import AppKit
import Foundation
import PostHog

@MainActor
final class PostHogAnalytics {
    static let shared = PostHogAnalytics()

    // The PostHog project API key is intentionally embedded in the app (it's a public key).
    private let apiKey = "phc_opOVu7oFzR9wD3I6ZahFGOV2h3mqGpl5EHyQvmHciDP"

    // PostHog Cloud US default (matches other cmux properties).
    private let host = "https://us.i.posthog.com"

    private let lastActiveDayUTCKey = "posthog.lastActiveDayUTC"
    private let lastActiveHourUTCKey = "posthog.lastActiveHourUTC"

    private var didStart = false
    private var activeCheckTimer: Timer?

    private var isEnabled: Bool {
#if DEBUG
        // Avoid polluting production analytics while iterating locally.
        return ProcessInfo.processInfo.environment["CMUX_POSTHOG_ENABLE"] == "1"
#else
        return !apiKey.isEmpty && apiKey != "REPLACE_WITH_POSTHOG_PUBLIC_KEY"
#endif
    }

    func startIfNeeded() {
        guard !didStart else { return }
        guard isEnabled else { return }

        let config = PostHogConfig(apiKey: apiKey, host: host)
        config.captureApplicationLifecycleEvents = false
        config.captureScreenViews = false
#if DEBUG
        config.debug = ProcessInfo.processInfo.environment["CMUX_POSTHOG_DEBUG"] == "1"
#endif

        PostHogSDK.shared.setup(config)

        // Tag every event so PostHog can distinguish desktop from web and
        // break events down by released app version/build.
        PostHogSDK.shared.register(Self.superProperties(infoDictionary: Bundle.main.infoDictionary ?? [:]))

        // The SDK automatically generates and persists an anonymous distinct ID.

        didStart = true

        // If the app stays in the foreground across midnight, `applicationDidBecomeActive`
        // won't fire again, so a periodic check avoids undercounting those users.
        activeCheckTimer?.invalidate()
        activeCheckTimer = Timer.scheduledTimer(withTimeInterval: 30 * 60, repeats: true) { [weak self] _ in
            guard let self else { return }
            guard NSApp.isActive else { return }
            self.trackDailyActive(reason: "activeTimer")
            self.trackHourlyActive(reason: "activeTimer")
        }
    }

    func trackDailyActive(reason: String) {
        startIfNeeded()
        guard didStart else { return }

        let today = utcDayString(Date())
        let defaults = UserDefaults.standard
        if defaults.string(forKey: lastActiveDayUTCKey) == today {
            return
        }

        defaults.set(today, forKey: lastActiveDayUTCKey)

        PostHogSDK.shared.capture(
            "cmux_daily_active",
            properties: Self.dailyActiveProperties(
                dayUTC: today,
                reason: reason,
                infoDictionary: Bundle.main.infoDictionary ?? [:]
            )
        )

        // For DAU we care more about delivery than batching.
        PostHogSDK.shared.flush()
    }

    func trackHourlyActive(reason: String) {
        startIfNeeded()
        guard didStart else { return }

        let hour = utcHourString(Date())
        let defaults = UserDefaults.standard
        if defaults.string(forKey: lastActiveHourUTCKey) == hour {
            return
        }

        defaults.set(hour, forKey: lastActiveHourUTCKey)

        PostHogSDK.shared.capture(
            "cmux_hourly_active",
            properties: Self.hourlyActiveProperties(
                hourUTC: hour,
                reason: reason,
                infoDictionary: Bundle.main.infoDictionary ?? [:]
            )
        )
    }

    func flush() {
        guard didStart else { return }
        PostHogSDK.shared.flush()
    }

    private func utcHourString(_ date: Date) -> String {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH"
        return formatter.string(from: date)
    }

    private func utcDayString(_ date: Date) -> String {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd"
        return formatter.string(from: date)
    }

    nonisolated static func superProperties(infoDictionary: [String: Any]) -> [String: Any] {
        var properties: [String: Any] = ["platform": "cmuxterm"]
        properties.merge(versionProperties(infoDictionary: infoDictionary)) { _, new in new }
        return properties
    }

    nonisolated static func dailyActiveProperties(
        dayUTC: String,
        reason: String,
        infoDictionary: [String: Any]
    ) -> [String: Any] {
        var properties: [String: Any] = [
            "day_utc": dayUTC,
            "reason": reason,
        ]
        properties.merge(versionProperties(infoDictionary: infoDictionary)) { _, new in new }
        return properties
    }

    nonisolated static func hourlyActiveProperties(
        hourUTC: String,
        reason: String,
        infoDictionary: [String: Any]
    ) -> [String: Any] {
        var properties: [String: Any] = [
            "hour_utc": hourUTC,
            "reason": reason,
        ]
        properties.merge(versionProperties(infoDictionary: infoDictionary)) { _, new in new }
        return properties
    }

    nonisolated private static func versionProperties(infoDictionary: [String: Any]) -> [String: Any] {
        var properties: [String: Any] = [:]
        if let value = infoDictionary["CFBundleShortVersionString"] as? String, !value.isEmpty {
            properties["app_version"] = value
        }
        if let value = infoDictionary["CFBundleVersion"] as? String, !value.isEmpty {
            properties["app_build"] = value
        }
        return properties
    }
}