Get the first 250 or 1000 followers of a user on bilibili

fetchBilibiliFollowers.swift

let id: Int = /*Replace with your bilibili user id*/
// You can simply copy paste the entire cookie, but the following is the minimum:
// If id is different from DedeUserID (i.e. you don't own such account), this doesn't matter
let cookie = "DedeUserID=XXXX;DedeUserID__ckMd5=XXXXXXXXXXXXXXXX;SESSDATA=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX;"

///////////////////////////////////////
//              Code                 //
///////////////////////////////////////

import Foundation

struct User: Codable {
    let mid: Int
    let uname: String
}

struct Wrapper: Codable {
    let data: Data
    struct Data: Codable {
        let list: [User]
        let total: Int
    }
}

func fetchFollowersOfUser(
    _ id: Int = id, page: Int, pageSize: Int = 50, 
    then process: @escaping (_ total: Int, _ list: [User]) -> Void
) {
    let url = URL(string: "http://api.bilibili.com/x/relation/followers?vmid=\(id)&pn=\(page)&ps=\(pageSize)")
    var request = URLRequest(url: url!)
    request.addValue(cookie, forHTTPHeaderField: "Cookie")
    URLSession.shared.dataTask(with: request) { (data, _, error) in
        guard let data = data else { fatalError(error?.localizedDescription ?? "Failed") }
        do {
            let wrapped = try JSONDecoder().decode(Wrapper.self, from: data)
            process(wrapped.data.total, wrapped.data.list)
        } catch {
            print(String(data: data, encoding: .utf8)!)
            process(0, [])
        }
    }.resume()
}

var allFollowers = [User]()
var page = 1

func run() {
    fetchFollowersOfUser(page: page) { (total, list) in
        if list.count == 50 {
            allFollowers += list
            page += 1
            print("\(allFollowers.count)/\(total)")
            run()
        } else {
            try! allFollowers.sorted {
                $0.mid < $1.mid		
            }.reduce("") {
                "\($0)\($1.mid) \($1.uname)\n"
            }.write(toFile: "\(id).txt", atomically: true, encoding: .utf8)
            exit(0)
        }
    }
}

run()

RunLoop.current.run()