package store

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

// CreateUser inserts a row. Username is lowercase-normalised so the
// case-insensitive unique index from migration 0017 doesn't surprise
// callers who insert 'Alice' and look up 'alice'.
func (s *Store) CreateUser(ctx context.Context, u User) error {
	u.Username = strings.ToLower(strings.TrimSpace(u.Username))
	must := 0
	if u.MustChangePassword {
		must = 1
	}
	_, err := s.db.ExecContext(ctx,
		`INSERT INTO users (id, username, password_hash, role, email,
		                    must_change_password, created_at)
		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
		u.ID, u.Username, u.PasswordHash, string(u.Role),
		nullable(u.Email), must,
		u.CreatedAt.UTC().Format(time.RFC3339Nano))
	if err != nil {
		return fmt.Errorf("store: create user: %w", err)
	}
	return nil
}

// GetUserByUsername resolves a user case-insensitively.
func (s *Store) GetUserByUsername(ctx context.Context, username string) (*User, error) {
	row := s.db.QueryRowContext(ctx,
		`SELECT id, username, password_hash, role, email, disabled_at,
		        must_change_password, created_at, last_login_at
		 FROM users WHERE LOWER(username) = LOWER(?)`, username)
	return scanUser(row.Scan)
}

// GetUserByID looks up a user by id. Returns ErrNotFound on miss.
func (s *Store) GetUserByID(ctx context.Context, id string) (*User, error) {
	row := s.db.QueryRowContext(ctx,
		`SELECT id, username, password_hash, role, email, disabled_at,
		        must_change_password, created_at, last_login_at
		 FROM users WHERE id = ?`, id)
	return scanUser(row.Scan)
}

// UserSort selects the column ListUsers orders by. OrderBy is
// allowlisted in usersOrderColumn so callers can't inject SQL via
// this field. Empty / unknown OrderBy falls back to "username".
type UserSort struct {
	OrderBy  string // "username" | "email" | "role" | "last_login_at"
	OrderAsc bool   // false = DESC; true = ASC
}

// usersOrderColumn validates s.OrderBy and returns the SQL fragment.
// last_login_at gets a NULL-tail trick so users who've never logged
// in sort to the bottom regardless of asc/desc — matches operator
// intuition ("show me real activity" not "show me NULLs first").
func usersOrderColumn(col string, asc bool) string {
	dir := "DESC"
	if asc {
		dir = "ASC"
	}
	switch col {
	case "email":
		return fmt.Sprintf("email IS NULL, email %s, username", dir)
	case "role":
		return fmt.Sprintf("role %s, username", dir)
	case "last_login_at":
		return fmt.Sprintf("last_login_at IS NULL, last_login_at %s, username", dir)
	default: // username (and unknown)
		return fmt.Sprintf("username %s", dir)
	}
}

// ListUsers returns users sorted per UserSort. Default (zero value)
// is username ASC. Used by the user-management page (sort headers)
// and by surfaces that need a user-id → username map (audit log
// filter, "ack'd by" projections) — those callers pass UserSort{}.
func (s *Store) ListUsers(ctx context.Context, sort UserSort) ([]User, error) {
	asc := sort.OrderAsc
	if sort.OrderBy == "" {
		// Default: username ASC (alphabetical), matching pre-sort behaviour.
		asc = true
	}
	q := `SELECT id, username, password_hash, role, email, disabled_at,
	             must_change_password, created_at, last_login_at
	      FROM users ORDER BY ` + usersOrderColumn(sort.OrderBy, asc)
	rows, err := s.db.QueryContext(ctx, q)
	if err != nil {
		return nil, fmt.Errorf("store: list users: %w", err)
	}
	defer func() { _ = rows.Close() }()
	var out []User
	for rows.Next() {
		u, err := scanUser(rows.Scan)
		if err != nil {
			return nil, err
		}
		out = append(out, *u)
	}
	return out, rows.Err()
}

// CountUsers returns the total number of user rows. The first-run
// bootstrap uses this to detect a fresh install.
func (s *Store) CountUsers(ctx context.Context) (int, error) {
	var n int
	if err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM users`).Scan(&n); err != nil {
		return 0, fmt.Errorf("store: count users: %w", err)
	}
	return n, nil
}

// CountEnabledAdmins returns the number of users with role='admin'
// AND disabled_at IS NULL. Used by the last-admin guard before
// disable / role-demote operations.
func (s *Store) CountEnabledAdmins(ctx context.Context) (int, error) {
	var n int
	if err := s.db.QueryRowContext(ctx,
		`SELECT COUNT(*) FROM users WHERE role = 'admin' AND disabled_at IS NULL`,
	).Scan(&n); err != nil {
		return 0, fmt.Errorf("store: count admins: %w", err)
	}
	return n, nil
}

// MarkUserLogin records a successful authentication.
func (s *Store) MarkUserLogin(ctx context.Context, id string, when time.Time) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET last_login_at = ? WHERE id = ?`,
		when.UTC().Format(time.RFC3339Nano), id)
	if err != nil {
		return fmt.Errorf("store: mark login: %w", err)
	}
	return nil
}

// SetUserEmail replaces the email field. Empty string clears it.
func (s *Store) SetUserEmail(ctx context.Context, id, email string) error {
	em := strings.ToLower(strings.TrimSpace(email))
	var v any
	if em == "" {
		v = nil
	} else {
		v = em
	}
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET email = ? WHERE id = ?`, v, id)
	if err != nil {
		return fmt.Errorf("store: set user email: %w", err)
	}
	return nil
}

// SetUserRole changes a user's role.
func (s *Store) SetUserRole(ctx context.Context, id string, role Role) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET role = ? WHERE id = ?`, string(role), id)
	if err != nil {
		return fmt.Errorf("store: set user role: %w", err)
	}
	return nil
}

// DisableUser sets disabled_at = when. Idempotent on already-disabled
// rows (no-op).
func (s *Store) DisableUser(ctx context.Context, id string, when time.Time) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET disabled_at = ?
		 WHERE id = ? AND disabled_at IS NULL`,
		when.UTC().Format(time.RFC3339Nano), id)
	if err != nil {
		return fmt.Errorf("store: disable user: %w", err)
	}
	return nil
}

// EnableUser clears disabled_at.
func (s *Store) EnableUser(ctx context.Context, id string) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET disabled_at = NULL WHERE id = ?`, id)
	if err != nil {
		return fmt.Errorf("store: enable user: %w", err)
	}
	return nil
}

// SetMustChangePassword toggles the must_change_password flag.
func (s *Store) SetMustChangePassword(ctx context.Context, id string, must bool) error {
	v := 0
	if must {
		v = 1
	}
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET must_change_password = ? WHERE id = ?`, v, id)
	if err != nil {
		return fmt.Errorf("store: set must_change_password: %w", err)
	}
	return nil
}

// SetPasswordHash stores a new password_hash and clears the
// must_change_password flag in one go.
func (s *Store) SetPasswordHash(ctx context.Context, id, hash string) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET password_hash = ?, must_change_password = 0 WHERE id = ?`,
		hash, id)
	if err != nil {
		return fmt.Errorf("store: set password: %w", err)
	}
	return nil
}

func scanUser(scan func(...any) error) (*User, error) {
	var u User
	var role string
	var email, disabledAt, lastLogin sql.NullString
	var must int
	var created string
	if err := scan(&u.ID, &u.Username, &u.PasswordHash, &role,
		&email, &disabledAt, &must, &created, &lastLogin); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, fmt.Errorf("store: scan user: %w", err)
	}
	u.Role = Role(role)
	if email.Valid {
		v := email.String
		u.Email = &v
	}
	if disabledAt.Valid {
		t, _ := time.Parse(time.RFC3339Nano, disabledAt.String)
		u.DisabledAt = &t
	}
	u.MustChangePassword = must == 1
	t, _ := time.Parse(time.RFC3339Nano, created)
	u.CreatedAt = t
	if lastLogin.Valid {
		t, _ := time.Parse(time.RFC3339Nano, lastLogin.String)
		u.LastLoginAt = &t
	}
	return &u, nil
}