import Foundation
import ManaCore

/// Cards-spezifischer API-Client. Wrapper um `AuthenticatedTransport`
/// aus ManaCore, der die Cardecky-Endpoints kennt.
actor CardsAPI {
    private let transport: AuthenticatedTransport
    private let decoder: JSONDecoder

    init(auth: AuthClient) {
        transport = AuthenticatedTransport(baseURL: AppConfig.apiBaseURL, auth: auth)
        decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601withFractional
    }

    /// Health-Probe — verifiziert dass cardecky-api erreichbar ist
    /// und der eigene JWT akzeptiert wird.
    func healthCheck() async throws -> Bool {
        let (_, http) = try await transport.request(path: "/healthz")
        return http.statusCode == 200
    }

    // MARK: - Decks

    /// `GET /api/v1/decks?archived=false` — alle aktiven Decks des Users.
    /// Optional: `forkedFromMarketplaceOnly` filtert auf Inbox-Decks
    /// (für den Inbox-Banner).
    func listDecks(forkedFromMarketplaceOnly: Bool = false) async throws -> [Deck] {
        var path = "/api/v1/decks"
        if forkedFromMarketplaceOnly {
            path += "?forked_from_marketplace=true"
        }
        let (data, http) = try await transport.request(path: path)
        try ensureOK(http, data: data)
        let body = try decoder.decode(DeckListResponse.self, from: data)
        return body.decks
    }

    /// `GET /api/v1/cards?deck_id=...` — Anzahl Karten in einem Deck.
    /// Web macht das pro Deck einzeln; identisches Pattern hier.
    func cardCount(deckId: String) async throws -> Int {
        let (data, http) = try await transport.request(path: "/api/v1/cards?deck_id=\(deckId)")
        try ensureOK(http, data: data)
        return try decoder.decode(CardListResponse.self, from: data).total
    }

    /// `GET /api/v1/reviews/due?deck_id=...&limit=500` — Anzahl fälliger
    /// Reviews in einem Deck.
    func dueCount(deckId: String) async throws -> Int {
        let (data, http) = try await transport.request(
            path: "/api/v1/reviews/due?deck_id=\(deckId)&limit=500"
        )
        try ensureOK(http, data: data)
        return try decoder.decode(DueReviewsResponse.self, from: data).total
    }

    // MARK: - Study

    /// `GET /api/v1/reviews/due?deck_id=...&limit=500` — fällige Reviews
    /// inklusive zugehöriger Card-Daten. Hot-Path für die Study-View.
    func dueReviews(deckId: String, limit: Int = 500) async throws -> [DueReview] {
        let (data, http) = try await transport.request(
            path: "/api/v1/reviews/due?deck_id=\(deckId)&limit=\(limit)"
        )
        try ensureOK(http, data: data)
        return try decoder.decode(DueReviewsListResponse.self, from: data).reviews
    }

    /// `POST /api/v1/reviews/:cardId/:subIndex/grade` — gibt eine
    /// Bewertung ab. Server rechnet FSRS, antwortet mit aktualisiertem
    /// Review.
    @discardableResult
    func gradeReview(
        cardId: String,
        subIndex: Int,
        rating: Rating,
        reviewedAt: Date = .now
    ) async throws -> Review {
        let body = try makeJSON(GradeReviewBody(rating: rating, reviewedAt: reviewedAt))
        let (data, http) = try await transport.request(
            path: "/api/v1/reviews/\(cardId)/\(subIndex)/grade",
            method: "POST",
            body: body
        )
        try ensureOK(http, data: data)
        return try decoder.decode(Review.self, from: data)
    }

    // MARK: - JSON-Encoding

    private func makeJSON<T: Encodable>(_ value: T) throws -> Data {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        return try encoder.encode(value)
    }

    // MARK: - Helpers

    private func ensureOK(_ http: HTTPURLResponse, data: Data) throws {
        guard (200 ..< 300).contains(http.statusCode) else {
            let message = (try? JSONDecoder().decode(CardsServerError.self, from: data))?.error
            throw AuthError.serverError(status: http.statusCode, message: message)
        }
    }
}

private struct CardsServerError: Decodable {
    let error: String?
}

extension JSONDecoder.DateDecodingStrategy {
    /// Cards-API liefert ISO8601 mit Fractional-Seconds aus
    /// `.toISOString()`. Standard-Strategy `.iso8601` akzeptiert die
    /// fractional seconds nicht — wir nutzen einen eigenen Formatter.
    static let iso8601withFractional: JSONDecoder.DateDecodingStrategy = .custom { decoder in
        let container = try decoder.singleValueContainer()
        let raw = try container.decode(String.self)
        let f = ISO8601DateFormatter()
        f.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        if let date = f.date(from: raw) { return date }
        f.formatOptions = [.withInternetDateTime]
        if let date = f.date(from: raw) { return date }
        throw DecodingError.dataCorruptedError(
            in: container,
            debugDescription: "Cannot decode ISO8601 date: \(raw)"
        )
    }
}