import type { IncomingMessage } from 'http'

import { parse } from 'next/dist/compiled/content-type'
import isError from '../../../lib/is-error'
import type { SizeLimit } from '../../../types'
import { ApiError } from '../index'

/**
 * Parse `JSON` and handles invalid `JSON` strings
 * @param str `JSON` string
 */
function parseJson(str: string): object {
  if (str.length === 0) {
    // special-case empty json body, as it's a common client-side mistake
    return {}
  }

  try {
    return JSON.parse(str)
  } catch (e) {
    throw new ApiError(400, 'Invalid JSON')
  }
}

/**
 * Parse incoming message like `json` or `urlencoded`
 * @param req request object
 */
export async function parseBody(
  req: IncomingMessage,
  limit: SizeLimit
): Promise<any> {
  let contentType
  try {
    contentType = parse(req.headers['content-type'] || 'text/plain')
  } catch {
    contentType = parse('text/plain')
  }
  const { type, parameters } = contentType
  const encoding = parameters.charset || 'utf-8'

  let buffer

  try {
    const getRawBody =
      require('next/dist/compiled/raw-body') as typeof import('next/dist/compiled/raw-body')
    buffer = await getRawBody(req, { encoding, limit })
  } catch (e) {
    if (isError(e) && e.type === 'entity.too.large') {
      throw new ApiError(413, `Body exceeded ${limit} limit`)
    } else {
      throw new ApiError(400, 'Invalid body')
    }
  }

  const body = buffer.toString()

  if (type === 'application/json' || type === 'application/ld+json') {
    return parseJson(body)
  } else if (type === 'application/x-www-form-urlencoded') {
    const qs = require('querystring') as typeof import('querystring')
    return qs.decode(body)
  } else {
    return body
  }
}