import Foundation

// Banked limit-reset credits ("goodwill resets"): OpenAI grants a Codex account
// a credit that restores a rate-limit window early. They arrive without warning
// from the app's point of view — the only evidence we have is that a new credit
// appears in the `rate-limit-reset-credits` inventory we already fetch on the
// existing usage cadence. Nothing here polls, and nothing here ever spends a
// credit: this is a notice, not an action.

// MARK: - Persisted state

/// What we have already seen, so a credit announces itself exactly once — across
/// refreshes, across a failed fetch, and across a relaunch.
///
/// Persisted with the same mechanism `SubscriptionSnapshotStore` uses (one JSON
/// document in the CodeBurn cache directory, written through `SafeFile`), not a
/// second one.
struct CodexBankedResetState: Codable, Sendable, Equatable {
    struct SeenCredit: Codable, Sendable, Equatable {
        let id: String
        let firstSeenAt: Date
    }

    /// Nil until the first successful observation. Its absence is what makes
    /// that first observation a baseline instead of a burst of notifications
    /// for every credit the account already held.
    var baselineAt: Date?
    var credits: [SeenCredit]

    init(baselineAt: Date? = nil, credits: [SeenCredit] = []) {
        self.baselineAt = baselineAt
        self.credits = credits
    }
}

// MARK: - Detection

/// Pure: takes an observation and the state it is judged against, returns the
/// events and the state to persist. No clock, no disk, no network.
enum CodexBankedResetDetector {
    /// Ids of credits that are gone from the payload are kept this long before
    /// being forgotten, so a credit that flickers out of one response and back
    /// into the next cannot announce itself twice. Mirrors the 30-day retention
    /// `SubscriptionSnapshotStore` prunes to.
    static let retentionSeconds: TimeInterval = 30 * 24 * 3600

    struct Outcome: Equatable {
        /// Credits observed for the first time, in payload order. Empty for a
        /// baseline observation, for an unchanged inventory, and for every
        /// observation we have no opinion about.
        let events: [CodexUsage.ResetCredits.Grant]
        let state: CodexBankedResetState
    }

    /// `observed == nil` means the credits payload was absent or malformed. That
    /// is "no opinion", never an event and never a state change: a reconnect
    /// after a failed fetch must not re-baseline, and a schema drift must not
    /// silently forget every credit we have already announced.
    static func evaluate(
        observed: CodexUsage.ResetCredits?,
        state: CodexBankedResetState,
        now: Date
    ) -> Outcome {
        guard let observed else { return Outcome(events: [], state: state) }
        // Only credits the parser could give a stable identity to are in here;
        // an unidentifiable credit still counts toward `availableCount` but can
        // never be told apart from the next one, so it never fires.
        let grants = observed.grants

        guard state.baselineAt != nil else {
            // First-ever observation: everything the account holds is history,
            // not news.
            return Outcome(
                events: [],
                state: CodexBankedResetState(
                    baselineAt: now,
                    credits: grants.map { .init(id: $0.id, firstSeenAt: now) }
                )
            )
        }

        var knownIDs = Set(state.credits.map(\.id))
        var credits = state.credits
        var events: [CodexUsage.ResetCredits.Grant] = []
        for grant in grants where knownIDs.insert(grant.id).inserted {
            events.append(grant)
            credits.append(.init(id: grant.id, firstSeenAt: now))
        }

        // A credit that disappears was consumed or expired — never an event. Its
        // id is held for the retention window so it cannot come back as news.
        let observedIDs = Set(grants.map(\.id))
        let cutoff = now.addingTimeInterval(-retentionSeconds)
        credits = credits.filter { observedIDs.contains($0.id) || $0.firstSeenAt >= cutoff }

        return Outcome(events: events, state: CodexBankedResetState(baselineAt: state.baselineAt, credits: credits))
    }
}

// MARK: - Wording

/// The one place the banked-reset wording lives. `src/quota/codex.ts` carries a
/// line-for-line mirror of `detail` and `compactAge` so the CLI and the menubar
/// say the same sentence.
enum CodexBankedResetPresentation {
    /// Label the detail hangs off, in the Plan tab and in front of the detail on
    /// every other surface.
    static var rowLabel: String { L("Limit resets") }

    /// `2 available · 1 usable now · latest weekly reset granted 2h ago · next expires in 16h`
    /// Nil when the account holds nothing — the row hides rather than printing a zero.
    static func detail(_ credits: CodexUsage.ResetCredits, now: Date) -> String? {
        guard credits.availableCount > 0 else { return nil }
        var parts = [L("%lld available", credits.availableCount)]
        // Only worth saying when it disagrees with the headline count: equal
        // numbers would just be the same fact twice.
        if let applicable = credits.applicableAvailableCount, applicable != credits.availableCount {
            parts.append(L("%lld usable now", applicable))
        }
        if let grant = credits.latestGrant, let grantedAt = grant.grantedAt {
            let type = resetTypeLabel(grant.resetType)
            parts.append(grantedAt > now
                ? L("next %1$@ lands %2$@", type, compactAge(of: grantedAt, now: now))
                : L("latest %1$@ granted %2$@", type, compactAge(of: grantedAt, now: now)))
        }
        if let expiry = credits.nextExpiresAt {
            parts.append(L("next expires %@", compactAge(of: expiry, now: now)))
        }
        return parts.joined(separator: " · ")
    }

    /// `Limit resets · 2 available · …`, the single-string form the quota hover
    /// card and `codeburn quota` both print.
    static func line(_ credits: CodexUsage.ResetCredits, now: Date) -> String? {
        detail(credits, now: now).map { "\(rowLabel) · \($0)" }
    }

    /// Notification copy for one newly observed credit: what was granted, when,
    /// and how many the account can use. Never the credit id — it is an account
    /// identifier of sorts and says nothing to the user.
    static func notice(
        for grant: CodexUsage.ResetCredits.Grant,
        credits: CodexUsage.ResetCredits,
        now: Date
    ) -> (title: String, body: String) {
        let type = resetTypeLabel(grant.resetType)
        var body: String
        if let grantedAt = grant.grantedAt {
            body = grantedAt > now
                ? L("A %1$@ lands %2$@.", type, compactAge(of: grantedAt, now: now))
                : L("A %1$@ was added to your account %2$@.", type, compactAge(of: grantedAt, now: now))
        } else {
            body = L("A %@ was added to your account.", type)
        }
        // `applicable_available_count` is the number that answers "can I use one
        // right now"; the plain count is the fallback when it is absent.
        let usable = credits.applicableAvailableCount ?? credits.availableCount
        body += " " + L("You have %lld available to use.", usable)
        return (L("Codex banked a limit reset"), body)
    }

    /// "weekly" -> "weekly reset". An absent or empty `reset_type` degrades to
    /// the bare noun rather than inventing a scope the payload did not state.
    ///
    /// `reset_type` is vendor data with no fixed vocabulary, so only the cadence
    /// words OpenAI has actually sent are translated; anything else rides
    /// through verbatim inside a translated frame.
    static func resetTypeLabel(_ resetType: String?) -> String {
        let raw = (resetType ?? "")
            .trimmingCharacters(in: .whitespacesAndNewlines)
            .replacingOccurrences(of: "_", with: " ")
            .replacingOccurrences(of: "-", with: " ")
            .lowercased()
        guard !raw.isEmpty else { return L("limit reset") }
        let cadence = switch raw {
        case "weekly": L("weekly")
        case "daily": L("daily")
        case "monthly": L("monthly")
        case "hourly": L("hourly")
        default: raw
        }
        return L("%@ reset", cadence)
    }

    /// Deliberately not `RelativeDateTimeFormatter`: the English form has to
    /// come out character-identical in Swift and in TypeScript, so the rules
    /// are spelled out instead of delegated to a locale-aware formatter. The
    /// catalog keeps that: `en` is an identity table, so English is the key.
    /// Other locales diverge from the CLI, which is not localized.
    static func compactAge(of date: Date, now: Date) -> String {
        let elapsed = now.timeIntervalSince(date)
        if elapsed >= 0 {
            if elapsed < 60 { return L("just now") }
            if elapsed < 3600 { return L("%lldm ago", Int(elapsed / 60)) }
            if elapsed < 86_400 { return L("%lldh ago", Int(elapsed / 3600)) }
            return L("%lldd ago", Int(elapsed / 86_400))
        }
        let ahead = -elapsed
        if ahead < 60 { return L("in under a minute") }
        if ahead < 3600 { return L("in %lldm", Int(ahead / 60)) }
        if ahead < 86_400 { return L("in %lldh", Int(ahead / 3600)) }
        return L("in %lldd", Int(ahead / 86_400))
    }
}

// MARK: - Persistence

protocol CodexBankedResetStateStoring: Sendable {
    func load() async -> CodexBankedResetState
    func save(_ state: CodexBankedResetState) async
}

private let bankedResetFilename = "codex-banked-resets.json"

private func bankedResetPath() -> String {
    (CodeBurnCacheDirectory.resolve() as NSString).appendingPathComponent(bankedResetFilename)
}

private actor BankedResetLock {
    static let shared = BankedResetLock()
    func run<T>(_ fn: () throws -> T) rethrows -> T { try fn() }
}

/// Same shape as `SubscriptionSnapshotStore`: one JSON document in the CodeBurn
/// cache directory, serialized behind an actor, written 0600 through `SafeFile`
/// (which refuses a symlinked target and does the tmp+rename dance).
struct CodexBankedResetStore: CodexBankedResetStateStoring {
    func load() async -> CodexBankedResetState {
        await BankedResetLock.shared.run {
            let path = bankedResetPath()
            guard FileManager.default.fileExists(atPath: path),
                  let data = try? SafeFile.read(from: path) else { return CodexBankedResetState() }
            let decoder = JSONDecoder()
            decoder.dateDecodingStrategy = .iso8601
            return (try? decoder.decode(CodexBankedResetState.self, from: data)) ?? CodexBankedResetState()
        }
    }

    func save(_ state: CodexBankedResetState) async {
        await BankedResetLock.shared.run {
            do {
                let encoder = JSONEncoder()
                encoder.dateEncodingStrategy = .iso8601
                try SafeFile.write(encoder.encode(state), to: bankedResetPath(), mode: 0o600)
            } catch {
                NSLog("CodeBurn: codex banked-reset state write failed: %@", String(describing: error))
            }
        }
    }

    /// Called on disconnect, so a reconnect under a different account baselines
    /// again instead of announcing that account's whole inventory.
    static func clearAll() async {
        await BankedResetLock.shared.run {
            try? FileManager.default.removeItem(atPath: bankedResetPath())
        }
    }
}

// MARK: - Preference

/// Absent key is true, matching `UpdateNotificationPreference`: existing installs
/// get the notice without visiting Settings first.
enum CodexBankedResetNotificationPreference {
    static let defaultsKey = "codeburn.codex.bankedResetNotificationsEnabled"

    static func isEnabled(defaults: UserDefaults = .standard) -> Bool {
        defaults.object(forKey: defaultsKey) as? Bool ?? true
    }
}

// MARK: - Announcer

/// Wires the pure detector to the existing notification path. Owns no fetch: it
/// is handed whatever the usage refresh already decoded.
@MainActor
final class CodexBankedResetAnnouncer {
    private let defaults: UserDefaults
    private let store: any CodexBankedResetStateStoring
    private let makeNotifier: () -> any UpdateNotifier
    private var notifier: (any UpdateNotifier)?
    private var isObserving = false

    init(
        defaults: UserDefaults = .standard,
        store: any CodexBankedResetStateStoring = CodexBankedResetStore(),
        makeNotifier: @escaping () -> any UpdateNotifier = { SystemUpdateNotifier() }
    ) {
        self.defaults = defaults
        self.store = store
        self.makeNotifier = makeNotifier
    }

    func observe(_ credits: CodexUsage.ResetCredits?, now: Date = Date()) async {
        // The load/save pair spans two awaits; a second refresh landing inside
        // it would judge against pre-save state and post twice. Skipping is
        // free — the next refresh observes the same inventory.
        guard !isObserving else { return }
        isObserving = true
        defer { isObserving = false }

        let state = await store.load()
        let outcome = CodexBankedResetDetector.evaluate(observed: credits, state: state, now: now)
        guard outcome.state != state else { return }
        // Persisted before the post, not after: a notice we drop is a smaller
        // failure than one that repeats on every refresh.
        await store.save(outcome.state)
        guard !outcome.events.isEmpty, let credits else { return }
        // The state is recorded either way, so turning the toggle back on does
        // not release a backlog of grants that landed while it was off.
        guard CodexBankedResetNotificationPreference.isEnabled(defaults: defaults) else { return }
        let notifier = notifier ?? makeNotifier()
        self.notifier = notifier
        guard await notifier.requestAuthorizationIfNeeded() else { return }
        for event in outcome.events {
            let copy = CodexBankedResetPresentation.notice(for: event, credits: credits, now: now)
            notifier.post(title: copy.title, body: copy.body, identifier: "CodexBankedReset.\(event.id)")
        }
    }
}