import Foundation
import CoreGraphics

/// Owns the visual side of one recording session: picks the app's adapter, runs a
/// `VisualObserver` over the call window, and on stop writes `visual_timeline.json`
/// and returns the speaker segments for the backend hand-off.
///
/// Strictly best-effort: if there's no adapter for the app, or the window can't be
/// captured, the session simply records audio-only — visuals never block or break
/// the proven audio path. `init?` returns nil when the app has no visual adapter.
@available(macOS 13.0, *)
final class VisualCapture {
    let app: CallDetector.DetectedApp
    private let adapter: any AppAdapter
    private let observer: VisualObserver

    init?(app: CallDetector.DetectedApp, bundleID: String, windowID: CGWindowID?, t0Host: Double) {
        guard let adapter = AdapterRegistry.adapter(for: app) else { return nil }
        self.app = app
        self.adapter = adapter
        self.observer = VisualObserver(bundleID: bundleID, windowID: windowID, adapter: adapter,
                                       t0Host: t0Host, fps: adapter.preferredFPS)
    }

    /// Start window capture. Throws if the window isn't capturable (no window yet,
    /// Screen Recording denied) — the caller catches and falls back to audio-only.
    func start() async throws {
        try await observer.start()
    }

    /// Stop and discard capture without writing anything (used when the session
    /// ends before capture was fully adopted).
    func cancel() async {
        _ = await observer.stop()
    }

    /// Clamp segment ends to the audio duration; drop any that become empty. Keeps
    /// `visual_timeline.json` internally consistent and never sends the backend a
    /// segment longer than the audio. (`duration <= 0` → passthrough.)
    static func clampSegments(_ segs: [VisualTimeline.Segment], to duration: Double) -> [VisualTimeline.Segment] {
        guard duration > 0 else { return segs }
        return segs.compactMap { s in
            let end = min(s.end, duration)
            guard end > s.start else { return nil }
            return .init(start: s.start, end: end, name: s.name, confidence: s.confidence, source: s.source)
        }
    }

    static func clampGaps(_ gaps: [VisualTimeline.Gap], to duration: Double) -> [VisualTimeline.Gap] {
        guard duration > 0 else { return gaps }
        return gaps.compactMap { g in
            let end = min(g.end, duration)
            guard end > g.start else { return nil }
            return .init(start: g.start, end: end, reason: g.reason)
        }
    }

    /// Stop capture, fold in the mic-VAD self spans, write `visual_timeline.json`
    /// into the session folder, and return the merged segments for `label-merge`.
    func finish(selfSpans: [VADSpan], selfName: String,
                sessionId: String, t0Unix: Double, durationSec: Double,
                folder: URL) async -> [VisualTimeline.Segment] {
        observer.addSelfSpans(selfSpans, selfName: selfName)
        let (rawSegments, rawGaps) = await observer.stop()

        // The observer stops slightly after audio fixes `durationSec`, so a trailing
        // gap/segment can run past it. Clamp ends so the JSON is internally consistent
        // (and we never hand the backend a segment longer than the audio).
        let segments = Self.clampSegments(rawSegments, to: durationSec)
        let gaps = Self.clampGaps(rawGaps, to: durationSec)

        let names = Set(segments.map { $0.name })
        let participants = names.sorted().map {
            VisualTimeline.Participant(name: $0, isSelf: $0 == selfName ? true : nil, aliases: nil)
        }
        let timeline = VisualTimeline(
            sessionId: sessionId, app: app.label, adapterVersion: adapter.adapterVersion,
            t0Unix: t0Unix, durationSec: durationSec, fpsSampled: adapter.preferredFPS,
            selfName: selfName, participants: participants, segments: segments, visualGaps: gaps)
        try? timeline.write(to: folder.appendingPathComponent("visual_timeline.json"))
        return segments
    }
}