import OptionalSubscripts

var ?: Any?

? = nil
? = []
? = [:]

?[] = "?"
try ?[] == "?"

?["one"] = 1
try ?["one"] == 1

?["one", 2] = 2
try ?["one", 2] == 2

?["one", 10] = nil
try ?["one"] as [Int?] == [nil, nil, 2]

?["one", 2] = ["three": 4]
try ?["one", 2, "three"] == 4
try ?[\.["one"][2]["three"]] == 4
        
?["one", 2] = nil
?["one"] == nil

?["one", "two"] = nil
?[] == nil

let o = Any?.Store()

let stream = await o.stream("me", 2, "you").filter(String.self).prefix(3)

Task {
    var hearts: [String] = []
    
    for await o in stream {
        hearts.append(o)
    }
    
    hearts == ["❤️", "?", "?"]
}

await o.set("me", 2, "you", to: "❤️")
await o.set("me", 2, to: ["you": "?"])
await o.set("me", to: [nil, nil, ["you": "?"]])

let db = SomeDatabase() // conforms to Geyser protocol and streams entire documents
let pond = Any?.Pond(source: db)

await db.store.set("v/2.0/way/to", "my", "heart", to: "?")

var hearts = ""

loop:
for await heart in pond.stream("way", "to", "my", "heart").filter(String?.self) {  
    // observing a nested field in a versioned document ↑
    
    hearts += heart ?? ""
    
    switch heart {
    case nil   where hearts.isEmpty:
               await db.store.set("v/1.0/way/to", "my", "heart", to: "❤️")
    case "❤️": await db.store.set("v/1.0/way/to", "my", "heart", to: "?")
    case "?": await db.store.set("v/1.0/way/to", "my", "heart", to: "?")
    case "?": await db.setVersion(to: "v/2.0/")
    case "?": break loop
    default:   assertionFailure()
    }
}

hearts == "❤️???"

await pond.gushSources["v/1.0/way/to"]?.referenceCount == nil
await pond.gushSources["v/2.0/way/to"]?.referenceCount == 1

protocol Geyser {

    associatedtype GushID: Hashable
    
    associatedtype Gushes: AsyncSequence where Gushes.Element == Any?
    
    associatedtype GushToRouteMapping: AsyncSequence where GushToRouteMapping.Element == (id: GushID, route: Optional<Any>.Route)?

    func stream(_ gush: GushID) async -> Gushes
    
    func source<Route>(of route: Route) async -> GushToRouteMapping where Route: Collection, Route.Index == Int, Route.Element == Optional<Any>.Location
}