//Made by Lumaa

import Combine
import Foundation
import Observation
import os
import SwiftUI

@Observable
public final class Client: Equatable, Identifiable, Hashable {
    public static func == (lhs: Client, rhs: Client) -> Bool {
        let lhsToken = lhs.critical.withLock { $0.oauthToken }
        let rhsToken = rhs.critical.withLock { $0.oauthToken }
        
        return (lhsToken != nil) == (rhsToken != nil) &&
        lhs.server == rhs.server &&
        lhsToken?.accessToken == rhsToken?.accessToken
    }
    
    public enum Version: String, Sendable {
        case v1, v2
    }
    
    public enum ClientError: Error {
        case unexpectedRequest
    }
    
    public enum OauthError: Error {
        case missingApp
        case invalidRedirectURL
    }
    
    public var id: String {
        critical.withLock {
            let isAuth = $0.oauthToken != nil
            return "\(isAuth)\(server)\($0.oauthToken?.createdAt ?? 0)"
        }
    }
    
    public func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
    
    public let server: String
    public let version: Version
    private let urlSession: URLSession
    private let decoder = JSONDecoder()
    
    // Putting all mutable state inside an `OSAllocatedUnfairLock` makes `Client`
    // provably `Sendable`. The lock is a struct, but it uses a `ManagedBuffer`
    // reference type to hold its associated state.
    private let critical: OSAllocatedUnfairLock<Critical>
    private struct Critical: Sendable {
        /// Only used as a transitionary app while in the oauth flow.
        var oauthApp: InstanceApp?
        var oauthToken: OauthToken?
        var connections: Set<String> = []
    }
    
    public var isAuth: Bool {
        critical.withLock { $0.oauthToken != nil }
    }
    
    public var connections: Set<String> {
        critical.withLock { $0.connections }
    }
    
    public init(server: String, version: Version = .v1, oauthToken: OauthToken? = nil) {
        self.server = server
        self.version = version
        critical = .init(initialState: Critical(oauthToken: oauthToken, connections: [server]))
        urlSession = URLSession.shared
        decoder.keyDecodingStrategy = .convertFromSnakeCase
    }
    
    public func addConnections(_ connections: [String]) {
        critical.withLock {
            $0.connections.formUnion(connections)
        }
    }
    
    public func hasConnection(with url: URL) -> Bool {
        guard let host = url.host else { return false }
        return critical.withLock {
            if let rootHost = host.split(separator: ".", maxSplits: 1).last {
                // Sometimes the connection is with the root host instead of a subdomain
                // eg. Mastodon runs on mastdon.domain.com but the connection is with domain.com
                $0.connections.contains(host) || $0.connections.contains(String(rootHost))
            } else {
                $0.connections.contains(host)
            }
        }
    }
    
    private func makeURL(scheme: String = "https",
                         endpoint: Endpoint,
                         forceVersion: Version? = nil,
                         forceServer: String? = nil) throws -> URL
    {
        var components = URLComponents()
        components.scheme = scheme
        components.host = forceServer ?? server
        if type(of: endpoint) == Oauth.self {
            components.path += "/\(endpoint.path())"
        } else {
            components.path += "/api/\(forceVersion?.rawValue ?? version.rawValue)/\(endpoint.path())"
        }
        components.queryItems = endpoint.queryItems()
        guard let url = components.url else {
            throw ClientError.unexpectedRequest
        }
        return url
    }
    
    private func makeURLRequest(url: URL, endpoint: Endpoint, httpMethod: String) -> URLRequest {
        var request = URLRequest(url: url)
        request.httpMethod = httpMethod
        if let oauthToken = critical.withLock({ $0.oauthToken }) {
            request.setValue("Bearer \(oauthToken.accessToken)", forHTTPHeaderField: "Authorization")
        }
        if let json = endpoint.jsonValue {
            let encoder = JSONEncoder()
            encoder.keyEncodingStrategy = .convertToSnakeCase
            encoder.outputFormatting = .sortedKeys
            do {
                let jsonData = try encoder.encode(json)
                request.httpBody = jsonData
                request.setValue("application/json", forHTTPHeaderField: "Content-Type")
            } catch {
                print("Client Error encoding JSON: \(error.localizedDescription)")
            }
        }
        return request
    }
    
    private func makeGet(endpoint: Endpoint) throws -> URLRequest {
        let url = try makeURL(endpoint: endpoint)
        return makeURLRequest(url: url, endpoint: endpoint, httpMethod: "GET")
    }
    
    public func get<Entity: Decodable>(endpoint: Endpoint, forceVersion: Version? = nil) async throws -> Entity {
        try await makeEntityRequest(endpoint: endpoint, method: "GET", forceVersion: forceVersion)
    }
    
    public func getWithLink<Entity: Decodable>(endpoint: Endpoint) async throws -> (Entity, LinkHandler?) {
        let (data, httpResponse) = try await urlSession.data(for: makeGet(endpoint: endpoint))
        var linkHandler: LinkHandler?
        if let response = httpResponse as? HTTPURLResponse,
           let link = response.allHeaderFields["Link"] as? String
        {
            linkHandler = .init(rawLink: link)
        }
        logResponseOnError(httpResponse: httpResponse, data: data)
        return try (decoder.decode(Entity.self, from: data), linkHandler)
    }
    
    public func post<Entity: Decodable>(endpoint: Endpoint, forceVersion: Version? = nil) async throws -> Entity {
        try await makeEntityRequest(endpoint: endpoint, method: "POST", forceVersion: forceVersion)
    }
    
    public func post(endpoint: Endpoint, forceVersion: Version? = nil) async throws -> HTTPURLResponse? {
        let url = try makeURL(endpoint: endpoint, forceVersion: forceVersion)
        let request = makeURLRequest(url: url, endpoint: endpoint, httpMethod: "POST")
        let (_, httpResponse) = try await urlSession.data(for: request)
        return httpResponse as? HTTPURLResponse
    }
    
    public func patch(endpoint: Endpoint) async throws -> HTTPURLResponse? {
        let url = try makeURL(endpoint: endpoint)
        let request = makeURLRequest(url: url, endpoint: endpoint, httpMethod: "PATCH")
        let (_, httpResponse) = try await urlSession.data(for: request)
        return httpResponse as? HTTPURLResponse
    }
    
    public func put<Entity: Decodable>(endpoint: Endpoint, forceVersion: Version? = nil) async throws -> Entity {
        try await makeEntityRequest(endpoint: endpoint, method: "PUT", forceVersion: forceVersion)
    }
    
    public func delete(endpoint: Endpoint, forceVersion: Version? = nil) async throws -> HTTPURLResponse? {
        let url = try makeURL(endpoint: endpoint, forceVersion: forceVersion)
        let request = makeURLRequest(url: url, endpoint: endpoint, httpMethod: "DELETE")
        let (_, httpResponse) = try await urlSession.data(for: request)
        return httpResponse as? HTTPURLResponse
    }
    
    private func makeEntityRequest<Entity: Decodable>(endpoint: Endpoint,
                                                      method: String,
                                                      forceVersion: Version? = nil) async throws -> Entity
    {
        let url = try makeURL(endpoint: endpoint, forceVersion: forceVersion)
        let request = makeURLRequest(url: url, endpoint: endpoint, httpMethod: method)
        let (data, httpResponse) = try await urlSession.data(for: request)
        logResponseOnError(httpResponse: httpResponse, data: data)
        do {
            return try decoder.decode(Entity.self, from: data)
        } catch {
            print(error)
            if var serverError = try? decoder.decode(ServerError.self, from: data) {
                if let httpResponse = httpResponse as? HTTPURLResponse {
                    serverError.httpCode = httpResponse.statusCode
                }
                throw serverError
            }
            throw error
        }
    }
    
    public func oauthURL() async throws -> URL {
        let app: InstanceApp = try await post(endpoint: Apps.registerApp)
        critical.withLock { $0.oauthApp = app }
        return try makeURL(endpoint: Oauth.authorize(clientId: app.clientId))
    }
    
    public func continueOauthFlow(url: URL) async throws -> OauthToken {
        guard let app = critical.withLock({ $0.oauthApp }) else {
            throw OauthError.missingApp
        }
        guard let components = URLComponents(url: url, resolvingAgainstBaseURL: false),
              let code = components.queryItems?.first(where: { $0.name == "code" })?.value
        else {
            throw OauthError.invalidRedirectURL
        }
        let token: OauthToken = try await post(endpoint: Oauth.token(code: code,
                                                                     clientId: app.clientId,
                                                                     clientSecret: app.clientSecret))
        critical.withLock { $0.oauthToken = token }
        return token
    }
    
    public func makeWebSocketTask(endpoint: Endpoint, instanceStreamingURL: URL?) throws -> URLSessionWebSocketTask {
        let url = try makeURL(scheme: "wss", endpoint: endpoint, forceServer: instanceStreamingURL?.host)
        var subprotocols: [String] = []
        if let oauthToken = critical.withLock({ $0.oauthToken }) {
            subprotocols.append(oauthToken.accessToken)
        }
        return urlSession.webSocketTask(with: url, protocols: subprotocols)
    }
    
    public func mediaUpload<Entity: Decodable>(endpoint: Endpoint,
                                               version: Version,
                                               method: String,
                                               mimeType: String,
                                               filename: String,
                                               data: Data) async throws -> Entity
    {
        let url = try makeURL(endpoint: endpoint, forceVersion: version)
        var request = makeURLRequest(url: url, endpoint: endpoint, httpMethod: method)
        let boundary = UUID().uuidString
        request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
        let httpBody = NSMutableData()
        httpBody.append("--\(boundary)\r\n".data(using: .utf8)!)
        httpBody.append("Content-Disposition: form-data; name=\"\(filename)\"; filename=\"\(filename)\"\r\n".data(using: .utf8)!)
        httpBody.append("Content-Type: \(mimeType)\r\n".data(using: .utf8)!)
        httpBody.append("\r\n".data(using: .utf8)!)
        httpBody.append(data)
        httpBody.append("\r\n--\(boundary)--\r\n".data(using: .utf8)!)
        request.httpBody = httpBody as Data
        let (data, httpResponse) = try await urlSession.data(for: request)
        logResponseOnError(httpResponse: httpResponse, data: data)
        do {
            return try decoder.decode(Entity.self, from: data)
        } catch {
            if let serverError = try? decoder.decode(ServerError.self, from: data) {
                throw serverError
            }
            throw error
        }
    }
    
    private func logResponseOnError(httpResponse: URLResponse, data: Data) {
        if let httpResponse = httpResponse as? HTTPURLResponse, httpResponse.statusCode > 299 {
            print(httpResponse)
            print(String(data: data, encoding: .utf8) ?? "")
        }
    }
}

extension Client: Sendable {}