nucleic-remote-ios/NucleicRemote/NucleicRemote/LiveActivityManager.swift

import ActivityKit
import Foundation
import NucleicProtocol

/// Owns the one aggregate session Live Activity (UX_IOS §5.3): started when work exists,
/// updated as sessions change, ended when everything is idle or the device unpairs. State
/// flows in from `RemoteStore` on every session-list change; the widget extension renders it
/// (`SessionLiveActivity`).
@MainActor
final class LiveActivityManager {
    static let shared = LiveActivityManager()
    private init() {}

    /// How many sessions the detail rows show. The glance stays a glance — the counts and churn
    /// still summarize everything, this just bounds the per-session list.
    private static let maxLines = 3

    private var activity: Activity<NucleicSessionAttributes>?

    /// The last content we pushed. Updates that don't change it are skipped so we don't spend
    /// ActivityKit's update budget on no-ops — `sync` fires on every host message (dashboard,
    /// connectivity, pong, diff ticks…), most of which leave the aggregate identical. Burning the
    /// budget on those is exactly what makes a *real* change land late and the glance read stale.
    private var lastState: NucleicSessionAttributes.ContentState?
    /// The newest state waiting to be applied, and the single task draining it. Coalescing to the
    /// latest through one serial task means the newest data always wins — firing an unstructured
    /// `Task` per `sync` let a later update lose a race to an earlier one and freeze the glance.
    private var pendingState: NucleicSessionAttributes.ContentState?
    private var updateTask: Task<Void, Never>?

    /// Set by `RemoteStore` to ship the activity's APNS push token to the paired Macs (and to tell
    /// them it ended). The Macs use the token to keep this glance fresh over APNs while the phone
    /// is backgrounded and its sync socket is suspended (UX_IOS §5.3).
    var onPushToken: ((_ token: String, _ activityID: String) -> Void)?
    var onActivityEnded: ((_ activityID: String) -> Void)?
    /// Streams the activity's per-activity APNS update token (it can rotate); cancelled on end.
    private var tokenObservation: Task<Void, Never>?

    /// Reconcile the Activity with the current session set.
    func sync(hostName: String, sessions: [WireSessionSummary]) {
        guard ActivityAuthorizationInfo().areActivitiesEnabled else { return }
        let live = sessions.filter { !$0.archived }
        let running = live.filter { $0.status == .running || $0.status == .provisioning }
        let needsYou = live.filter { $0.status.needsYou($0.disposition) }

        guard !running.isEmpty || !needsYou.isEmpty else {
            end()
            return
        }

        // Everything in flight or waiting on the user, attention-first (approvals, then waiting
        // input, then running), freshest within a rank. This is both the detail-row source and
        // the set the aggregate churn/approval totals sum over.
        let active = live
            .filter {
                $0.status == .running || $0.status == .provisioning
                    || $0.status.needsYou($0.disposition)
            }
            .sorted { lhs, rhs in
                let l = StatusStyle.sortRank(lhs), r = StatusStyle.sortRank(rhs)
                return l == r ? lhs.updatedAt > rhs.updatedAt : l < r
            }

        let approvals = active.reduce(0) { $0 + $1.pendingApprovalCount }
        let files = active.reduce(0) { $0 + ($1.diffStat?.filesChanged ?? 0) }
        let added = active.reduce(0) { $0 + ($1.diffStat?.added ?? 0) }
        let removed = active.reduce(0) { $0 + ($1.diffStat?.removed ?? 0) }
        let lines = active.prefix(Self.maxLines).map(Self.line(for:))

        let state = NucleicSessionAttributes.ContentState(
            runningCount: running.count,
            needsYouCount: needsYou.count,
            approvalCount: approvals,
            filesChanged: files,
            linesAdded: added,
            linesRemoved: removed,
            lines: Array(lines))

        push(state, hostName: hostName)
    }

    /// Apply `state` to the Activity — deduped against the last push and coalesced through one
    /// serial task so the newest state always wins.
    private func push(_ state: NucleicSessionAttributes.ContentState, hostName: String) {
        guard state != lastState else { return }
        lastState = state

        guard let activity else {
            // Recover an Activity that survived an app relaunch before starting a new one; the
            // recovered one still needs the fresh state, so fall through to the update pipeline.
            if let existing = Activity<NucleicSessionAttributes>.activities.first {
                activity = existing
                observePushToken(existing)
                enqueue(state)
            } else {
                // `pushType: .token` opts the activity into APNs updates — the Macs push new
                // content-state to the token so the glance stays fresh while the phone is locked.
                let started = try? Activity.request(
                    attributes: NucleicSessionAttributes(hostName: hostName),
                    content: ActivityContent(state: state, staleDate: nil),
                    pushType: .token)
                activity = started
                if let started { observePushToken(started) }
            }
            return
        }
        enqueue(state)
    }

    /// Forward the activity's APNS update token (and its rotations) to `RemoteStore`.
    private func observePushToken(_ activity: Activity<NucleicSessionAttributes>) {
        tokenObservation?.cancel()
        tokenObservation = Task { [weak self] in
            for await tokenData in activity.pushTokenUpdates {
                let hex = tokenData.map { String(format: "%02x", $0) }.joined()
                self?.onPushToken?(hex, activity.id)
            }
        }
    }

    /// Hand the newest state to the serial drainer (starting it if idle).
    private func enqueue(_ state: NucleicSessionAttributes.ContentState) {
        pendingState = state
        guard updateTask == nil else { return }  // the running drainer will pick this up
        updateTask = Task { @MainActor [weak self] in
            guard let self else { return }
            while let next = self.pendingState {
                self.pendingState = nil
                await self.activity?.update(ActivityContent(state: next, staleDate: nil))
            }
            self.updateTask = nil
        }
    }

    /// End the Activity (all idle, or unpaired).
    func end() {
        updateTask?.cancel()
        updateTask = nil
        tokenObservation?.cancel()
        tokenObservation = nil
        pendingState = nil
        lastState = nil
        guard let activity else { return }
        self.activity = nil
        onActivityEnded?(activity.id)  // let the Macs stop pushing to this token
        Task {
            await activity.end(
                ActivityContent(state: activity.content.state, staleDate: nil),
                dismissalPolicy: .immediate)
        }
    }

    // MARK: - Projection

    /// Project a wire summary into the widget's self-contained row model.
    private static func line(for s: WireSessionSummary) -> NucleicSessionAttributes.SessionLine {
        NucleicSessionAttributes.SessionLine(
            id: s.sessionID.rawValue,
            title: s.title.isEmpty ? s.projectName : s.title,
            project: s.projectName,
            backend: backend(s.backend),
            kind: kind(for: s),
            detail: detail(for: s))
    }

    private static func kind(for s: WireSessionSummary) -> NucleicSessionAttributes.Kind {
        switch s.status {
        case .awaitingApproval: .approval
        case .running: .running
        case .provisioning: .provisioning
        case .awaitingInput: s.disposition == .completed ? .done : .needsInput
        case .idle: .idle
        case .finished: .done
        case .interrupted, .error: .error
        }
    }

    private static func backend(_ id: BackendID) -> NucleicSessionAttributes.Backend {
        switch id {
        case .claudeCode: .claude
        case .codex, .codexExec: .codex
        case .grok: .grok
        }
    }

    /// The compact right-aligned status for a row: the actionable ask wins (approvals, then
    /// "waiting on you"), else the worktree churn, else what the agent is up to.
    private static func detail(for s: WireSessionSummary) -> String {
        if s.status == .awaitingApproval || s.pendingApprovalCount > 0 {
            let n = max(s.pendingApprovalCount, 1)
            return "\(n) to approve"
        }
        if s.status == .awaitingInput, s.disposition != .completed {
            return "Waiting on you"
        }
        if let d = s.diffStat, d.filesChanged > 0 {
            return "\(d.filesChanged) file\(d.filesChanged == 1 ? "" : "s")  +\(d.added) −\(d.removed)"
        }
        switch s.status {
        case .provisioning: return "Starting…"
        case .running: return "Working…"
        case .awaitingInput: return "Done"
        default: return StatusStyle.label(s.status, disposition: s.disposition)
        }
    }
}