//
//  HealthService.swift
//  Feels
//
//  Manages Apple Health integration for mood correlation insights.
//

import Foundation
import HealthKit
import SwiftUI

@MainActor
class HealthService: ObservableObject {

    static let shared = HealthService()

    // MARK: - Published State

    @Published var isAuthorized: Bool = false
    @Published var isAvailable: Bool = false

    // MARK: - App Storage

    @AppStorage(UserDefaultsStore.Keys.healthKitEnabled.rawValue, store: GroupUserDefaults.groupDefaults)
    var isEnabled: Bool = false

    // MARK: - HealthKit Store

    private let healthStore = HKHealthStore()

    // MARK: - Data Types

    private let stepCountType = HKQuantityType.quantityType(forIdentifier: .stepCount)!
    private let exerciseTimeType = HKQuantityType.quantityType(forIdentifier: .appleExerciseTime)!
    private let heartRateType = HKQuantityType.quantityType(forIdentifier: .heartRate)!
    private let sleepAnalysisType = HKCategoryType.categoryType(forIdentifier: .sleepAnalysis)!

    private var readTypes: Set<HKObjectType> {
        [stepCountType, exerciseTimeType, heartRateType, sleepAnalysisType]
    }

    // MARK: - Initialization

    init() {
        isAvailable = HKHealthStore.isHealthDataAvailable()
    }

    // MARK: - Authorization

    func requestAuthorization() async -> Bool {
        guard isAvailable else {
            print("HealthService: HealthKit not available on this device")
            return false
        }

        do {
            try await healthStore.requestAuthorization(toShare: [], read: readTypes)
            isAuthorized = true
            isEnabled = true
            EventLogger.log(event: "healthkit_authorized")
            return true
        } catch {
            print("HealthService: Authorization failed: \(error.localizedDescription)")
            EventLogger.log(event: "healthkit_auth_failed", withData: ["error": error.localizedDescription])
            return false
        }
    }

    // MARK: - Fetch Health Data for Date

    struct DailyHealthData {
        let date: Date
        let steps: Int?
        let exerciseMinutes: Int?
        let averageHeartRate: Double?
        let sleepHours: Double?

        var hasData: Bool {
            steps != nil || exerciseMinutes != nil || averageHeartRate != nil || sleepHours != nil
        }
    }

    func fetchHealthData(for date: Date) async -> DailyHealthData {
        let calendar = Calendar.current
        let startOfDay = calendar.startOfDay(for: date)
        let endOfDay = calendar.date(byAdding: .day, value: 1, to: startOfDay)!

        async let steps = fetchSteps(start: startOfDay, end: endOfDay)
        async let exercise = fetchExerciseMinutes(start: startOfDay, end: endOfDay)
        async let heartRate = fetchAverageHeartRate(start: startOfDay, end: endOfDay)
        async let sleep = fetchSleepHours(for: date)

        return await DailyHealthData(
            date: date,
            steps: steps,
            exerciseMinutes: exercise,
            averageHeartRate: heartRate,
            sleepHours: sleep
        )
    }

    // MARK: - Steps

    private func fetchSteps(start: Date, end: Date) async -> Int? {
        guard isAuthorized else { return nil }

        let predicate = HKQuery.predicateForSamples(withStart: start, end: end, options: .strictStartDate)

        return await withCheckedContinuation { continuation in
            let query = HKStatisticsQuery(
                quantityType: stepCountType,
                quantitySamplePredicate: predicate,
                options: .cumulativeSum
            ) { _, result, error in
                guard error == nil,
                      let sum = result?.sumQuantity() else {
                    continuation.resume(returning: nil)
                    return
                }

                let steps = Int(sum.doubleValue(for: .count()))
                continuation.resume(returning: steps)
            }

            healthStore.execute(query)
        }
    }

    // MARK: - Exercise Minutes

    private func fetchExerciseMinutes(start: Date, end: Date) async -> Int? {
        guard isAuthorized else { return nil }

        let predicate = HKQuery.predicateForSamples(withStart: start, end: end, options: .strictStartDate)

        return await withCheckedContinuation { continuation in
            let query = HKStatisticsQuery(
                quantityType: exerciseTimeType,
                quantitySamplePredicate: predicate,
                options: .cumulativeSum
            ) { _, result, error in
                guard error == nil,
                      let sum = result?.sumQuantity() else {
                    continuation.resume(returning: nil)
                    return
                }

                let minutes = Int(sum.doubleValue(for: .minute()))
                continuation.resume(returning: minutes)
            }

            healthStore.execute(query)
        }
    }

    // MARK: - Heart Rate

    private func fetchAverageHeartRate(start: Date, end: Date) async -> Double? {
        guard isAuthorized else { return nil }

        let predicate = HKQuery.predicateForSamples(withStart: start, end: end, options: .strictStartDate)

        return await withCheckedContinuation { continuation in
            let query = HKStatisticsQuery(
                quantityType: heartRateType,
                quantitySamplePredicate: predicate,
                options: .discreteAverage
            ) { _, result, error in
                guard error == nil,
                      let avg = result?.averageQuantity() else {
                    continuation.resume(returning: nil)
                    return
                }

                let bpm = avg.doubleValue(for: HKUnit.count().unitDivided(by: .minute()))
                continuation.resume(returning: bpm)
            }

            healthStore.execute(query)
        }
    }

    // MARK: - Sleep

    private func fetchSleepHours(for date: Date) async -> Double? {
        guard isAuthorized else { return nil }

        // Sleep data is typically recorded for the night before
        // So for mood on date X, we look at sleep from evening of X-1 to morning of X
        let calendar = Calendar.current
        let endOfSleep = calendar.date(bySettingHour: 12, minute: 0, second: 0, of: date)!
        let startOfSleep = calendar.date(byAdding: .hour, value: -18, to: endOfSleep)!

        let predicate = HKQuery.predicateForSamples(withStart: startOfSleep, end: endOfSleep, options: .strictStartDate)

        return await withCheckedContinuation { continuation in
            let query = HKSampleQuery(
                sampleType: sleepAnalysisType,
                predicate: predicate,
                limit: HKObjectQueryNoLimit,
                sortDescriptors: nil
            ) { _, samples, error in
                guard error == nil,
                      let sleepSamples = samples as? [HKCategorySample] else {
                    continuation.resume(returning: nil)
                    return
                }

                // Sum up asleep time (not in bed time)
                var totalSleepSeconds: TimeInterval = 0
                for sample in sleepSamples {
                    // Filter for actual sleep states (not in bed)
                    if sample.value == HKCategoryValueSleepAnalysis.asleepCore.rawValue ||
                       sample.value == HKCategoryValueSleepAnalysis.asleepDeep.rawValue ||
                       sample.value == HKCategoryValueSleepAnalysis.asleepREM.rawValue ||
                       sample.value == HKCategoryValueSleepAnalysis.asleepUnspecified.rawValue {
                        totalSleepSeconds += sample.endDate.timeIntervalSince(sample.startDate)
                    }
                }

                if totalSleepSeconds > 0 {
                    let hours = totalSleepSeconds / 3600
                    continuation.resume(returning: hours)
                } else {
                    continuation.resume(returning: nil)
                }
            }

            healthStore.execute(query)
        }
    }

    // MARK: - Batch Fetch for Insights

    func fetchHealthData(for entries: [MoodEntryModel]) async -> [Date: DailyHealthData] {
        guard isEnabled && isAuthorized else { return [:] }

        var results: [Date: DailyHealthData] = [:]
        let calendar = Calendar.current

        // Get unique dates
        let dates = Set(entries.map { calendar.startOfDay(for: $0.forDate) })

        // Fetch health data for each date
        await withTaskGroup(of: (Date, DailyHealthData).self) { group in
            for date in dates {
                group.addTask {
                    let data = await self.fetchHealthData(for: date)
                    return (date, data)
                }
            }

            for await (date, data) in group {
                results[date] = data
            }
        }

        return results
    }

    // MARK: - Correlation Analysis

    struct HealthMoodCorrelation {
        let metric: String
        let correlation: String  // "positive", "negative", or "none"
        let insight: String
        let averageWithHighMetric: Double
        let averageWithLowMetric: Double
    }

    func analyzeCorrelations(entries: [MoodEntryModel], healthData: [Date: DailyHealthData]) -> [HealthMoodCorrelation] {
        var correlations: [HealthMoodCorrelation] = []
        let calendar = Calendar.current

        // Prepare data pairs
        var stepsAndMoods: [(steps: Int, mood: Int)] = []
        var exerciseAndMoods: [(minutes: Int, mood: Int)] = []
        var sleepAndMoods: [(hours: Double, mood: Int)] = []
        var heartRateAndMoods: [(bpm: Double, mood: Int)] = []

        for entry in entries {
            let date = calendar.startOfDay(for: entry.forDate)
            guard let health = healthData[date] else { continue }

            let moodValue = entry.moodValue + 1  // Use 1-5 scale

            if let steps = health.steps {
                stepsAndMoods.append((steps, moodValue))
            }
            if let exercise = health.exerciseMinutes {
                exerciseAndMoods.append((exercise, moodValue))
            }
            if let sleep = health.sleepHours {
                sleepAndMoods.append((sleep, moodValue))
            }
            if let hr = health.averageHeartRate {
                heartRateAndMoods.append((hr, moodValue))
            }
        }

        // Analyze steps correlation
        if stepsAndMoods.count >= 5 {
            let threshold = 8000
            let highSteps = stepsAndMoods.filter { $0.steps >= threshold }
            let lowSteps = stepsAndMoods.filter { $0.steps < threshold }

            if !highSteps.isEmpty && !lowSteps.isEmpty {
                let avgHigh = Double(highSteps.map { $0.mood }.reduce(0, +)) / Double(highSteps.count)
                let avgLow = Double(lowSteps.map { $0.mood }.reduce(0, +)) / Double(lowSteps.count)
                let diff = avgHigh - avgLow

                if abs(diff) >= 0.3 {
                    correlations.append(HealthMoodCorrelation(
                        metric: "Steps",
                        correlation: diff > 0 ? "positive" : "negative",
                        insight: diff > 0
                            ? "Your mood averages \(String(format: "%.1f", diff)) points higher on days with 8k+ steps"
                            : "Interestingly, your mood is slightly lower on high-step days",
                        averageWithHighMetric: avgHigh,
                        averageWithLowMetric: avgLow
                    ))
                }
            }
        }

        // Analyze sleep correlation
        if sleepAndMoods.count >= 5 {
            let threshold = 7.0
            let goodSleep = sleepAndMoods.filter { $0.hours >= threshold }
            let poorSleep = sleepAndMoods.filter { $0.hours < threshold }

            if !goodSleep.isEmpty && !poorSleep.isEmpty {
                let avgGood = Double(goodSleep.map { $0.mood }.reduce(0, +)) / Double(goodSleep.count)
                let avgPoor = Double(poorSleep.map { $0.mood }.reduce(0, +)) / Double(poorSleep.count)
                let diff = avgGood - avgPoor

                if abs(diff) >= 0.3 {
                    correlations.append(HealthMoodCorrelation(
                        metric: "Sleep",
                        correlation: diff > 0 ? "positive" : "negative",
                        insight: diff > 0
                            ? "7+ hours of sleep correlates with \(String(format: "%.1f", diff)) point higher mood"
                            : "Sleep duration doesn't seem to strongly affect your mood",
                        averageWithHighMetric: avgGood,
                        averageWithLowMetric: avgPoor
                    ))
                }
            }
        }

        // Analyze exercise correlation
        if exerciseAndMoods.count >= 5 {
            let threshold = 30
            let active = exerciseAndMoods.filter { $0.minutes >= threshold }
            let inactive = exerciseAndMoods.filter { $0.minutes < threshold }

            if !active.isEmpty && !inactive.isEmpty {
                let avgActive = Double(active.map { $0.mood }.reduce(0, +)) / Double(active.count)
                let avgInactive = Double(inactive.map { $0.mood }.reduce(0, +)) / Double(inactive.count)
                let diff = avgActive - avgInactive

                if abs(diff) >= 0.3 {
                    correlations.append(HealthMoodCorrelation(
                        metric: "Exercise",
                        correlation: diff > 0 ? "positive" : "negative",
                        insight: diff > 0
                            ? "30+ minutes of exercise correlates with \(String(format: "%.1f", diff)) point mood boost"
                            : "Exercise doesn't show a strong mood correlation for you",
                        averageWithHighMetric: avgActive,
                        averageWithLowMetric: avgInactive
                    ))
                }
            }
        }

        return correlations
    }
}