Observable collection updater

observable-coll-updater.js

type Socket = {
    create(url: string): Observable;
}

type PostAueryArg = {
    id: string;
}

type Comment = {
    id: string;
    text: string;
    from: string;
}

class CommentImpl {
    id: string;
    text: string;
    from: string;
}

@asyncmodel(commentsUpdater)
class CommentCollection extends BaseCollection {
    createItem(): Comment {
        return new CommentImpl()
    }
}

type InitEvent = {
    kind: 'init';
    comments: Array<Comment>;
}

type CreateCommentEvent = {
    kind: 'create';
    comment: Comment;
}

type DeleteEvent = {
    kind: 'delete';
    id: string;
}

type UpdateCommentEvent = {
    kind: 'update';
    comment: Comment;
}

type CRUDEvent = InitEvent | CreateCommentEvent | UpdateCommentEvent | DeleteEvent;

type Getter<V> = () => V;

// #1
@loader(getter(CommentCollection), SocketImpl, PostAueryArgImpl)
function commentsUpdater(getColl: Getter<CommentCollection>, socket: Socket, post: PostAueryArg) {
    const observable: Observable = socket.create(`/post/${post.id}comments/crud`);

    return observable.map(function onEvent(event: CRUDEvent) {
        const coll: CommentCollection = getColl()
        switch (event.kind) {
            case 'init':
                return coll.init(event.comments)
            case 'create':
                return coll.add(event.comment)
            case 'delete':
                return coll.delete(event.id)
            case 'update':
                return coll.set(event.comment.id, (comment: Comment) => event.comment))
            default:
                throw new Error('Unknown comments update event: ' + event.kind)
        }
    })
}

// #2
@loader(SocketImpl, PostAueryArgImpl)
function commentsUpdater(socket: Socket, post: PostAueryArg) {
    const observable: Observable = socket.create(`/post/${post.id}comments/crud`);

    return observable.map(function onEvent(event: CRUDEvent) {
        return function updateCommentsEvent(coll: CommentCollection) {
            switch (event.kind) {
                case 'init':
                    return coll.init(event.comments)
                case 'create':
                    return coll.add(event.comment)
                case 'delete':
                    return coll.delete(event.id)
                case 'update':
                    return coll.set(event.comment.id, (comment: Comment) => event.comment))
                default:
                    throw new Error('Unknown comments update event: ' + event.kind)
            }
        }
    })
}


// #3
@asyncFacet(SocketImpl, PostAueryArgImpl)
function commentsCrud(socket: Socket, post: PostAueryArg): Observable {
    return socket.create(`/post/${post.id}comments/crud`);
}

@facet(commentsCrud, CommentCollection)
function commentsUpdater(commentsCrud: Observable, coll: CommentCollection) {
    return commentsCrud.map(function onEvent(event: CRUDEvent) {
        switch (event.kind) {
            case 'init':
                return coll.init(event.comments)
            case 'create':
                return coll.add(event.comment)
            case 'delete':
                return coll.delete(event.id)
            case 'update':
                return coll.set(event.comment.id, (comment: Comment) => event.comment))
            default:
                throw new Error('Unknown comments update event: ' + event.kind)
        }
    })
}