import Foundation
import Observation

private let cacheTTLSeconds: TimeInterval = 30

struct CachedPayload {
    let payload: MenubarPayload
    let fetchedAt: Date
    var isFresh: Bool { Date().timeIntervalSince(fetchedAt) < cacheTTLSeconds }
}

struct PayloadCacheKey: Hashable {
    let period: Period
    let provider: ProviderFilter
}

@MainActor
@Observable
final class AppStore {
    var selectedProvider: ProviderFilter = .all
    var selectedPeriod: Period = .today
    var selectedInsight: InsightMode = .trend
    var currency: String = "USD"
    var isLoading: Bool = false
    var lastError: String?
    var subscription: SubscriptionUsage?
    var subscriptionError: String?
    var subscriptionLoadState: SubscriptionLoadState = .idle
    var capacityEstimates: [String: CapacityEstimate] = [:]

    private var cache: [PayloadCacheKey: CachedPayload] = [:]

    private var currentKey: PayloadCacheKey {
        PayloadCacheKey(period: selectedPeriod, provider: selectedProvider)
    }

    var payload: MenubarPayload {
        cache[currentKey]?.payload ?? .empty
    }

    /// Today (across all providers) is pinned for the always-visible menubar icon, independent of
    /// the popover's selected period or provider.
    var todayPayload: MenubarPayload? {
        cache[PayloadCacheKey(period: .today, provider: .all)]?.payload
    }

    var hasCachedData: Bool {
        cache[currentKey] != nil
    }

    var findingsCount: Int {
        payload.optimize.findingCount
    }

    /// Switch to a period. Always fetches fresh data so the user never sees stale numbers.
    func switchTo(period: Period) async {
        selectedPeriod = period
        await refresh(includeOptimize: true)
    }

    /// Switch to a provider filter. Always fetches fresh data so the user never sees stale numbers.
    func switchTo(provider: ProviderFilter) async {
        selectedProvider = provider
        await refresh(includeOptimize: true)
    }

    private var inFlightKeys: Set<PayloadCacheKey> = []

    /// Refresh the currently selected (period, provider) combination. Guards against concurrent
    /// fetches for the same key so a slow initial request can't overwrite a newer one that
    /// finished first (which would show stale numbers the user has already moved past).
    func refresh(includeOptimize: Bool) async {
        let key = currentKey
        guard !inFlightKeys.contains(key) else { return }
        inFlightKeys.insert(key)
        let showLoading = cache[key] == nil
        if showLoading { isLoading = true }
        defer {
            inFlightKeys.remove(key)
            if showLoading { isLoading = false }
        }
        do {
            let fresh = try await DataClient.fetch(period: key.period, provider: key.provider, includeOptimize: includeOptimize)
            cache[key] = CachedPayload(payload: fresh, fetchedAt: Date())
            lastError = nil
        } catch {
            lastError = String(describing: error)
            NSLog("CodeBurn: fetch failed for \(key.period.rawValue)/\(key.provider.rawValue): \(error)")
        }
    }

    /// Background refresh for a period other than the visible one (e.g. keeping today fresh for the menubar badge).
    /// Does not toggle isLoading, so the popover's loading overlay is unaffected.
    /// Always uses the .all provider since the menubar badge shows total spend.
    func refreshQuietly(period: Period) async {
        do {
            let fresh = try await DataClient.fetch(period: period, provider: .all, includeOptimize: true)
            cache[PayloadCacheKey(period: period, provider: .all)] = CachedPayload(payload: fresh, fetchedAt: Date())
        } catch {
            NSLog("CodeBurn: quiet refresh failed for \(period.rawValue): \(error)")
        }
    }

    /// Fetch Claude subscription usage. Sets subscription = nil on missing creds (API users / unauthenticated).
    /// Triggered lazily when the user opens the Plan pill, so the Keychain prompt only fires on intent.
    func refreshSubscription() async {
        subscriptionLoadState = .loading
        do {
            let usage = try await SubscriptionClient.fetch()
            subscription = usage
            subscriptionError = nil
            subscriptionLoadState = .loaded
            await captureSnapshots(for: usage)
        } catch SubscriptionError.noCredentials {
            subscription = nil
            subscriptionError = nil
            subscriptionLoadState = .noCredentials
        } catch {
            subscription = nil
            subscriptionError = String(describing: error)
            subscriptionLoadState = .failed
            NSLog("CodeBurn: subscription fetch failed: \(error)")
        }
    }

    /// Persist one snapshot per window so we can answer "what did the prior cycle end at?"
    /// when the current window has just reset and projection from current data isn't meaningful.
    /// Also computes the effective_tokens consumed inside each 7-day window from local history,
    /// which the CapacityEstimator uses to derive the absolute token capacity per tier.
    private func captureSnapshots(for usage: SubscriptionUsage) async {
        let now = Date()
        let history = payload.history.daily

        let captures: [(key: String, percent: Double?, resetsAt: Date?, effective: Double?)] = [
            ("five_hour", usage.fiveHourPercent, usage.fiveHourResetsAt, nil),
            ("seven_day", usage.sevenDayPercent, usage.sevenDayResetsAt,
             effectiveTokensInLast7Days(history: history, asOf: now)),
            ("seven_day_opus", usage.sevenDayOpusPercent, usage.sevenDayOpusResetsAt, nil),
            ("seven_day_sonnet", usage.sevenDaySonnetPercent, usage.sevenDaySonnetResetsAt, nil),
        ]
        for capture in captures {
            guard let percent = capture.percent, let resetsAt = capture.resetsAt else { continue }
            await SubscriptionSnapshotStore.record(SubscriptionSnapshot(
                windowKey: capture.key,
                percent: percent,
                resetsAt: resetsAt,
                capturedAt: now,
                effectiveTokens: capture.effective
            ))
        }

        await refreshCapacityEstimates()
    }

    /// Sum effective tokens (input + 5*output + cache_creation + 0.1*cache_read) across the
    /// last 7 days of dailyHistory. Used as the "tokens consumed in 7-day window" reading paired
    /// with the API-reported percent for capacity estimation.
    private func effectiveTokensInLast7Days(history: [DailyHistoryEntry], asOf now: Date) -> Double {
        let cutoff = ISO8601DateFormatter().string(from: now.addingTimeInterval(-7 * 86400)).prefix(10)
        return history
            .filter { $0.date >= cutoff }
            .reduce(0.0) { $0 + $1.effectiveTokens }
    }

    /// Run CapacityEstimator over each window's accumulated snapshots. Only snapshots with a
    /// non-nil effectiveTokens contribute. Result lives in capacityEstimates dict for UI gating.
    private func refreshCapacityEstimates() async {
        var next: [String: CapacityEstimate] = [:]
        for key in ["seven_day", "seven_day_opus", "seven_day_sonnet"] {
            let snaps = await SubscriptionSnapshotStore.snapshots(for: key)
            let capacitySnaps = snaps.compactMap { s -> CapacitySnapshot? in
                guard let effective = s.effectiveTokens, effective > 0 else { return nil }
                return CapacitySnapshot(percent: s.percent, effectiveTokens: effective, capturedAt: s.capturedAt)
            }
            if let estimate = CapacityEstimator.estimate(capacitySnaps) {
                next[key] = estimate
            }
        }
        capacityEstimates = next
    }
}

enum SupportedCurrency: String, CaseIterable, Identifiable {
    case USD, GBP, EUR, AUD, CAD, NZD, JPY, CHF, INR, BRL, SEK, SGD, HKD, KRW, MXN, ZAR, DKK
    var id: String { rawValue }
    var displayName: String {
        switch self {
        case .USD: "US Dollar"
        case .GBP: "British Pound"
        case .EUR: "Euro"
        case .AUD: "Australian Dollar"
        case .CAD: "Canadian Dollar"
        case .NZD: "New Zealand Dollar"
        case .JPY: "Japanese Yen"
        case .CHF: "Swiss Franc"
        case .INR: "Indian Rupee"
        case .BRL: "Brazilian Real"
        case .SEK: "Swedish Krona"
        case .SGD: "Singapore Dollar"
        case .HKD: "Hong Kong Dollar"
        case .KRW: "South Korean Won"
        case .MXN: "Mexican Peso"
        case .ZAR: "South African Rand"
        case .DKK: "Danish Krone"
        }
    }
}

enum ProviderFilter: String, CaseIterable, Identifiable {
    case all = "All"
    case claude = "Claude"
    case codex = "Codex"
    case cursor = "Cursor"
    case copilot = "Copilot"
    case opencode = "OpenCode"
    case pi = "Pi"

    var id: String { rawValue }

    /// Maps to the CLI's `--provider` argument values.
    var cliArg: String {
        switch self {
        case .all: "all"
        case .claude: "claude"
        case .codex: "codex"
        case .cursor: "cursor"
        case .copilot: "copilot"
        case .opencode: "opencode"
        case .pi: "pi"
        }
    }
}

enum SubscriptionLoadState: Sendable, Equatable {
    case idle           // never tried, awaiting user intent
    case loading        // fetch in progress
    case loaded         // success; subscription is populated
    case noCredentials  // tried; user has no Claude OAuth (API user / not logged in)
    case failed         // tried; error occurred
}

enum InsightMode: String, CaseIterable, Identifiable {
    case plan = "Plan"
    case trend = "Trend"
    case forecast = "Forecast"
    case pulse = "Pulse"
    case stats = "Stats"
    var id: String { rawValue }
}

enum Period: String, CaseIterable, Identifiable {
    case today = "Today"
    case sevenDays = "7 Days"
    case thirtyDays = "30 Days"
    case month = "Month"
    case all = "All"

    var id: String { rawValue }

    /// Maps to the CLI's `--period` argument values.
    var cliArg: String {
        switch self {
        case .today: "today"
        case .sevenDays: "week"
        case .thirtyDays: "30days"
        case .month: "month"
        case .all: "all"
        }
    }
}

/// NumberFormatter is expensive to instantiate (~microseconds each) and currency/token values
/// are formatted dozens of times per popover refresh. These shared instances avoid thousands of
/// allocations per frame while SwiftUI's Observation framework still triggers redraws when
/// CurrencyState.shared mutates.
private let groupedDecimalFormatter: NumberFormatter = {
    let f = NumberFormatter()
    f.numberStyle = .decimal
    f.groupingSeparator = ","
    f.decimalSeparator = "."
    f.maximumFractionDigits = 2
    f.minimumFractionDigits = 2
    return f
}()

private let thousandsFormatter: NumberFormatter = {
    let f = NumberFormatter()
    f.numberStyle = .decimal
    f.groupingSeparator = ","
    return f
}()

extension Double {
    func asCurrency() -> String {
        let state = CurrencyState.shared
        let converted = self * state.rate
        return state.symbol + (groupedDecimalFormatter.string(from: NSNumber(value: converted)) ?? "\(converted)")
    }

    func asCompactCurrency() -> String {
        let state = CurrencyState.shared
        return String(format: "\(state.symbol)%.2f", self * state.rate)
    }
}

extension Int {
    func asThousandsSeparated() -> String {
        thousandsFormatter.string(from: NSNumber(value: self)) ?? "\(self)"
    }
}