// ── Crash Reporter ────────────────────────────────────────────
// MetricKit-based crash and performance reporting for TestFlight/Production

import Foundation
import MetricKit

@MainActor
final class CrashReporter: NSObject, ObservableObject, MXMetricManagerSubscriber {
    static let shared = CrashReporter()

    @Published var lastCrashReport: Date?
    @Published var diagnosticCount: Int = 0

    private let persistenceKey = "chronomind-crash-reports"

    override private init() {
        super.init()
        MXMetricManager.shared.add(self)
        loadStats()
    }

    deinit {
        MXMetricManager.shared.remove(self)
    }

    // MARK: - MXMetricManagerSubscriber

    nonisolated func didReceive(_ payloads: [MXMetricPayload]) {
        // MetricKit delivers daily aggregated metrics
        Task { @MainActor in
            for payload in payloads {
                processMetricPayload(payload)
            }
        }
    }

    nonisolated func didReceive(_ payloads: [MXDiagnosticPayload]) {
        // Crash diagnostics — delivered after app restart following crash
        Task { @MainActor in
            for payload in payloads {
                processDiagnosticPayload(payload)
            }
            self.diagnosticCount += payloads.count
            self.lastCrashReport = Date()
            self.saveStats()
        }
    }

    // MARK: - Processing

    private func processMetricPayload(_ payload: MXMetricPayload) {
        // Log key performance metrics
        if let launchTime = payload.applicationLaunchMetrics {
            let resumeTime = launchTime.histogrammedResumeTime
            logMetric("app_resume_time", histogram: resumeTime)
        }

        if let responsiveness = payload.applicationResponsivenessMetrics {
            let hangTime = responsiveness.histogrammedApplicationHangTime
            logMetric("hang_time", histogram: hangTime)
        }
    }

    private func processDiagnosticPayload(_ payload: MXDiagnosticPayload) {
        // Store crash data locally for feedback form
        if let crashDiagnostics = payload.crashDiagnostics {
            for crash in crashDiagnostics {
                let report = CrashReport(
                    date: Date(),
                    exceptionType: crash.exceptionType?.description,
                    signal: crash.signal?.description,
                    terminationReason: crash.terminationReason?.description,
                    callStackTree: crash.callStackTree.jsonRepresentation()
                )
                storeCrashReport(report)
            }
        }

        if let hangDiagnostics = payload.hangDiagnostics {
            for hang in hangDiagnostics {
                let report = CrashReport(
                    date: Date(),
                    exceptionType: nil,
                    signal: nil,
                    terminationReason: "Hang: \(hang.hangDuration.description)",
                    callStackTree: hang.callStackTree.jsonRepresentation()
                )
                storeCrashReport(report)
            }
        }
    }

    // MARK: - Storage

    private func storeCrashReport(_ report: CrashReport) {
        var reports = loadCrashReports()
        reports.append(report)
        // Keep last 50 reports
        if reports.count > 50 {
            reports = Array(reports.suffix(50))
        }
        if let data = try? JSONEncoder().encode(reports) {
            UserDefaults.standard.set(data, forKey: persistenceKey)
        }
    }

    func loadCrashReports() -> [CrashReport] {
        guard let data = UserDefaults.standard.data(forKey: persistenceKey),
              let reports = try? JSONDecoder().decode([CrashReport].self, from: data) else {
            return []
        }
        return reports
    }

    func clearReports() {
        UserDefaults.standard.removeObject(forKey: persistenceKey)
        diagnosticCount = 0
    }

    private func loadStats() {
        diagnosticCount = loadCrashReports().count
    }

    private func saveStats() {
        // Stats are derived from stored reports
    }

    private func logMetric(_ name: String, histogram: MXHistogram<UnitDuration>) {
        // In production, send to analytics service
        // For now, just track locally
    }
}

// MARK: - Crash Report Model

struct CrashReport: Codable, Identifiable {
    let id: String
    let date: Date
    let exceptionType: String?
    let signal: String?
    let terminationReason: String?
    let callStackData: Data?

    init(date: Date, exceptionType: String?, signal: String?, terminationReason: String?, callStackTree: Data) {
        self.id = UUID().uuidString
        self.date = date
        self.exceptionType = exceptionType
        self.signal = signal
        self.terminationReason = terminationReason
        self.callStackData = callStackTree
    }
}