Instructions

In this exercise, you'll be providing a TranslationService that provides basic translation services to free members, and advanced translation to premium members with quality assurances.

The API

You have found an outer space translation API that fulfills any translation request in a reasonable amount of time. You want to capitalize on this. The space translators are extremely fickle and hate redundancy, so they also provide API storage satellites where you can fetch past translations without bothering them.

Fetching a translation

api.fetch(text) fetches a translation of text from the API storage and returns a promise that provides two values:

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

If a translation is not found in the API storage, the API throws a NotAvailable error. Translations can be added using the api.request method. If 'text' is not translatable, the API throws an Untranslatable error.

Requesting a translation

Some translations are sure to exist, but haven't been added to the API storage yet. That's the difference between NotAvailable ( not in storage, but can be requested ) and Untranslatable ( cannot be translated ).

api.request(text, callback) requests that a translation of text be performed and added into the API storage. On completion the callback function is called.

• On success callback is passed undefined: this indicates the translation was successful and is accessible using the api.fetch method.
• On failure callback is passed an error: this indicates something went wrong. The outspace API is unstable, which means that the API fails often. If that happens, it is okay to api.request again.

⚠ Warning! ⚠

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1. Fetch a translation, ignoring the quality

The free service only provides translations that are currently in the API storage.

Implement a method free(text) that provides free members with translation that already exist in the API storage. Ignore the quality and forward any errors thrown by the API.

• Returns the translation if it can be retrieved, regardless of its quality
• Forwards any error from the translation API
• Uses the api.fetch method (api.fetch returns a promise)

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

Implement a method batch([text, text, ...]) for free members that translates an array of text using the free service, returning all the translations, or a single error.

• 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 premium user method request(text), that requests a translation be added to the API storage. The request should automatically retry if a failure occurs. It should perform no more than 3 calls for the same request (don't upset the space translators!!!).

• If api.request does not return an error, resolve with undefined
• If api.request returns an error, retry at most two times
• If you run out of retries, reject with the last error received

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

Implement a premium user method premium(text, quality) to fetch a translation. If a translation is NotAvailable, request the translation and fetch it after its been added to the API storage. The method should only return the translation if it meets a certain quality threshold.

• If api.fetch resolves, check the quality before resolving
• If api.fetch rejects, request the translation instead
• If api.request rejects, forward the error

N.B.

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