Meet distributed actors in Swift

4:49 - actor OfflinePlayer

public actor OfflinePlayer: Identifiable {
    nonisolated public let id: ActorIdentity = .random

    let team: CharacterTeam
    let model: GameViewModel
    var movesMade: Int = 0

    public init(team: CharacterTeam, model: GameViewModel) {
        self.team = team
        self.model = model
    }

    public func makeMove(at position: Int) async throws -> GameMove {
        let move = GameMove(
            playerID: id,
            position: position,
            team: team,
            teamCharacterID: team.characterID(for: movesMade))
        await model.userMadeMove(move: move)

        movesMade += 1 
        return move
    }

    public func opponentMoved(_ move: GameMove) async throws {
        do {
            try await model.markOpponentMove(move)
        } catch {
            log("player", "Opponent made illegal move! \(move)")
        }
    }

}

5:39 - actor BotPlayer

public actor BotPlayer: Identifiable {
    nonisolated public let id: ActorIdentity = .random
    
    var ai: RandomPlayerBotAI
    var gameState: GameState
    
    public init(team: CharacterTeam) {
        self.gameState = .init()
        self.ai = RandomPlayerBotAI(playerID: self.id, team: team)
    }
    
    public func makeMove() throws -> GameMove {
        return try ai.decideNextMove(given: &gameState)
    }
    
    public func opponentMoved(_ move: GameMove) async throws {
        try gameState.mark(move)
    }
}

6:11 - distributed actor BotPlayer

import Distributed 

public distributed actor BotPlayer: Identifiable {
    typealias ActorSystem = LocalTestingDistributedActorSystem
  
    var ai: RandomPlayerBotAI
    var gameState: GameState
    
    public init(team: CharacterTeam, actorSystem: ActorSystem) {
        self.actorSystem = actorSystem // first, initialize the implicitly synthesized actor system property
        self.gameState = .init()
        self.ai = RandomPlayerBotAI(playerID: self.id, team: team) // use the synthesized `id` property
    }
    
    public distributed func makeMove() throws -> GameMove {
        return try ai.decideNextMove(given: &gameState)
    }
    
    public distributed func opponentMoved(_ move: GameMove) async throws {
        try gameState.mark(move)
    }
}

12:08 - Resolving a remote BotPlayer

let sampleSystem: SampleWebSocketActorSystem

let opponentID: BotPlayer.ID = .randomID(opponentFor: self.id)
let bot = try BotPlayer.resolve(id: opponentID, using: sampleSystem) // resolve potentially remote bot player

13:35 - Server-side actor system app

import Distributed
import TicTacFishShared

/// Stand alone server-side swift application, running our SampleWebSocketActorSystem in server mode.
@main
struct Boot {
    
    static func main() {
        let system = try! SampleWebSocketActorSystem(mode: .serverOnly(host: "localhost", port: 8888))
        
        system.registerOnDemandResolveHandler { id in
            // We create new BotPlayers "ad-hoc" as they are requested for.
            // Subsequent resolves are able to resolve the same instance.
            if system.isBotID(id) {
                return system.makeActorWithID(id) {
                    OnlineBotPlayer(team: .rodents, actorSystem: system)
                }
            }
            
            return nil // unable to create-on-demand for given id
        }
        
        print("========================================================")
        print("=== TicTacFish Server Running on: ws://\(system.host):\(system.port) ==")
        print("========================================================")
        
        try await server.terminated // waits effectively forever (until we shut down the system)
    }
}

20:02 - Receptionist listing

/// As we are playing for our `model.team` team, we try to find a player of the opposing team
let opponentTeam = model.team == .fish ? CharacterTeam.rodents : CharacterTeam.fish

/// The local network actor system provides a receptionist implementation that provides us an async sequence
/// of discovered actors (past and new)
let listing = await localNetworkSystem.receptionist.listing(of: OpponentPlayer.self, tag: opponentTeam.tag)
for try await opponent in listing where opponent.id != self.player.id {
    log("matchmaking", "Found opponent: \(opponent)")
    model.foundOpponent(opponent, myself: self.player, informOpponent: true)
    // inside foundOpponent:
    // if informOpponent {
    //     Task {
    //         try await opponent.startGameWith(opponent: myself, startTurn: false)
    //     }
    // }

    return // make sure to return here, we only need to discover a single opponent
}

20:23 - distributed actor LocalNetworkPlayer

public distributed actor LocalNetworkPlayer: GamePlayer {
    public typealias ActorSystem = SampleLocalNetworkActorSystem

    let team: CharacterTeam
    let model: GameViewModel

    var movesMade: Int = 0

    public init(team: CharacterTeam, model: GameViewModel, actorSystem: ActorSystem) {
        self.team = team
        self.model = model
        self.actorSystem = actorSystem
    }

    public distributed func makeMove() async -> GameMove {
        let field = await model.humanSelectedField()

        movesMade += 1
        let move = GameMove(
            playerID: self.id,
            position: field,
            team: team,
            teamCharacterID: movesMade % 2)

        return move
    }

    public distributed func makeMove(at position: Int) async -> GameMove {
        let move = GameMove(
            playerID: id,
            position: position,
            team: team,
            teamCharacterID: movesMade % 2)

        log("player", "Player makes move: \(move)")
        _ = await model.userMadeMove(move: move)

        movesMade += 1
        return move
    }

    public distributed func opponentMoved(_ move: GameMove) async throws {
        do {
            try await model.markOpponentMove(move)
        } catch {
            log("player", "Opponent made illegal move! \(move)")
        }
    }

    public distributed func startGameWith(opponent: OpponentPlayer, startTurn: Bool) async {
        log("local-network-player", "Start game with \(opponent.id), startTurn:\(startTurn)")
        await model.foundOpponent(opponent, myself: self, informOpponent: false)

        await model.waitForOpponentMove(shouldWaitForOpponentMove(myselfID: self.id, opponentID: opponent.id))
    }
}