// Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import Foundation

private enum Constants {
  static let longType = "type.googleapis.com/google.protobuf.Int64Value"
  static let unsignedLongType = "type.googleapis.com/google.protobuf.UInt64Value"
  static let dateType = "type.googleapis.com/google.protobuf.Timestamp"
}

extension FunctionsSerializer {
  enum Error: Swift.Error {
    case unsupportedType(typeName: String)
    case unknownNumberType(charValue: String, number: NSNumber)
    case invalidValueForType(value: String, requestedType: String)
  }
}

final class FunctionsSerializer: Sendable {
  // MARK: - Internal APIs

  func encode(_ object: Any) throws -> Any {
    if object is NSNull {
      return object
    } else if object is NSNumber {
      return try encodeNumber(object as! NSNumber)
    } else if object is NSString {
      return object
    } else if let dict = object as? NSDictionary {
      let encoded = NSMutableDictionary()
      try dict.forEach { key, value in
        encoded[key] = try encode(value)
      }
      return encoded
    } else if let array = object as? NSArray {
      return try array.map { element in
        try encode(element)
      }
    } else {
      throw Error.unsupportedType(typeName: typeName(of: object))
    }
  }

  func decode(_ object: Any) throws -> Any {
    // Return these types as is. PORTING NOTE: Moved from the bottom of the func for readability.
    if let dict = object as? NSDictionary {
      if let requestedType = dict["@type"] as? String {
        guard let value = dict["value"] as? String else {
          // Seems like we should throw here - but this maintains compatibility.
          return dict
        }
        if let result = try decodeWrappedType(requestedType, value) {
          return result
        }

        // Treat unknown types as dictionaries, so we don't crash old clients when we add types.
      }

      let decoded = NSMutableDictionary()
      try dict.forEach { key, value in
        decoded[key] = try decode(value)
      }
      return decoded
    } else if let array = object as? NSArray {
      let decoded = NSMutableArray(capacity: array.count)
      try array.forEach { element in
        try decoded.add(decode(element) as Any)
      }
      return decoded
    } else if object is NSNumber || object is NSString || object is NSNull {
      return object as AnyObject
    }

    throw Error.unsupportedType(typeName: typeName(of: object))
  }

  // MARK: - Private Helpers

  private func typeName(of value: Any) -> String {
    String(describing: type(of: value))
  }

  private func encodeNumber(_ number: NSNumber) throws -> AnyObject {
    // Recover the underlying type of the number, using the method described here:
    // http://stackoverflow.com/questions/2518761/get-type-of-nsnumber
    let cType = number.objCType

    // Type Encoding values taken from
    // https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/
    // Articles/ocrtTypeEncodings.html
    switch cType[0] {
    case CChar("q".utf8.first!):
      // "long long" might be larger than JS supports, so make it a string.
      return ["@type": Constants.longType, "value": "\(number)"] as AnyObject

    case CChar("Q".utf8.first!):
      // "unsigned long long" might be larger than JS supports, so make it a string.
      return ["@type": Constants.unsignedLongType,
              "value": "\(number)"] as AnyObject

    case CChar("i".utf8.first!),
         CChar("s".utf8.first!),
         CChar("l".utf8.first!),
         CChar("I".utf8.first!),
         CChar("S".utf8.first!):
      // If it"s an integer that isn"t too long, so just use the number.
      return number

    case CChar("f".utf8.first!), CChar("d".utf8.first!):
      // It"s a float/double that"s not too large.
      return number

    case CChar("B".utf8.first!), CChar("c".utf8.first!), CChar("C".utf8.first!):
      // Boolean values are weird.
      //
      // On arm64, objCType of a BOOL-valued NSNumber will be "c", even though @encode(BOOL)
      // returns "B". "c" is the same as @encode(signed char). Unfortunately this means that
      // legitimate usage of signed chars is impossible, but this should be rare.
      //
      // Just return Boolean values as-is.
      return number

    default:
      // All documented codes should be handled above, so this shouldn"t happen.
      throw Error.unknownNumberType(charValue: String(cType[0]), number: number)
    }
  }

  private func decodeWrappedType(_ type: String, _ value: String) throws -> AnyObject? {
    switch type {
    case Constants.longType:
      let formatter = NumberFormatter()
      guard let n = formatter.number(from: value) else {
        throw Error.invalidValueForType(value: value, requestedType: type)
      }
      return n

    case Constants.unsignedLongType:
      // NSNumber formatter doesn't handle unsigned long long, so we have to parse it.
      let str = (value as NSString).utf8String
      var endPtr: UnsafeMutablePointer<CChar>?
      let returnValue = UInt64(strtoul(str, &endPtr, 10))
      guard String(returnValue) == value else {
        throw Error.invalidValueForType(value: value, requestedType: type)
      }
      return NSNumber(value: returnValue)

    default:
      return nil
    }
  }
}