//! Utility functions for Header implementations.

use std::str;
use std::fmt::{self, Display};

/// Reads a single raw string when parsing a header
pub fn from_one_raw_str<T: str::FromStr>(raw: &[Vec<u8>]) -> Option<T> {
    if raw.len() != 1 {
        return None;
    }
    // we JUST checked that raw.len() == 1, so raw[0] WILL exist.
    if let Ok(s) = str::from_utf8(& unsafe { raw.get_unchecked(0) }[..]) {
        if s != "" {
            return str::FromStr::from_str(s).ok();
        }
    }
    None
}

/// Reads a comma-delimited raw header into a Vec.
#[inline]
pub fn from_comma_delimited<T: str::FromStr>(raw: &[Vec<u8>]) -> Option<Vec<T>> {
    if raw.len() != 1 {
        return None;
    }
    // we JUST checked that raw.len() == 1, so raw[0] WILL exist.
    from_one_comma_delimited(& unsafe { raw.get_unchecked(0) }[..])
}

/// Reads a comma-delimited raw string into a Vec.
pub fn from_one_comma_delimited<T: str::FromStr>(raw: &[u8]) -> Option<Vec<T>> {
    match str::from_utf8(raw) {
        Ok(s) => {
            Some(s
                 .split(',')
                 .filter_map(|x| match x.trim() {
                     "" => None,
                     y => Some(y)
                     })
                 .filter_map(|x| x.parse().ok())
                 .collect())
        }
        Err(_) => None
    }
}

/// Format an array into a comma-delimited string.
pub fn fmt_comma_delimited<T: Display>(f: &mut fmt::Formatter, parts: &[T]) -> fmt::Result {
    for (i, part) in parts.iter().enumerate() {
        if i != 0 {
            try!(f.write_str(", "));
        }
        try!(Display::fmt(part, f));
    }
    Ok(())
}