Adds Flagsmith adapter

[tiagoapolo]

This pull request introduces a new provider adapter for the Flags SDK that integrates with Flagsmith. The changes include adding configuration files, updating dependencies, and creating the necessary code for the adapter.

Flagsmith documentation: https://docs.flagsmith.com/clients/next-ssr

Usage

import { createFlagsmithAdapter } from '@flags-sdk/adapter-flagsmith';
import { flag } from 'flags';

// Create the Flagsmith adapter
const flagsmithAdapter = createFlagsmithAdapter({
  environmentID: 'your-environment-id',
  // Optional: Add any other Flagsmith configuration options
  // See: https://docs.flagsmith.com/clients/javascript/
});

// Define your flags
const myFeatureFlag = flag({
  key: 'my-feature',
  adapter: flagsmithAdapter,
});

// Use the flag in your application
const flag = await myFeatureFlag();

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[dferber90]

Thank you for your contributions so far! I left a bit of early guidance

[dferber90]

Do you work for Flagsmith? If we merge this PR we'd also put up some actual docs on flags-sdk.dev. Would you be wiling to link to our Flags SDK and those docs from https://docs.flagsmith.com?

[matthewelwell]

Hey @dferber90, just jumping in here since Tiago is on vacation - yes, Tiago works for Flagsmith.

In answer to your question, for sure, we'd be happy to link to your docs from https://docs.flagsmith.com - would you be happy with adding reciprocal backlink(s) too?

[dferber90]

Great! We'd add you to https://flags-sdk.dev/providers and create a docs page for FlagSmith

[tiagoapolo]

@dferber90 could you take one more look at my PR ?

[dferber90]

@tiagoapolo I‘m out of office this week, but @AAorris will take over leading adapter work and help you get this finalized, listed and released 👍

[AAorris]

Thanks for your PR! Please consider the following input:

Strongly recommended:

• Support identity through entities
• Optimize performance for multiple features in one request

Recommended:

• Add origin to link flags to your customers' dashboards

[AAorris]

Note that if there are multiple flags, getState() might be called many times in one request:

a = flag({ key: 'a', adapter: flagSmith.getFeature() })
b = flag({ key: 'a', adapter: flagSmith.getFeature() })
...
await Promise.all([a(), b()])

You may consider ways to reduce duplicate work if it's not deduplicated in your SDK

[AAorris]

Entities is unused right now, but it's where Flags SDK usually receives user information. I'd expect identity to be passed to flagsmith.init({}) here if that's how your SDK works
https://docs.flagsmith.com/clients/next-ssr#comparing-ssr-and-client-side-flagsmith-usage

If you expect your customers to pass an identity, you should strongly consider using entities to drive that here.

What I'd expect is something like:

import type { Identity } from 'flagsmith'

// ...
ValueType extends IFlagsmithFeature,
EntitiesType extends IFlagsmithIdentity,

// ...
decide({ entities }) => {
  // identity is either entities itself, or a part of it
  init({ identity: entities })
}

[AAorris]

It looks like flagsmith may be initialized with a user — In that case, this pattern won't work because we'll never re-initialize for another user. I'll need to better understand how identity fits in here, and how it will handle the case where there's multiple different users depending on the request.

https://github.com/Flagsmith/flagsmith-js-examples/blob/main/nextjs-middleware/middleware.ts#L15

[AAorris]

Adapters can provide origin here, which is a hyperlink to the feature flag defined in code. If you can provide this hyperlink, it will allow users to get to the right place in one click from the Flags Explorer

https://flags-sdk.dev/frameworks/next#flags-explorer

Ex. something like

return { 
  origin: `${configParams.api}/${configParams.environmentId}/feature/${key}`
  decide,
}