// Package files is the Files tab: browse, read, write, upload, download, mkdir,
// rename, chmod and delete anywhere on the host.
//
// Two backends share one interface. Local runs in-process as the daemon's user. Sudo
// re-executes this same binary as root (`sudo -n hamlab fs …`) for one operation at a
// time, streaming file bodies over its stdin/stdout, so root access uses exactly the
// same code and the same validation as the unprivileged path.
package files

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"os/signal"
	"os/user"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"syscall"
	"time"

	"hamlab/internal/priv"
	"hamlab/internal/thumbs"
)

type Entry struct {
	Name    string `json:"name"`
	Type    string `json:"type"` // dir | file | link | other
	Size    int64  `json:"size"`
	Mode    string `json:"mode"` // "-rw-r--r--"
	Perm    string `json:"perm"` // "0644"
	Mtime   int64  `json:"mtime"`
	User    string `json:"user"`
	Group   string `json:"group"`
	Target  string `json:"target,omitempty"`  // link target
	Broken  bool   `json:"broken,omitempty"`  // dangling link
	Preview string `json:"preview,omitempty"` // "image" | "video": the Files tab can show a thumbnail of it
}

type Listing struct {
	Path    string  `json:"path"`
	Parent  string  `json:"parent,omitempty"`
	Entries []Entry `json:"entries"`
}

type Info struct {
	Entry
	Path string `json:"path"`
	Text bool   `json:"text"` // looks like text (for the editor)
}

// FS is what the API talks to.
type FS interface {
	List(ctx context.Context, path string) (Listing, error)
	Stat(ctx context.Context, path string) (Info, error)
	Open(ctx context.Context, path string) (io.ReadCloser, error)
	OpenAt(ctx context.Context, path string, offset int64) (io.ReadCloser, error) // Open from a byte offset: a range request, a player seeking
	Write(ctx context.Context, path string, r io.Reader) error
	Mkdir(ctx context.Context, path string) error
	Touch(ctx context.Context, path string) error
	Rename(ctx context.Context, from, to string) error
	Move(ctx context.Context, from, to string, progress io.Writer) error // Rename, or across filesystems a copy and a removal; long, so callers run it as a task
	Delete(ctx context.Context, path string, recursive bool) error
	Chmod(ctx context.Context, path string, perm os.FileMode) error
}

// ---- path rules ----

// Clean rejects relative paths and normalises the rest. Everything else on the host is
// reachable on purpose: this is a root-capable console, the gate is the login.
func Clean(p string) (string, error) {
	if p == "" {
		return "", errors.New("path required")
	}
	if !strings.HasPrefix(p, "/") {
		return "", errors.New("path must be absolute")
	}
	c := filepath.Clean(p)
	if strings.ContainsRune(c, 0) {
		return "", errors.New("bad path")
	}
	return c, nil
}

// protected are never deleted or renamed as a whole, no matter who asks.
var protected = map[string]bool{"/": true, "/bin": true, "/boot": true, "/dev": true, "/etc": true, "/home": true, "/lib": true, "/lib64": true,
	"/opt": true, "/proc": true, "/root": true, "/run": true, "/sbin": true, "/srv": true, "/sys": true, "/tmp": true, "/usr": true, "/var": true}

func ParsePerm(s string) (os.FileMode, error) {
	v, err := strconv.ParseUint(strings.TrimPrefix(s, "0"), 8, 32)
	if err != nil || v > 0o7777 {
		return 0, errors.New("mode must be octal like 0644")
	}
	return os.FileMode(v), nil
}

// ---- Local ----

type Local struct{}

var uidCache, gidCache = map[uint32]string{}, map[uint32]string{}

func owner(st os.FileInfo) (string, string) {
	sys, ok := st.Sys().(*syscall.Stat_t)
	if !ok {
		return "", ""
	}
	u, ok := uidCache[sys.Uid]
	if !ok {
		u = strconv.Itoa(int(sys.Uid))
		if x, err := user.LookupId(u); err == nil {
			u = x.Username
		}
		uidCache[sys.Uid] = u
	}
	g, ok := gidCache[sys.Gid]
	if !ok {
		g = strconv.Itoa(int(sys.Gid))
		if x, err := user.LookupGroupId(g); err == nil {
			g = x.Name
		}
		gidCache[sys.Gid] = g
	}
	return u, g
}

func entryOf(dir, name string, lst os.FileInfo) Entry {
	e := Entry{Name: name, Size: lst.Size(), Mode: lst.Mode().String(), Perm: fmt.Sprintf("%04o", lst.Mode().Perm()), Mtime: lst.ModTime().UnixMilli()}
	e.User, e.Group = owner(lst)
	switch {
	case lst.Mode()&os.ModeSymlink != 0:
		e.Type = "link"
		full := filepath.Join(dir, name)
		e.Target, _ = os.Readlink(full)
		if st, err := os.Stat(full); err != nil {
			e.Broken = true
		} else if st.IsDir() {
			e.Type = "dir" // keep dir semantics for navigation; Target says it's a link
		} else {
			e.Size = st.Size()
		}
	case lst.IsDir():
		e.Type = "dir"
	case lst.Mode().IsRegular():
		e.Type = "file"
	default:
		e.Type = "other"
	}
	if e.Type == "file" || (e.Type == "link" && !e.Broken) {
		e.Preview = thumbs.Kind(name)
	}
	return e
}

func (Local) List(_ context.Context, path string) (Listing, error) {
	ents, err := os.ReadDir(path)
	if err != nil {
		return Listing{}, err
	}
	l := Listing{Path: path, Entries: make([]Entry, 0, len(ents))}
	if path != "/" {
		l.Parent = filepath.Dir(path)
	}
	for _, d := range ents {
		lst, err := d.Info() // Lstat
		if err != nil {
			continue
		}
		l.Entries = append(l.Entries, entryOf(path, d.Name(), lst))
	}
	sort.Slice(l.Entries, func(i, j int) bool {
		a, b := l.Entries[i], l.Entries[j]
		if (a.Type == "dir") != (b.Type == "dir") {
			return a.Type == "dir"
		}
		return strings.ToLower(a.Name) < strings.ToLower(b.Name)
	})
	return l, nil
}

func (Local) Stat(_ context.Context, path string) (Info, error) {
	lst, err := os.Lstat(path)
	if err != nil {
		return Info{}, err
	}
	in := Info{Entry: entryOf(filepath.Dir(path), filepath.Base(path), lst), Path: path}
	if in.Type == "file" && in.Size <= 8<<20 {
		if f, err := os.Open(path); err == nil {
			buf := make([]byte, 4096)
			n, _ := f.Read(buf)
			f.Close()
			in.Text = looksText(buf[:n])
		}
	}
	return in, nil
}

func looksText(b []byte) bool {
	if len(b) == 0 {
		return true
	}
	ctrl := 0
	for _, c := range b {
		if c == 0 {
			return false
		}
		if c < 32 && c != '\n' && c != '\r' && c != '\t' && c != '\f' && c != 0x1b {
			ctrl++
		}
	}
	return ctrl*20 < len(b)
}

// Open refuses anything that isn't a regular file: devices stream forever (/dev/zero),
// FIFOs block on open, sockets can't be read. /proc files are regular and still work.
func (Local) Open(_ context.Context, path string) (io.ReadCloser, error) {
	st, err := os.Stat(path)
	if err != nil {
		return nil, err
	}
	if st.IsDir() {
		return nil, errors.New("is a directory")
	}
	if !st.Mode().IsRegular() {
		return nil, errors.New("not a regular file (device, pipe or socket)")
	}
	return os.Open(path)
}

func (l Local) OpenAt(ctx context.Context, path string, offset int64) (io.ReadCloser, error) {
	f, err := l.Open(ctx, path)
	if err != nil {
		return nil, err
	}
	if offset > 0 {
		if _, err := f.(*os.File).Seek(offset, io.SeekStart); err != nil {
			f.Close()
			return nil, err
		}
	}
	return f, nil
}

// Write replaces the file's contents, keeping its mode; new files get 0644 (umask).
func (Local) Write(_ context.Context, path string, r io.Reader) error {
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
	if err != nil {
		return err
	}
	if _, err := io.Copy(f, r); err != nil {
		f.Close()
		return err
	}
	return f.Close()
}

func (Local) Mkdir(_ context.Context, path string) error { return os.Mkdir(path, 0o755) }

func (Local) Touch(_ context.Context, path string) error {
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
	if err != nil {
		return err
	}
	return f.Close()
}

func (Local) Rename(_ context.Context, from, to string) error {
	if protected[from] {
		return errors.New("refusing to move " + from)
	}
	if _, err := os.Lstat(to); err == nil {
		return errors.New("destination exists")
	}
	return os.Rename(from, to)
}

func (Local) Delete(_ context.Context, path string, recursive bool) error {
	if protected[path] {
		return errors.New("refusing to delete " + path)
	}
	lst, err := os.Lstat(path)
	if err != nil {
		return err
	}
	if lst.IsDir() && recursive {
		return os.RemoveAll(path)
	}
	return os.Remove(path) // fails on a non-empty dir, by design
}

func (Local) Chmod(_ context.Context, path string, perm os.FileMode) error {
	return os.Chmod(path, perm)
}

// ---- Sudo: the same operations, run as root in a child hamlab ----

type Sudo struct{ Self string }

func (s Sudo) cmd(ctx context.Context, args ...string) *exec.Cmd {
	full := priv.Wrap(append([]string{s.Self, "fs"}, args...)...)
	return exec.CommandContext(ctx, full[0], full[1:]...)
}

func (s Sudo) runJSON(ctx context.Context, out any, args ...string) error {
	c := s.cmd(ctx, args...)
	var errb strings.Builder
	c.Stderr = &errb
	b, err := c.Output()
	if err != nil {
		if msg := strings.TrimSpace(errb.String()); msg != "" {
			return errors.New(msg)
		}
		return err
	}
	if out == nil {
		return nil
	}
	return json.Unmarshal(b, out)
}

func (s Sudo) List(ctx context.Context, path string) (Listing, error) {
	var l Listing
	err := s.runJSON(ctx, &l, "list", path)
	return l, err
}

func (s Sudo) Stat(ctx context.Context, path string) (Info, error) {
	var in Info
	err := s.runJSON(ctx, &in, "stat", path)
	return in, err
}

type cmdReader struct {
	io.ReadCloser
	cmd  *exec.Cmd
	errb *strings.Builder
}

func (r *cmdReader) Close() error {
	r.ReadCloser.Close()
	err := r.cmd.Wait()
	if err != nil && r.errb.Len() > 0 {
		return errors.New(strings.TrimSpace(r.errb.String()))
	}
	return err
}

func (s Sudo) Open(ctx context.Context, path string) (io.ReadCloser, error) {
	return s.open(ctx, "read", path)
}

func (s Sudo) OpenAt(ctx context.Context, path string, offset int64) (io.ReadCloser, error) {
	return s.open(ctx, "read", "--offset", strconv.FormatInt(offset, 10), path)
}

func (s Sudo) open(ctx context.Context, args ...string) (io.ReadCloser, error) {
	c := s.cmd(ctx, args...)
	errb := &strings.Builder{}
	c.Stderr = errb
	out, err := c.StdoutPipe()
	if err != nil {
		return nil, err
	}
	if err := c.Start(); err != nil {
		return nil, err
	}
	// Fail early on "no such file" etc.: the helper stats before writing anything.
	head := make([]byte, 1)
	n, rerr := out.Read(head)
	if n == 0 && rerr != nil {
		_ = c.Wait()
		if msg := strings.TrimSpace(errb.String()); msg != "" {
			return nil, errors.New(msg)
		}
		if rerr != io.EOF {
			return nil, rerr
		}
	}
	return &cmdReader{ReadCloser: struct {
		io.Reader
		io.Closer
	}{io.MultiReader(strings.NewReader(string(head[:n])), out), out}, cmd: c, errb: errb}, nil
}

func (s Sudo) Write(ctx context.Context, path string, r io.Reader) error {
	c := s.cmd(ctx, "write", path)
	c.Stdin = r
	var errb strings.Builder
	c.Stderr = &errb
	if err := c.Run(); err != nil {
		if msg := strings.TrimSpace(errb.String()); msg != "" {
			return errors.New(msg)
		}
		return err
	}
	return nil
}

func (s Sudo) Mkdir(ctx context.Context, path string) error {
	return s.runJSON(ctx, nil, "mkdir", path)
}
func (s Sudo) Touch(ctx context.Context, path string) error {
	return s.runJSON(ctx, nil, "touch", path)
}
func (s Sudo) Rename(ctx context.Context, from, to string) error {
	return s.runJSON(ctx, nil, "rename", from, to)
}

// Move as root: the helper does the copying and talks on stdout.
func (s Sudo) Move(ctx context.Context, from, to string, progress io.Writer) error {
	c := s.cmd(ctx, "move", from, to)
	c.Stdout = progress
	var errb strings.Builder
	c.Stderr = &errb
	if err := c.Run(); err != nil {
		if msg := strings.TrimSpace(errb.String()); msg != "" {
			return errors.New(msg)
		}
		return err
	}
	return nil
}

// MoveCmd is the command a task runs for a long move: this binary's helper, as root when
// the backend is.
func MoveCmd(ctx context.Context, fsys FS, self, from, to string) *exec.Cmd {
	if s, ok := fsys.(Sudo); ok {
		return s.cmd(ctx, "move", from, to)
	}
	return exec.CommandContext(ctx, self, "fs", "move", from, to)
}
func (s Sudo) Delete(ctx context.Context, path string, recursive bool) error {
	if recursive {
		return s.runJSON(ctx, nil, "delete", "-r", path)
	}
	return s.runJSON(ctx, nil, "delete", path)
}
func (s Sudo) Chmod(ctx context.Context, path string, perm os.FileMode) error {
	return s.runJSON(ctx, nil, "chmod", fmt.Sprintf("%04o", perm), path)
}

// Helper implements `hamlab fs <op> …` for the Sudo backend. Returns the exit code.
func Helper(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) int {
	fail := func(err error) int { fmt.Fprintln(stderr, err.Error()); return 1 }
	if len(args) < 2 {
		return fail(errors.New("usage: hamlab fs <list|stat|read|write|mkdir|touch|rename|move|delete|chmod> …"))
	}
	ctx := context.Background()
	var l Local
	op := args[0]
	var offset int64
	if op == "read" && len(args) >= 4 && args[1] == "--offset" { // read --offset N <path>
		offset, _ = strconv.ParseInt(args[2], 10, 64)
		args = append([]string{"read"}, args[3:]...)
	}
	clean := func(i int) (string, error) {
		if i >= len(args) {
			return "", errors.New("path required")
		}
		return Clean(args[i])
	}
	switch op {
	case "list", "stat", "read", "write", "mkdir", "touch":
		p, err := clean(1)
		if err != nil {
			return fail(err)
		}
		switch op {
		case "list":
			out, err := l.List(ctx, p)
			if err != nil {
				return fail(err)
			}
			return emit(stdout, out, stderr)
		case "stat":
			out, err := l.Stat(ctx, p)
			if err != nil {
				return fail(err)
			}
			return emit(stdout, out, stderr)
		case "read":
			f, err := l.OpenAt(ctx, p, offset)
			if err != nil {
				return fail(err)
			}
			defer f.Close()
			if _, err := io.Copy(stdout, f); err != nil {
				return fail(err)
			}
			return 0
		case "write":
			if err := l.Write(ctx, p, stdin); err != nil {
				return fail(err)
			}
		case "mkdir":
			if err := l.Mkdir(ctx, p); err != nil {
				return fail(err)
			}
		case "touch":
			if err := l.Touch(ctx, p); err != nil {
				return fail(err)
			}
		}
	case "rename", "move":
		from, err := clean(1)
		if err != nil {
			return fail(err)
		}
		to, err := clean(2)
		if err != nil {
			return fail(err)
		}
		if op == "move" {
			// A cancelled task is a SIGTERM: stop copying and take the partial copy away.
			mctx, stop := signal.NotifyContext(ctx, syscall.SIGTERM, syscall.SIGINT)
			defer stop()
			if err := l.Move(mctx, from, to, stdout); err != nil {
				return fail(err)
			}
			return 0
		}
		if err := l.Rename(ctx, from, to); err != nil {
			return fail(err)
		}
	case "delete":
		rec := false
		i := 1
		if args[1] == "-r" {
			rec, i = true, 2
		}
		p, err := clean(i)
		if err != nil {
			return fail(err)
		}
		if err := l.Delete(ctx, p, rec); err != nil {
			return fail(err)
		}
	case "chmod":
		perm, err := ParsePerm(args[1])
		if err != nil {
			return fail(err)
		}
		p, err := clean(2)
		if err != nil {
			return fail(err)
		}
		if err := l.Chmod(ctx, p, perm); err != nil {
			return fail(err)
		}
	default:
		return fail(errors.New("unknown op " + op))
	}
	fmt.Fprintln(stdout, "{}")
	return 0
}

func emit(w io.Writer, v any, stderr io.Writer) int {
	if err := json.NewEncoder(w).Encode(v); err != nil {
		fmt.Fprintln(stderr, err.Error())
		return 1
	}
	return 0
}

// ModTime helper for handlers.
func Now() time.Time { return time.Now() }