package store

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"
)

// Roles, from the most to the least privileged.
const (
	RoleAdmin    = "admin"    // everything, including clusters, settings and users
	RoleOperator = "operator" // dry-run and synchronization
	RoleViewer   = "viewer"   // read only
)

// ValidRole tells whether r is a known role.
func ValidRole(r string) bool { return r == RoleAdmin || r == RoleOperator || r == RoleViewer }

// RoleRank orders the roles: admin 3, operator 2, viewer 1, unknown 0.
func RoleRank(r string) int {
	switch r {
	case RoleAdmin:
		return 3
	case RoleOperator:
		return 2
	case RoleViewer:
		return 1
	}
	return 0
}

// User is a local account (password hash never returned).
type User struct {
	Name      string    `json:"name"`
	Role      string    `json:"role"`
	Epoch     int64     `json:"-"` // changes with the password: ends the sessions
	CreatedAt time.Time `json:"createdAt"`
	LastLogin time.Time `json:"lastLogin"`
	hash      string
}

// Users lists the local accounts.
func (s *Store) Users(ctx context.Context) ([]User, error) {
	rows, err := s.db.QueryContext(ctx, `SELECT name, role, epoch, created_at, last_login FROM users ORDER BY name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []User
	for rows.Next() {
		var u User
		var c, l int64
		if err := rows.Scan(&u.Name, &u.Role, &u.Epoch, &c, &l); err != nil {
			return nil, err
		}
		u.CreatedAt = time.Unix(c, 0).UTC()
		if l > 0 {
			u.LastLogin = time.Unix(l, 0).UTC()
		}
		out = append(out, u)
	}
	return out, rows.Err()
}

// User returns one account.
func (s *Store) User(ctx context.Context, name string) (User, error) {
	var u User
	var c, l int64
	err := s.db.QueryRowContext(ctx, `SELECT name, role, password, epoch, created_at, last_login FROM users WHERE name = ?`, name).
		Scan(&u.Name, &u.Role, &u.hash, &u.Epoch, &c, &l)
	if errors.Is(err, sql.ErrNoRows) {
		return u, ErrNotFound
	}
	u.CreatedAt = time.Unix(c, 0).UTC()
	if l > 0 {
		u.LastLogin = time.Unix(l, 0).UTC()
	}
	return u, err
}

// CountUsers returns the number of local accounts.
func (s *Store) CountUsers(ctx context.Context) (int, error) {
	var n int
	err := s.db.QueryRowContext(ctx, `SELECT count(*) FROM users`).Scan(&n)
	return n, err
}

// Authenticate checks a password and records the login.
func (s *Store) Authenticate(ctx context.Context, name, pass string) (User, bool) {
	u, err := s.User(ctx, name)
	if err != nil {
		// same cost as a real check: the answer time does not tell whether the user exists
		CheckPassword(dummyHash, pass)
		return User{}, false
	}
	if !CheckPassword(u.hash, pass) {
		return User{}, false
	}
	_, _ = s.db.ExecContext(ctx, `UPDATE users SET last_login = ? WHERE name = ?`, time.Now().Unix(), name)
	return u, true
}

var dummyHash, _ = HashPassword("dummy password")

// SaveUser creates an account or changes its role and/or password (empty: unchanged).
func (s *Store) SaveUser(ctx context.Context, name, role, pass string) error {
	name = strings.TrimSpace(name)
	if name == "" || strings.ContainsAny(name, " \t\r\n") {
		return errors.New("invalid user name")
	}
	if !ValidRole(role) {
		return fmt.Errorf("unknown role %q", role)
	}
	if pass != "" && len(pass) < 8 {
		return errors.New("password: 8 characters minimum")
	}
	var hash string
	if pass != "" {
		var err error
		if hash, err = HashPassword(pass); err != nil {
			return err
		}
	}
	now := time.Now()
	_, err := s.User(ctx, name)
	switch {
	case errors.Is(err, ErrNotFound):
		if pass == "" {
			return errors.New("a password is required for a new user")
		}
		_, err = s.db.ExecContext(ctx, `INSERT INTO users (name, role, password, epoch, created_at) VALUES (?,?,?,?,?)`,
			name, role, hash, now.UnixNano(), now.Unix())
		return err
	case err != nil:
		return err
	}
	if err := s.keepAnAdmin(ctx, name, role); err != nil {
		return err
	}
	if pass == "" {
		_, err = s.db.ExecContext(ctx, `UPDATE users SET role = ? WHERE name = ?`, role, name)
	} else {
		_, err = s.db.ExecContext(ctx, `UPDATE users SET role = ?, password = ?, epoch = ? WHERE name = ?`, role, hash, now.UnixNano(), name)
	}
	return err
}

// DeleteUser removes an account (never the last administrator).
func (s *Store) DeleteUser(ctx context.Context, name string) error {
	if err := s.keepAnAdmin(ctx, name, ""); err != nil {
		return err
	}
	res, err := s.db.ExecContext(ctx, `DELETE FROM users WHERE name = ?`, name)
	if err != nil {
		return err
	}
	if n, _ := res.RowsAffected(); n == 0 {
		return ErrNotFound
	}
	return nil
}

// keepAnAdmin refuses a change that would leave no local administrator
// (OIDC may be down: a local admin is the way back in).
func (s *Store) keepAnAdmin(ctx context.Context, name, newRole string) error {
	if newRole == RoleAdmin {
		return nil
	}
	var n int
	if err := s.db.QueryRowContext(ctx, `SELECT count(*) FROM users WHERE role = 'admin' AND name <> ?`, name).Scan(&n); err != nil {
		return err
	}
	var cur string
	_ = s.db.QueryRowContext(ctx, `SELECT role FROM users WHERE name = ?`, name).Scan(&cur)
	if cur == RoleAdmin && n == 0 {
		return errors.New("this is the last local administrator")
	}
	return nil
}

// ErrSetupDone: the first administrator already exists.
var ErrSetupDone = errors.New("the first administrator already exists")

// CreateFirstAdmin creates the first administrator from the web page shown on an
// empty database. The insert only happens while the table is empty: two
// concurrent requests cannot both succeed.
func (s *Store) CreateFirstAdmin(ctx context.Context, name, pass string) error {
	name = strings.TrimSpace(name)
	if name == "" || strings.ContainsAny(name, " \t\r\n") {
		return errors.New("invalid user name")
	}
	if len(pass) < 12 {
		return errors.New("password: 12 characters minimum")
	}
	hash, err := HashPassword(pass)
	if err != nil {
		return err
	}
	now := time.Now()
	res, err := s.db.ExecContext(ctx, `INSERT INTO users (name, role, password, epoch, created_at)
		SELECT ?, 'admin', ?, ?, ? WHERE NOT EXISTS (SELECT 1 FROM users)`, name, hash, now.UnixNano(), now.Unix())
	if err != nil {
		return err
	}
	if n, _ := res.RowsAffected(); n == 0 {
		return ErrSetupDone
	}
	return nil
}