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    // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.
    //
    // ignore-lexer-test FIXME #15679

    //! Base64 binary-to-text encoding

    pub use self::FromBase64Error::*;
    pub use self::CharacterSet::*;

    use std::fmt;
    use std::error;

    /// Available encoding character sets
    #[derive(Clone, Copy, Debug)]
    pub enum CharacterSet {
        /// The standard character set (uses `+` and `/`)
        Standard,
        /// The URL safe character set (uses `-` and `_`)
        UrlSafe
    }

    /// Available newline types
    #[derive(Clone, Copy, Debug)]
    pub enum Newline {
        /// A linefeed (i.e. Unix-style newline)
        LF,
        /// A carriage return and a linefeed (i.e. Windows-style newline)
        CRLF
    }

    /// Contains configuration parameters for `to_base64`.
    #[derive(Clone, Copy, Debug)]
    pub struct Config {
        /// Character set to use
        pub char_set: CharacterSet,
        /// Newline to use
        pub newline: Newline,
        /// True to pad output with `=` characters
        pub pad: bool,
        /// `Some(len)` to wrap lines at `len`, `None` to disable line wrapping
        pub line_length: Option<usize>
    }

    /// Configuration for RFC 4648 standard base64 encoding
    pub static STANDARD: Config =
        Config {char_set: Standard, newline: Newline::CRLF, pad: true, line_length: None};

    /// Configuration for RFC 4648 base64url encoding
    pub static URL_SAFE: Config =
        Config {char_set: UrlSafe, newline: Newline::CRLF, pad: false, line_length: None};

    /// Configuration for RFC 2045 MIME base64 encoding
    pub static MIME: Config =
        Config {char_set: Standard, newline: Newline::CRLF, pad: true, line_length: Some(76)};

    static STANDARD_CHARS: &'static[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                                            abcdefghijklmnopqrstuvwxyz\
                                            0123456789+/";

    static URLSAFE_CHARS: &'static[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                                           abcdefghijklmnopqrstuvwxyz\
                                           0123456789-_";

    /// A trait for converting a value to base64 encoding.
    pub trait ToBase64 {
        /// Converts the value of `self` to a base64 value following the specified
        /// format configuration, returning the owned string.
        fn to_base64(&self, config: Config) -> String;
    }

    impl ToBase64 for [u8] {
        /// Turn a vector of `u8` bytes into a base64 string.
        ///
        /// # Example
        ///
        /// ```rust
        /// extern crate rustc_serialize;
        /// use rustc_serialize::base64::{ToBase64, STANDARD};
        ///
        /// fn main () {
        ///     let str = [52,32].to_base64(STANDARD);
        ///     println!("base 64 output: {:?}", str);
        /// }
        /// ```
        fn to_base64(&self, config: Config) -> String {
            let bytes = match config.char_set {
                Standard => STANDARD_CHARS,
                UrlSafe => URLSAFE_CHARS
            };

            let len = self.len();
            let newline = match config.newline {
                Newline::LF => "\n",
                Newline::CRLF => "\r\n",
            };

            // Preallocate memory.
            let mut prealloc_len = (len + 2) / 3 * 4;
            if let Some(line_length) = config.line_length {
                let num_lines = match prealloc_len {
                    0 => 0,
                    n => (n - 1) / line_length
                };
                prealloc_len += num_lines * newline.bytes().count();
            }

            let mut out_bytes = vec![b'='; prealloc_len];

            // Deal with padding bytes
            let mod_len = len % 3;

            // Use iterators to reduce branching
            {
                let mut cur_length = 0;

                let mut s_in = self[..len - mod_len].iter().map(|&x| x as u32);
                let mut s_out = out_bytes.iter_mut();

                // Convenient shorthand
                let enc = |val| bytes[val as usize];
                let mut write = |val| *s_out.next().unwrap() = val;

                // Iterate though blocks of 4
                while let (Some(first), Some(second), Some(third)) =
                            (s_in.next(), s_in.next(), s_in.next()) {

                    // Line break if needed
                    if let Some(line_length) = config.line_length {
                        if cur_length >= line_length {
                            for b in newline.bytes() { write(b) };
                            cur_length = 0;
                        }
                    }

                    let n = first << 16 | second << 8 | third;

                    // This 24-bit number gets separated into four 6-bit numbers.
                    write(enc((n >> 18) & 63));
                    write(enc((n >> 12) & 63));
                    write(enc((n >> 6 ) & 63));
                    write(enc((n >> 0 ) & 63));

                    cur_length += 4;
                }

                // Line break only needed if padding is required
                if mod_len != 0 {
                    if let Some(line_length) = config.line_length {
                        if cur_length >= line_length {
                            for b in newline.bytes() { write(b) };
                        }
                    }
                }

                // Heh, would be cool if we knew this was exhaustive
                // (the dream of bounded integer types)
                match mod_len {
                    0 => (),
                    1 => {
                        let n = (self[len-1] as u32) << 16;
                        write(enc((n >> 18) & 63));
                        write(enc((n >> 12) & 63));
                    }
                    2 => {
                        let n = (self[len-2] as u32) << 16 |
                                (self[len-1] as u32) << 8;
                        write(enc((n >> 18) & 63));
                        write(enc((n >> 12) & 63));
                        write(enc((n >> 6 ) & 63));
                    }
                    _ => panic!("Algebra is broken, please alert the math police")
                }
            }

            // We get padding for "free", so only have to drop it if unwanted.
            if !config.pad {
                while let Some(&b'=') = out_bytes.last() {
                    out_bytes.pop();
                }
            }

            unsafe { String::from_utf8_unchecked(out_bytes) }
        }
    }

    impl<'a, T: ?Sized + ToBase64> ToBase64 for &'a T {
        fn to_base64(&self, config: Config) -> String {
            (**self).to_base64(config)
        }
    }

    /// A trait for converting from base64 encoded values.
    pub trait FromBase64 {
        /// Converts the value of `self`, interpreted as base64 encoded data, into
        /// an owned vector of bytes, returning the vector.
        fn from_base64(&self) -> Result<Vec<u8>, FromBase64Error>;
    }

    /// Errors that can occur when decoding a base64 encoded string
    #[derive(Clone, Copy)]
    pub enum FromBase64Error {
        /// The input contained a character not part of the base64 format
        InvalidBase64Byte(u8, usize),
        /// The input had an invalid length
        InvalidBase64Length,
    }

    impl fmt::Debug for FromBase64Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            match *self {
                InvalidBase64Byte(ch, idx) =>
                    write!(f, "Invalid character '{}' at position {}", ch, idx),
                InvalidBase64Length => write!(f, "Invalid length"),
            }
        }
    }

    impl error::Error for FromBase64Error {
        fn description(&self) -> &str {
            match *self {
                InvalidBase64Byte(_, _) => "invalid character",
                InvalidBase64Length => "invalid length",
            }
        }
    }

    impl fmt::Display for FromBase64Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Debug::fmt(&self, f)
        }
    }

    impl FromBase64 for str {
        /// Convert any base64 encoded string (literal, `@`, `&`, or `~`)
        /// to the byte values it encodes.
        ///
        /// You can use the `String::from_utf8` function to turn a `Vec<u8>` into a
        /// string with characters corresponding to those values.
        ///
        /// # Example
        ///
        /// This converts a string literal to base64 and back.
        ///
        /// ```rust
        /// extern crate rustc_serialize;
        /// use rustc_serialize::base64::{ToBase64, FromBase64, STANDARD};
        ///
        /// fn main () {
        ///     let hello_str = b"Hello, World".to_base64(STANDARD);
        ///     println!("base64 output: {}", hello_str);
        ///     let res = hello_str.from_base64();
        ///     if res.is_ok() {
        ///       let opt_bytes = String::from_utf8(res.unwrap());
        ///       if opt_bytes.is_ok() {
        ///         println!("decoded from base64: {:?}", opt_bytes.unwrap());
        ///       }
        ///     }
        /// }
        /// ```
        #[inline]
        fn from_base64(&self) -> Result<Vec<u8>, FromBase64Error> {
            self.as_bytes().from_base64()
        }
    }

    impl FromBase64 for [u8] {
        fn from_base64(&self) -> Result<Vec<u8>, FromBase64Error> {
            let mut r = Vec::with_capacity(self.len());
            let mut buf: u32 = 0;
            let mut modulus = 0;

            let mut it = self.iter();
            for byte in it.by_ref() {
                let code = DECODE_TABLE[*byte as usize];
                if code >= SPECIAL_CODES_START {
                    match code {
                        NEWLINE_CODE => continue,
                        EQUALS_CODE => break,
                        INVALID_CODE => return Err(InvalidBase64Byte(
                                *byte, (byte as *const _ as usize) - self.as_ptr() as usize)),
                        _ => unreachable!(),
                    }
                }
                buf = (buf | code as u32) << 6;
                modulus += 1;
                if modulus == 4 {
                    modulus = 0;
                    r.push((buf >> 22) as u8);
                    r.push((buf >> 14) as u8);
                    r.push((buf >> 6 ) as u8);
                }
            }

            for byte in it {
                match *byte {
                    b'=' | b'\r' | b'\n' => continue,
                    _ => return Err(InvalidBase64Byte(
                            *byte, (byte as *const _ as usize) - self.as_ptr() as usize)),
                }
            }

            match modulus {
                2 => {
                    r.push((buf >> 10) as u8);
                }
                3 => {
                    r.push((buf >> 16) as u8);
                    r.push((buf >> 8 ) as u8);
                }
                0 => (),
                _ => return Err(InvalidBase64Length),
            }

            Ok(r)
        }
    }

    impl<'a, T: ?Sized + FromBase64> FromBase64 for &'a T {
        fn from_base64(&self) -> Result<Vec<u8>, FromBase64Error> {
            (**self).from_base64()
        }
    }

    /// Base64 decoding lookup table, generated using:
    ///
    /// ```
    /// let mut ch = 0u8;
    /// for ch in 0..255 {
    ///     let mut ch = ch as u8;
    ///     let code = match ch {
    ///         b'A'...b'Z' => ch - 0x41,
    ///         b'a'...b'z' => ch - 0x47,
    ///         b'0'...b'9' => ch + 0x04,
    ///         b'+' | b'-' => 0x3E,
    ///         b'/' | b'_' => 0x3F,
    ///         b'=' => 0xFE,
    ///         b'\r' | b'\n' => 0xFD,
    ///         _ => 0xFF,
    ///     };
    ///     print!("0x{:02X}, ", code);
    ///     if ch % 16  == 15 { println!(""); }
    ///     else if ch == 0xFF { break; }
    ///     ch += 1;
    /// }
    /// println!("");
    /// ```
    const DECODE_TABLE: [u8; 256] = [
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFD, 0xFF, 0xFF, 0xFD, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x3E, 0xFF, 0x3E, 0xFF, 0x3F,
        0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0xFF, 0xFF, 0xFF, 0xFE, 0xFF, 0xFF,
        0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
        0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0x3F,
        0xFF, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
        0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    ];
    const INVALID_CODE: u8 = 0xFF;
    const EQUALS_CODE: u8 = 0xFE;
    const NEWLINE_CODE: u8 = 0xFD;
    const SPECIAL_CODES_START: u8 = NEWLINE_CODE;

    #[cfg(test)]
    mod tests {
        use base64::{Config, Newline, FromBase64, ToBase64, STANDARD, URL_SAFE};

        #[test]
        fn test_to_base64_basic() {
            assert_eq!("".as_bytes().to_base64(STANDARD), "");
            assert_eq!("f".as_bytes().to_base64(STANDARD), "Zg==");
            assert_eq!("fo".as_bytes().to_base64(STANDARD), "Zm8=");
            assert_eq!("foo".as_bytes().to_base64(STANDARD), "Zm9v");
            assert_eq!("foob".as_bytes().to_base64(STANDARD), "Zm9vYg==");
            assert_eq!("fooba".as_bytes().to_base64(STANDARD), "Zm9vYmE=");
            assert_eq!("foobar".as_bytes().to_base64(STANDARD), "Zm9vYmFy");
        }

        #[test]
        fn test_to_base64_crlf_line_break() {
            assert!(![0; 1000].to_base64(Config {line_length: None, ..STANDARD})
                                  .contains("\r\n"));
            assert_eq!(b"foobar".to_base64(Config {line_length: Some(4),
                                                   ..STANDARD}),
                       "Zm9v\r\nYmFy");
        }

        #[test]
        fn test_to_base64_lf_line_break() {
            assert!(![0; 1000].to_base64(Config {line_length: None,
                                                     newline: Newline::LF,
                                                     ..STANDARD})
                                  .contains("\n"));
            assert_eq!(b"foobar".to_base64(Config {line_length: Some(4),
                                                   newline: Newline::LF,
                                                   ..STANDARD}),
                       "Zm9v\nYmFy");
        }

        #[test]
        fn test_to_base64_padding() {
            assert_eq!("f".as_bytes().to_base64(Config {pad: false, ..STANDARD}), "Zg");
            assert_eq!("fo".as_bytes().to_base64(Config {pad: false, ..STANDARD}), "Zm8");
        }

        #[test]
        fn test_to_base64_url_safe() {
            assert_eq!([251, 255].to_base64(URL_SAFE), "-_8");
            assert_eq!([251, 255].to_base64(STANDARD), "+/8=");
        }

        #[test]
        fn test_to_base64_empty_line_length() {
            [].to_base64(Config {line_length: Some(72), ..STANDARD});
        }

        #[test]
        fn test_from_base64_basic() {
            assert_eq!("".from_base64().unwrap(), b"");
            assert_eq!("Zg==".from_base64().unwrap(), b"f");
            assert_eq!("Zm8=".from_base64().unwrap(), b"fo");
            assert_eq!("Zm9v".from_base64().unwrap(), b"foo");
            assert_eq!("Zm9vYg==".from_base64().unwrap(), b"foob");
            assert_eq!("Zm9vYmE=".from_base64().unwrap(), b"fooba");
            assert_eq!("Zm9vYmFy".from_base64().unwrap(), b"foobar");
        }

        #[test]
        fn test_from_base64_bytes() {
            assert_eq!(b"Zm9vYmFy".from_base64().unwrap(), b"foobar");
        }

        #[test]
        fn test_from_base64_newlines() {
            assert_eq!("Zm9v\r\nYmFy".from_base64().unwrap(),
                       b"foobar");
            assert_eq!("Zm9vYg==\r\n".from_base64().unwrap(),
                       b"foob");
            assert_eq!("Zm9v\nYmFy".from_base64().unwrap(),
                       b"foobar");
            assert_eq!("Zm9vYg==\n".from_base64().unwrap(),
                       b"foob");
        }

        #[test]
        fn test_from_base64_urlsafe() {
            assert_eq!("-_8".from_base64().unwrap(), "+/8=".from_base64().unwrap());
        }

        #[test]
        fn test_from_base64_invalid_char() {
            assert!("Zm$=".from_base64().is_err());
            assert!("Zg==$".from_base64().is_err());
        }

        #[test]
        fn test_from_base64_invalid_padding() {
            assert!("Z===".from_base64().is_err());
        }

        #[test]
        fn test_base64_random() {
            use rand::{thread_rng, Rng};

            for _ in 0..1000 {
                let times = thread_rng().gen_range(1, 100);
                let v = thread_rng().gen_iter::<u8>().take(times)
                                    .collect::<Vec<_>>();
                assert_eq!(v.to_base64(STANDARD)
                            .from_base64()
                            .unwrap(),
                           v);
            }
        }
    }

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