import SpriteKit
import NetworkCityCore

/// Traffic of one class to/from one endpoint in a single tick.
struct ClassFlow {
    let cls: TrafficClass
    let inBytes: UInt64
    let outBytes: UInt64
}

/// One endpoint's traffic within a district for a single tick, split by class.
struct EndpointTraffic {
    let host: String
    let flows: [ClassFlow]
    var inBytes: UInt64 { flows.reduce(0) { $0 + $1.inBytes } }
    var outBytes: UInt64 { flows.reduce(0) { $0 + $1.outBytes } }
}

/// One org's traffic for a single tick, ready to render as a district.
struct DistrictTraffic {
    let key: String
    let title: String
    var subtitle: String
    var inBytes: UInt64
    var outBytes: UInt64
    var endpoints: [EndpointTraffic]
    var rttMs: Double? = nil   // measured round-trip time → distance from downtown
}

/// The city. Downtown (your Mac) glows at the origin; every org is a district
/// hub placed at a deterministic spot around it, connected by a road. Busy
/// districts fan out into their endpoints (hub-and-spoke); cars of light flow
/// the full path — cyan inbound for downloads, amber outbound for uploads.
final class CityScene: SKScene {

    private let cam = SKCameraNode()
    private let worldRadius: CGFloat = 540
    private var buildings: [String: BuildingNode] = [:]
    private var roads: [String: SKShapeNode] = [:]
    private var latencyRadius: [String: CGFloat] = [:]
    private var targetPos: [String: CGPoint] = [:]   // where each hub is heading
    private var ringKey: String?
    private let roadLayer = SKNode()
    private let carLayer = SKNode()
    private let buildingLayer = SKNode()

    // Auto-expand: an org's spokes stay open for a few ticks after it last
    // ranked among the busiest, giving a smooth tail instead of flicker.
    private let expansion = ExpansionPolicy()

    /// Number of districts currently on the map (for the HUD).
    var buildingCount: Int { buildings.count }

    /// Called with a district key when a hub is clicked, or nil when empty space
    /// is clicked (deselect).
    var onSelect: ((String?) -> Void)?
    /// Called when a district is demolished, so the controller can prune its state.
    var onReap: ((String) -> Void)?
    /// Demolish a district after this many idle ticks (~2s each). Env-tunable for testing.
    private let reapAfterTicks = Int(ProcessInfo.processInfo.environment["NC_REAP_TICKS"] ?? "") ?? 20
    private let selectionRing = SKShapeNode(circleOfRadius: 24)
    private var dragDistance: CGFloat = 0

    override func didMove(to view: SKView) {
        backgroundColor = Palette.background
        scaleMode = .resizeFill
        anchorPoint = CGPoint(x: 0.5, y: 0.5)

        drawGrid()
        addChild(roadLayer)
        addChild(carLayer)
        addChild(buildingLayer)
        addDowntown()

        selectionRing.strokeColor = .white
        selectionRing.lineWidth = 2
        selectionRing.glowWidth = 4
        selectionRing.alpha = 0
        selectionRing.zPosition = 40
        addChild(selectionRing)

        camera = cam
        cam.setScale(1.25)
        addChild(cam)
    }

    // MARK: - Selection

    /// Rings the selected district (or fades the ring out when nil).
    func highlight(key: String?) {
        ringKey = key
        selectionRing.removeAllActions()
        if let key, let building = buildings[key] {
            selectionRing.position = building.position
            selectionRing.alpha = 1
            selectionRing.run(.repeatForever(.sequence([
                .scale(to: 1.18, duration: 0.7), .scale(to: 1.0, duration: 0.7),
            ])))
        } else {
            selectionRing.run(.fadeOut(withDuration: 0.2))
        }
    }

    /// Nearest district hub within a (zoom-aware) radius of the point.
    private func districtKey(at point: CGPoint) -> String? {
        let radius = 30 * cam.xScale
        var best: (key: String, dist: CGFloat)?
        for (key, building) in buildings {
            let d = hypot(point.x - building.position.x, point.y - building.position.y)
            if d < radius, best == nil || d < best!.dist { best = (key, d) }
        }
        return best?.key
    }

    // MARK: - Static scenery

    private func drawGrid() {
        let grid = SKNode()
        let step: CGFloat = 80
        let extent: CGFloat = 1400
        let path = CGMutablePath()
        var x = -extent
        while x <= extent { path.move(to: CGPoint(x: x, y: -extent)); path.addLine(to: CGPoint(x: x, y: extent)); x += step }
        var y = -extent
        while y <= extent { path.move(to: CGPoint(x: -extent, y: y)); path.addLine(to: CGPoint(x: extent, y: y)); y += step }
        let line = SKShapeNode(path: path)
        line.strokeColor = Palette.grid.withAlphaComponent(0.18)
        line.lineWidth = 1
        grid.addChild(line)
        grid.zPosition = -100
        addChild(grid)
    }

    private func addDowntown() {
        let glow = SKSpriteNode(texture: Textures.softCircle)
        glow.color = Palette.hub
        glow.colorBlendFactor = 1
        glow.blendMode = .add
        glow.setScale(1.1)
        glow.zPosition = -10
        glow.run(.repeatForever(.sequence([
            .fadeAlpha(to: 0.6, duration: 1.8),
            .fadeAlpha(to: 1.0, duration: 1.8),
        ])))
        addChild(glow)

        let core = SKShapeNode(circleOfRadius: 9)
        core.fillColor = Palette.hub
        core.strokeColor = .white
        core.glowWidth = 2
        addChild(core)

        let label = SKLabelNode(text: "▸ this mac")
        label.fontName = "Menlo-Bold"
        label.fontSize = 13
        label.fontColor = Palette.hub
        label.verticalAlignmentMode = .top
        label.position = CGPoint(x: 0, y: -16)
        addChild(label)
    }

    // MARK: - Live data

    /// Render a tick of per-org traffic: ensure each district exists, decide
    /// which ones are busy enough to fan out, then dispatch cars accordingly.
    func apply(_ districts: [DistrictTraffic]) {
        // 0. Age every hub: decay its glow and count idle ticks. Active hubs
        //    reset below; dead ones get reaped at the end of the tick.
        for (_, hub) in buildings {
            hub.decay()
            hub.idleTicks += 1
        }

        // 1. Ensure hubs exist and learn their endpoints.
        for t in districts {
            let hub = building(forKey: t.key, title: t.title, subtitle: t.subtitle)
            hub.idleTicks = 0
            hub.note(activeHosts: t.endpoints.map(\.host))
            hub.receive(bytes: Double(t.inBytes + t.outBytes))
            if let rtt = t.rttMs { repositionToLatency(key: t.key, rttMs: rtt) }
        }

        // 2. Decide which districts fan out. Evaluate *every* known district
        //    (not just this tick's active ones) so a TTL tail keeps idle hubs
        //    open. A district needs ≥2 endpoints to have anything to expand.
        let bytesByKey = Dictionary(districts.map { ($0.key, $0.inBytes + $0.outBytes) },
                                    uniquingKeysWith: +)
        let entries = buildings.map { key, hub in
            ExpansionPolicy.District(key: key, bytes: bytesByKey[key] ?? 0, endpointCount: hub.knownHostCount)
        }
        let expanded = expansion.update(entries)

        if ProcessInfo.processInfo.environment["NC_DEBUG"] != nil {
            let top = districts.sorted { ($0.inBytes + $0.outBytes) > ($1.inBytes + $1.outBytes) }.prefix(3)
                .map { "\($0.title)=\(($0.inBytes + $0.outBytes) / 1024)KB/ep\(buildings[$0.key]?.knownHostCount ?? 0)/\(expanded.contains($0.key) ? "EXP" : "—")" }
                .joined(separator: "  ")
            var classKB: [TrafficClass: UInt64] = [:]
            for d in districts { for e in d.endpoints { for f in e.flows { classKB[f.cls, default: 0] += f.inBytes + f.outBytes } } }
            let mix = TrafficClass.allCases.compactMap { c in classKB[c].map { "\(c.rawValue):\($0 / 1024)KB" } }.joined(separator: " ")
            FileHandle.standardError.write(Data("[tick] \(top)  |  \(mix)\n".utf8))
        }

        // 3. Apply expansion state to all hubs, then route this tick's cars.
        for (key, hub) in buildings { hub.setExpanded(expanded.contains(key)) }

        for t in districts {
            guard let hub = buildings[t.key] else { continue }
            if expanded.contains(t.key) {
                // Per endpoint, per class: cars run the full Mac→hub→endpoint path.
                for e in t.endpoints {
                    let dest = hub.worldPosition(forEndpoint: e.host)
                    for f in e.flows {
                        dispatchSpokeCars(carCount(f.inBytes), hub: hub.position, endpoint: dest, inbound: true, cls: f.cls, bytes: f.inBytes)
                        dispatchSpokeCars(carCount(f.outBytes), hub: hub.position, endpoint: dest, inbound: false, cls: f.cls, bytes: f.outBytes)
                    }
                    if e.inBytes + e.outBytes > 0 { hub.pulseEndpoint(e.host) }
                }
            } else {
                // Collapsed: aggregate every endpoint's flows by class onto the hub.
                var byClass: [TrafficClass: (UInt64, UInt64)] = [:]
                for e in t.endpoints {
                    for f in e.flows {
                        let prior = byClass[f.cls] ?? (0, 0)
                        byClass[f.cls] = (prior.0 + f.inBytes, prior.1 + f.outBytes)
                    }
                }
                for (cls, bytes) in byClass {
                    dispatchDirectCars(carCount(bytes.0), to: hub.position, inbound: true, cls: cls, bytes: bytes.0)
                    dispatchDirectCars(carCount(bytes.1), to: hub.position, inbound: false, cls: cls, bytes: bytes.1)
                }
            }
        }

        // 4. Demolish districts that have been idle too long.
        for key in buildings.keys where (buildings[key]?.idleTicks ?? 0) > reapAfterTicks {
            reap(key)
        }
    }

    /// Fade out and remove a dead district, clearing all of its scene state.
    private func reap(_ key: String) {
        buildings[key]?.run(.sequence([.fadeOut(withDuration: 0.7), .removeFromParent()]))
        roads[key]?.run(.sequence([.fadeOut(withDuration: 0.7), .removeFromParent()]))
        buildings[key] = nil
        roads[key] = nil
        latencyRadius[key] = nil
        targetPos[key] = nil
        if ringKey == key { highlight(key: nil); onSelect?(nil) }
        onReap?(key)
        if ProcessInfo.processInfo.environment["NC_DEBUG"] != nil {
            FileHandle.standardError.write(Data("[reap] \(key)\n".utf8))
        }
    }

    private func carCount(_ bytes: UInt64) -> Int {
        guard bytes > 0 else { return 0 }
        return max(1, min(7, Int(Double(bytes) / 16_384)))   // ~1 car / 16 KB, capped
    }

    // MARK: - Buildings & roads

    private func building(forKey key: String, title: String, subtitle: String) -> BuildingNode {
        if let existing = buildings[key] {
            existing.update(subtitle: subtitle)
            return existing
        }

        let node = BuildingNode(title: title, subtitle: subtitle)
        node.position = placement(for: key, footprint: node.labelFootprint)
        targetPos[key] = node.position
        node.alpha = 0
        node.run(.fadeIn(withDuration: 0.6))
        buildingLayer.addChild(node)
        buildings[key] = node

        if ProcessInfo.processInfo.environment["NC_DEBUG"] != nil {
            let f = node.labelFootprint
            FileHandle.standardError.write(Data(String(format: "[place] %@ pos=(%.0f,%.0f) box=%.0fx%.0f\n",
                title, node.position.x, node.position.y, f.width, f.height).utf8))
        }

        let path = CGMutablePath()
        path.move(to: .zero)
        path.addLine(to: node.position)
        let road = SKShapeNode(path: path)
        road.strokeColor = Palette.road.withAlphaComponent(0.55)
        road.lineWidth = 1.5
        road.zPosition = -20
        roadLayer.addChild(road)
        roads[key] = road

        return node
    }

    /// Glide a hub to the radius implied by its measured RTT, keeping its angle.
    /// The road (and selection ring, if attached) follow.
    private func repositionToLatency(key: String, rttMs: Double) {
        guard let building = buildings[key] else { return }
        let target = LatencyLayout.radius(forRTT: rttMs)
        if let current = latencyRadius[key], abs(current - target) < 18 { return }
        latencyRadius[key] = target

        // Keep distance = latency, but rotate/nudge the (arbitrary) angle to
        // clear other labels — otherwise gliding hubs land on top of each other.
        let angle = atan2(building.position.y, building.position.x)
        let others = buildings.compactMap { (k, b) -> CGRect? in
            guard k != key else { return nil }
            let p = targetPos[k] ?? b.position
            return b.labelFootprint.offsetBy(dx: p.x, dy: p.y)
        }
        let dest = LayoutSolver.placeNonOverlapping(
            baseAngle: angle, baseRadius: Double(target),
            localRect: building.labelFootprint, existing: others, pad: 18
        )
        targetPos[key] = dest
        building.run(.move(to: dest, duration: 0.8))

        if let road = roads[key] {
            let path = CGMutablePath()
            path.move(to: .zero)
            path.addLine(to: dest)
            road.path = path
        }
        if ringKey == key { selectionRing.run(.move(to: dest, duration: 0.8)) }
    }

    /// Deterministic radial seed (angle + ring from the key's hash), then spiral
    /// out from there until the label box clears every existing district.
    private func placement(for key: String, footprint: CGRect) -> CGPoint {
        let h = stableHash(key)
        let baseAngle = Double(h % 3600) / 3600 * 2 * .pi
        let ring = Double((h >> 16) % 1000) / 1000
        let baseRadius = 165 + Double(ring) * Double(worldRadius - 165)

        let existing = buildings.map { (k, b) in
            let p = targetPos[k] ?? b.position
            return b.labelFootprint.offsetBy(dx: p.x, dy: p.y)
        }
        return LayoutSolver.placeNonOverlapping(
            baseAngle: baseAngle, baseRadius: baseRadius,
            localRect: footprint, existing: existing, pad: 18
        )
    }

    // MARK: - Cars

    private func dispatchDirectCars(_ count: Int, to dest: CGPoint, inbound: Bool, cls: TrafficClass, bytes: UInt64) {
        guard count > 0 else { return }
        let style = carStyle(cls, bytes: bytes)
        stagger(count) { [weak self] in
            guard let self else { return }
            let path = CGMutablePath()
            path.move(to: inbound ? dest : .zero)
            path.addLine(to: inbound ? .zero : dest)
            self.runCar(along: path, start: inbound ? dest : .zero, distance: hypot(dest.x, dest.y), style: style)
        }
    }

    private func dispatchSpokeCars(_ count: Int, hub: CGPoint, endpoint: CGPoint, inbound: Bool, cls: TrafficClass, bytes: UInt64) {
        guard count > 0 else { return }
        let style = carStyle(cls, bytes: bytes)
        stagger(count) { [weak self] in
            guard let self else { return }
            let path = CGMutablePath()
            if inbound {
                path.move(to: endpoint); path.addLine(to: hub); path.addLine(to: .zero)
            } else {
                path.move(to: .zero); path.addLine(to: hub); path.addLine(to: endpoint)
            }
            let dist = hypot(hub.x, hub.y) + hypot(endpoint.x - hub.x, endpoint.y - hub.y)
            self.runCar(along: path, start: inbound ? endpoint : .zero, distance: dist, style: style)
        }
    }

    /// Spreads `count` spawns across most of the interval so cars stream rather
    /// than appear all at once.
    private func stagger(_ count: Int, _ spawn: @escaping () -> Void) {
        guard count > 0 else { return }
        for i in 0..<count {
            let delay = Double(i) / Double(count) * 1.4
            run(.sequence([.wait(forDuration: delay), .run(spawn)]))
        }
    }

    private func runCar(along path: CGPath, start: CGPoint, distance: CGFloat, style: CarStyle) {
        let car = SKSpriteNode(texture: Textures.softCircle)
        car.color = style.color
        car.colorBlendFactor = 1
        car.blendMode = .add
        car.xScale = style.scale * style.elongation
        car.yScale = style.scale
        car.position = start
        car.zPosition = 5
        carLayer.addChild(car)

        let orient = style.elongation > 1.05   // streaks orient along their path
        let duration = Double((distance / style.speed).clamped(0.6, 2.8)) * Double.random(in: 0.85...1.15)
        car.run(.sequence([
            .group([
                .follow(path, asOffset: false, orientToPath: orient, duration: duration),
                .sequence([.fadeAlpha(to: 1.0, duration: duration * 0.15),
                           .wait(forDuration: duration * 0.55),
                           .fadeAlpha(to: 0.0, duration: duration * 0.3)]),
            ]),
            .removeFromParent(),
        ]))
    }

    // MARK: - Pan, zoom & click (macOS)

    override func scrollWheel(with event: NSEvent) {
        let factor = 1 - event.scrollingDeltaY * 0.006
        cam.setScale((cam.xScale * factor).clamped(0.45, 3.2))
    }

    override func mouseDown(with event: NSEvent) {
        dragDistance = 0
    }

    override func mouseDragged(with event: NSEvent) {
        dragDistance += abs(event.deltaX) + abs(event.deltaY)
        cam.position.x -= event.deltaX * cam.xScale
        cam.position.y += event.deltaY * cam.xScale
    }

    override func mouseUp(with event: NSEvent) {
        // A near-stationary press is a click (select); a drag is a pan.
        guard dragDistance < 6, let view else { return }
        // Canonical, camera-correct window → view → scene conversion.
        let viewPoint = view.convert(event.locationInWindow, from: nil)
        onSelect?(districtKey(at: convertPoint(fromView: viewPoint)))
    }
}