@middy/core/index.d.ts

import {
  Callback as LambdaCallback,
  Context as LambdaContext,
  Handler as LambdaHandler
} from 'aws-lambda'

declare type PluginHook = () => void
declare type PluginHookWithMiddlewareName = (middlewareName: string) => void
declare type PluginHookPromise = (request: Request) => Promise<unknown> | unknown

interface PluginObject {
  internal?: any
  beforePrefetch?: PluginHook
  requestStart?: PluginHook
  beforeMiddleware?: PluginHookWithMiddlewareName
  afterMiddleware?: PluginHookWithMiddlewareName
  beforeHandler?: PluginHook
  timeoutEarlyInMillis?: number
  timeoutEarlyResponse?: PluginHook
  afterHandler?: PluginHook
  requestEnd?: PluginHookPromise
}

interface Request<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> {
  event: TEvent
  context: TContext
  response: TResult | null
  error: TErr | null
  internal: {
    [key: string]: any
  }
}

declare type MiddlewareFn<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> = (request: Request<TEvent, TResult, TErr, TContext>) => any

export interface MiddlewareObj<TEvent = unknown, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> {
  before?: MiddlewareFn<TEvent, TResult, TErr, TContext>
  after?: MiddlewareFn<TEvent, TResult, TErr, TContext>
  onError?: MiddlewareFn<TEvent, TResult, TErr, TContext>
}

// The AWS provided Handler type uses void | Promise<TResult> so we have no choice but to follow and suppress the linter warning
// eslint-disable-next-line @typescript-eslint/no-invalid-void-type
type MiddyInputHandler<TEvent, TResult, TContext extends LambdaContext = LambdaContext> = (event: TEvent, context: TContext, callback: LambdaCallback<TResult>) => void | Promise<TResult>
type MiddyInputPromiseHandler<TEvent, TResult, TContext extends LambdaContext = LambdaContext> = (event: TEvent, context: TContext,) => Promise<TResult>

export interface MiddyfiedHandler<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> extends MiddyInputHandler<TEvent, TResult, TContext>,
  MiddyInputPromiseHandler<TEvent, TResult, TContext> {
  use: UseFn<TEvent, TResult, TErr, TContext>
  before: AttachMiddlewareFn<TEvent, TResult, TErr, TContext>
  after: AttachMiddlewareFn<TEvent, TResult, TErr, TContext>
  onError: AttachMiddlewareFn<TEvent, TResult, TErr, TContext>
  handler: (handler: MiddlewareHandler<LambdaHandler<TEvent, TResult>, TContext>) => MiddyfiedHandler<TEvent, TResult, TErr, TContext>
}

declare type AttachMiddlewareFn<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> =
  (middleware: MiddlewareFn<TEvent, TResult, TErr, TContext>) => MiddyfiedHandler<TEvent, TResult, TErr, TContext>

declare type AttachMiddlewareObj<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> =
  (middleware: MiddlewareObj<TEvent, TResult, TErr, TContext>) => MiddyfiedHandler<TEvent, TResult, TErr, TContext>

declare type UseFn<TEvent = any, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> =
  <TMiddleware extends MiddlewareObj<any, any, Error, any>>(middlewares: TMiddleware | TMiddleware[]) => TMiddleware extends MiddlewareObj<infer TMiddlewareEvent, any, Error, infer TMiddlewareContext>
    ? MiddyfiedHandler<TMiddlewareEvent & TEvent, TResult, TErr, TMiddlewareContext & TContext> // always true
    : never

declare type MiddlewareHandler<THandler extends LambdaHandler<any, any>, TContext extends LambdaContext = LambdaContext> =
  THandler extends LambdaHandler<infer TEvent, infer TResult> // always true
    ? MiddyInputHandler<TEvent, TResult, TContext>
    : never

/**
 * Middy factory function. Use it to wrap your existing handler to enable middlewares on it.
 * @param handler your original AWS Lambda function
 * @param plugin wraps around each middleware and handler to add custom lifecycle behaviours (e.g. to profile performance)
 */
declare function middy<TEvent = unknown, TResult = any, TErr = Error, TContext extends LambdaContext = LambdaContext> (handler?: MiddlewareHandler<LambdaHandler<TEvent, TResult>, TContext>, plugin?: PluginObject): MiddyfiedHandler<TEvent, TResult, TErr, TContext>

declare namespace middy {
  export {
    Request,
    PluginHook,
    PluginHookWithMiddlewareName,
    PluginObject,
    MiddlewareFn,
    MiddlewareObj,
    MiddyfiedHandler
  }
}

export default middy