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    use byteorder::ReadBytesExt;
    use error::{Error, Result};
    use marker::Marker;
    use parser::ScanInfo;
    use std::io::Read;
    use std::iter::repeat;

    const LUT_BITS: u8 = 8;

    #[derive(Debug)]
    pub struct HuffmanDecoder {
        bits: u64,
        num_bits: u8,
        marker: Option<Marker>,
    }

    impl HuffmanDecoder {
        pub fn new() -> HuffmanDecoder {
            HuffmanDecoder {
                bits: 0,
                num_bits: 0,
                marker: None,
            }
        }

        // Section F.2.2.3
        // Figure F.16
        pub fn decode<R: Read>(&mut self, reader: &mut R, table: &HuffmanTable) -> Result<u8> {
            if self.num_bits < 16 {
                self.read_bits(reader)?;
            }

            let (value, size) = table.lut[self.peek_bits(LUT_BITS) as usize];

            if size > 0 {
                self.consume_bits(size);
                Ok(value)
            }
            else {
                let bits = self.peek_bits(16);

                for i in LUT_BITS .. 16 {
                    let code = (bits >> (15 - i)) as i32;

                    if code <= table.maxcode[i as usize] {
                        self.consume_bits(i + 1);

                        let index = (code + table.delta[i as usize]) as usize;
                        return Ok(table.values[index]);
                    }
                }

                Err(Error::Format("failed to decode huffman code".to_owned()))
            }
        }

        pub fn decode_fast_ac<R: Read>(&mut self, reader: &mut R, table: &HuffmanTable) -> Result<Option<(i16, u8)>> {
            if let Some(ref ac_lut) = table.ac_lut {
                if self.num_bits < LUT_BITS {
                    self.read_bits(reader)?;
                }

                let (value, run_size) = ac_lut[self.peek_bits(LUT_BITS) as usize];

                if run_size != 0 {
                    let run = run_size >> 4;
                    let size = run_size & 0x0f;

                    self.consume_bits(size);
                    return Ok(Some((value, run)));
                }
            }

            Ok(None)
        }

        #[inline]
        pub fn get_bits<R: Read>(&mut self, reader: &mut R, count: u8) -> Result<u16> {
            if self.num_bits < count {
                self.read_bits(reader)?;
            }

            let bits = self.peek_bits(count);
            self.consume_bits(count);

            Ok(bits)
        }

        #[inline]
        pub fn receive_extend<R: Read>(&mut self, reader: &mut R, count: u8) -> Result<i16> {
            let value = self.get_bits(reader, count)?;
            Ok(extend(value, count))
        }

        pub fn reset(&mut self) {
            self.bits = 0;
            self.num_bits = 0;
        }

        pub fn take_marker<R: Read>(&mut self, reader: &mut R) -> Result<Option<Marker>> {
            self.read_bits(reader).map(|_| self.marker.take())
        }

        #[inline]
        fn peek_bits(&mut self, count: u8) -> u16 {
            debug_assert!(count <= 16);
            debug_assert!(self.num_bits >= count);

            ((self.bits >> (64 - count)) & ((1 << count) - 1)) as u16
        }

        #[inline]
        fn consume_bits(&mut self, count: u8) {
            debug_assert!(self.num_bits >= count);

            self.bits <<= count as usize;
            self.num_bits -= count;
        }

        fn read_bits<R: Read>(&mut self, reader: &mut R) -> Result<()> {
            while self.num_bits <= 56 {
                // Fill with zero bits if we have reached the end.
                let byte = match self.marker {
                    Some(_) => 0,
                    None => reader.read_u8()?,
                };

                if byte == 0xFF {
                    let mut next_byte = reader.read_u8()?;

                    // Check for byte stuffing.
                    if next_byte != 0x00 {
                        // We seem to have reached the end of entropy-coded data and encountered a
                        // marker. Since we can't put data back into the reader, we have to continue
                        // reading to identify the marker so we can pass it on.

                        // Section B.1.1.2
                        // "Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’."
                        while next_byte == 0xFF {
                            next_byte = reader.read_u8()?;
                        }

                        match next_byte {
                            0x00 => return Err(Error::Format("FF 00 found where marker was expected".to_owned())),
                            _    => self.marker = Some(Marker::from_u8(next_byte).unwrap()),
                        }

                        continue;
                    }
                }

                self.bits |= (byte as u64) << (56 - self.num_bits);
                self.num_bits += 8;
            }

            Ok(())
        }
    }

    // Section F.2.2.1
    // Figure F.12
    fn extend(value: u16, count: u8) -> i16 {
        let vt = 1 << (count as u16 - 1);

        if value < vt {
            value as i16 + (-1 << count as i16) + 1
        } else {
            value as i16
        }
    }

    #[derive(Clone, Copy, Debug, PartialEq)]
    pub enum HuffmanTableClass {
        DC,
        AC,
    }

    pub struct HuffmanTable {
        values: Vec<u8>,
        delta: [i32; 16],
        maxcode: [i32; 16],

        lut: [(u8, u8); 1 << LUT_BITS],
        ac_lut: Option<[(i16, u8); 1 << LUT_BITS]>,
    }

    impl HuffmanTable {
        pub fn new(bits: &[u8; 16], values: &[u8], class: HuffmanTableClass) -> Result<HuffmanTable> {
            let (huffcode, huffsize) = derive_huffman_codes(bits)?;

            // Section F.2.2.3
            // Figure F.15
            // delta[i] is set to VALPTR(I) - MINCODE(I)
            let mut delta = [0i32; 16];
            let mut maxcode = [-1i32; 16];
            let mut j = 0;

            for i in 0 .. 16 {
                if bits[i] != 0 {
                    delta[i] = j as i32 - huffcode[j] as i32;
                    j += bits[i] as usize;
                    maxcode[i] = huffcode[j - 1] as i32;
                }
            }

            // Build a lookup table for faster decoding.
            let mut lut = [(0u8, 0u8); 1 << LUT_BITS];

            for (i, &size) in huffsize.iter().enumerate().filter(|&(_, &size)| size <= LUT_BITS) {
                let bits_remaining = LUT_BITS - size;
                let start = (huffcode[i] << bits_remaining) as usize;

                for j in 0 .. 1 << bits_remaining {
                    lut[start + j] = (values[i], size);
                }
            }

            // Build a lookup table for small AC coefficients which both decodes the value and does the
            // equivalent of receive_extend.
            let ac_lut = match class {
                HuffmanTableClass::DC => None,
                HuffmanTableClass::AC => {
                    let mut table = [(0i16, 0u8); 1 << LUT_BITS];

                    for (i, &(value, size)) in lut.iter().enumerate() {
                        let run_length = value >> 4;
                        let magnitude_category = value & 0x0f;

                        if magnitude_category > 0 && size + magnitude_category <= LUT_BITS {
                            let unextended_ac_value = (((i << size) & ((1 << LUT_BITS) - 1)) >> (LUT_BITS - magnitude_category)) as u16;
                            let ac_value = extend(unextended_ac_value, magnitude_category);

                            table[i] = (ac_value, (run_length << 4) | (size + magnitude_category));
                        }
                    }

                    Some(table)
                },
            };

            Ok(HuffmanTable {
                values: values.to_vec(),
                delta: delta,
                maxcode: maxcode,
                lut: lut,
                ac_lut: ac_lut,
            })
        }
    }

    // Section C.2
    fn derive_huffman_codes(bits: &[u8; 16]) -> Result<(Vec<u16>, Vec<u8>)> {
        // Figure C.1
        let huffsize = bits.iter()
                           .enumerate()
                           .fold(Vec::new(), |mut acc, (i, &value)| {
                               let mut repeated_size: Vec<u8> = repeat((i + 1) as u8).take(value as usize).collect();
                               acc.append(&mut repeated_size);
                               acc
                           });

        // Figure C.2
        let mut huffcode = vec![0u16; huffsize.len()];
        let mut code_size = huffsize[0];
        let mut code = 0u32;

        for (i, &size) in huffsize.iter().enumerate() {
            while code_size < size {
                code <<= 1;
                code_size += 1;
            }

            if code >= (1u32 << size) {
                return Err(Error::Format("bad huffman code length".to_owned()));
            }

            huffcode[i] = code as u16;
            code += 1;
        }

        Ok((huffcode, huffsize))
    }

    // https://www.loc.gov/preservation/digital/formats/fdd/fdd000063.shtml
    // "Avery Lee, writing in the rec.video.desktop newsgroup in 2001, commented that "MJPEG, or at
    //  least the MJPEG in AVIs having the MJPG fourcc, is restricted JPEG with a fixed -- and
    //  *omitted* -- Huffman table. The JPEG must be YCbCr colorspace, it must be 4:2:2, and it must
    //  use basic Huffman encoding, not arithmetic or progressive.... You can indeed extract the
    //  MJPEG frames and decode them with a regular JPEG decoder, but you have to prepend the DHT
    //  segment to them, or else the decoder won't have any idea how to decompress the data.
    //  The exact table necessary is given in the OpenDML spec.""
    pub fn fill_default_mjpeg_tables(scan: &ScanInfo,
                                     dc_huffman_tables: &mut[Option<HuffmanTable>],
                                     ac_huffman_tables: &mut[Option<HuffmanTable>]) {
        // Section K.3.3

        if dc_huffman_tables[0].is_none() && scan.dc_table_indices.iter().any(|&i| i == 0) {
            // Table K.3
            dc_huffman_tables[0] = Some(HuffmanTable::new(
                &[0x00, 0x01, 0x05, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
                &[0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B], HuffmanTableClass::DC).unwrap());
        }
        if dc_huffman_tables[1].is_none() && scan.dc_table_indices.iter().any(|&i| i == 1) {
            // Table K.4
            dc_huffman_tables[1] = Some(HuffmanTable::new(
                &[0x00, 0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00],
                &[0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B], HuffmanTableClass::DC).unwrap());
        }
        if ac_huffman_tables[0].is_none() && scan.ac_table_indices.iter().any(|&i| i == 0) {
            // Table K.5
            ac_huffman_tables[0] = Some(HuffmanTable::new(
                &[0x00, 0x02, 0x01, 0x03, 0x03, 0x02, 0x04, 0x03, 0x05, 0x05, 0x04, 0x04, 0x00, 0x00, 0x01, 0x7D],
                &[0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12, 0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
                  0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xA1, 0x08, 0x23, 0x42, 0xB1, 0xC1, 0x15, 0x52, 0xD1, 0xF0,
                  0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0A, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x25, 0x26, 0x27, 0x28,
                  0x29, 0x2A, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
                  0x4A, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
                  0x6A, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
                  0x8A, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7,
                  0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xC2, 0xC3, 0xC4, 0xC5,
                  0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xE1, 0xE2,
                  0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8,
                  0xF9, 0xFA
                ], HuffmanTableClass::AC).unwrap());
        }
        if ac_huffman_tables[1].is_none() && scan.ac_table_indices.iter().any(|&i| i == 1) {
            // Table K.6
            ac_huffman_tables[1] = Some(HuffmanTable::new(
                &[0x00, 0x02, 0x01, 0x02, 0x04, 0x04, 0x03, 0x04, 0x07, 0x05, 0x04, 0x04, 0x00, 0x01, 0x02, 0x77],
                &[0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21, 0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
                  0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91, 0xA1, 0xB1, 0xC1, 0x09, 0x23, 0x33, 0x52, 0xF0,
                  0x15, 0x62, 0x72, 0xD1, 0x0A, 0x16, 0x24, 0x34, 0xE1, 0x25, 0xF1, 0x17, 0x18, 0x19, 0x1A, 0x26,
                  0x27, 0x28, 0x29, 0x2A, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
                  0x49, 0x4A, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
                  0x69, 0x6A, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
                  0x88, 0x89, 0x8A, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0xA2, 0xA3, 0xA4, 0xA5,
                  0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xC2, 0xC3,
                  0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA,
                  0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8,
                  0xF9, 0xFA
                ], HuffmanTableClass::AC).unwrap());
        }
    }

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