// Notification categories and actions from docs/api.md, and what each action does. Allow, Deny
// and Reply run in the background against the gateway; tapping a notification opens its thread.

import Foundation
import UserNotifications

/// What a notification response asks for, parsed out of the payload.
enum NotificationCommand: Equatable, Sendable {
    case respond(hostId: String, threadId: String, requestId: String, decision: ApprovalDecision)
    case reply(hostId: String, threadId: String, text: String)
    case open(Route?)
    case none

    enum Action {
        static let allow = "allow"
        static let deny = "deny"
        static let reply = "reply"
        static let open = "open"
    }

    /// `userInfo` holds the custom keys `hostId`, `threadId` and, for approvals, `requestId`.
    init(actionIdentifier: String, userInfo: [AnyHashable: Any], text: String?) {
        // The gateway sends `threadId: ""` on host notifications, so empty means absent.
        func value(_ key: String) -> String? {
            (userInfo[key] as? String).flatMap { $0.isEmpty ? nil : $0 }
        }
        let hostId = value("hostId")
        let threadId = value("threadId")
        let requestId = value("requestId")
        let thread: Route? = if let hostId, let threadId { .thread(hostId: hostId, threadId: threadId) } else { nil }

        switch actionIdentifier {
        case Action.allow, Action.deny:
            guard let hostId, let threadId, let requestId else { self = .open(thread); return }
            self = .respond(
                hostId: hostId, threadId: threadId, requestId: requestId,
                decision: actionIdentifier == Action.allow ? .accept : .decline)
        case Action.reply:
            let text = text?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
            guard let hostId, let threadId, !text.isEmpty else { self = .open(thread); return }
            self = .reply(hostId: hostId, threadId: threadId, text: text)
        case UNNotificationDismissActionIdentifier:
            self = .none
        default:
            // The Open action, or a tap on the notification itself.
            self = .open(thread)
        }
    }
}

@MainActor
final class NotificationHandler: NSObject, UNUserNotificationCenterDelegate {
    static let shared = NotificationHandler()

    func install() {
        let center = UNUserNotificationCenter.current()
        center.delegate = self
        center.setNotificationCategories(Self.categories)
    }

    static var categories: Set<UNNotificationCategory> {
        typealias Action = NotificationCommand.Action
        let allow = UNNotificationAction(identifier: Action.allow, title: "Allow", options: [])
        let deny = UNNotificationAction(identifier: Action.deny, title: "Deny", options: [.destructive])
        let open = UNNotificationAction(identifier: Action.open, title: "Open", options: [.foreground])
        let reply = UNTextInputNotificationAction(
            identifier: Action.reply, title: "Reply", options: [],
            textInputButtonTitle: "Send", textInputPlaceholder: "Reply")

        func category(_ id: PushCategory, _ actions: [UNNotificationAction]) -> UNNotificationCategory {
            UNNotificationCategory(identifier: id.rawValue, actions: actions, intentIdentifiers: [], options: [])
        }
        return [
            category(.approval, [allow, deny]),
            category(.input, [open]),
            category(.finished, [reply, open]),
            category(.failed, [open]),
            category(.host, []),
            category(.test, []),
        ]
    }

    nonisolated func userNotificationCenter(
        _ center: UNUserNotificationCenter, willPresent notification: UNNotification
    ) async -> UNNotificationPresentationOptions {
        await AppModel.shared.notificationArrived()
        return [.banner, .list, .sound]
    }

    nonisolated func userNotificationCenter(
        _ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse
    ) async {
        let command = NotificationCommand(
            actionIdentifier: response.actionIdentifier,
            userInfo: response.notification.request.content.userInfo,
            text: (response as? UNTextInputNotificationResponse)?.userText)
        await run(command)
    }

    private func run(_ command: NotificationCommand) async {
        let model = AppModel.shared
        switch command {
        case .none:
            return
        case let .open(route):
            if let route { model.open(route) } else { model.path = [] }
            model.reloadComplication()
            await model.refreshFeed()
            return
        case let .respond(hostId, threadId, requestId, decision):
            guard model.mode != .unpaired else { return }
            await attempt("Couldn't answer") {
                try await model.api.respond(
                    hostId: hostId, threadId: threadId,
                    request: .decision(requestId: requestId, decision: decision))
            }
        case let .reply(hostId, threadId, text):
            guard model.mode != .unpaired else { return }
            await attempt("Couldn't send your reply") {
                try await model.api.sendMessage(hostId: hostId, threadId: threadId, text: text)
            }
        }
        model.reloadComplication()
        await model.refreshFeed()
    }

    /// Runs a background action. If it fails, says so with a local notification, since nothing is
    /// on screen.
    private func attempt(_ title: String, _ action: () async throws -> Void) async {
        do {
            try await action()
        } catch let error as GatewayError where error.isStale {
            return
        } catch {
            guard let message = AppModel.shared.message(for: error) else { return }
            let content = UNMutableNotificationContent()
            content.title = title
            content.body = message
            let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
            try? await UNUserNotificationCenter.current().add(request)
        }
    }
}