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// The shift characters are stored as nulls, as the conversion code doesn't
// care what value they have.  WRU? maps to ASCII ENQ (\x05), I think.
const ITA2: (&'static [u8], &'static [u8]) =
            (b"\0E\nA SIU\rDRJNFCKTZLWHYPQOBG\0MXV\0",
             b"\03\n- \x0787\r\x054',!:(5\")2#6019?&\0./;\0");

#[derive(Clone, Copy, PartialEq, Eq)]
pub enum ShiftState {
    Letters,
    Figures
}

/// Given a sequence of 5-bit baudot codes, produce a string
/// TODO: No reason this shouldn't be iterators
pub fn decode(buf: &[u8], mut state: ShiftState) -> Option<String> {
    use ShiftState::{Figures, Letters};
    let mut out = String::new();
    for &byte in buf.iter() {
        match (byte, state) {
           (0b11011u8, _) => { state = Figures; }
           (0b11111u8, _) => { state = Letters; }
           (letter, Letters) => out.push(ITA2.0[letter as usize] as char),
           (figure, Figures) => out.push(ITA2.1[figure as usize] as char),
        }
    }
    Some(out)
}

#[test]
fn it_works() {
  // Test data from http://uva.ulb.ac.be/cit_courseware/datacomm/dc_009.htm
  let phrase = &[31, 11, 3, 28, 1, 5, 4, 25, 24, 12, 9, 4, 27, 22, 22, 7, 4, 31, 5, 3, 21, 5, 4,
                 20, 6, 27, 13];
  let decoded = decode(phrase, ShiftState::Letters);
  assert_eq!(decoded, Some("JAMES BOND 007 SAYS HI!".into()));
  let exercise = &[31,21,1,3,10,4,27,23,24,24,7,4,31,16,6,28,1,4,27,23,22,31,3,28];
  let decoded = decode(exercise, ShiftState::Letters);
  assert_eq!(decoded, Some("YEAR 1997 TIME 10AM".into()));
}