merges GraphQL requests

mergeRequests.js

import { parse, print, visit } from "graphql"

export default function mergeRequests(requests) {
  const numberedAsts = requests.map(({ query }, index) => {
    let ast = parse(query)
    ast = numberVars(ast, index)
    ast = numberSelectionSet(ast, index)
    return ast
  })

  const mergedSelections = numberedAsts.reduce(
    (selections, ast) =>
      selections.concat(ast.definitions[0].selectionSet.selections),
    []
  )
  const mergedVarNodes = numberedAsts.reduce(
    (vars, ast) => vars.concat(ast.definitions[0].variableDefinitions),
    []
  )

  const mergedAst = numberedAsts[0]
  mergedAst.definitions[0].selectionSet.selections = mergedSelections
  mergedAst.definitions[0].variableDefinitions = mergedVarNodes

  const mergedQuery = print(mergedAst)

  const mergedVars = requests.reduce(
    (result, { vars }, index) =>
      vars
        ? Object.entries(vars).reduce(
            (result, [name, value]) => ({
              ...result,
              [`q${index}_${name}`]: value
            }),
            result
          )
        : result,
    {}
  )

  return { query: mergedQuery, vars: mergedVars }
}

/**
 * Takes a query and returns the same query with all the variables numbered.
 *
 * For example
 *   query ($id:ID) { ... }
 * becomes
 *   query ($id1:ID) { ... }
 */
function numberVars(ast, number) {
  return visit(ast, {
    Variable(node) {
      return {
        ...node,
        name: { ...node.name, value: `q${number}_${node.name.value}` }
      }
    }
  })
}

function numberSelectionSet(ast, number) {
  return visit(ast, {
    SelectionSet(node, key, parent, path, ancestors) {
      // only top level selections need renaming
      if (ancestors.length > 2) return node

      return {
        ...node,
        selections: node.selections.map(selection => {
          // @ts-ignore
          const alias = selection.alias
          return {
            ...selection,
            alias: alias
              ? {
                  ...alias,
                  value: `q${number}_${alias.value}`
                }
              : {
                  kind: "Name",
                  // @ts-ignore
                  value: `q${number}_${selection.name.value}`
                }
          }
        })
      }
    }
  })
}