use std::convert::TryFrom;
use std::io;
use crate::error::IntoIOError;
use crate::util::read_big_endian;

macro_rules! guard {
    ($cond:expr) => {
        if !$cond {
            return None;
        }
    }
}

pub fn from_latin_1(bytes: &[u8]) -> Option<String> {
    guard!(bytes.len() >= 1);

    Some(bytes.iter().map(|&b| char::from(b)).collect())
}

pub fn from_ucs_2_bom(bytes: &[u8]) -> Option<String> {
    let len = bytes.len();

    guard!(len % 2 == 0);
    guard!(len >= 2);

    let bom = read_big_endian(&bytes[0..2], 8);
    guard!(bom == 0xfeff || bom == 0xfffe);

    let mut res = String::with_capacity(len/2 - 1);

    for i in 1 .. len/2 {
        let val = if bom == 0xfeff {
            256 * bytes[2*i] as u16 + bytes[2*i+1] as u16
        } else {
            256 * bytes[2*i+1] as u16 + bytes[2*i] as u16
        };

        match char::try_from(val as u32) {
            Ok(c) => res.push(c),
            Err(_) => return None,
        };
    }

    Some(res)
}

pub fn from_utf8_mistaken_as_latin1(latin1: &str) -> io::Result<String> {
    latin1
        .chars()
        .map(|c| u8::try_from(u32::from(c)))
        .collect::<Result<Vec<u8>, _>>()
        .map_err(|e| e.ioerr())
        .and_then(|v| std::str::from_utf8(&v)
                        .map(|s| s.to_string())
                        .map_err(|e| e.ioerr()))
}