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    //! This modules provides an implementation of the Lempel–Ziv–Welch Compression Algorithm

    // Note: This implementation borrows heavily from the work of Julius Pettersson
    // See http://www.cplusplus.com/articles/iL18T05o/ for his extensive explanations
    // and a C++ implementatation

    use std::io;
    use std::io::{Read, Write};

    use bitstream::{Bits, BitReader, BitWriter};

    const MAX_CODESIZE: u8 = 12;
    const MAX_ENTRIES: usize = 1 << MAX_CODESIZE as usize;

    /// Alias for a LZW code point
    type Code = u16;

    /// Decoding dictionary.
    ///
    /// It is not generic due to current limitations of Rust
    /// Inspired by http://www.cplusplus.com/articles/iL18T05o/
    #[derive(Debug)]
    struct DecodingDict {
        min_size: u8,
        table: Vec<(Option<Code>, u8)>,
        buffer: Vec<u8>,
    }

    impl DecodingDict {
        /// Creates a new dict
        fn new(min_size: u8) -> DecodingDict {
            DecodingDict {
                min_size: min_size,
                table: Vec::with_capacity(512),
                buffer: Vec::with_capacity((1 << MAX_CODESIZE as usize) - 1)
            }
        }

        /// Resets the dictionary
        fn reset(&mut self) {
            self.table.clear();
            for i in 0..(1u16 << self.min_size as usize) {
                self.table.push((None, i as u8));
            }
        }

        /// Inserts a value into the dict
        #[inline(always)]
        fn push(&mut self, key: Option<Code>, value: u8) {
            self.table.push((key, value))
        }

        /// Reconstructs the data for the corresponding code
        fn reconstruct(&mut self, code: Option<Code>) -> io::Result<&[u8]> {
            self.buffer.clear();
            let mut code = code;
            let mut cha;
            // Check the first access more thoroughly since a bad code
            // could occur if the data is malformed
            if let Some(k) = code {
                match self.table.get(k as usize) {
                    Some(&(code_, cha_)) => {
                        code = code_;
                        cha = cha_;
                    }
                    None => return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        &*format!("Invalid code {:X}, expected code <= {:X}", k, self.table.len())
                    ))
                }
                self.buffer.push(cha);
            }
            while let Some(k) = code {
                if self.buffer.len() >= MAX_ENTRIES {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "Invalid code sequence. Cycle in decoding table."
                    ))
                }
                //(code, cha) = self.table[k as usize];
                // Note: This could possibly be replaced with an unchecked array access if
                //  - value is asserted to be < self.next_code() in push
                //  - min_size is asserted to be < MAX_CODESIZE
                let entry = self.table[k as usize]; code = entry.0; cha = entry.1;
                self.buffer.push(cha);
            }
            self.buffer.reverse();
            Ok(&self.buffer)
        }

        /// Returns the buffer constructed by the last reconstruction
        #[inline(always)]
        fn buffer(&self) -> &[u8] {
            &self.buffer
        }

        /// Number of entries in the dictionary
        #[inline(always)]
        fn next_code(&self) -> u16 {
            self.table.len() as u16
        }
    }

    macro_rules! define_decoder_struct {
        {$(
            $name:ident, $offset:expr, #[$doc:meta];
        )*} => {

    $( // START struct definition

    #[$doc]
    ///
    /// The maximum supported code size is 16 bits. The decoder assumes two
    /// special code word to be present in the stream:
    ///
    ///  * `CLEAR_CODE == 1 << min_code_size`
    ///  * `END_CODE   == CLEAR_CODE + 1`
    ///
    ///Furthermore the decoder expects the stream to start with a `CLEAR_CODE`. This
    /// corresponds to the implementation needed for en- and decoding GIF and TIFF files.
    #[derive(Debug)]
    pub struct $name<R: BitReader> {
        r: R,
        prev: Option<Code>,
        table: DecodingDict,
        buf: [u8; 1],
        code_size: u8,
        min_code_size: u8,
        clear_code: Code,
        end_code: Code,
    }

    impl<R> $name<R> where R: BitReader {
        /// Creates a new LZW decoder.
        pub fn new(reader: R, min_code_size: u8) -> $name<R> {
            $name {
                r: reader,
                prev: None,
                table: DecodingDict::new(min_code_size),
                buf: [0; 1],
                code_size: min_code_size + 1,
                min_code_size: min_code_size,
                clear_code: 1 << min_code_size,
                end_code: (1 << min_code_size) + 1,
            }
        }

        /// Tries to obtain and decode a code word from `bytes`.
        ///
        /// Returns the number of bytes that have been consumed from `bytes`. An empty
        /// slice does not indicate `EOF`.
        pub fn decode_bytes(&mut self, bytes: &[u8]) -> io::Result<(usize, &[u8])> {
            Ok(match self.r.read_bits(bytes, self.code_size) {
                Bits::Some(consumed, code) => {
                    (consumed, if code == self.clear_code {
                        self.table.reset();
                        self.table.push(None, 0); // clear code
                        self.table.push(None, 0); // end code
                        self.code_size = self.min_code_size + 1;
                        self.prev = None;
                        &[]
                    } else if code == self.end_code {
                        &[]
                    } else {
                        let next_code = self.table.next_code();
                        if code > next_code {
                            return Err(io::Error::new(
                                io::ErrorKind::InvalidInput,
                                &*format!("Invalid code {:X}, expected code <= {:X}",
                                          code,
                                          next_code
                                )
                            ))
                        }
                        let prev = self.prev;
                        let result = if prev.is_none() {
                            self.buf = [code as u8];
                            &self.buf[..]
                        } else {
                            let data = if code == next_code {
                                let cha = try!(self.table.reconstruct(prev))[0];
                                self.table.push(prev, cha);
                                try!(self.table.reconstruct(Some(code)))
                            } else if code < next_code {
                                let cha = try!(self.table.reconstruct(Some(code)))[0];
                                self.table.push(prev, cha);
                                self.table.buffer()
                            } else {
                                // code > next_code is already tested a few lines earlier
                                unreachable!()
                            };
                            data
                        };
                        if next_code == (1 << self.code_size as usize) - 1 - $offset
                           && self.code_size < MAX_CODESIZE {
                            self.code_size += 1;
                        }
                        self.prev = Some(code);
                        result
                    })
                },
                Bits::None(consumed) => {
                    (consumed, &[])
                }
            })
        }
    }

    )* // END struct definition

        }
    }

    define_decoder_struct!{
        Decoder, 0, #[doc = "Decoder for a LZW compressed stream (this algorithm is used for GIF files)."];
        DecoderEarlyChange, 1, #[doc = "Decoder for a LZW compressed stream using an “early change” algorithm (used in TIFF files)."];
    }

    struct Node {
        prefix: Option<Code>,
        c: u8,
        left: Option<Code>,
        right: Option<Code>,
    }

    impl Node {
        #[inline(always)]
        fn new(c: u8) -> Node {
            Node {
                prefix: None,
                c: c,
                left: None,
                right: None
            }
        }
    }

    struct EncodingDict {
        table: Vec<Node>,
        min_size: u8,

    }

    /// Encoding dictionary based on a binary tree
    impl EncodingDict {
        fn new(min_size: u8) -> EncodingDict {
            let mut this = EncodingDict {
                table: Vec::with_capacity(MAX_ENTRIES),
                min_size: min_size
            };
            this.reset();
            this
        }

        fn reset(&mut self) {
            self.table.clear();
            for i in 0 .. (1u16 << self.min_size as usize) {
                self.push_node(Node::new(i as u8));
            }
        }

        #[inline(always)]
        fn push_node(&mut self, node: Node) {
            self.table.push(node)
        }

        #[inline(always)]
        fn clear_code(&self) -> Code {
            1u16 << self.min_size
        }

        #[inline(always)]
        fn end_code(&self) -> Code {
            self.clear_code() + 1
        }

        // Searches for a new prefix
        fn search_and_insert(&mut self, i: Option<Code>, c: u8) -> Option<Code> {
            if let Some(i) = i.map(|v| v as usize) {
                let table_size = self.table.len() as Code;
                if let Some(mut j) = self.table[i].prefix {
                    loop {
                        let entry = &mut self.table[j as usize];
                        if c < entry.c {
                            if let Some(k) = entry.left {
                                j = k
                            } else {
                                entry.left = Some(table_size);
                                break
                            }
                        } else if c > entry.c {
                            if let Some(k) = entry.right {
                                j = k
                            } else {
                                entry.right = Some(table_size);
                                break
                            }
                        } else {
                            return Some(j)
                        }
                    }
                } else {
                    self.table[i].prefix = Some(table_size);
                }
                self.table.push(Node::new(c));
                None
            } else {
                Some(self.search_initials(c as Code))
            }
        }

        fn next_code(&self) -> usize {
            self.table.len()
        }

        fn search_initials(&self, i: Code) -> Code {
            self.table[i as usize].c as Code
        }
    }

    /// Convenience function that reads and compresses all bytes from `R`.
    pub fn encode<R, W>(r: R, mut w: W, min_code_size: u8) -> io::Result<()>
    where R: Read, W: BitWriter {
        let mut dict = EncodingDict::new(min_code_size);
        dict.push_node(Node::new(0)); // clear code
        dict.push_node(Node::new(0)); // end code
        let mut code_size = min_code_size + 1;
        let mut i = None;
        // gif spec: first clear code
        try!(w.write_bits(dict.clear_code(), code_size));
        let mut r = r.bytes();
        while let Some(Ok(c)) = r.next() {
            let prev = i;
            i = dict.search_and_insert(prev, c);
            if i.is_none() {
                if let Some(code) = prev {
                    try!(w.write_bits(code, code_size));
                }
                i = Some(dict.search_initials(c as Code))
            }
            // There is a hit: do not write out code but continue
            let next_code = dict.next_code();
            if next_code > (1 << code_size as usize)
               && code_size < MAX_CODESIZE {
                code_size += 1;
            }
            if next_code > MAX_ENTRIES {
                dict.reset();
                dict.push_node(Node::new(0)); // clear code
                dict.push_node(Node::new(0)); // end code
                try!(w.write_bits(dict.clear_code(), code_size));
                code_size = min_code_size + 1;
            }

        }
        if let Some(code) = i {
            try!(w.write_bits(code, code_size));
        }
        try!(w.write_bits(dict.end_code(), code_size));
        try!(w.flush());
        Ok(())
    }

    /// LZW encoder using the algorithm of GIF files.
    pub struct Encoder<W: BitWriter> {
        w: W,
        dict: EncodingDict,
        min_code_size: u8,
        code_size: u8,
        i: Option<Code>
    }

    impl<W: BitWriter> Encoder<W> {
        /// Creates a new LZW encoder.
        ///
        /// **Note**: If `min_code_size < 8` then `Self::encode_bytes` might panic when
        /// the supplied data containts values that exceed `1 << min_code_size`.
        pub fn new(mut w: W, min_code_size: u8) -> io::Result<Encoder<W>> {
            let mut dict = EncodingDict::new(min_code_size);
            dict.push_node(Node::new(0)); // clear code
            dict.push_node(Node::new(0)); // end code
            let code_size = min_code_size + 1;
            try!(w.write_bits(dict.clear_code(), code_size));
            Ok(Encoder {
                w: w,
                dict: dict,
                min_code_size: min_code_size,
                code_size: code_size,
                i: None
            })
        }

        /// Compresses `bytes` and writes the result into the writer.
        ///
        /// ## Panics
        ///
        /// This function might panic if any of the input bytes exceeds `1 << min_code_size`.
        /// This cannot happen if `min_code_size >= 8`.
        pub fn encode_bytes(&mut self, bytes: &[u8]) -> io::Result<()> {
            let w = &mut self.w;
            let dict = &mut self.dict;
            let code_size = &mut self.code_size;
            let i = &mut self.i;
            for &c in bytes {
                let prev = *i;
                *i = dict.search_and_insert(prev, c);
                if i.is_none() {
                    if let Some(code) = prev {
                        try!(w.write_bits(code, *code_size));
                    }
                    *i = Some(dict.search_initials(c as Code))
                }
                // There is a hit: do not write out code but continue
                let next_code = dict.next_code();
                if next_code > (1 << *code_size as usize)
                   && *code_size < MAX_CODESIZE {
                    *code_size += 1;
                }
                if next_code > MAX_ENTRIES {
                    dict.reset();
                    dict.push_node(Node::new(0)); // clear code
                    dict.push_node(Node::new(0)); // end code
                    try!(w.write_bits(dict.clear_code(), *code_size));
                    *code_size = self.min_code_size + 1;
                }

            }
            Ok(())
        }
    }

    impl<W: BitWriter> Drop for Encoder<W> {
        #[cfg(feature = "raii_no_panic")]
        fn drop(&mut self) {
            let w = &mut self.w;
            let code_size = &mut self.code_size;

            if let Some(code) = self.i {
                let _ = w.write_bits(code, *code_size);
            }
            let _ = w.write_bits(self.dict.end_code(), *code_size);
            let _ = w.flush();
        }
        #[cfg(not(feature = "raii_no_panic"))]
        fn drop(&mut self) {
            (|| {
                let w = &mut self.w;
                let code_size = &mut self.code_size;
                if let Some(code) = self.i {
                    try!(w.write_bits(code, *code_size));
                }
                try!(w.write_bits(self.dict.end_code(), *code_size));
                w.flush()
             })().unwrap()

        }
    }

    #[cfg(test)]
    #[test]
    fn round_trip() {
        use {LsbWriter, LsbReader};

        let size = 8;
        let data = b"TOBEORNOTTOBEORTOBEORNOT";
        let mut compressed = vec![];
        {
            let mut enc = Encoder::new(LsbWriter::new(&mut compressed), size).unwrap();
            enc.encode_bytes(data).unwrap();
        }
        println!("{:?}", compressed);
        let mut dec = Decoder::new(LsbReader::new(), size);
        let mut compressed = &compressed[..];
        let mut data2 = vec![];
        while compressed.len() > 0 {
            let (start, bytes) = dec.decode_bytes(&compressed).unwrap();
            compressed = &compressed[start..];
            data2.extend(bytes.iter().map(|&i| i));
        }
        assert_eq!(data2, data)
    }

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