPerm = 0700
				z.HostNet = flagNet
				z.RetainSession = flagSession
				z.Hostname = "localhost"
				z.Uid, z.Gid = (1<<10)-1, (1<<10)-1
				z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr
				if s, ok := os.LookupEnv("TERM"); ok {
					z.Env = append(z.Env, "TERM="+s)
				}

				var tempdir *check.Absolute
				if s, err := filepath.Abs(os.TempDir()); err != nil {
					return err
				} else if tempdir, err = check.NewAbs(s); err != nil {
					return err
				}

				z.Dir = fhs.AbsRoot
				z.Env = []string{
					"SHELL=/system/bin/mksh",
					"PATH=/system/bin",
					"HOME=/",
				}
				z.Path = rosa.AbsSystem.Append("bin", "mksh")
				z.Args = []string{"mksh"}
				z.
					OverlayEphemeral(fhs.AbsRoot, layers...).
					Place(
						fhs.AbsEtc.Append("hosts"),
						[]byte("127.0.0.1 localhost\n"),
					).
					Place(
						fhs.AbsEtc.Append("passwd"),
						[]byte("media_rw:x:1023:1023::/:/system/bin/sh\n"+
							"nobody:x:65534:65534::/proc/nonexistent:/system/bin/false\n"),
					).
					Place(
						fhs.AbsEtc.Append("group"),
						[]byte("media_rw:x:1023:\nnobody:x:65534:\n"),
					).
					Bind(tempdir, fhs.AbsTmp, std.BindWritable).
					Proc(fhs.AbsProc).Dev(fhs.AbsDev, true)

				if err := z.Start(); err != nil {
					return err
				}
				if err := z.Serve(); err != nil {
					return err
				}
				return z.Wait()
			},
		).Flag(
			&flagNet,
			"net", command.BoolFlag(false),
			"Share host net namespace",
		).Flag(
			&flagSession,
			"session", command.BoolFlag(true),
			"Retain session",
		).Flag(
			&flagWithToolchain,
			"with-toolchain", command.BoolFlag(false),
			"Include the stage2 LLVM toolchain",
		)

	}

	c.Command(
		"help",
		"Show this help message",
		func([]string) error { c.PrintHelp(); return nil },
	)

	c.MustParse(os.Args[1:], func(err error) {
		cm.Close()
		if w, ok := err.(interface{ Unwrap() []error }); !ok {
			log.Fatal(err)
		} else {
			errs := w.Unwrap()
			for i, e := range errs {
				if i == len(errs)-1 {
					log.Fatal(e)
				}
				log.Println(e)
			}
		}
	})
}