package shares

import (
	"context"
	"errors"
	"fmt"
	"log"
	"os/exec"
	"os/user"
	"strings"
	"time"

	"nasmon/internal/hostrun"
)

const (
	DefaultSMBConf = "/etc/samba/smb.conf"
	DefaultExports = "/etc/exports.d/nasmon.exports"
	// DefaultOwnerUID is the account SMB sessions and squashed NFS clients act
	// as: the user that owns the data and runs the containers on this NAS.
	DefaultOwnerUID = "1000"
)

// Manager writes the generated config files on the host and reloads the daemons.
type Manager struct {
	Run      hostrun.Runner
	LookPath func(string) (string, error)
	Owner    string // Unix user name for force user
	UID, GID string
	SMBConf  string
	Exports  string
	Timeout  time.Duration
}

func New(run hostrun.Runner) *Manager {
	m := &Manager{Run: run, LookPath: exec.LookPath, UID: DefaultOwnerUID, GID: DefaultOwnerUID,
		SMBConf: DefaultSMBConf, Exports: DefaultExports, Timeout: 90 * time.Second}
	m.Owner = m.UID
	if u, err := user.LookupId(m.UID); err == nil {
		m.Owner, m.GID = u.Username, u.Gid
	}
	return m
}

func (m *Manager) ctx() (context.Context, context.CancelFunc) {
	return context.WithTimeout(context.Background(), m.Timeout)
}

func (m *Manager) installed(bin string) bool {
	_, err := m.LookPath(bin)
	return err == nil
}

func (m *Manager) SMBInstalled() bool { return m.installed("smbd") }
func (m *Manager) NFSInstalled() bool { return m.installed("exportfs") }

// Apply regenerates both config files and reloads/enables/disables the
// services. SMB and NFS are applied independently; errors are joined.
func (m *Manager) Apply(c Config) error {
	var errs []error
	if m.SMBInstalled() {
		if err := m.applySMB(c); err != nil {
			errs = append(errs, fmt.Errorf("SMB: %w", err))
		}
	}
	if m.NFSInstalled() {
		if err := m.applyNFS(c); err != nil {
			errs = append(errs, fmt.Errorf("NFS: %w", err))
		}
	}
	return errors.Join(errs...)
}

func (m *Manager) applySMB(c Config) error {
	ctx, cancel := m.ctx()
	defer cancel()
	if err := hostrun.WriteFile(ctx, m.Run, m.SMBConf, RenderSMB(c, m.Owner)); err != nil {
		return fmt.Errorf("write %s: %w", m.SMBConf, err)
	}
	if out, err := m.Run(ctx, "", "testparm", "-s", "--suppress-prompt", m.SMBConf); err != nil {
		_ = hostrun.Restore(ctx, m.Run, m.SMBConf)
		return fmt.Errorf("testparm rejected the config, previous file restored: %s", firstLines(out, 4))
	}
	active := c.SMB.Enabled && len(c.SMB.Shares) > 0
	if !active {
		_, err := m.Run(ctx, "", "systemctl", "disable", "--now", "smbd", "nmbd")
		if err != nil {
			return fmt.Errorf("stop smbd: %w", err)
		}
		log.Printf("shares: SMB disabled (%d shares, enabled=%v)", len(c.SMB.Shares), c.SMB.Enabled)
		return nil
	}
	if _, err := m.Run(ctx, "", "systemctl", "enable", "--now", "smbd", "nmbd"); err != nil {
		return fmt.Errorf("start smbd: %w", err)
	}
	if out, err := m.Run(ctx, "", "smbcontrol", "all", "reload-config"); err != nil {
		return fmt.Errorf("reload smbd: %s", firstLines(out, 2))
	}
	log.Printf("shares: SMB config applied, %d shares", len(c.SMB.Shares))
	return nil
}

func (m *Manager) applyNFS(c Config) error {
	ctx, cancel := m.ctx()
	defer cancel()
	if err := hostrun.WriteFile(ctx, m.Run, m.Exports, RenderExports(c, m.UID, m.GID)); err != nil {
		return fmt.Errorf("write %s: %w", m.Exports, err)
	}
	active := c.NFS.Enabled && len(c.NFS.Exports) > 0
	if !active {
		if _, err := m.Run(ctx, "", "systemctl", "disable", "--now", "nfs-server"); err != nil {
			return fmt.Errorf("stop nfs-server: %w", err)
		}
		log.Printf("shares: NFS disabled (%d exports, enabled=%v)", len(c.NFS.Exports), c.NFS.Enabled)
		return nil
	}
	if _, err := m.Run(ctx, "", "systemctl", "enable", "--now", "nfs-server"); err != nil {
		return fmt.Errorf("start nfs-server: %w", err)
	}
	if out, err := m.Run(ctx, "", "exportfs", "-ra"); err != nil {
		_ = hostrun.Restore(ctx, m.Run, m.Exports)
		_, _ = m.Run(ctx, "", "exportfs", "-ra")
		return fmt.Errorf("exportfs rejected the exports, previous file restored: %s", firstLines(out, 4))
	}
	log.Printf("shares: NFS exports applied, %d exports", len(c.NFS.Exports))
	return nil
}

func firstLines(s string, n int) string {
	lines := strings.Split(strings.TrimSpace(s), "\n")
	if len(lines) > n {
		lines = lines[:n]
	}
	return strings.Join(lines, " | ")
}

// ---- SMB users

// ListUsers returns the Samba accounts (pdbedit -L: "name:uid:full name").
func (m *Manager) ListUsers() ([]string, error) {
	if !m.SMBInstalled() {
		return nil, nil
	}
	ctx, cancel := m.ctx()
	defer cancel()
	out, err := m.Run(ctx, "", "pdbedit", "-L")
	if err != nil {
		return nil, err
	}
	var users []string
	for _, l := range strings.Split(out, "\n") {
		name, _, ok := strings.Cut(strings.TrimSpace(l), ":")
		if ok && name != "" {
			users = append(users, name)
		}
	}
	return users, nil
}

// SetPassword creates the Samba account (and a login-less Unix account if
// needed) or changes the password of an existing one.
func (m *Manager) SetPassword(name, pass string) error {
	if err := ValidateUserName(name); err != nil {
		return err
	}
	if len(pass) < 4 || strings.ContainsAny(pass, "\n\r") {
		return errors.New("password must be at least 4 characters")
	}
	ctx, cancel := m.ctx()
	defer cancel()
	if _, err := m.Run(ctx, "", "getent", "passwd", name); err != nil {
		// Unix account is required by Samba; no shell, no home, data owner's group
		if out, err := m.Run(ctx, "", "useradd", "-M", "-N", "-g", m.GID, "-s", "/usr/sbin/nologin", "-c", "nasmon SMB user", name); err != nil {
			return fmt.Errorf("create system user: %s", firstLines(out, 2))
		}
		log.Printf("shares: system user %s created for SMB", name)
	}
	if out, err := m.Run(ctx, pass+"\n"+pass+"\n", "smbpasswd", "-s", "-a", name); err != nil {
		return fmt.Errorf("smbpasswd: %s", firstLines(out, 2))
	}
	log.Printf("shares: SMB password set for %s", name)
	return nil
}

// DeleteUser removes the Samba account; the Unix account is removed too when
// it is one nasmon created (nologin shell).
func (m *Manager) DeleteUser(name string) error {
	if err := ValidateUserName(name); err != nil {
		return err
	}
	ctx, cancel := m.ctx()
	defer cancel()
	if out, err := m.Run(ctx, "", "smbpasswd", "-x", name); err != nil {
		return fmt.Errorf("smbpasswd -x: %s", firstLines(out, 2))
	}
	if ent, err := m.Run(ctx, "", "getent", "passwd", name); err == nil && strings.HasSuffix(strings.TrimSpace(ent), "/usr/sbin/nologin") && name != m.Owner {
		if out, err := m.Run(ctx, "", "userdel", name); err != nil {
			return fmt.Errorf("SMB account removed, but userdel failed: %s", firstLines(out, 2))
		}
	}
	log.Printf("shares: SMB user %s deleted", name)
	return nil
}