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In this exercise you'll be providing a TranslationService where paid members have some quality assurance.

You have found a magical translation API that is able to fulfill any translation request in a reasonable amount of time, and you want to capitalize on this.

The magical API has a very minimal interface:

Fetching a translation

api.fetch(text) fetches the translation of text, returning two values:

  • translation: the actual translation
  • quality: the quality expressed as a number

If there is no translation available (because it has not been requested yet), the API throws an error. This also happens if a piece of text is untranslatable.

Requesting a translation

api.request(text, callback) requests the translation of text, calling the callback once it's ready, without a value.

The request API is unstable, which means that sometimes the API will call the callback with an error. If that happens, it is okay to re-request.

⚠ Warning! ⚠

Because of some previous users being lazy when programming, always requesting a translation, without even checking if the text was already translated, the API returns an error if the text has already been translated ánd blocks all access completely, forever.

Tasks

1. Fetch a translation, ignoring the quality

Implement a function to fetch a translation, ignoring the quality, and forwarding any errors thrown by the API:

service.free('jIyaj')
// => Promise<...> resolves "I understand."

service.free("jIyajbe'")
// => Promise<...> rejects Error("Not yet translated")
  • Returns the translation if it can be retrieved, regardless its quality
  • Forwards any error from the translation API

2. Fetch a batch of translations, all-or-nothing

Implement a function that batch translates the given texts using the free service, returning all the translations, or a single error.

service.batch(['jIyaj', "majQa'"])
// => Promise<...> resolves ["I understand.", "Well done!"]

service.batch(['jIyaj', "jIyajbe'"])
// => Promise<...> rejects new Error("Not yet translated")

service.batch([])
// => Promise<...> rejects BatchIsEmpty()
  • Resolves with all the translations (in the same order), if they are all available
  • Rejects with the first error that is encountered
  • Rejects with a BatchIsEmpty error if no texts are given

3. Request a translation, retrying at most 2 times

Implement a function that requests a translation, with automatic retries, up to a total of 3 calls for the same request.

service.request("jIyajbe'")
// => Promise<...> resolves (with nothing), can now be retrieved using the fetch API

4. Fetch a translation, inspect the quality, or request it

Implement the function for premium users which fetch a translation, request it if it's not available, and only return it if it meets a certain threshold.

service.premium("jIyajbe'", 100)
// => Promise<...> resolves "I don't understand."

service.premium("'arlogh Qoylu'pu'?", 100)
// => Promise<...> rejects QualityThresholdNotMet()

service.premium("'arlogh Qoylu'pu'?", 40)
// => Promise<...> resolves "What time is it?"

N.B.

The correct translation of 'arlogh Qoylu'pu'? is How many times has it been heard?.