You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: enable_ca.go
    path of file: ./repos/golang-samples/privateca
    
    the code of the file until where you have to start completion: // Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS 
    
func enableCa(w io.Writer, projectId string, location string, caPoolId string, caId string) error {
	// projectId := "your_project_id"
	// location := "us-central1"	// For a list of locations, see: https://cloud.google.com/certificate-authority-service/docs/locations.
	// caPoolId := "ca-pool-id"		// The id of the CA pool under which the CA is present.
	// caId := "ca-id"				// The id of the CA to be enabled.

	ctx := context.Background()
	caClient, err := privateca.NewCertificateAuthorityClient(ctx)
	if err != nil {
		return fmt.Errorf("NewCertificateAuthorityClient creation failed: %w", err)
	}
	defer caClient.Close()

	fullCaName := fmt.Sprintf("projects/%s/locations/%s/caPools/%s/certificateAuthorities/%s",
		projectId, location, caPoolId, caId)

	// Create the EnableCertificateAuthorityRequest.
	// See https://pkg.go.dev/cloud.google.com/go/security/privateca/apiv1/privatecapb#EnableCertificateAuthorityRequest.
	req := &privatecapb.EnableCertificateAuthorityRequest{Name: fullCaName}

	op, err := caClient.EnableCertificateAuthority(ctx, req)
	if err != nil {
		return fmt.Errorf("EnableCertificateAuthority failed: %w", err)
	}

	var caResp *privatecapb.CertificateAuthority
	if caResp, err = op.Wait(ctx); err != nil {
		return fmt.Errorf("EnableCertificateAuthority failed during wait: %w", err)
	}

	if caResp.State != privatecapb.CertificateAuthority_ENABLED {
		return fmt.Errorf("unable to enable Certificate Authority. Current state: %s", caResp.State.String())
	}

	fmt.Fprintf(w, "Successfully enabled Certificate Authority: %s.", caId)
	return nil
}