Lesson_4_source_code

import Iter "mo:base/Iter";
import List "mo:base/List";
import Principal "mo:base/Principal";
import Time "mo:base/Time";
import Debug "mo:base/Debug";
import Text "mo:base/Text";
import Nat64 "mo:base/Nat64";
import Int "mo:base/Int";

actor {
    public type Message = Text;
    
    public type Microblog = actor {
        follow: shared(Principal) -> async (); // 增添关注对象
        follows: shared query() -> async [Principal]; // 返回关注列表
        post: shared(Text) -> async (); // 发布新消息
        posts: shared query() -> async [Message]; // 返回所有发布的消息
        timeline: shared () -> async [Message]; // 返回所有关注对象发布的消息
    };

    stable var followed : List.List<Principal> = List.nil();

    public shared func follow(id: Principal) : async (){
        followed := List.push(id, followed);
    };

    public shared query func follows() : async [Principal]{
        List.toArray(followed);
    };

    stable var messages : List.List<Message> = List.nil();

    public shared func post(text: Text) : async (){
        messages := List.push(text, messages);
    };

    

    
    public shared query func posts(s : Int) : async [Message]{
    
        List.toArray(messages);
        
    };

    public shared func timeline() : async [Message]{
        
        var all : List.List<Message> = List.nil();

        for (id in Iter.fromList(followed)){
            let canister : Microblog = actor(Principal.toText(id));
            let s : Int = 5;
            let msgs = await canister.posts(s);
            for (msg in Iter.fromArray(msgs)){
                all := List.push(msg, all);
            };
        };
        List.toArray(all);
    };
};