importing .graphql schema files with #import statements

buildSchema.js

const fs = require('fs');
const { graphql, buildSchema, introspectionQuery } = require('graphql');

const importSchema = require('./importSchema');

module.exports = async function buildSchemaDocument({
  // schema.graphql
  schemaPath,
  // schema.json
  outputPath,
}) {
  const schemaDef = importSchema(schemaPath);

  const introspection = await graphql(buildSchema(schemaDef), introspectionQuery);

  const json = JSON.stringify(introspection, undefined, 2);

  fs.writeFileSync(outputPath, json, 'utf8');
};

importSchema.js

const os = require('os');
const fs = require('fs');
const path = require('path');

function getPath(pathname, base) {
  return path.isAbsolute(pathname) ?
    pathname : path.resolve(base, pathname);
}

module.exports = function importSchema(pathname) {
  // read the schema file.
  const schema = fs.readFileSync(getPath(pathname)).toString();

  // grab the base for relative imports.
  const dirname = path.dirname(pathname);

  return schema
    // split line-by-line | inspired by graphql-tag/loader.
    .split(/\r\n|\r|\n/)
    // go through each line and inject in the import.
    .map((statement) => {
      // test if it matches import statement.
      if (/^#import.*/.test(statement)) {
        // strip to the bare path.
        const importPath = statement.replace(/#import|['"\s]+/g, '');
        // grab the full path.
        const pathToSchema = getPath(dirname, importPath);

        // recursively check each import for its own imports.
        const seam = importSchema(pathToSchema);

        // replace the import statement with the seam.
        return seam;
        // or return the original line.
      } return statement;
    })
    // stitch all the seams together.
    .join(os.EOL);
};