function buildAvatarUrl(employeeId, avatarPath) {
  return avatarPath ? `/api/avatars/${employeeId}` : null;
}

function compareByEmployeeNo(left, right) {
  return left.employee_no.localeCompare(right.employee_no, "en");
}

function mapDepartmentSummary(department) {
  if (!department) {
    return null;
  }
  return {
    id: department.id,
    name: department.name,
  };
}

function mapExternalManager(employee, departmentId, activeEmployeeById) {
  if (!employee.direct_manager_id) {
    return null;
  }

  const manager = activeEmployeeById.get(employee.direct_manager_id) ?? null;
  if (!manager) {
    return null;
  }

  if (manager.department_id === departmentId) {
    return null;
  }

  return {
    id: manager.id,
    employeeNo: manager.employee_no,
    name: manager.name,
    department: mapDepartmentSummary(manager.department),
  };
}

function mapOrganizationNode(employee, departmentId, activeEmployeeById, childrenByManagerId, stack) {
  const nextStack = new Set(stack);
  nextStack.add(employee.id);

  const children = (childrenByManagerId.get(employee.id) ?? [])
    .slice()
    .sort(compareByEmployeeNo)
    .filter((item) => !nextStack.has(item.id))
    .map((item) => mapOrganizationNode(item, departmentId, activeEmployeeById, childrenByManagerId, nextStack));

  return {
    id: employee.id,
    employeeNo: employee.employee_no,
    name: employee.name,
    title: employee.title,
    status: employee.status,
    avatarUrl: buildAvatarUrl(employee.id, employee.avatar_path),
    department: mapDepartmentSummary(employee.department),
    externalManager: mapExternalManager(employee, departmentId, activeEmployeeById),
    children,
  };
}

function buildDepartmentSection(department, employees, activeEmployeeById) {
  const departmentId = department.id;
  const departmentEmployeeById = new Map(employees.map((item) => [item.id, item]));
  const childrenByManagerId = new Map();

  for (const employee of employees) {
    childrenByManagerId.set(employee.id, []);
  }

  for (const employee of employees) {
    if (!employee.direct_manager_id) {
      continue;
    }
    const manager = activeEmployeeById.get(employee.direct_manager_id);
    if (!manager || manager.department_id !== departmentId) {
      continue;
    }
    if (!departmentEmployeeById.has(manager.id)) {
      continue;
    }
    childrenByManagerId.get(manager.id).push(employee);
  }

  const roots = employees
    .filter((employee) => {
      if (!employee.direct_manager_id) {
        return true;
      }
      const manager = activeEmployeeById.get(employee.direct_manager_id);
      return !manager || manager.department_id !== departmentId;
    })
    .slice()
    .sort(compareByEmployeeNo)
    .map((employee) => mapOrganizationNode(employee, departmentId, activeEmployeeById, childrenByManagerId, new Set()));

  return {
    department: mapDepartmentSummary(department),
    roots,
  };
}

async function listOrganizationDepartments(prisma) {
  const employees = await prisma.employee.findMany({
    where: { status: "active" },
    select: {
      id: true,
      employee_no: true,
      name: true,
      title: true,
      status: true,
      avatar_path: true,
      department_id: true,
      direct_manager_id: true,
      department: {
        select: {
          id: true,
          name: true,
        },
      },
    },
  });

  const activeEmployeeById = new Map(employees.map((item) => [item.id, item]));
  const departmentGroups = new Map();

  for (const employee of employees) {
    const departmentId = employee.department?.id ?? employee.department_id;
    if (!departmentId || !employee.department) {
      continue;
    }
    if (!departmentGroups.has(departmentId)) {
      departmentGroups.set(departmentId, {
        department: employee.department,
        employees: [],
      });
    }
    departmentGroups.get(departmentId).employees.push(employee);
  }

  return [...departmentGroups.values()]
    .sort((left, right) => left.department.name.localeCompare(right.department.name, "zh-CN"))
    .map((group) => buildDepartmentSection(group.department, group.employees, activeEmployeeById));
}

module.exports = {
  listOrganizationDepartments,
  __testables: {
    buildDepartmentSection,
    mapOrganizationNode,
  },
};