use std::borrow::Cow;
// this import will become unused in future rust versions
// but won't be removed for now for supporting current
// rust versions
#[allow(warnings)]
use std::ascii::AsciiExt;

use error::{Error, Result};

use self::CharType::*;

/// A lookup table for chars < 0x80
static QTEXT_INFO: &'static [CharType] = &[
    //0x00
    Unquotable, Unquotable, Unquotable, Unquotable,
    Unquotable, Unquotable, Unquotable, Unquotable,
    //0x08
    Unquotable, Ws, Unquotable, Unquotable,
    Unquotable, Unquotable, Unquotable, Unquotable,
    //0x10
    Unquotable, Unquotable, Unquotable, Unquotable,
    Unquotable, Unquotable, Unquotable, Unquotable,
    //0x18
    Unquotable, Unquotable, Unquotable, Unquotable,
    Unquotable, Unquotable, Unquotable, Unquotable,
    //0x20
    Ws, Token, NeedsQuoting, Token,
    Token, Token, Token, Token,
    //0x28
    TSpecial, TSpecial, Token, Token,
    TSpecial, Token, Token, TSpecial,
    //0x30
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x38
    Token, Token, TSpecial, TSpecial,
    TSpecial, TSpecial, TSpecial, TSpecial,
    //0x40
    TSpecial, Token, Token, Token,
    Token, Token, Token, Token,
    //0x48
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x50
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x58
    Token, Token, Token, TSpecial,
    NeedsQuoting, TSpecial, Token, Token,
    //0x60
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x68
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x70
    Token, Token, Token, Token,
    Token, Token, Token, Token,
    //0x78
    Token, Token, Token, Token,
    Token, Token, Token, Unquotable
];

/// A enum for usage in combination with the QTEXT_INFO lookup table
///
/// To see if a character is valid inside a quoted string
/// use `char_type > 1`  which means any token, tspecial (except '"' and '\\')
/// ws and non us-ascii character is included.
///
/// To see if a character needs to be represented as a quoted-pair in
/// a quoted string use `char_type == NeedsQuoting`.
///
/// # Example
/// ```
/// use quoted_string::CharType::{self, Unquotable, NeedsQuoting, Token};
///
/// fn simple_quote(s: &str) -> String {
///     let mut buffer = String::new();
///     buffer.push('"');
///     for ch in s.chars() {
///         match CharType::from(ch) {
///             Unquotable => panic!("can not quote: {:?}", ch),
///             NeedsQuoting => { buffer.push('\\'); buffer.push(ch); },
///             _ => buffer.push(ch)
///         }
///     }
///     buffer.push('"');
///     buffer
/// }
///
/// fn is_token(s: &str) -> bool {
///     s.chars().all(|ch| CharType::from(ch) == Token)
/// }
///
/// let x = "hallo\"there";
/// let y = "abc";
///
/// assert!(!is_token(x));
/// assert!(is_token(y));
///
/// let quoted_x = simple_quote(x);
/// assert_eq!(quoted_x, "\"hallo\\\"there\"");
/// ```
#[derive(Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Copy, Clone)]
#[repr(u8)]
pub enum CharType {
    /// a unquotable character (all CTLs expect "\t")
    Unquotable = 0,
    /// either '"' or '\\'
    NeedsQuoting = 1,
    /// a rfc2045 token character
    Token = 2,
    /// a rfc2045 tspecial character (except '"' and '\\')
    TSpecial = 3,
    /// a allowed white space character (either '\t' or ' ')
    Ws = 4,
    /// a non us-ascii character
    NonAscii = 5,
}

impl PartialEq<u8> for CharType {
    fn eq(&self, other: &u8) -> bool {
        *self as u8 == *other
    }
}
impl PartialEq<CharType> for u8 {
    fn eq(&self, other: &CharType) -> bool {
        *self == *other as u8
    }
}

impl From<char> for CharType {
    fn from(ch: char) -> Self {
        let ch_num = ch as usize;
        if ch_num > 128 {
            CharType::NonAscii
        } else {
            QTEXT_INFO[ch_num]
        }
    }
}




/// Indicates what kind of quoted-strings are used
///
/// As parameter this normally means if Utf8 is allowed
/// or only Ascii.
///
/// In return position it is sometimes used to indicate
/// whether or not a validated string contains non-us-ascci
/// utf8 characters.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum QuotedStringType {
    /// the content can be/is utf-8
    Utf8,
    /// the content can be/is only ascii
    AsciiOnly
}

impl QuotedStringType {

    /// creates a QuotedString type from a bool
    ///
    /// - if `is_ascii == true` then `AsciiOnly` is returned
    /// - if `is_ascii == false` then `Utf8` is returned
    #[inline]
    pub fn from_is_ascii(is_ascii: bool) -> Self {
        if is_ascii {
            QuotedStringType::AsciiOnly
        } else {
            QuotedStringType::Utf8
        }
    }
}


/// Used to determine
/// 1. if the string needs quoting
/// 2. where the first char which could require quoting appears
///
/// Note that a string consisiting only of chars which do not need quoting by them self
/// could still need quoting. For example the string `"a."` requires quoting if it appears
/// in a position where only a `dot-atom` or `quoted-string` is allowed.
pub trait ValidWithoutQuotationCheck {

    /// should return true if the next char is valid without quotation
    fn next_char(&mut self, ch: char) -> bool;

    /// Called after the last char was passed to `next_char`.
    /// It should return true if the whole string is valid without
    /// quotation _assuming_ that before all chars where passed in
    /// order to `next_char` and all calls to `next_char` returned
    /// true.
    ///
    /// This can be used to checks not possible with on a char by
    /// char basis e.g. if it does not end in a `.`.
    ///
    /// Note that because it is only called after one iteration,
    /// validation should be done, if possible, in the `next_char`
    /// method.
    #[inline]
    fn end(&mut self, _all: &str) -> bool { true }
}

impl<T> ValidWithoutQuotationCheck for T
    where T: FnMut(char) -> bool
{
    fn next_char(&mut self, ch: char) -> bool {
        (self)(ch)
    }
}


/// quotes the input string returning the quoted string and if it contains non us-ascii chars.
#[inline]
pub fn quote(input: &str) -> Result<(QuotedStringType, String)> {
    //TODO: we could implement this with `quote_if_needed` in the future, but
    // due to the additional capabilities of `quote_if_needed` this might be
    // more trublesome for the compiler to optimize (so benchmark it)
    let mut out = String::with_capacity(input.len()+2);
    out.push('"');
    let mut ascii = true;
    for ch in input.chars() {
        match CharType::from(ch) {
            Unquotable => return Err(Error::UnquotableCharacter(ch)),
            NeedsQuoting => {
                out.push('\\');
                out.push(ch);
            },
            NonAscii => {
                ascii = false;
                out.push(ch);
            },
            _ => out.push(ch)
        }

    }
    out.push('"');

    Ok((QuotedStringType::from_is_ascii(ascii), out))
}

/// quotes the input string if needed(RFC 5322/6532/822/2045)
///
/// The `valid_without_quoting` parameter accepts a function,
/// which should _only_ return true if the char is valid
/// without quoting. So this function should never return true
/// for e.g. `\0`. Use this function if some characters are
/// only valid in a quoted-string context.
///
/// If the `allowed_mail_type` parameter is set to `Ascii`
/// the algorithm will return a error if it stumbles over
/// a non-ascii character, else it will just indicate the
/// appearance of one through the returned quoted string type. Note
/// that if you set `quoted_string_type` to `Utf8`
/// the function still can returns a `QuotedStringType::AsciiOnly` which
/// means only ascii characters where contained, even through non ascii
/// character where allowed.
///
/// The quoting process can fail if characters are contained,
/// which can not appear in a quoted string independent of
/// quoted string type. This are chars which are neither
/// `qtext`,`vchar` nor WS (`' '` and `'\t'`).
/// Which are basically only 0x7F (DEL) and the
/// characters < 0x20 (`' '`) except 0x09 (`'\t'`).
///
/// Note that if the `valid_without_quoting` function states a CTL
/// char is valid without quoting then the algorithm will see it
/// as such even through there shouldn't be any context in which a
/// CTL char is valid without quoting.
///
pub fn quote_if_needed<'a, FN>(
    input: &'a str,
    mut valid_without_quoting: FN,
    quoted_string_type: QuotedStringType
) -> Result<(QuotedStringType, Cow<'a, str>)>
    where FN: ValidWithoutQuotationCheck
{
    let (ascii, offset) = scan_ahead(input, &mut valid_without_quoting, quoted_string_type)?;
    if offset == input.len() && valid_without_quoting.end(input) {
        //NOTE: no need to check ascii scan_ahead errors if !ascii && allowed_mail_type == Ascii
        return Ok((QuotedStringType::from_is_ascii(ascii), Cow::Borrowed(input)))
    }

    let (ascii, out) = _quote(input, ascii, quoted_string_type, offset)?;

    Ok( (QuotedStringType::from_is_ascii(ascii), Cow::Owned(out)) )
}

fn _quote(
    input: &str,
    was_ascii: bool,
    quoted_string_type: QuotedStringType,
    start_escape_check_from: usize
) -> Result<(bool, String)>
{
    use self::CharType::*;
    let ascii_only = quoted_string_type == QuotedStringType::AsciiOnly;
    debug_assert!(!(ascii_only && !was_ascii));

    let (ok, rest) = input.split_at(start_escape_check_from);
    //just guess half of the remaining chars needs escaping
    let mut out = String::with_capacity((rest.len() as f64 * 1.5) as usize);
    out.push('\"');
    out.push_str(ok);

    let mut ascii = was_ascii;
    for ch in rest.chars() {
        match CharType::from(ch) {
            Unquotable => {
                return Err(Error::UnquotableCharacter(ch));
            },
            NonAscii => {
                if ascii_only {
                    return Err(Error::NonUsAsciiInput);
                }
                ascii = false;

                //any on us-ascii char is valid qtext
                out.push(ch);
            },
            NeedsQuoting => {
                out.push('\\');
                out.push(ch);
            },
            _ => {
                out.push(ch);
            }
        }
    }
    out.push( '"' );
    Ok((ascii, out))

}



fn scan_ahead<FN>(inp: &str, valid_without_quoting: &mut FN, tp: QuotedStringType) -> Result<(bool, usize)>
    where FN: ValidWithoutQuotationCheck
{
    let ascii_only = tp == QuotedStringType::AsciiOnly;
    let mut ascii = true;
    for (offset, ch) in inp.char_indices() {
        if ascii && !ch.is_ascii() {
            if ascii_only {
                return Err(Error::NonUsAsciiInput);
            } else {
                ascii = false;
            }
        }
        if !valid_without_quoting.next_char(ch) {
            return Ok((ascii, offset))
        }
    }
    Ok((ascii, inp.len()))
}


#[cfg(test)]
mod test {
    // this import will become unused in future rust versions
    // but won't be removed for now for supporting current
    // rust versions
    #[allow(warnings)]
    use std::ascii::AsciiExt;
    use super::*;
    fn is_qtext(ch: char) -> bool {
        match ch {
            //not ' ' [d:32]
            '!' |
            //not '"' [d:34]
            '#'...'[' |
            //not '\\' [d:92]
            ']'...'~' => true,
            _ => false
        }
    }

    fn is_tspecial(ch: char) -> bool {
        match ch {
            '(' | ')' | '<' | '>'  | '@' |
            ',' | ';' | ':' | '\\' | '"' |
            '/' | '[' | ']' | '?'  | '=' => true,
            _ => false
        }
    }

    struct TokenCheck;
    impl ValidWithoutQuotationCheck for TokenCheck {
        fn next_char(&mut self, ch: char) -> bool {
            match ch {
                'a'...'z' |
                'A'...'Z' |
                '-' => true,
                _ => false
            }
        }

        fn end(&mut self, all: &str) -> bool {
            all.len() > 0
        }

    }

    #[test]
    fn quote_ascii() {
        let mti = QuotedStringType::Utf8;
        let data = &[
            ("this is simple", "\"this is simple\""),
            ("also\tsimple", "\"also\tsimple\""),
            ("with quotes\"<-", "\"with quotes\\\"<-\""),
            ("with slash\\<-", "\"with slash\\\\<-\"")
        ];
        for &(unquoted, quoted) in data.iter() {
            let (mail_type, got_quoted) = assert_ok!(
                quote_if_needed( unquoted, |ch| ch > ' ' && ch <= '~', mti));
            assert_eq!(QuotedStringType::AsciiOnly, mail_type);
            assert_eq!(quoted, &*got_quoted);
        }
    }

    #[test]
    fn quote_utf8() {
        let data = &[
            ("has → uft8", "\"has → uft8\""),
            ("also\t→\tsimple", "\"also\t→\tsimple\""),
            ("with→quotes\"<-", "\"with→quotes\\\"<-\""),
            ("with→slash\\<-", "\"with→slash\\\\<-\"")
        ];
        for &(unquoted, quoted) in data.iter() {
            let res = quote_if_needed( unquoted, |_|false, QuotedStringType::Utf8 );
            let (mail_type, got_quoted) = assert_ok!(res);
            assert_eq!(QuotedStringType::Utf8, mail_type);
            assert_eq!(quoted, &*got_quoted);
        }
    }


    #[test]
    fn no_quotation_needed_ascii() {
        let res = quote_if_needed("simple", |ch| ch >= 'a' && ch <= 'z', QuotedStringType::AsciiOnly);
        let (qst, res) = assert_ok!(res);
        assert_eq!(QuotedStringType::AsciiOnly, qst);
        assert_eq!("simple", &*res);
        let is_borrowed = if let Cow::Borrowed(_) = res { true } else { false };
        assert_eq!(true, is_borrowed);
    }

    #[test]
    fn no_quotation_needed_utf8() {
        let mt = QuotedStringType::Utf8;
        let (mt, res) = assert_ok!(
            quote_if_needed("simp↓e", |ch: char| !ch.is_ascii() || is_qtext(ch), mt));
        assert_eq!(QuotedStringType::Utf8, mt);
        assert_eq!("simp↓e", &*res);
        let is_borrowed = if let Cow::Borrowed(_) = res { true } else { false };
        assert_eq!(true, is_borrowed);
    }

    #[test]
    fn no_del() {
        assert_err!(quote_if_needed("\x7F", |_|false, QuotedStringType::AsciiOnly));
    }

    #[test]
    fn no_ctl() {
        let mut text = String::with_capacity(1);
        let bad_chars = (b'\0'..b' ').filter(|&b| b != b'\t' ).map(|byte| byte as char);
        for char in bad_chars {
            text.clear();
            text.insert(0, char);
            assert_err!(quote_if_needed(&*text, |_|false, QuotedStringType::AsciiOnly));
        }
    }

    #[test]
    fn quote_always_quotes() {
        assert_eq!(
            (QuotedStringType::AsciiOnly, "\"simple\"".to_owned()),
            assert_ok!(quote("simple"))
        );
    }

    #[test]
    fn using_valid_without_quoting() {
        let data = &[
            ("not@a-token", "\"not@a-token\"", true),
            ("not a-token", "\"not a-token\"", true),
            ("a-token-it-is", "a-token-it-is", false)
        ];
        for &(unquoted, exp_res, quoted) in data.iter() {
            let res = quote_if_needed(unquoted, TokenCheck, QuotedStringType::AsciiOnly);
            let (mt, res) = assert_ok!(res);
            assert_eq!(QuotedStringType::AsciiOnly, mt);
            if quoted {
                let owned: Cow<str> = Cow::Owned(exp_res.to_owned());
                assert_eq!(owned, res);
            } else {
                assert_eq!(Cow::Borrowed(exp_res), res);
            }
        }
    }

    #[test]
    fn quotes_utf8() {
        let res = assert_ok!(quote_if_needed("l↓r", TokenCheck, QuotedStringType::Utf8));
        let was_quoted = if let &Cow::Owned(..) = &res.1 { true } else { false };
        assert_eq!( true, was_quoted );
    }

    #[test]
    fn error_with_quotable_utf8_but_ascii_only() {
        assert_err!(quote_if_needed("l→r", TokenCheck, QuotedStringType::AsciiOnly));
    }

    #[test]
    fn check_end_is_used() {
        let qt = QuotedStringType::AsciiOnly;
        let res = quote_if_needed("", TokenCheck, qt);
        let (got_mt, quoted) = assert_ok!(res);
        assert_eq!(QuotedStringType::AsciiOnly, got_mt);
        assert_eq!("\"\"", quoted);
    }

    #[test]
    fn qtext_info_check() {
        for bch in 0u8..0x80 {
            let ch = bch as char;
            let res = QTEXT_INFO[bch as usize];
            match res {
                Unquotable => assert!(!is_qtext(ch)),
                NeedsQuoting => assert!(ch == '\\' || ch == '"' ),
                Token => {
                    assert!(is_qtext(ch));
                    assert!(!is_tspecial(ch));
                    assert!(ch > ' ');
                    assert!(ch <= '~');
                },
                TSpecial => assert!(is_tspecial(ch)),
                Ws => assert!(ch == ' ' || ch == '\t'),
                NonAscii => unreachable!()
            }
        }
    }

}