package apply

// A directory or archive that says unknown "move-out" keeps only what it knows (issue 1024, novox/hq ADR 0422).
//
// Everything inside it that nothing declared, no archive unpacked and `knows` does not name is moved, whole, into
// `<home>/.local/state/mesh-moved/<module>/<UTC time>/`, with a list beside it that names each move before it is
// made (ADR 0417 §7). Nothing is deleted: the owner of the path reacts to a file it did not write by keeping it
// where its writer can find it. The pass runs after the resources of an apply, so a reconcile (every five minutes)
// runs it too.

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"github.com/novox/mesh-host/internal/declaration"
	"github.com/novox/mesh-host/internal/store"
)

// movedOutWait is how old a path is before it is moved: a younger one may be mid-write by whatever made it, and
// waits for the next look (ADR 0417 §4).
const movedOutWait = time.Minute

// MovedOut is one path a move-out directory moved.
type MovedOut struct {
	Resource string `json:"resource"`
	From     string `json:"from"`
	To       string `json:"to"`
}

// LeftInPlace is a socket, pipe or device a move-out directory did not move (ADR 0422 §4).
type LeftInPlace struct {
	Resource string `json:"resource"`
	Path     string `json:"path"`
}

// renamePath and deviceOf are the machine's calls, variables so a test can fail a move or name another file system.
// renamePath renames from to to without following a link in either parent below home (move_out_linux.go).
var renamePath = renameUnder

type movedEntry struct {
	From string `json:"from"`
	To   string `json:"to"`
}

// moveOutOwner is the user and group the kept folders and the list are given: the declared owner, or the home's
// account.
func moveOutOwner(home, owner string) (uid, gid int, err error) {
	if owner != "" {
		return idsOf(owner)
	}
	acc, ok := accountsOfHomes()[home]
	if !ok {
		return 0, 0, fmt.Errorf("%s is not the home of an account", home)
	}
	if u, g, err := idsOf(acc.Name); err == nil {
		return u, g, nil
	}
	return acc.UID, acc.UID, nil
}

// knownUnder is what a directory knows of its own contents: the declared targets, the files an archive unpacked,
// `knows` entries, and every folder above one of them.
type knownUnder struct {
	exact    map[string]bool
	prefixes []string
	// own are nested directories and archives that say what they do with unknown paths themselves.
	own map[string]bool
}

func (k *knownUnder) add(root, path string) {
	path = filepath.Clean(path)
	for path != root && strings.HasPrefix(path, root+string(os.PathSeparator)) {
		k.exact[path] = true
		path = filepath.Dir(path)
	}
}

func (k *knownUnder) knows(path string) bool {
	if k.exact[path] {
		return true
	}
	for _, p := range k.prefixes {
		if path == p || strings.HasPrefix(path, p+string(os.PathSeparator)) {
			return true
		}
	}
	return false
}

func knownOf(d *declaration.Declaration, known store.State, id, root string, knows []string) *knownUnder {
	k := &knownUnder{exact: map[string]bool{}, own: map[string]bool{}}
	for _, r := range d.Resources {
		target := filepath.Clean(r.Target())
		if target == "" || target == "." {
			continue
		}
		if r.Identity() != id && strings.HasPrefix(target, root+string(os.PathSeparator)) {
			k.add(root, target)
			switch o := r.(type) {
			case *declaration.Directory:
				if o.Unknown != "" {
					k.own[target] = true
				}
			case *declaration.Archive:
				if o.Unknown != "" {
					k.own[target] = true
				}
			}
		}
		if a, ok := r.(*declaration.Archive); ok {
			if rec, found := known.Find(a.ID); found && rec.Unpacked != nil {
				base := filepath.Clean(a.Path)
				for _, f := range append(append([]string{}, rec.Unpacked.Files...), rec.Unpacked.Dirs...) {
					p := filepath.Join(base, filepath.FromSlash(f))
					if p == root || strings.HasPrefix(p, root+string(os.PathSeparator)) {
						k.add(root, p)
					}
				}
			}
		}
	}
	for _, e := range knows {
		p := filepath.Join(root, filepath.FromSlash(strings.TrimSuffix(e, "/")))
		if strings.HasSuffix(e, "/") {
			k.prefixes = append(k.prefixes, p)
		} else {
			k.exact[p] = true
		}
		k.add(root, p)
	}
	return k
}

// moveOut moves what the directory at dir does not know, for the resource id. It answers the paths moved.
func moveOut(d *declaration.Declaration, known store.State, id, module, dir, owner string, knows []string,
	log func(string)) ([]MovedOut, []LeftInPlace, error) {
	dir = filepath.Clean(dir)
	home := homeAbove(dir)
	if home == "" {
		return nil, nil, fmt.Errorf("%s: move-out is only for a directory under an account's home, and %s is under none "+
			"(ADR 0422 §5); nothing was moved", id, dir)
	}
	k := knownOf(d, known, id, dir, knows)
	skip := filepath.Join(keptRoot(home), module)
	var candidates []string
	var left []string
	err := filepath.WalkDir(dir, func(path string, e fs.DirEntry, err error) error {
		if err != nil {
			if errors.Is(err, fs.ErrNotExist) {
				return nil
			}
			return err
		}
		if path == dir {
			return nil
		}
		if path == skip || path == keptRoot(home) {
			return fs.SkipDir
		}
		if k.own[path] {
			if e.IsDir() {
				return fs.SkipDir
			}
			return nil
		}
		if k.knows(path) {
			if e.IsDir() && !k.exact[path] {
				return fs.SkipDir
			}
			return nil
		}
		// Unknown. Moved whole, so never descended into.
		info, err := e.Info()
		if err != nil {
			if errors.Is(err, fs.ErrNotExist) {
				return nil
			}
			return err
		}
		switch {
		case info.Mode()&(os.ModeSocket|os.ModeNamedPipe|os.ModeDevice|os.ModeCharDevice) != 0:
			left = append(left, path)
		case time.Since(info.ModTime()) < movedOutWait:
		default:
			candidates = append(candidates, path)
		}
		if e.IsDir() {
			return fs.SkipDir
		}
		return nil
	})
	if err != nil {
		return nil, nil, fmt.Errorf("%s: cannot look through %s: %w", id, dir, err)
	}
	for _, p := range left {
		log(fmt.Sprintf("  left %s in %s: a socket, pipe or device is not moved (ADR 0422)", p, dir))
	}
	var stayed []LeftInPlace
	for _, p := range left {
		stayed = append(stayed, LeftInPlace{Resource: id, Path: p})
	}
	if len(candidates) == 0 {
		return nil, stayed, nil
	}
	sort.Strings(candidates)

	uid, gid, err := moveOutOwner(home, owner)
	if err != nil {
		return nil, nil, fmt.Errorf("%s: %w", id, err)
	}

	// The same file system first, so a move is a rename and nothing is copied (ADR 0417 §5).
	ancestor := skip
	for {
		if _, err := os.Lstat(ancestor); err == nil {
			break
		}
		ancestor = filepath.Dir(ancestor)
	}
	devDir, err1 := deviceOf(dir)
	devKept, err2 := deviceOf(ancestor)
	if err1 != nil || err2 != nil {
		return nil, nil, fmt.Errorf("%s: cannot read the file system of %s or %s: %v %v", id, dir, ancestor, err1, err2)
	}
	if devDir != devKept {
		return nil, nil, fmt.Errorf("%s: %s and %s are on different file systems (devices %d and %d), so a move would "+
			"copy; nothing was moved (ADR 0417 §5)", id, dir, ancestor, devDir, devKept)
	}

	// The kept folder and the list, named by the second; a clash in the same second gets -2, -3.
	stamp := time.Now().UTC().Format("20060102T150405Z")
	kept, listPath := "", ""
	for n := 1; ; n++ {
		name := stamp
		if n > 1 {
			name = fmt.Sprintf("%s-%d", stamp, n)
		}
		kept, listPath = filepath.Join(skip, name), filepath.Join(skip, name+".json")
		if !pathExists(kept) && !pathExists(listPath) {
			break
		}
	}
	var made []string
	cleanup := func() {
		_ = os.Remove(listPath)
		// In the reverse of the order they were made, so a folder goes after what is in it.
		for i := len(made) - 1; i >= 0; i-- {
			_ = os.Remove(made[i])
		}
	}
	chown := func(paths []string) error {
		for _, p := range paths {
			if err := chownIfNeeded(home, p, uid, gid); err != nil {
				return err
			}
		}
		return nil
	}
	madeNow, err := mkdirAllUnder(home, kept, 0o700)
	made = append(made, reversed(madeNow)...)
	if err == nil {
		err = chown(madeNow)
	}
	if err != nil {
		cleanup()
		return nil, nil, fmt.Errorf("%s: cannot make the kept folder %s: %w", id, kept, err)
	}

	var list []movedEntry
	var moved []MovedOut
	var failures []string
	for _, from := range candidates {
		rel, _ := filepath.Rel(dir, from)
		to := filepath.Join(kept, rel)
		// Named before it is moved: a move that stops half way leaves its entry (ADR 0417 §7).
		list = append(list, movedEntry{From: from, To: to})
		raw, _ := json.MarshalIndent(list, "", "  ")
		if err := writeUnder(home, listPath, append(raw, '\n'), 0o600); err != nil {
			failures = append(failures, fmt.Sprintf("cannot write the list %s: %v", listPath, err))
			break
		}
		if err := chownIfNeeded(home, listPath, uid, gid); err != nil {
			failures = append(failures, err.Error())
			break
		}
		parents, err := mkdirAllUnder(home, filepath.Dir(to), 0o700)
		made = append(made, reversed(parents)...)
		if err == nil {
			err = chown(parents)
		}
		if err == nil {
			err = renamePath(home, from, to)
		}
		if err != nil {
			failures = append(failures, fmt.Sprintf("cannot move %s to %s: %v", from, to, err))
			continue
		}
		log(fmt.Sprintf("  moved %s to %s (ADR 0422)", from, to))
		moved = append(moved, MovedOut{Resource: id, From: from, To: to})
	}
	if len(moved) == 0 {
		cleanup()
	}
	if len(failures) > 0 {
		return moved, stayed, fmt.Errorf("%s: %s", id, strings.Join(failures, "; "))
	}
	return moved, stayed, nil
}

// reversed is paths shallowest first: mkdirAllUnder answers deepest first.
func reversed(in []string) []string {
	out := make([]string, len(in))
	for i, p := range in {
		out[len(in)-1-i] = p
	}
	return out
}

func keptRoot(home string) string { return filepath.Join(home, ".local", "state", "mesh-moved") }

// chownIfNeeded gives a path to uid and gid through the home-safe call, unless it is theirs already.
func chownIfNeeded(home, path string, uid, gid int) error {
	if u, g, ok := ownerIDs(path); ok && u == uid && g == gid {
		return nil
	}
	return chownUnder(home, path, uid, gid)
}

// moveOutPass runs move-out for every directory and archive of d that says so and applied in this run.
func moveOutPass(d *declaration.Declaration, known store.State, applied map[string]bool, log func(string)) (
	moved []MovedOut, left []LeftInPlace, failures []*Error) {
	for _, r := range d.Resources {
		var unknown, owner string
		var knows []string
		switch o := r.(type) {
		case *declaration.Directory:
			unknown, owner, knows = o.Unknown, o.Owner, o.Knows
		case *declaration.Archive:
			unknown, owner, knows = o.Unknown, o.Owner, o.Knows
		default:
			continue
		}
		if unknown != declaration.UnknownMoveOut || !applied[r.Identity()] {
			continue
		}
		module, _ := d.ModuleOfID(r.Identity())
		if module == "" {
			module = r.Identity()
		}
		m, l, err := moveOut(d, known, r.Identity(), module, r.Target(), owner, knows, log)
		moved = append(moved, m...)
		left = append(left, l...)
		if err != nil {
			log(fmt.Sprintf("  failed %s (%s): %v", r.Identity(), r.Target(), err))
			failures = append(failures, &Error{Resource: r.Identity(), Err: err})
		}
	}
	return moved, left, failures
}

func pathExists(path string) bool {
	_, err := os.Lstat(path)
	return err == nil
}