package store

import (
	"context"

	"github.com/jackc/pgx/v5"
)

const userCols = "id, username, password_hash, role, created_at"

func (s *Store) CountUsers(ctx context.Context) (int, error) {
	var n int
	err := s.p.QueryRow(ctx, "SELECT count(*) FROM users").Scan(&n)
	return n, err
}

func (s *Store) CreateUser(ctx context.Context, username, hash, role string) (int64, error) {
	var id int64
	err := s.p.QueryRow(ctx,
		"INSERT INTO users (username, password_hash, role) VALUES ($1,$2,$3) RETURNING id",
		username, hash, role).Scan(&id)
	return id, err
}

func (s *Store) GetUserByName(ctx context.Context, username string) (User, error) {
	return scanUser(s.p.QueryRow(ctx, "SELECT "+userCols+" FROM users WHERE username=$1", username))
}

func (s *Store) GetUserByID(ctx context.Context, id int64) (User, error) {
	return scanUser(s.p.QueryRow(ctx, "SELECT "+userCols+" FROM users WHERE id=$1", id))
}

func (s *Store) ListUsers(ctx context.Context) ([]User, error) {
	rows, err := s.p.Query(ctx, "SELECT "+userCols+" FROM users ORDER BY id")
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []User
	for rows.Next() {
		var u User
		if err := rows.Scan(&u.ID, &u.Username, &u.PasswordHash, &u.Role, &u.CreatedAt); err != nil {
			return nil, err
		}
		out = append(out, u)
	}
	return out, rows.Err()
}

// DeleteUser deletes a user with a transactional last-admin check (B5).
// Returns ErrLastAdmin if the target is the last admin.
func (s *Store) DeleteUser(ctx context.Context, id int64) error {
	tx, err := s.p.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(ctx)
	var role string
	if err := tx.QueryRow(ctx, "SELECT role FROM users WHERE id=$1 FOR UPDATE", id).Scan(&role); err != nil {
		return err // includes pgx.ErrNoRows
	}
	if role == "admin" {
		var n int
		if err := tx.QueryRow(ctx, "SELECT count(*) FROM users WHERE role='admin'").Scan(&n); err != nil {
			return err
		}
		if n <= 1 {
			return ErrLastAdmin
		}
	}
	if _, err := tx.Exec(ctx, "DELETE FROM users WHERE id=$1", id); err != nil {
		return err
	}
	return tx.Commit(ctx)
}

func scanUser(row pgx.Row) (User, error) {
	var u User
	err := row.Scan(&u.ID, &u.Username, &u.PasswordHash, &u.Role, &u.CreatedAt)
	return u, err
}