MacMonitor/Sources/Intelligence/AlertEngine.swift

import Foundation
import UserNotifications

// MARK: - Alert Engine

/// Evaluates threshold rules against each decoded telemetry snapshot.
/// Runs on `@MainActor` — it performs only in-memory comparisons over
/// `AlertEvaluationContext` and never touches IOKit/Mach/sysctl, preserving
/// the zero-UI-blocking invariant.
///
/// Lifecycle per alert identifier:
///   breach edge  -> fire notification (subject to cooldown), log `.triggered`
///   persistent   -> re-fire only after `cooldownMinutes` elapse
///   recovery     -> remove from active set, log `.resolved`, clear cooldown so
///                   the next breach alerts immediately
@Observable
@MainActor
public final class AlertEngine {
    public static let shared = AlertEngine()

    /// Currently breached conditions, refreshed every evaluation pass.
    public private(set) var activeAlerts: [SystemAlert] = []
    /// Newest-first audit log of trigger/resolve events (capped).
    public private(set) var history: [AlertEvent] = []

    /// Threshold settings. Mutations are persisted immediately.
    public var configuration: AlertConfiguration {
        didSet { configuration.save(to: defaults) }
    }

    public let dispatcher: any AlertNotificationDispatching
    private let defaults: UserDefaults
    private let historyLimit = 200
    private var lastFiredAt: [String: Date] = [:]
    private var breachedAlerts: [String: SystemAlert] = [:]

    private convenience init() {
        self.init(dispatcher: UNAlertNotificationDispatcher(), defaults: .standard)
    }

    init(dispatcher: any AlertNotificationDispatching, defaults: UserDefaults) {
        self.dispatcher = dispatcher
        self.defaults = defaults
        self.configuration = AlertConfiguration.load(from: defaults)
    }

    /// Forwards to the dispatcher; call once at launch (and from Settings).
    public func requestNotificationAuthorization() {
        dispatcher.requestAuthorization()
    }

    public func notificationAuthorizationStatus() async -> UNAuthorizationStatus {
        await dispatcher.authorizationStatus()
    }

    // MARK: Evaluation

    public func evaluate(_ context: AlertEvaluationContext) {
        guard configuration.alertsEnabled else {
            // Wipe silently so stale alerts do not linger while disabled.
            activeAlerts = []
            breachedAlerts = [:]
            lastFiredAt = [:]
            return
        }

        let candidates = buildCandidates(for: context)
        var currentIDs = Set<String>()

        for alert in candidates {
            currentIDs.insert(alert.id)
            breachedAlerts[alert.id] = alert
            if shouldFire(alertID: alert.id, at: context.timestamp) {
                fire(alert, at: context.timestamp)
            }
        }

        let resolvedIDs = breachedAlerts.keys
            .filter { !currentIDs.contains($0) }
            .sorted()
        for id in resolvedIDs {
            let resolved = breachedAlerts.removeValue(forKey: id)
            lastFiredAt.removeValue(forKey: id)
            let kind = resolved?.kind ?? Self.kind(fromAlertID: id)
            appendEvent(
                alertID: id,
                kind: kind,
                outcome: .resolved,
                message: String(localized: "\(resolved?.title ?? id) — condition cleared"),
                at: context.timestamp
            )
        }

        activeAlerts = candidates
    }

    /// Clears all active/breached state and the audit log.
    public func reset() {
        activeAlerts = []
        history = []
        breachedAlerts = [:]
        lastFiredAt = [:]
    }

    public func clearHistory() {
        history = []
    }

    // MARK: Rule Evaluation

    private func buildCandidates(for ctx: AlertEvaluationContext) -> [SystemAlert] {
        let cfg = configuration
        var alerts: [SystemAlert] = []

        // 1. High CPU temperature
        if cfg.cpuTempEnabled {
            let temp = max(ctx.peakCoreTemperature, ctx.packageTemperature)
            if temp >= cfg.cpuTempThresholdC {
                alerts.append(SystemAlert(
                    id: AlertKind.cpuTemperature.rawValue,
                    kind: .cpuTemperature,
                    severity: .critical,
                    title: String(localized: "High CPU Temperature"),
                    message: String(localized: "CPU reached \(Int(temp))°C — threshold is \(Int(cfg.cpuTempThresholdC))°C"),
                    timestamp: ctx.timestamp
                ))
            }
        }

        // 2. Cooling fan stall — only meaningful when fans are reported and the
        //    CPU is hot enough that a working fan should be spinning.
        if cfg.fanStallEnabled,
           !ctx.fanRPMs.isEmpty,
           ctx.packageTemperature >= cfg.fanStallTempThresholdC {
            for (index, rpm) in ctx.fanRPMs.sorted(by: { $0.key < $1.key }) where rpm <= 0 {
                alerts.append(SystemAlert(
                    id: "\(AlertKind.fanStall.rawValue):\(index)",
                    kind: .fanStall,
                    severity: .critical,
                    title: String(localized: "Cooling Fan Failure"),
                    message: String(localized: "Fan \(index + 1) reads 0 RPM while the CPU is at \(Int(ctx.packageTemperature))°C"),
                    timestamp: ctx.timestamp
                ))
            }
        }

        // 3. Low free memory / critical pressure
        if cfg.memoryEnabled {
            let freeMB = Double(ctx.memoryFreeBytes) / (1024 * 1024)
            let critical = cfg.memoryAlertOnCriticalPressure
                && ctx.memoryPressureLevel.localizedCaseInsensitiveContains("critical")
            if freeMB < cfg.memoryFreeMBThreshold || critical {
                alerts.append(SystemAlert(
                    id: AlertKind.memoryPressure.rawValue,
                    kind: .memoryPressure,
                    severity: critical ? .critical : .warning,
                    title: String(localized: "Memory Pressure"),
                    message: String(localized: "Only \(Int(freeMB)) MB RAM free — pressure is \(ctx.memoryPressureLevel)"),
                    timestamp: ctx.timestamp
                ))
            }
        }

        // 4. Low storage space (per mounted volume)
        if cfg.storageEnabled {
            for volume in ctx.volumes {
                let freeGB = Double(volume.freeBytes) / (1024 * 1024 * 1024)
                if freeGB < cfg.storageFreeGBThreshold || volume.freePercent < cfg.storageFreePercentThreshold {
                    alerts.append(SystemAlert(
                        id: "\(AlertKind.lowStorage.rawValue):\(volume.mountPoint)",
                        kind: .lowStorage,
                        severity: .warning,
                        title: String(localized: "Low Disk Space"),
                        message: String(localized: "\"\(volume.volumeName)\" has \(String(format: "%.1f", freeGB)) GB free (\(Int(volume.freePercent))%)"),
                        timestamp: ctx.timestamp
                    ))
                }
            }
        }

        // 5. Low battery — only while actually discharging on battery power.
        if cfg.batteryEnabled,
           ctx.hasBattery,
           !ctx.onExternalPower,
           !ctx.isCharging,
           ctx.batteryLevel <= cfg.batteryPercentThreshold {
            alerts.append(SystemAlert(
                id: AlertKind.lowBattery.rawValue,
                kind: .lowBattery,
                severity: .critical,
                title: String(localized: "Low Battery"),
                message: String(localized: "Battery is at \(Int(ctx.batteryLevel))% and not charging"),
                timestamp: ctx.timestamp
            ))
        }

        return alerts
    }

    // MARK: Cooldown & History

    private func shouldFire(alertID: String, at date: Date) -> Bool {
        guard let last = lastFiredAt[alertID] else { return true }
        return date.timeIntervalSince(last) >= configuration.cooldownMinutes * 60
    }

    private func fire(_ alert: SystemAlert, at date: Date) {
        lastFiredAt[alert.id] = date
        dispatcher.dispatch(alert)
        appendEvent(alertID: alert.id, kind: alert.kind, outcome: .triggered, message: alert.message, at: date)
    }

    private func appendEvent(alertID: String, kind: AlertKind, outcome: AlertEventOutcome, message: String, at date: Date) {
        history.insert(
            AlertEvent(timestamp: date, alertID: alertID, kind: kind, outcome: outcome, message: message),
            at: 0
        )
        if history.count > historyLimit {
            history.removeLast(history.count - historyLimit)
        }
    }

    private static func kind(fromAlertID id: String) -> AlertKind {
        let prefix = id.prefix { $0 != ":" }
        return AlertKind(rawValue: String(prefix)) ?? .cpuTemperature
    }
}