index.js

'use strict'

const AWS = require('aws-sdk'),
      s3 = new AWS.S3()

module.exports.put = (bucket, key, highwatermark) => s3
  .putObject({ Bucket: bucket, Key: key, Body: JSON.stringify(highwatermark) })
  .promise()
  .catch((error) => console.error('WARNING: Failed to update high water mark for %j: %j', highwatermark, error))

module.exports.get = (bucket, key, options) => {
  options = options || {}

  let promise
  if(options.override) {
    promise = Promise.resolve(options.override)
  } else {
    promise = s3
      .getObject({ Bucket: bucket, Key: key })
      .promise()
      .then(s3Object => JSON.parse(s3Object.Body.toString()))
      .catch(err => {
        if (err.statusCode === 404 && 'default' in options) {
          return options.default
        }
        throw err
      })
  }

  return promise.then(highwatermark => {
    if (options.map) {
      highwatermark = options.map(highwatermark)
    }
    if (options.isValid && !options.isValid(highwatermark)) {
      throw new Error('Invalid high water mark')
    }

    return highwatermark
  })
}

module.exports.delete = (bucket, key) => s3
  .deleteObject({ Bucket: bucket, Key: key})
  .promise()
  .catch((error) => console.error(`WARNING: Failed to delete high water mark: ${error.message || error}`))