InputFilter.swift

//

import Foundation

public final class InputFilter {

  private final class Storage<T> {

    let lock = NSLock()

    var rawStorage: [CodeLocation : T] = [:]

    func value(for key: CodeLocation) -> T? {
      guard let value = rawStorage[key] else {
        return nil
      }

      return value
    }

    func setValue(_ value: T, for key: CodeLocation) {
      rawStorage[key] = value
    }
  }

  private struct CodeLocation: Hashable {
    let file: String
    let line: UInt
    let column: UInt
  }

  private let _anyStorage: Storage<Any> = .init()
  private let _intStorage: Storage<Int> = .init()
  private let _stringStorage: Storage<String> = .init()

  private func _doIfChanged<T>(
    targetStorage: Storage<Any>,
    key: CodeLocation,
    value: T,
    compare: (T, T) -> Bool,
    perform: (T) -> Void
  ) {

    targetStorage.lock.lock()

    guard let cachedRawValue = targetStorage.value(for: key) else {
      targetStorage.setValue(value, for: key)
      targetStorage.lock.unlock()
      perform(value)
      return
    }

    let cachedValue = cachedRawValue as! T

    guard compare(cachedValue, value) == false else {
      targetStorage.lock.unlock()
      return
    }

    targetStorage.setValue(value, for: key)

    targetStorage.lock.unlock()

    perform(value)

  }

  private func _specialized_doIfChanged<T>(
    targetStorage: Storage<T>,
    key: CodeLocation,
    value: T,
    compare: (T, T) -> Bool,
    perform: (T) -> Void
  ) {

    targetStorage.lock.lock()

    guard let cachedValue: T = targetStorage.value(for: key) else {
      targetStorage.setValue(value, for: key)
      targetStorage.lock.unlock()
      perform(value)
      return
    }

    guard compare(cachedValue, value) == false else {
      targetStorage.lock.unlock()
      return
    }

    targetStorage.setValue(value, for: key)

    targetStorage.lock.unlock()

    perform(value)

  }

  /// [Experimental]
  /// should be renamed
  public func doIfChanged<T>(
    file: StaticString = #file,
    line: UInt = #line,
    column: UInt = #column,
    _ value: T,
    _ compare: @escaping (T, T) -> Bool,
    _ perform: (T) -> Void
  ) {

    _doIfChanged(
      targetStorage: _anyStorage,
      key: .init(file: file.description, line: line, column: column),
      value: value,
      compare: compare,
      perform: perform
    )

  }

  /// [Experimental]
  /// should be renamed
  public func doIfChanged<T: Equatable>(
    file: StaticString = #file,
    line: UInt = #line,
    column: UInt = #column,
    _ value: T,
    _ perform: (T) -> Void
  ) {

    _doIfChanged(
      targetStorage: _anyStorage,
      key: .init(file: file.description, line: line, column: column),
      value: value,
      compare: ==,
      perform: perform
    )

  }

  /// [Experimental] [Specialized]
  /// should be renamed
  public func doIfChanged(
    file: StaticString = #file,
    line: UInt = #line,
    column: UInt = #column,
    _ value: Int,
    _ perform: (Int) -> Void
  ) {

    _specialized_doIfChanged(
      targetStorage: _intStorage,
      key: .init(file: file.description, line: line, column: column),
      value: value,
      compare: ==,
      perform: perform
    )

  }

  /// [Experimental] [Specialized]
  /// should be renamed
  public func doIfChanged(
    file: StaticString = #file,
    line: UInt = #line,
    column: UInt = #column,
    _ value: String,
    _ perform: (String) -> Void
  ) {

    _specialized_doIfChanged(
      targetStorage: _stringStorage,
      key: .init(file: file.description, line: line, column: column),
      value: value,
      compare: ==,
      perform: perform
    )

  }

}

private var _storageKey: Void?

extension NSObject {

  public var associatedFilter: InputFilter {

    objc_sync_enter(self)
    defer {
      objc_sync_exit(self)
    }

    if let associated = objc_getAssociatedObject(self, &_storageKey)
        as? InputFilter
    {
      return associated
    } else {
      let associated = InputFilter()
      objc_setAssociatedObject(self, &_storageKey, associated, .OBJC_ASSOCIATION_RETAIN)
      return associated
    }

  }

}