text: import React from 'react';
  import PropTypes from 'prop-types';
  import Helmet from 'react-helmet';
  import { StaticQuery, graphql } from 'gatsby';
  
  function SEO ({ description, lang, meta, keywords, title }) {
      return (
          <StaticQuery
              query={detailsQuery}
              render={data => {
                  const metaDescription =
            description || data.site.siteMetadata.description;
                  return (
                      <Helmet
                          htmlAttributes={{
                              lang
                          }}
                          title={title}
                          titleTemplate={`%s | ${ data.site.siteMetadata.title }`}
                          meta={[
                              {
                                  name: `description`,
                                  content: metaDescription
                              },
                              {
                                  property: `og:title`,
                                  content: title
                              },
                              {
                                  property: `og:description`,
                                  content: metaDescription
                              },
                              {
                                  property: `og:type`,
                                  content: `website`
                              },
                              {
                                  name: `twitter:card`,
                                  content: `summary`
                              },
                              {
                                  name: `twitter:creator`,
                                  content: data.site.siteMetadata.author
                              },
                              {
                                  name: `twitter:title`,
                                  content: title
                              },
                              {
                                  name: `twitter:description`,
                                  content: metaDescription
                              }
                          ]
                              .concat(
                                  keywords.length > 0
                                      ? {
                                          name: `keywords`,
                                          content: keywords.join(`, `)
                                      }
                                      : []
                              )
                              .concat(meta)}
                      />
                  );
              }}
          />
      );
  }
  
  SEO.defaultProps = {
      lang: `en`,
      meta: [],
      keywords: []
  };
  
  SEO.propTypes = {
      description: PropTypes.string,
      lang: PropTypes.string,
      meta: PropTypes.array,
      keywords: PropTypes.arrayOf(PropTypes.string),
      title: PropTypes.string.isRequired
  };
  
  export default SEO;
  
  const detailsQuery = graphql`
    query DefaultSEOQuery {
      site {
        siteMetadata {
          title
          description
          author
        }
      }
    }
  `;
  