index.js

#!/usr/bin/env node
const fs = require('fs')
const path = require('path')
const getStdin = require('get-stdin')
const { buildASTSchema, graphql, parse } = require('graphql')
const { introspectionQuery } = require('graphql/utilities')

const log = x => (console.trace(x), x)

// Turns an array of objects into an object indexed by a given field.
function index(array, field) {
  const index = {}
  array.forEach(item => {
    index[item[field]] = item
  })
  return index
}

function indentedLine(level) {
  let line = '\n'
  for (let i = 0; i < level; i++) {
    line += '  '
  }
  return line
}

async function introspect(schemaContents) {
  const schema = buildASTSchema(parse(schemaContents))
  return await graphql(schema, introspectionQuery)
}

function makeFragments(schemaContents) {
  const schema = schemaContents.data.__schema
  const types = schema.types.filter(
    ({ kind, name }) =>
      kind === 'OBJECT' &&
      !name.startsWith('__') &&
      name !== schema.queryType.name &&
      name !== schema.mutationType.name,
  )
  const typesByName = index(types, 'name')
  const definitions = types
    .filter(
      ({ kind, name }) =>
        kind === 'OBJECT' &&
        !name.startsWith('__') &&
        name !== schema.queryType.name,
    )
    .map(type => {
      const { name, fields } = type
      return {
        name,
        fragment: `fragment ${name} on ${name} {
  ${fields
    .map(field => printField(field, typesByName))
    // Some fields should not be printed, ie. fields with arguments.
    // Remove those from the output by returning null from printField.
    .filter(field => field != null)
    .join(indentedLine(1))}
}
`,
      }
    })
  return `// This file was auto-generated by graphql-fragment-codegen. Do not edit it by hand.
${definitions
    .map(
      ({ name, fragment }) => `
export const ${name} = \`${fragment}\`
`,
    )
    .join('')}`
}

function printField(field, typesByName, indent = 1) {
  const { name, type } = field
  if ('args' in field && field.args.length > 0) {
    return null
  }
  if (type.kind === 'SCALAR') {
    return name
  }
  if (type.kind === 'OBJECT') {
    return (
      name +
      ' {' +
      indentedLine(indent + 1) +
      typesByName[type.name].fields
        .map(field => printField(field, typesByName, indent + 1))
        .filter(field => field != null)
        .join(indentedLine(indent + 1)) +
      indentedLine(indent) +
      '}'
    )
  }
  if (type.kind === 'LIST') {
    return printField({ ...field, type: type.ofType }, typesByName)
  }
  console.error('unmatched type kind: ', type.kind)
  return null
}

async function main() {
  const stdin = await getStdin()
  if (stdin === '') {
    process.exit(1)
  }
  const schemaContents = await introspect(stdin)
  process.stdout.write(makeFragments(schemaContents))
}
main()