/**
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @file Add built in plug and play web framework support for lambda HTTP Proxy API gateway
 */

import { Framework, StandardHandler, Headers } from './framework'
import { JsonObject } from '../common'
import { Context, Callback } from 'aws-lambda'
import { getLogger } from '../logger'

export interface LambdaHandler {
  /** @public */
  (event: JsonObject, context: Context, callback: Callback): Promise<void>
}

export interface LambdaMetadata {
  /** @public */
  event: JsonObject

  /** @public */
  context: Context
}

/** @hidden */
export class Lambda implements Framework<LambdaHandler> {
  handle(standard: StandardHandler) {
    return async (event: JsonObject, context: Context, callback: Callback) => {
      const metadata: LambdaMetadata = {
        context,
        event,
      }
      const logger = getLogger()
      const entireBodyFormat = typeof event.headers !== 'object' || Array.isArray(event.headers)
      // convert header keys to lowercase for case insensitive header retrieval
      const headers = entireBodyFormat ? {} as Headers :
        Object.keys(event.headers).reduce((o, k) => {
          o[k.toLowerCase()] = event.headers[k]
          return o
        }, {} as Headers)
      const body = entireBodyFormat ? event :
        (typeof event.body === 'string' ? JSON.parse(event.body) : event.body)
      const result = await standard(body, headers, { lambda: metadata })
      .catch((e: Error) => {
        logger.error(e.stack || e)
        callback(e)
      })
      if (!result) {
        return
      }
      const { status } = result
      callback(null, {
        statusCode: status,
        body: JSON.stringify(result.body),
        headers: result.headers,
      })
    }
  }

  isContext(second: {}): second is Context {
    return typeof (second as Context).succeed === 'function'
  }

  isCallback(third: {}): third is Callback {
    return typeof third === 'function'
  }

  check(first: {}, second: {}, third: {}) {
    return this.isContext(second) && this.isCallback(third)
  }
}

/** @hidden */
export const lambda = new Lambda()