import CoreImage
import CoreImage.CIFilterBuiltins
import Foundation
import UIKit
import Vision

/// Renders a QR image (used by the UI and by the self-test, which round-trips
/// an image through the reader).
enum QRCodeImage {
  static func make(_ text: String, scale: CGFloat = 10) -> UIImage? {
    guard !text.isEmpty else { return nil }
    let filter = CIFilter.qrCodeGenerator()
    filter.message = Data(text.utf8)
    filter.correctionLevel = "M"
    guard let output = filter.outputImage else { return nil }
    let scaled = output.transformed(by: CGAffineTransform(scaleX: scale, y: scale))
    let context = CIContext()
    guard let cgImage = context.createCGImage(scaled, from: scaled.extent) else { return nil }
    return UIImage(cgImage: cgImage)
  }
}

/// A payment request decoded from a QR code: the address plus whatever else the
/// code carried.
struct QRPayload {
  var address: String
  var amount: String?
  var tag: UInt32?
  var paymentId: String?
  var memo: String?
}

enum QRCodeReader {
  /// Reads the first QR code found in an image (used for photo-library import).
  static func decodeText(in data: Data) -> String? {
    guard let image = UIImage(data: data), let cgImage = image.cgImage else { return nil }
    return decodeText(in: cgImage)
  }

  static func decodeText(in image: UIImage) -> String? {
    guard let cgImage = image.cgImage else { return nil }
    return decodeText(in: cgImage)
  }

  private static func decodeText(in cgImage: CGImage) -> String? {
    if let text = decodeWithVision(cgImage) { return text }
    // Vision's barcode detector does not work on the iOS simulator, so fall
    // back to CoreImage, which does (and adds redundancy on device).
    return decodeWithCoreImage(cgImage)
  }

  private static func decodeWithVision(_ cgImage: CGImage) -> String? {
    let request = VNDetectBarcodesRequest()
    request.symbologies = [.qr]
    let handler = VNImageRequestHandler(cgImage: cgImage, orientation: .up)
    try? handler.perform([request])
    for observation in request.results ?? [] {
      if let payload = observation.payloadStringValue, !payload.isEmpty {
        return payload
      }
    }
    return nil
  }

  private static func decodeWithCoreImage(_ cgImage: CGImage) -> String? {
    let detector = CIDetector(ofType: CIDetectorTypeQRCode,
                              context: nil,
                              options: [CIDetectorAccuracy: CIDetectorAccuracyHigh])
    let features = detector?.features(in: CIImage(cgImage: cgImage)) ?? []
    for feature in features {
      if let code = feature as? CIQRCodeFeature, let message = code.messageString, !message.isEmpty {
        return message
      }
    }
    return nil
  }

  /// Understands plain addresses as well as the payment URIs wallets emit:
  /// `monero:` (tx_amount, tx_payment_id, tx_description) and `ripple:`
  /// (amount, dt).
  static func parse(_ raw: String) -> QRPayload? {
    let text = raw.trimmingCharacters(in: .whitespacesAndNewlines)
    guard !text.isEmpty else { return nil }

    var body = text
    var query: [String: String] = [:]

    if let separator = text.firstIndex(of: "?") {
      body = String(text[text.startIndex..<separator])
      let queryText = String(text[text.index(after: separator)...])
      for pair in queryText.split(separator: "&") {
        let parts = pair.split(separator: "=", maxSplits: 1)
        guard let key = parts.first else { continue }
        let value = parts.count > 1 ? String(parts[1]) : ""
        query[key.lowercased()] = value.removingPercentEncoding ?? value
      }
    }

    let lowered = body.lowercased()
    if let range = lowered.range(of: "monero:") {
      body = String(body[range.upperBound...])
    } else if let range = lowered.range(of: "ripple:") {
      body = String(body[range.upperBound...])
    }
    while body.hasPrefix("/") { body.removeFirst() }

    let address = body.trimmingCharacters(in: .whitespacesAndNewlines)
    guard !address.isEmpty else { return nil }

    var payload = QRPayload(address: address)
    payload.amount = query["tx_amount"] ?? query["amount"]
    payload.memo = query["tx_description"] ?? query["name"] ?? query["message"]
    payload.paymentId = query["tx_payment_id"] ?? query["payment_id"] ?? query["pid"]
    if let tag = query["dt"] ?? query["destination_tag"] ?? query["destinationtag"] {
      payload.tag = UInt32(tag)
    }
    return payload
  }
}

enum AddressFormat {
  private static let moneroAlphabet = Set("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")

  /// Monero addresses are 95 characters (primary/subaddress) or 106
  /// (integrated), all base58.
  static func isMonero(_ address: String) -> Bool {
    let text = address.trimmingCharacters(in: .whitespacesAndNewlines)
    guard text.count == 95 || text.count == 106 else { return false }
    return text.allSatisfy { moneroAlphabet.contains($0) }
  }

  static func isXRP(_ address: String) -> Bool {
    XRPKey.isValidAddress(address.trimmingCharacters(in: .whitespacesAndNewlines))
  }
}