PW5107

module feed.speculative

import context.{ current_session }
import capability.{ Session, SessionId }

opaque type InteractionId = String

type Post = Post { id: String, text: String }

type FeedError =
    | Unavailable

fn latest() -> List<Post> !{ database.read<Post> }
    host "feed:data/posts#latest"

fn publish(s: Session<SessionId>, text: String) -> Result<Post, FeedError> !{ database.write<Post> }
    host "feed:data/posts#publish"

public query Latest() -> List<Post>
    freshness 5.seconds
    cache     shared
{
    latest()
}

fn with_post(posts: List<Post>, text: String) -> List<Post> !{} {
    posts
}

command post(text: String) -> Result<Post, FeedError>
    idempotent_by InteractionId
    optimistic    Latest() as posts => with_post(posts, text)
{
    publish(current_session(), text)
}