ApplyTransformFW2HW

ApplyTransformFW2HW.swift

// (c) 2021 and onwards The vChewing Project (MIT-NTL License).
// ====================
// This code is released under the MIT license (SPDX-License-Identifier: MIT)
// ... with NTL restriction stating that:
// No trademark license is granted to use the trade names, trademarks, service
// marks, or product names of Contributor, except as required to fulfill notice
// requirements defined in MIT License.

extension String {
  // This only works with ASCII chars.
  func applyingTransformFW2HW(reverse: Bool) -> String {
    var arr: [Character] = map { $0 }
    for i in 0..<arr.count {
      let oldChar = arr[i]
      guard oldChar.unicodeScalars.count == 1 else { continue }
      guard let oldCodePoint = oldChar.unicodeScalars.first?.value else { continue }
      if reverse {
        guard oldChar.isASCII else { continue }
      } else {
        guard oldCodePoint > 0xFEE0 || oldCodePoint == 0x3000 else { continue }
      }
      var newCodePoint: Int32 = reverse ? (Int32(oldCodePoint) + 0xFEE0) : (Int32(oldCodePoint) - 0xFEE0)
      checkSpace: switch (oldCodePoint, reverse) {
        case (0x3000, false): newCodePoint = 0x20
        case (0x20, true): newCodePoint = 0x3000
        default: break checkSpace
      }
      guard newCodePoint > 0 else { continue }
      guard let newScalar = Unicode.Scalar(UInt16(newCodePoint)) else { continue }
      let newChar = Character(newScalar)
      arr[i] = newChar
    }
    return String(arr)
  }
}