use crate::ReadSeek;
use byteorder::ReadBytesExt;
use std::char::decode_utf16;
use std::fmt::Write;
use std::io;

pub fn to_hex_string(bytes: &[u8]) -> String {
    let len = bytes.len();
    // Each byte is represented by 2 ascii bytes.
    let mut s = String::with_capacity(len * 2);

    for byte in bytes {
        write!(s, "{:02X}", byte).expect("Writing to an allocated string cannot fail");
    }

    s
}

/// Reads a utf16 string from the given stream.
/// If `len` is given, exactly `len` u16 values are read from the stream.
/// If `len` is None, the string is assumed to be null terminated and the stream will be read to the first null (0).
pub fn read_utf16_string<T: ReadSeek>(stream: &mut T, len: Option<usize>) -> io::Result<String> {
    let mut buffer = match len {
        Some(len) => Vec::with_capacity(len),
        None => Vec::new(),
    };

    match len {
        Some(len) => {
            for _ in 0..len {
                let next_char = stream.read_u16::<byteorder::LittleEndian>()?;
                buffer.push(next_char);
            }
        }
        None => loop {
            let next_char = stream.read_u16::<byteorder::LittleEndian>()?;

            if next_char == 0 {
                break;
            }

            buffer.push(next_char);
        },
    }

    // We need to stop if we see a NUL byte, even if asked for more bytes.
    decode_utf16(buffer.into_iter().take_while(|&byte| byte != 0x00))
        .map(|r| r.map_err(|_e| io::Error::from(io::ErrorKind::InvalidData)))
        .collect()
}