graphql-typed-client/src/client/chain.ts

A tool that generates a strongly typed client library for any GraphQL endpoint. The client allows writing GraphQL queries as plain JS objects (with type safety, awesome code completion experience, custom scalar type mapping, type guards and more)

interface Chain {
  (): void
  path: string[][]
}

const newChain = (path: string[][] = []) => {
  const chain = <Chain>(() => {})
  chain.path = path
  return chain
}

const pathToRequest = (path: string[][], executeFields: any): any => {
  if (path.length === 0) return undefined

  const [[field, arg], ...rest] = path

  const nextFields = pathToRequest(rest, executeFields) || executeFields

  return {
    [field]: arg
      ? nextFields && typeof nextFields !== 'boolean' && typeof nextFields !== 'number'
        ? [arg, nextFields]
        : [arg]
      : nextFields
      ? nextFields
      : 1,
  }
}

const wrapInProxy = (chain: Chain, onExecute: (path: string[], request: any, defaultValue: any) => any): any =>
  new Proxy(chain, {
    get(target, prop) {
      if (typeof prop !== 'string') throw new Error('property is not a string')

      if (prop === 'execute') {
        return (fields: any, defaultValue: any) =>
          onExecute(target.path.map(i => i[0]), pathToRequest(target.path, fields), defaultValue)
      } else {
        const newPath = [...target.path, [prop]]
        return wrapInProxy(newChain(newPath), onExecute)
      }
    },
    apply(target, _, argArray) {
      const newPath = [...target.path.slice(0, -1), [target.path[target.path.length - 1][0], argArray[0]]]
      return wrapInProxy(newChain(newPath), onExecute)
    },
  })

export const chain = (onExecute: (path: string[], request: any, defaultValue: any) => any) =>
  wrapInProxy(newChain(), onExecute)