import Foundation

/// USD prices for the two tickers the wallet supports, fetched from a public
/// price API and cached briefly so a screen does not fetch on every refresh.
final class PriceService {
  static let shared = PriceService()

  struct Prices: Codable {
    var xrp: Double?
    var xmr: Double?
    var fetchedAt: Date?
  }

  private static let cacheLifetime: TimeInterval = 60
  private var memory: Prices?
  private var inFlight: Task<Prices, Never>?

  private init() {}

  func prices() async -> Prices {
    if let memory, let fetchedAt = memory.fetchedAt,
       Date().timeIntervalSince(fetchedAt) < Self.cacheLifetime {
      return memory
    }
    if let inFlight { return await inFlight.value }

    let task = Task<Prices, Never> { [weak self] in
      guard let self else { return Prices(fetchedAt: nil) }
      let prices = await self.fetch()
      self.memory = prices
      return prices
    }
    inFlight = task
    let result = await task.value
    inFlight = nil
    return result
  }

  private func fetch() async -> Prices {
    if let prices = try? await fromCoinGecko() { return prices }
    return (try? await fromKraken()) ?? Prices(fetchedAt: nil)
  }

  private func fromCoinGecko() async throws -> Prices {
    guard let url = URL(string: "https://api.coingecko.com/api/v3/simple/price?ids=monero,ripple&vs_currencies=usd") else {
      throw XRPError.network("Invalid price endpoint")
    }
    let (data, response) = try await URLSession.shared.data(from: url)
    guard let http = response as? HTTPURLResponse, (200..<300).contains(http.statusCode) else {
      throw XRPError.network("CoinGecko request failed")
    }
    let json = try JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
    return Prices(
      xrp: (json["ripple"] as? [String: Any]).flatMap { ($0["usd"] as? NSNumber)?.doubleValue },
      xmr: (json["monero"] as? [String: Any]).flatMap { ($0["usd"] as? NSNumber)?.doubleValue },
      fetchedAt: Date())
  }

  private func fromKraken() async throws -> Prices {
    guard let url = URL(string: "https://api.kraken.com/0/public/Ticker?pair=XRPUSD,XMRUSD") else {
      throw XRPError.network("Invalid price endpoint")
    }
    let (data, response) = try await URLSession.shared.data(from: url)
    guard let http = response as? HTTPURLResponse, (200..<300).contains(http.statusCode) else {
      throw XRPError.network("Kraken request failed")
    }
    let json = try JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
    let result = json["result"] as? [String: Any] ?? [:]

    func lastTrade(_ key: String) -> Double? {
      (result[key] as? [String: Any])
        .flatMap { entry in (entry["c"] as? [Any])?.first }
        .flatMap { ($0 as? String).flatMap(Double.init) }
    }
    return Prices(xrp: lastTrade("XXRPZUSD") ?? lastTrade("XRPUSD"),
                  xmr: lastTrade("XXMRZUSD") ?? lastTrade("XMRUSD"),
                  fetchedAt: Date())
  }
}