use std::convert::TryFrom;
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) -> Option<String> {
    guard!(latin1.chars().all(|c| (c as usize) < 256));
    match std::str::from_utf8(latin1.as_bytes()) {
        Ok(res) => Some(res.to_string()),
        Err(_) => None,
    }
}