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//! Utility functions for Header implementations.

use language_tags::LanguageTag;
use std::str;
use std::str::FromStr;
use std::fmt::{self, Display};
use url::percent_encoding;

use header::shared::Charset;

/// Reads a single raw string when parsing a header.
pub fn from_one_raw_str<T: str::FromStr>(raw: &[Vec<u8>]) -> ::Result<T> {
    if raw.len() != 1 || unsafe { raw.get_unchecked(0) } == b"" { return Err(::Error::Header) }
    // we JUST checked that raw.len() == 1, so raw[0] WILL exist.
    from_raw_str(& unsafe { raw.get_unchecked(0) })
}

/// Reads a raw string into a value.
pub fn from_raw_str<T: str::FromStr>(raw: &[u8]) -> ::Result<T> {
    let s = try!(str::from_utf8(raw));
    T::from_str(s).or(Err(::Error::Header))
}

/// Reads a comma-delimited raw header into a Vec.
#[inline]
pub fn from_comma_delimited<T: str::FromStr>(raw: &[Vec<u8>]) -> ::Result<Vec<T>> {
    if raw.len() != 1 {
        return Err(::Error::Header);
    }
    // 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]) -> ::Result<Vec<T>> {
    let s = try!(str::from_utf8(raw));
    Ok(s.split(',')
        .filter_map(|x| match x.trim() {
            "" => None,
            y => Some(y)
        })
        .filter_map(|x| x.parse().ok())
        .collect())
}

/// 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(())
}

/// An extended header parameter value (i.e., tagged with a character set and optionally,
/// a language), as defined in [RFC 5987](https://tools.ietf.org/html/rfc5987#section-3.2).
pub struct ExtendedValue {
    pub charset: Charset,
    pub language_tag: Option<LanguageTag>,
    pub value: Vec<u8>,
}

/// Parses extended header parameter values (`ext-value`), as defined in
/// [RFC 5987](https://tools.ietf.org/html/rfc5987#section-3.2).
///
/// Extended values are denoted by parameter names that end with `*`.
///
/// ## ABNF
/// ```plain
/// ext-value     = charset  "'" [ language ] "'" value-chars
///               ; like RFC 2231's <extended-initial-value>
///               ; (see [RFC2231], Section 7)
///
/// charset       = "UTF-8" / "ISO-8859-1" / mime-charset
///
/// mime-charset  = 1*mime-charsetc
/// mime-charsetc = ALPHA / DIGIT
///               / "!" / "#" / "$" / "%" / "&"
///               / "+" / "-" / "^" / "_" / "`"
///               / "{" / "}" / "~"
///               ; as <mime-charset> in Section 2.3 of [RFC2978]
///               ; except that the single quote is not included
///               ; SHOULD be registered in the IANA charset registry
///
/// language      = <Language-Tag, defined in [RFC5646], Section 2.1>
///
/// value-chars   = *( pct-encoded / attr-char )
///
/// pct-encoded   = "%" HEXDIG HEXDIG
///               ; see [RFC3986], Section 2.1
///
/// attr-char     = ALPHA / DIGIT
///               / "!" / "#" / "$" / "&" / "+" / "-" / "."
///               / "^" / "_" / "`" / "|" / "~"
///               ; token except ( "*" / "'" / "%" )
/// ```
pub fn parse_extended_value(val: &str) -> ::Result<ExtendedValue> {

    // Break into three pieces separated by the single-quote character
    let mut parts = val.splitn(3,'\'');

    // Interpret the first piece as a Charset
    let charset: Charset = match parts.next() {
        None => return Err(::Error::Header),
        Some(n) => try!(FromStr::from_str(n)),
    };

    // Interpret the second piece as a language tag
    let lang: Option<LanguageTag> = match parts.next() {
        None => return Err(::Error::Header),
        Some("") => None,
        Some(s) => match s.parse() {
            Ok(lt) => Some(lt),
            Err(_) => return Err(::Error::Header),
        }
    };

    // Interpret the third piece as a sequence of value characters
    let value: Vec<u8> = match parts.next() {
        None => return Err(::Error::Header),
        Some(v) => percent_encoding::percent_decode(v.as_bytes()),
    };

    Ok(ExtendedValue {
        charset: charset,
        language_tag: lang,
        value: value,
    })
}

#[cfg(test)]
mod tests {
    use header::shared::Charset;
    use super::parse_extended_value;

    #[test]
    fn test_parse_extended_value_with_encoding_and_language_tag() {
        let expected_language_tag = langtag!(en);
        // RFC 5987, Section 3.2.2
        // Extended notation, using the Unicode character U+00A3 (POUND SIGN)
        let result = parse_extended_value("iso-8859-1'en'%A3%20rates");
        assert!(result.is_ok());
        let extended_value = result.unwrap();
        assert_eq!(Charset::Iso_8859_1, extended_value.charset);
        assert!(extended_value.language_tag.is_some());
        assert_eq!(expected_language_tag, extended_value.language_tag.unwrap());
        assert_eq!(vec![163, b' ', b'r', b'a', b't', b'e', b's'], extended_value.value);
    }

    #[test]
    fn test_parse_extended_value_with_encoding() {
        // RFC 5987, Section 3.2.2
        // Extended notation, using the Unicode characters U+00A3 (POUND SIGN)
        // and U+20AC (EURO SIGN)
        let result = parse_extended_value("UTF-8''%c2%a3%20and%20%e2%82%ac%20rates");
        assert!(result.is_ok());
        let extended_value = result.unwrap();
        assert_eq!(Charset::Ext("UTF-8".to_string()), extended_value.charset);
        assert!(extended_value.language_tag.is_none());
        assert_eq!(vec![194, 163, b' ', b'a', b'n', b'd', b' ', 226, 130, 172, b' ', b'r', b'a', b't', b'e', b's'], extended_value.value);
    }

    #[test]
    fn test_parse_extended_value_missing_language_tag_and_encoding() {
        // From: https://greenbytes.de/tech/tc2231/#attwithfn2231quot2
        let result = parse_extended_value("foo%20bar.html");
        assert!(result.is_err());
    }

    #[test]
    fn test_parse_extended_value_partially_formatted() {
        let result = parse_extended_value("UTF-8'missing third part");
        assert!(result.is_err());
    }

    #[test]
    fn test_parse_extended_value_partially_formatted_blank() {
        let result = parse_extended_value("blank second part'");
        assert!(result.is_err());
    }
}