import Foundation
import Observation

/// Runs podcast generation (generate → poll → download) **off** the player, so a
/// new episode can be produced in the background while another one keeps playing.
/// The finished audio is written to the on-disk cache and recorded in
/// `PodcastIndex`; the optional `onReady` callback lets a caller start playback
/// only when nothing else is playing.
@Observable
@MainActor
final class PodcastGenerationManager {
    struct Job: Identifiable {
        let id: String          // articleUrl
        var articleUrl: String
        var title: String
        var progress: Double    // 0…1
        var label: String
        var failed: Bool = false
        var error: String?
    }

    private(set) var jobs: [Job] = []

    private var tasks: [String: Task<Void, Never>] = [:]
    private let claude = ClaudeService()

    /// Jobs still working (not failed). Drives the "Generating…" banner.
    var activeJobs: [Job] { jobs.filter { !$0.failed } }
    var hasActive: Bool { !activeJobs.isEmpty }

    func isGenerating(_ articleUrl: String) -> Bool { tasks[articleUrl] != nil }
    func job(for articleUrl: String) -> Job? { jobs.first { $0.articleUrl == articleUrl } }

    /// Enqueue a background generation for `articleUrl`. Idempotent per URL.
    /// If audio is already cached, `onReady` fires immediately and nothing runs.
    /// `onReady` is invoked on the main actor once audio is available.
    func enqueue(articleUrl: String,
                 title: String,
                 parentBookmarkUrl: String? = nil,
                 onReady: ((URL, String) -> Void)? = nil) {
        let cached = ClaudeService.cachedPodcastURL(for: articleUrl)
        if FileManager.default.fileExists(atPath: cached.path) {
            onReady?(cached, title)
            return
        }
        if tasks[articleUrl] != nil { return }   // already in flight

        jobs.insert(Job(id: articleUrl, articleUrl: articleUrl, title: title,
                        progress: 0, label: "Starting…"), at: 0)
        Analytics.track("podcast.bg_started", ["url": articleUrl])

        let task = Task { [weak self] in
            guard let self else { return }
            do {
                let jobId = try await claude.generatePodcast(url: articleUrl)
                while !Task.isCancelled {
                    let status = try await claude.podcastStatus(jobId: jobId)
                    update(articleUrl) {
                        $0.progress = Double(status.progress) / 100
                        $0.label = PodcastPlayerViewModel.statusLabel(status.status)
                    }
                    if status.isDone {
                        update(articleUrl) { $0.label = "Preparing audio…"; $0.progress = 1 }
                        let url = try await claude.downloadPodcastAudio(
                            jobId: jobId, articleUrl: articleUrl,
                            title: status.title, parentBookmarkUrl: parentBookmarkUrl)
                        let finalTitle = status.title ?? title
                        finish(articleUrl)
                        Analytics.track("podcast.bg_completed", ["url": articleUrl])
                        onReady?(url, finalTitle)
                        return
                    }
                    if status.isFailed {
                        fail(articleUrl, status.error ?? "Generation failed")
                        return
                    }
                    try await Task.sleep(for: .seconds(3))
                }
            } catch is CancellationError {
                finish(articleUrl)
            } catch {
                fail(articleUrl, error.localizedDescription)
            }
        }
        tasks[articleUrl] = task
    }

    /// Cancel an in-flight job and drop it from the list.
    func cancel(_ articleUrl: String) {
        tasks[articleUrl]?.cancel()
        tasks[articleUrl] = nil
        jobs.removeAll { $0.articleUrl == articleUrl }
    }

    func dismiss(_ articleUrl: String) { jobs.removeAll { $0.articleUrl == articleUrl } }

    // MARK: - Mutations

    private func update(_ url: String, _ mutate: (inout Job) -> Void) {
        guard let i = jobs.firstIndex(where: { $0.articleUrl == url }) else { return }
        mutate(&jobs[i])
    }

    private func finish(_ url: String) {
        tasks[url] = nil
        jobs.removeAll { $0.articleUrl == url }
    }

    private func fail(_ url: String, _ message: String) {
        tasks[url] = nil
        update(url) { $0.failed = true; $0.error = message; $0.label = message }
        Analytics.track("podcast.bg_failed", ["url": url, "error": message])
        // Failed jobs linger briefly so the user sees them, then self-clear.
        Task { [weak self] in
            try? await Task.sleep(for: .seconds(8))
            self?.dismiss(url)
        }
    }
}