import CoreGraphics
import Foundation
import MusubiCore
import NDIKit

/// Appends one CSV line per output and minute to ~/Library/Logs/Musubi/stats-<date>.csv (for long-run tests).
@MainActor
final class StatsRecorder {
    private let interval: TimeInterval = 60
    private var lastWrite = Date()
    private var lastCPU = StatsRecorder.cpuTime()
    private var lastReceived: [CGDirectDisplayID: Int64] = [:]
    private let directory = FileManager.default.homeDirectoryForCurrentUser.appending(path: "Library/Logs/Musubi")

    private static let header = "time,display,refresh_hz,source,state,width,height,source_fps,shown_fps,received,missing,dropped_by_ndi,loss_rate,cpu_percent\n"

    func recordIfDue(outputs: [ActiveOutput], screens: [ScreenInfo]) {
        let now = Date()
        let elapsed = now.timeIntervalSince(lastWrite)
        guard elapsed >= interval else { return }

        let cpu = Self.cpuTime()
        let cpuPercent = (cpu - lastCPU) / elapsed * 100
        lastCPU = cpu
        lastWrite = now
        guard !outputs.isEmpty else { return }

        let time = now.ISO8601Format()
        var lines = ""
        for output in outputs {
            let s = output.snapshot
            let previous = lastReceived[output.displayID] ?? s.stats.received
            lastReceived[output.displayID] = s.stats.received
            let shownFPS = Double(s.stats.received - previous) / elapsed
            let refresh = screens.first { $0.id == output.displayID }?.refreshRate ?? 0
            let state: String = switch s.state {
            case .connecting: "connecting"
            case .live: "live"
            case .stalled: "stalled"
            }
            let name = output.source.ndiName.replacingOccurrences(of: "\"", with: "'")
            lines += "\(time),\(output.displayID),\(refresh),\"\(name)\",\(state),\(s.width),\(s.height),"
            lines += String(format: "%.2f,%.2f,%lld,%lld,%lld,%.6f,%.1f\n",
                            s.frameRate, shownFPS, s.stats.received, s.stats.missing, s.stats.droppedByReceiver,
                            s.stats.lossRate, cpuPercent)
        }
        append(lines, date: now)
    }

    private func append(_ text: String, date: Date) {
        let day = date.formatted(.iso8601.year().month().day())
        let file = directory.appending(path: "stats-\(day).csv")
        do {
            try FileManager.default.createDirectory(at: directory, withIntermediateDirectories: true)
            if !FileManager.default.fileExists(atPath: file.path) {
                try Self.header.write(to: file, atomically: true, encoding: .utf8)
            }
            let handle = try FileHandle(forWritingTo: file)
            defer { try? handle.close() }
            try handle.seekToEnd()
            try handle.write(contentsOf: Data(text.utf8))
        } catch {
            Log.ndi.error("Stats CSV: \(error.localizedDescription, privacy: .public)")
        }
    }

    /// User + system CPU seconds of this process.
    private static func cpuTime() -> Double {
        var usage = rusage()
        getrusage(RUSAGE_SELF, &usage)
        func seconds(_ t: timeval) -> Double { Double(t.tv_sec) + Double(t.tv_usec) / 1_000_000 }
        return seconds(usage.ru_utime) + seconds(usage.ru_stime)
    }
}