//
//  JellyfinQuickConnect.swift
//
//  Copyright 2026 Brendan Szymanski <hello@bscubed.dev>
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
//  SPDX-License-Identifier: GPL-3.0-or-later
//

/// Drives one Quick Connect pairing attempt as an async event stream.
///
/// Reach it through ``JellyfinService/quickConnect``. Iterating ``connect(pollInterval:maxPolls:)``
/// initiates the request, yields the code to show the user, then polls the server on the caller's
/// behalf until the request is approved from another signed-in client:
///
/// ```swift
/// for try await event in client.quickConnect.connect() {
///     switch event {
///     case let .polling(code: code):
///         showCode(code)
///     case let .authenticated(secret: secret):
///         let authentication = try await client.authenticateWithQuickConnect(secret: secret)
///         accessToken = authentication.accessToken
///     }
/// }
/// ```
///
/// The polling loop is a plain `Task` owned by the stream, cancelled from
/// `Continuation.onTermination` -- ending iteration (breaking out of the loop, or the enclosing
/// `.task` being cancelled on unmount) stops the polling task with it. Nothing keeps requesting
/// once nobody is listening.
package struct JellyfinQuickConnect: Sendable {
    /// One step of a Quick Connect pairing attempt.
    package enum Event: Equatable, Sendable {
        /// The request was created; show the associated code to the user.
        case polling(code: String)
        /// The request was approved from another client; redeem the secret for a token via
        /// ``JellyfinService/authenticateWithQuickConnect(secret:)``.
        case authenticated(secret: String)
    }

    private let service: any JellyfinService

    /// Wraps a service for Quick Connect.
    ///
    /// - Parameter service: The service to initiate and poll through. Use
    ///   ``JellyfinService/quickConnect`` instead of calling this directly.
    init(service: any JellyfinService) {
        self.service = service
    }

    /// Starts a Quick Connect pairing attempt when iterated.
    ///
    /// - Parameters:
    ///   - pollInterval: Time between polls. Defaults to five seconds, matching Jellyfin's web
    ///     client.
    ///   - maxPolls: The maximum number of polls before giving up. Defaults to 200, about sixteen
    ///     minutes at the default interval.
    /// - Returns: A stream of one ``Event/polling(code:)`` followed by at most one
    ///   ``Event/authenticated(secret:)``. The stream throws ``JellyfinClientError/notFound`` if
    ///   the server expires the request first, or ``JellyfinClientError/quickConnectTimedOut`` if
    ///   `maxPolls` is exhausted without an answer either way.
    package func connect(
        pollInterval: Duration = .seconds(5),
        maxPolls: Int = 200
    ) -> AsyncThrowingStream<Event, Error> {
        precondition(pollInterval > .zero, "Poll interval must be positive")
        precondition(maxPolls > 0, "Maximum poll count must be positive")

        return AsyncThrowingStream { continuation in
            let task = Task {
                do {
                    try await run(pollInterval: pollInterval, maxPolls: maxPolls, into: continuation)
                    continuation.finish()
                } catch is CancellationError {
                    continuation.finish()
                } catch {
                    continuation.finish(throwing: error)
                }
            }

            continuation.onTermination = { _ in task.cancel() }
        }
    }

    /// Initiates the request, yields its code, then polls until it is approved or exhausted.
    ///
    /// - Throws: ``JellyfinClientError/missingPayload(operation:)`` if the server omitted the
    ///   secret or code, whatever ``JellyfinService/quickConnectState(secret:)`` throws (notably
    ///   ``JellyfinClientError/notFound`` once the server expires the request), or
    ///   ``JellyfinClientError/quickConnectTimedOut`` after `maxPolls` unanswered polls.
    private func run(
        pollInterval: Duration,
        maxPolls: Int,
        into continuation: AsyncThrowingStream<Event, Error>.Continuation
    ) async throws {
        let state = try await service.initiateQuickConnect()
        guard let secret = state.secret, let code = state.code else {
            throw JellyfinClientError.missingPayload(operation: "InitiateQuickConnect")
        }

        continuation.yield(.polling(code: code))

        for _ in 0..<maxPolls {
            try Task.checkCancellation()

            if try await service.quickConnectState(secret: secret).authenticated == true {
                continuation.yield(.authenticated(secret: secret))
                return
            }

            try await Task.sleep(for: pollInterval)
        }

        throw JellyfinClientError.quickConnectTimedOut
    }
}