package ncurses

import (
	"os"
	"sync/atomic"
)

func bitmatch(b byte, pattern byte, length int) bool {
  mask := ^(byte(1 << (8 - length)) - 1)
  return (b ^ pattern) & mask == 0
}

func UTF8Listen(file *os.File, channel chan []byte, active *atomic.Bool) {
  b := [4]byte{}
  for active.Load() {
    out := make([]byte, 4)
    file.Read(b[0:1])
    if bitmatch(b[0], 0b00000000, 1) {
      copy(out, b[0:1])
      channel <- out[0:1]
    } else if bitmatch(b[0], 0b11000000, 3) {
      file.Read(b[1:2])
      copy(out, b[0:2])
      channel <- out[0:2]
    } else if bitmatch(b[0], 0b11100000, 4) {
      file.Read(b[1:3])
      copy(out, b[0:3])
      channel <- out[0:3]
    } else if bitmatch(b[0], 0b11110000, 5) {
      file.Read(b[1:4])
      copy(out, b[0:4])
      channel <- out[0:4]
    }
  }
}

// To cleanup, set active to false then close the channel
func UTF8Listener(buffer int, file *os.File) (chan []byte, *atomic.Bool) {
  channel := make(chan []byte, buffer)
  active := new(atomic.Bool)
  active.Store(true)

  go UTF8Listen(file, channel, active)
  
  return channel, active
}