export default function doctypeToString(doctype) {
    if (doctype === null) {
        return ''
    }
    // Checking with instanceof DocumentType might be neater, but how to get a
    // reference to DocumentType without assuming it to be available globally?
    // To play nice with custom DOM implementations, we resort to duck-typing.
    if (!doctype
        || doctype.nodeType !== doctype.DOCUMENT_TYPE_NODE
        || typeof doctype.name !== 'string'
        || typeof doctype.publicId !== 'string'
        || typeof doctype.systemId !== 'string'
    ) {
        throw new TypeError('Expected a DocumentType')
    }
    const doctypeString = `<!DOCTYPE ${doctype.name}`
        + (doctype.publicId ? ` PUBLIC "${doctype.publicId}"` : '')
        + (doctype.systemId
            ? (doctype.publicId ? `` : ` SYSTEM`) + ` "${doctype.systemId}"`
            : ``)
        + `>`
    return doctypeString
}