rawchars.swift

import Foundation
import Darwin

/// Raw mode handling for character-by-character input in term
///
/// Via [this stack overflow post][post]
///
/// [post]: https://stackoverflow.com/questions/49748507/listening-to-stdin-in-swift
public enum RawMode {
  /// Error states for raw mode entry
  public enum State: Error {
    case eof
  }
  
  /// Enable raw mode for user input
  ///
  /// Via [this example][example]
  ///
  /// [example]: https://viewsourcecode.org/snaptoken/kilo/02.enteringRawMode.html
  public static func enableRawMode(fileHandle: FileHandle) -> termios {
    let pointer = UnsafeMutablePointer<termios>.allocate(capacity: 1); defer { pointer.deallocate() }
    var raw = pointer.pointee
    tcgetattr(fileHandle.fileDescriptor, &raw)
    let original = raw
    raw.c_lflag &= ~(UInt(ECHO | ICANON))
    tcsetattr(fileHandle.fileDescriptor, TCSAFLUSH, &raw)
    return original
  }
  
  /// Disable raw mode for user input
  ///
  /// Via [this example][example]
  ///
  /// [example]: https://viewsourcecode.org/snaptoken/kilo/02.enteringRawMode.html
  public static func disableRawMode(fileHandle: FileHandle) {
    guard var term = term else { return }
    tcsetattr(fileHandle.fileDescriptor, TCSAFLUSH, &term);
    self.term = nil
  }
  
  /// The current termios
  private static var term: termios? = nil
  
  /// Fetch a byte at a time.
  ///
  /// Will establish a new termios instance if one is not already available.
  ///
  /// - Returns: A single `UInt8` if available, otherwise `nil`
  /// - Throws: `State.eof` on receiving ^D
  public static func getByte() throws -> UInt8? {
    if nil == term {
      term = enableRawMode(fileHandle: FileHandle.standardInput)
    }
    var byte: UInt8 = 0
    guard read(FileHandle.standardInput.fileDescriptor, &byte, 1) == 1 else { return nil }
    if byte == 0x04 { throw State.eof }
    return byte
  }
}

do {
  // Note: scalar.utf8 is only available in 10.15
  while let byte = try RawMode.getByte() {
    let scalar = UnicodeScalar(byte)
    switch scalar.isASCII {
    case true:
      print(Character(UnicodeScalar(byte)), ":", byte)
    case false:
      print(scalar.escaped(asASCII: true), ":", byte)
    }

  }
} catch RawMode.State.eof {
  print("\n" + "eof") // ^D
  RawMode.disableRawMode(fileHandle: FileHandle.standardInput)
}