Add currentOffering(forPlacement: String) to Offerings

[guido732]

Motivation

New function to get Offering by a placement identifier

Description

New currentOffering(forPlacement: String): Offering? method on Offerings

• Added demo button for this in purchase tester app

// Example usage
if let offering = offerings.currentOffering(forPlacement: "onboarding") {
  showPaywall(offering)
}

Logic flow

• If a placement identifier explicitly exists within the placements.offeringIdsByPlacement dictionary, the method attempts to fetch the corresponding Offering without resorting to a fallback
  • Example: when there is a nil / null value for a placement, we don't want to use the fallback
• If the placement identifier does not exist, the method then attempts to fetch a fallback offering defined by placements.fallbackOfferingId

New placements object in offerings response

{
    // other offerings stuff
    "placements": {
        "fallback_offering_id": "offering_a", // can be null
        "offering_ids_by_placement": {
            "onboarding_start": null,
            "onboarding_end": "offering_b",
        }
  }
}

[joshdholtz]

placements.offeringIdsByPlacement[placementIdentifier] returns at Offering?? because placements.offeringIdsByPlacement is a [String: String?]

The result of could be an explicit nil value. In that case, we don't want to use the fallback offering.

If placements.offeringIdsByPlacement[placementIdentifier] is not found and goes into the else, it means no key was found and we should use the fallback offering.

[tonidero]

Have a meeting, will continue reviewing after

[tonidero]

Nitpick but should we have an internal copy constructor from package so we can create a new package with a new context without having to pass all the parameters again?

[tonidero]

Some non-blocking comments. Looks good!

[aboedo]

looking great, left a couple of questions

[aboedo]

is it more swift-style to make this (for placement placementIdentifier: String) instead?
so the callsite is

getCurrentOffering(for: "HomePageBanner")

instead of

getCurrentOffering(forPlacement: "HomePageBanner")

or even

currentOffering(for: "HomePageBanner")

[aboedo]

we've historically reserved verbs like get or fetch as ways to indicate that it'll issue some work like network requests

[aboedo]

I'm late to the game here, but... what do I do with this class as a developer? Is it so I can use it for analytics?
The docstring for the class doesn't really provide any context on it

[joshdholtz]

@aboedo Oops, missed this comment from yesterday! This is mainly for internal usage. Instead of passing offeringIdentifier from get offerings to post receipt, this objects gets passed around instead. It holds offering identifier, placement information, and targeting information.