import Foundation
import Combine

@MainActor
class ChartsViewModel: ObservableObject {
    // MARK: - Chart Types

    enum ChartType: String, CaseIterable, Identifiable {
        case evolution = "Evolution"
        case allocation = "Allocation"
        case performance = "Performance"
        case contributions = "Contributions"
        case rollingReturn = "Rolling 12M"
        case riskReturn = "Risk vs Return"
        case cashflow = "Net vs Contributions"
        case drawdown = "Drawdown"
        case volatility = "Volatility"
        case prediction = "Prediction"

        var id: String { rawValue }

        var icon: String {
            switch self {
            case .evolution: return "chart.line.uptrend.xyaxis"
            case .allocation: return "chart.pie.fill"
            case .performance: return "chart.bar.fill"
            case .contributions: return "tray.and.arrow.down.fill"
            case .rollingReturn: return "arrow.triangle.2.circlepath"
            case .riskReturn: return "dot.square"
            case .cashflow: return "chart.bar.xaxis"
            case .drawdown: return "arrow.down.right.circle"
            case .volatility: return "waveform.path.ecg"
            case .prediction: return "wand.and.stars"
            }
        }

        var isPremium: Bool {
            switch self {
            case .evolution:
                return false
            case .allocation, .performance, .contributions, .rollingReturn, .riskReturn, .cashflow,
                 .drawdown, .volatility, .prediction:
                return true
            }
        }

        var description: String {
            switch self {
            case .evolution:
                return "Track your portfolio value over time"
            case .allocation:
                return "See how your investments are distributed"
            case .performance:
                return "Compare returns across categories"
            case .contributions:
                return "Review monthly inflows over time"
            case .rollingReturn:
                return "See rolling 12-month performance"
            case .riskReturn:
                return "Compare volatility vs return"
            case .cashflow:
                return "Compare growth vs contributions"
            case .drawdown:
                return "Analyze declines from peak values"
            case .volatility:
                return "Understand investment risk levels"
            case .prediction:
                return "View 12-month forecasts"
            }
        }
    }

    func availableChartTypes(calmModeEnabled: Bool) -> [ChartType] {
        let types: [ChartType] = calmModeEnabled
            ? [.evolution, .allocation, .performance, .contributions]
            : ChartType.allCases
        if !types.contains(selectedChartType) {
            selectedChartType = .evolution
        }
        return types
    }

    // MARK: - Published Properties

    @Published var selectedChartType: ChartType = .evolution
    @Published var selectedCategory: Category?
    @Published var selectedTimeRange: TimeRange = .year
    @Published var selectedAccount: Account?
    @Published var showAllAccounts = true

    @Published var evolutionData: [(date: Date, value: Decimal)] = []
    @Published var categoryEvolutionData: [CategoryEvolutionPoint] = []
    @Published var allocationData: [(category: String, value: Decimal, color: String)] = []
    @Published var performanceData: [(category: String, cagr: Double, color: String)] = []
    @Published var contributionsData: [(date: Date, amount: Decimal)] = []
    @Published var rollingReturnData: [(date: Date, value: Double)] = []
    @Published var riskReturnData: [(category: String, cagr: Double, volatility: Double, color: String)] = []
    @Published var cashflowData: [(date: Date, contributions: Decimal, netPerformance: Decimal)] = []
    @Published var drawdownData: [(date: Date, drawdown: Double)] = []
    @Published var volatilityData: [(date: Date, volatility: Double)] = []
    @Published var predictionData: [Prediction] = []

    @Published var isLoading = false
    @Published var showingPaywall = false
    @Published private var predictionMonthsAhead = 12

    // MARK: - Time Range

    enum TimeRange: String, CaseIterable, Identifiable {
        case month = "1M"
        case quarter = "3M"
        case halfYear = "6M"
        case year = "1Y"
        case all = "All"

        var id: String { rawValue }

        var months: Int? {
            switch self {
            case .month: return 1
            case .quarter: return 3
            case .halfYear: return 6
            case .year: return 12
            case .all: return nil
            }
        }
    }

    // MARK: - Dependencies

    private let sourceRepository: InvestmentSourceRepository
    private let categoryRepository: CategoryRepository
    private let snapshotRepository: SnapshotRepository
    private let calculationService: CalculationService
    private let predictionEngine: PredictionEngine
    private let freemiumValidator: FreemiumValidator
    private let maxHistoryMonths = 60
    private let maxStackedCategories = 6
    private let maxChartPoints = 500
    private var cancellables = Set<AnyCancellable>()
    private var allCategories: [Category] {
        categoryRepository.categories
    }

    // MARK: - Performance: Caching and State
    private var lastChartType: ChartType?
    private var lastTimeRange: TimeRange?
    private var lastCategoryId: UUID?
    private var lastAccountId: UUID?
    private var lastShowAllAccounts: Bool = true
    private var cachedSnapshots: [Snapshot]?
    private var cachedSnapshotsBySource: [UUID: [Snapshot]]?
    private var isUpdateInProgress = false

    // MARK: - Initialization

    init(
        sourceRepository: InvestmentSourceRepository? = nil,
        categoryRepository: CategoryRepository? = nil,
        snapshotRepository: SnapshotRepository? = nil,
        calculationService: CalculationService? = nil,
        predictionEngine: PredictionEngine? = nil,
        iapService: IAPService
    ) {
        self.sourceRepository = sourceRepository ?? InvestmentSourceRepository()
        self.categoryRepository = categoryRepository ?? CategoryRepository()
        self.snapshotRepository = snapshotRepository ?? SnapshotRepository()
        self.calculationService = calculationService ?? .shared
        self.predictionEngine = predictionEngine ?? .shared
        self.freemiumValidator = FreemiumValidator(iapService: iapService)

        setupObservers()
        loadData()
    }

    // MARK: - Setup

    private func setupObservers() {
        // Performance: Combine all selection changes into a single debounced stream
        // This prevents multiple rapid updates when switching between views
        Publishers.CombineLatest4($selectedChartType, $selectedCategory, $selectedTimeRange, $selectedAccount)
            .combineLatest($showAllAccounts)
            .debounce(for: .milliseconds(150), scheduler: DispatchQueue.main)
            .sink { [weak self] combined, showAll in
                guard let self else { return }
                let (chartType, category, timeRange, _) = combined

                // Performance: Skip update if nothing meaningful changed
                let hasChanges = self.lastChartType != chartType ||
                    self.lastTimeRange != timeRange ||
                    self.lastCategoryId != category?.id ||
                    self.lastAccountId != self.selectedAccount?.id ||
                    self.lastShowAllAccounts != showAll

                if hasChanges {
                    self.lastChartType = chartType
                    self.lastTimeRange = timeRange
                    self.lastCategoryId = category?.id
                    self.lastAccountId = self.selectedAccount?.id
                    self.lastShowAllAccounts = showAll
                    self.cachedSnapshots = nil // Invalidate cache on meaningful changes
                    self.cachedSnapshotsBySource = nil
                    self.updateChartData(chartType: chartType, category: category, timeRange: timeRange)
                }
            }
            .store(in: &cancellables)
    }

    // MARK: - Data Loading

    func loadData() {
        updateChartData(
            chartType: selectedChartType,
            category: selectedCategory,
            timeRange: selectedTimeRange
        )

        FirebaseService.shared.logScreenView(screenName: "Charts")
    }

    func selectChart(_ chartType: ChartType) {
        if chartType.isPremium && !freemiumValidator.isPremium {
            showingPaywall = true
            FirebaseService.shared.logPaywallShown(trigger: "advanced_charts")
            return
        }

        selectedChartType = chartType
        FirebaseService.shared.logChartViewed(
            chartType: chartType.rawValue,
            isPremium: chartType.isPremium
        )
    }

    private func updateChartData(chartType: ChartType, category: Category?, timeRange: TimeRange) {
        // Performance: Prevent re-entrancy
        guard !isUpdateInProgress else { return }
        isUpdateInProgress = true
        isLoading = true

        defer {
            isLoading = false
            isUpdateInProgress = false
        }

        let sources: [InvestmentSource]
        if let category = category {
            sources = sourceRepository.fetchSources(for: category).filter { shouldIncludeSource($0) }
        } else {
            sources = sourceRepository.sources.filter { shouldIncludeSource($0) }
        }

        let monthsLimit = timeRange.months ?? maxHistoryMonths
        let sourceIds = sources.compactMap { $0.id }

        // Performance: Reuse cached snapshots when possible
        var snapshots: [Snapshot]
        if let cached = cachedSnapshots {
            snapshots = cached
        } else {
            snapshots = snapshotRepository.fetchSnapshots(
                for: sourceIds,
                months: monthsLimit
            )
            snapshots = freemiumValidator.filterSnapshots(snapshots)
            cachedSnapshots = snapshots
        }

        // Performance: Cache snapshotsBySource
        let snapshotsBySource: [UUID: [Snapshot]]
        if let cached = cachedSnapshotsBySource {
            snapshotsBySource = cached
        } else {
            var grouped: [UUID: [Snapshot]] = [:]
            grouped.reserveCapacity(sources.count)
            for snapshot in snapshots {
                guard let id = snapshot.source?.id else { continue }
                grouped[id, default: []].append(snapshot)
            }
            snapshotsBySource = grouped
            cachedSnapshotsBySource = grouped
        }

        // Performance: Only calculate data for the selected chart type
        switch chartType {
        case .evolution:
            calculateEvolutionData(from: snapshots)
            let categoriesForChart = categoriesForStackedChart(
                sources: sources,
                selectedCategory: selectedCategory
            )
            calculateCategoryEvolutionData(from: snapshots, categories: categoriesForChart)
        case .allocation:
            calculateAllocationData(for: sources)
        case .performance:
            calculatePerformanceData(for: sources, snapshotsBySource: snapshotsBySource)
        case .contributions:
            calculateContributionsData(from: snapshots)
        case .rollingReturn:
            calculateRollingReturnData(from: snapshots)
        case .riskReturn:
            calculateRiskReturnData(for: sources, snapshotsBySource: snapshotsBySource)
        case .cashflow:
            calculateCashflowData(from: snapshots)
        case .drawdown:
            calculateDrawdownData(from: snapshots)
        case .volatility:
            calculateVolatilityData(from: snapshots)
        case .prediction:
            calculatePredictionData(from: snapshots)
        }

        if let selected = selectedCategory,
           !availableCategories(for: chartType, sources: sources).contains(where: { $0.id == selected.id }) {
            selectedCategory = nil
        }
    }

    func availableCategories(
        for chartType: ChartType,
        sources: [InvestmentSource]? = nil
    ) -> [Category] {
        let relevantSources = sources ?? sourceRepository.sources.filter { shouldIncludeSource($0) }
        let categoriesWithData = Set(relevantSources.compactMap { $0.category?.id })
        let filtered = allCategories.filter { categoriesWithData.contains($0.id) }

        switch chartType {
        case .evolution, .prediction:
            return filtered
        default:
            return []
        }
    }

    private func shouldIncludeSource(_ source: InvestmentSource) -> Bool {
        if showAllAccounts || selectedAccount == nil {
            return true
        }
        return source.account?.id == selectedAccount?.id
    }

    private func categoriesForStackedChart(
        sources: [InvestmentSource],
        selectedCategory: Category?
    ) -> [Category] {
        var totals: [UUID: Decimal] = [:]

        for source in sources {
            guard let categoryId = source.category?.id else { continue }
            totals[categoryId, default: 0] += source.latestValue
        }

        var topCategoryIds = Set(
            totals.sorted { $0.value > $1.value }
                .prefix(maxStackedCategories)
                .map { $0.key }
        )

        if let selectedCategory {
            topCategoryIds.insert(selectedCategory.id)
        }

        return categoryRepository.categories.filter { topCategoryIds.contains($0.id) }
    }

    private func downsampleSeries(
        _ data: [(date: Date, value: Decimal)],
        maxPoints: Int
    ) -> [(date: Date, value: Decimal)] {
        guard data.count > maxPoints, maxPoints > 0 else { return data }
        let bucketSize = max(1, Int(ceil(Double(data.count) / Double(maxPoints))))
        var sampled: [(date: Date, value: Decimal)] = []
        sampled.reserveCapacity(maxPoints)

        var index = 0
        while index < data.count {
            let end = min(index + bucketSize, data.count)
            let bucket = data[index..<end]
            if let last = bucket.last {
                sampled.append(last)
            }
            index += bucketSize
        }
        return sampled
    }

    private func downsampleDates(_ dates: [Date], maxPoints: Int) -> [Date] {
        guard dates.count > maxPoints, maxPoints > 0 else { return dates }
        let bucketSize = max(1, Int(ceil(Double(dates.count) / Double(maxPoints))))
        var sampled: [Date] = []
        sampled.reserveCapacity(maxPoints)

        var index = 0
        while index < dates.count {
            let end = min(index + bucketSize, dates.count)
            let bucket = dates[index..<end]
            if let last = bucket.last {
                sampled.append(last)
            }
            index += bucketSize
        }
        return sampled
    }

    // MARK: - Chart Calculations

    private func calculateEvolutionData(from snapshots: [Snapshot]) {
        let sortedSnapshots = snapshots.sorted { $0.date < $1.date }

        var dateValues: [Date: Decimal] = [:]

        for snapshot in sortedSnapshots {
            let day = Calendar.current.startOfDay(for: snapshot.date)
            dateValues[day, default: 0] += snapshot.decimalValue
        }

        let series = dateValues
            .map { (date: $0.key, value: $0.value) }
            .sorted { $0.date < $1.date }
        evolutionData = downsampleSeries(series, maxPoints: maxChartPoints)
    }

    private func calculateCategoryEvolutionData(from snapshots: [Snapshot], categories: [Category]) {
        let sortedSnapshots = snapshots.sorted { $0.date < $1.date }
        let categoriesWithData = Set(sortedSnapshots.compactMap { $0.source?.category?.id })
        let filteredCategories = categories.filter { categoriesWithData.contains($0.id) }
        let snapshotsByDay = Dictionary(grouping: sortedSnapshots) {
            Calendar.current.startOfDay(for: $0.date)
        }
        let uniqueDates = downsampleDates(snapshotsByDay.keys.sorted(), maxPoints: maxChartPoints)

        var latestBySource: [UUID: Snapshot] = [:]
        var points: [CategoryEvolutionPoint] = []

        for date in uniqueDates {
            if let daySnapshots = snapshotsByDay[date] {
                for snapshot in daySnapshots {
                    guard let sourceId = snapshot.source?.id else { continue }
                    latestBySource[sourceId] = snapshot
                }
            }

            var valuesByCategory: [UUID: Decimal] = [:]
            for snapshot in latestBySource.values {
                guard let category = snapshot.source?.category else { continue }
                valuesByCategory[category.id, default: 0] += snapshot.decimalValue
            }

            for category in filteredCategories {
                let value = valuesByCategory[category.id] ?? 0
                points.append(CategoryEvolutionPoint(
                    date: date,
                    categoryName: category.name,
                    colorHex: category.colorHex,
                    value: value
                ))
            }
        }

        categoryEvolutionData = points
    }

    private func calculateAllocationData(for sources: [InvestmentSource]) {
        let categories = categoryRepository.categories
        let valuesByCategory = Dictionary(grouping: sources) { $0.category?.id ?? UUID() }

        allocationData = categories.compactMap { category in
            let categorySources = valuesByCategory[category.id] ?? []
            let categoryValue = categorySources.reduce(Decimal.zero) { $0 + $1.latestValue }
            guard categoryValue > 0 else { return nil }

            return (
                category: category.name,
                value: categoryValue,
                color: category.colorHex
            )
        }.sorted { $0.value > $1.value }
    }

    private func calculatePerformanceData(
        for sources: [InvestmentSource],
        snapshotsBySource: [UUID: [Snapshot]]
    ) {
        let categories = categoryRepository.categories
        let sourcesByCategory = Dictionary(grouping: sources) { $0.category?.id ?? UUID() }

        performanceData = categories.compactMap { category in
            let categorySources = sourcesByCategory[category.id] ?? []
            let snapshots = categorySources.compactMap { source -> [Snapshot]? in
                let id = source.id
                return snapshotsBySource[id]
            }.flatMap { $0 }
            guard snapshots.count >= 2 else { return nil }

            let metrics = calculationService.calculateMetrics(for: snapshots)

            return (
                category: category.name,
                cagr: metrics.cagr,
                color: category.colorHex
            )
        }.sorted { $0.cagr > $1.cagr }
    }

    private func calculateContributionsData(from snapshots: [Snapshot]) {
        let grouped = Dictionary(grouping: snapshots) { $0.date.startOfMonth }
        contributionsData = grouped.map { date, items in
            let total = items.reduce(Decimal.zero) { $0 + $1.decimalContribution }
            return (date: date, amount: total)
        }
        .sorted { $0.date < $1.date }
    }

    private func calculateRollingReturnData(from snapshots: [Snapshot]) {
        let monthlyTotals = monthlyTotals(from: snapshots)
        guard monthlyTotals.count >= 13 else {
            rollingReturnData = []
            return
        }

        var returns: [(date: Date, value: Double)] = []
        for index in 12..<monthlyTotals.count {
            let current = monthlyTotals[index]
            let base = monthlyTotals[index - 12]
            guard base.totalValue > 0 else { continue }
            let change = current.totalValue - base.totalValue
            let percent = NSDecimalNumber(decimal: change / base.totalValue).doubleValue * 100
            returns.append((date: current.date, value: percent))
        }
        rollingReturnData = returns
    }

    private func calculateRiskReturnData(
        for sources: [InvestmentSource],
        snapshotsBySource: [UUID: [Snapshot]]
    ) {
        let categories = categoryRepository.categories
        let sourcesByCategory = Dictionary(grouping: sources) { $0.category?.id ?? UUID() }

        riskReturnData = categories.compactMap { category in
            let categorySources = sourcesByCategory[category.id] ?? []
            let snapshots = categorySources.compactMap { source -> [Snapshot]? in
                let id = source.id
                return snapshotsBySource[id]
            }.flatMap { $0 }
            guard snapshots.count >= 3 else { return nil }
            let metrics = calculationService.calculateMetrics(for: snapshots)
            return (
                category: category.name,
                cagr: metrics.cagr,
                volatility: metrics.volatility,
                color: category.colorHex
            )
        }.sorted { $0.cagr > $1.cagr }
    }

    private func calculateCashflowData(from snapshots: [Snapshot]) {
        let monthlyTotals = monthlyTotals(from: snapshots)
        let contributionsByMonth = Dictionary(grouping: snapshots) { $0.date.startOfMonth }
            .mapValues { items in
                items.reduce(Decimal.zero) { $0 + $1.decimalContribution }
            }

        var data: [(date: Date, contributions: Decimal, netPerformance: Decimal)] = []
        for index in 0..<monthlyTotals.count {
            let current = monthlyTotals[index]
            let previousTotal = index > 0 ? monthlyTotals[index - 1].totalValue : 0
            let contributions = contributionsByMonth[current.date] ?? 0
            let netPerformance = current.totalValue - previousTotal - contributions
            data.append((date: current.date, contributions: contributions, netPerformance: netPerformance))
        }
        cashflowData = data
    }

    private func calculateDrawdownData(from snapshots: [Snapshot]) {
        let sortedSnapshots = snapshots.sorted { $0.date < $1.date }
        guard !sortedSnapshots.isEmpty else {
            drawdownData = []
            return
        }

        var peak = sortedSnapshots.first!.decimalValue
        var data: [(date: Date, drawdown: Double)] = []

        for snapshot in sortedSnapshots {
            let value = snapshot.decimalValue
            if value > peak {
                peak = value
            }

            let drawdown = peak > 0
                ? NSDecimalNumber(decimal: (peak - value) / peak).doubleValue * 100
                : 0

            data.append((date: snapshot.date, drawdown: -drawdown))
        }

        drawdownData = data
    }

    private func calculateVolatilityData(from snapshots: [Snapshot]) {
        let sortedSnapshots = snapshots.sorted { $0.date < $1.date }
        guard sortedSnapshots.count >= 3 else {
            volatilityData = []
            return
        }

        var data: [(date: Date, volatility: Double)] = []
        let windowSize = 3

        for i in windowSize..<sortedSnapshots.count {
            let window = Array(sortedSnapshots[(i - windowSize)..<i])
            let values = window.map { NSDecimalNumber(decimal: $0.decimalValue).doubleValue }

            let mean = values.reduce(0, +) / Double(values.count)
            let variance = values.map { pow($0 - mean, 2) }.reduce(0, +) / Double(values.count)
            let stdDev = sqrt(variance)
            let volatility = mean > 0 ? (stdDev / mean) * 100 : 0

            data.append((date: sortedSnapshots[i].date, volatility: volatility))
        }

        volatilityData = data
    }

    private func calculatePredictionData(from snapshots: [Snapshot]) {
        guard freemiumValidator.canViewPredictions() else {
            predictionData = []
            return
        }

        let result = predictionEngine.predict(snapshots: snapshots, monthsAhead: predictionMonthsAhead)
        predictionData = result.predictions
    }

    private func monthlyTotals(from snapshots: [Snapshot]) -> [(date: Date, totalValue: Decimal)] {
        let sortedSnapshots = snapshots.sorted { $0.date < $1.date }
        let months = Array(Set(sortedSnapshots.map { $0.date.startOfMonth })).sorted()
        guard !months.isEmpty else { return [] }

        var snapshotsBySource: [UUID: [Snapshot]] = [:]
        for snapshot in sortedSnapshots {
            guard let sourceId = snapshot.source?.id else { continue }
            snapshotsBySource[sourceId, default: []].append(snapshot)
        }

        var indices: [UUID: Int] = [:]
        var totals: [(date: Date, totalValue: Decimal)] = []

        for (index, month) in months.enumerated() {
            let nextMonth = index + 1 < months.count ? months[index + 1] : Date.distantFuture
            var total: Decimal = 0

            for (sourceId, sourceSnapshots) in snapshotsBySource {
                var currentIndex = indices[sourceId] ?? 0
                var latest: Snapshot?

                while currentIndex < sourceSnapshots.count && sourceSnapshots[currentIndex].date < nextMonth {
                    latest = sourceSnapshots[currentIndex]
                    currentIndex += 1
                }

                indices[sourceId] = currentIndex
                total += latest?.decimalValue ?? 0
            }

            totals.append((date: month, totalValue: total))
        }

        return totals
    }

    func updatePredictionTargetDate(_ goals: [Goal]) {
        let futureGoalDates = goals.compactMap { $0.targetDate }.filter { $0 > Date() }
        guard let latestGoalDate = futureGoalDates.max(),
              let lastSnapshotDate = evolutionData.last?.date else {
            predictionMonthsAhead = 12
            return
        }

        let months = max(1, lastSnapshotDate.startOfMonth.monthsBetween(latestGoalDate.startOfMonth))
        predictionMonthsAhead = max(12, months)
        if selectedChartType == .prediction {
            updateChartData(chartType: selectedChartType, category: selectedCategory, timeRange: selectedTimeRange)
        }
    }

    // MARK: - Computed Properties

    var categories: [Category] {
        categoryRepository.categories
    }

    var availableChartTypes: [ChartType] {
        ChartType.allCases
    }

    var isPremium: Bool {
        freemiumValidator.isPremium
    }

    var hasData: Bool {
        !sourceRepository.sources.filter { shouldIncludeSource($0) }.isEmpty
    }
}