use crate::decode::lzbuffer::{LzBuffer, LzCircularBuffer};
use crate::decode::rangecoder::{BitTree, LenDecoder, RangeDecoder};
use crate::decompress::{Options, UnpackedSize};
use crate::error;
use crate::util::vec2d::Vec2D;
use byteorder::{LittleEndian, ReadBytesExt};
use std::io;

/// Maximum input data that can be processed in one iteration.
/// Libhtp uses the following equation to define the maximum number of bits
/// for the worst case scenario:
///   log2((2^11 / 31) ^ 22) + 26 < 134 + 26 = 160
const MAX_REQUIRED_INPUT: usize = 20;

/// Processing mode for decompression.
///
/// Tells the decompressor if we should expect more data after parsing the
/// current input.
#[derive(Debug, PartialEq)]
enum ProcessingMode {
    /// Streaming mode. Process the input bytes but assume there will be more
    /// chunks of input data to receive in future calls to `process_mode()`.
    Partial,
    /// Synchronous mode. Process the input bytes and confirm end of stream has been reached.
    /// Use this mode if you are processing a fixed buffer of compressed data, or after
    /// using `Mode::Partial` to check for the end of stream.
    Finish,
}

/// Result of the next iteration of processing.
///
/// Indicates whether processing should continue or is finished.
#[derive(Debug, PartialEq)]
enum ProcessingStatus {
    Continue,
    Finished,
}

#[derive(Debug, Copy, Clone)]
/// LZMA 'lclppb' decompression properties.
pub struct LzmaProperties {
    /// The number of literal context bits.
    ///
    /// The most `lc` significant bits of the previous byte are part of the literal context.
    /// `lc` must not be greater than 8.
    pub lc: u32, // 0..=8
    /// The number of literal position bits.
    ///
    /// `lp` must not be greater than 4.
    pub lp: u32, // 0..=4
    /// The number of position bits.
    ///
    /// The context for literal/match is plaintext offset modulo `2^pb`.
    /// `pb` must not be greater than 4.
    pub pb: u32, // 0..=4
}

impl LzmaProperties {
    /// Assert the validity of the LZMA properties.
    pub(crate) fn validate(&self) {
        assert!(self.lc <= 8);
        assert!(self.lp <= 4);
        assert!(self.pb <= 4);
    }
}

#[derive(Debug, Copy, Clone)]
/// LZMA decompression parameters.
pub struct LzmaParams {
    /// The LZMA 'lclppb' decompression properties.
    pub(crate) properties: LzmaProperties,
    /// The dictionary size to use when decompressing.
    pub(crate) dict_size: u32,
    /// The size of the unpacked data.
    pub(crate) unpacked_size: Option<u64>,
}

impl LzmaParams {
    /// Create an new instance of LZMA parameters.
    #[cfg(feature = "raw_decoder")]
    pub fn new(
        properties: LzmaProperties,
        dict_size: u32,
        unpacked_size: Option<u64>,
    ) -> LzmaParams {
        Self {
            properties,
            dict_size,
            unpacked_size,
        }
    }

    /// Read LZMA parameters from the LZMA stream header.
    pub fn read_header<R>(input: &mut R, options: &Options) -> error::Result<LzmaParams>
    where
        R: io::BufRead,
    {
        // Properties
        let props = input.read_u8().map_err(error::Error::HeaderTooShort)?;

        let mut pb = props as u32;
        if pb >= 225 {
            return Err(error::Error::LzmaError(format!(
                "LZMA header invalid properties: {} must be < 225",
                pb
            )));
        }

        let lc: u32 = pb % 9;
        pb /= 9;
        let lp: u32 = pb % 5;
        pb /= 5;

        lzma_info!("Properties {{ lc: {}, lp: {}, pb: {} }}", lc, lp, pb);

        // Dictionary
        let dict_size_provided = input
            .read_u32::<LittleEndian>()
            .map_err(error::Error::HeaderTooShort)?;
        let dict_size = if dict_size_provided < 0x1000 {
            0x1000
        } else {
            dict_size_provided
        };

        lzma_info!("Dict size: {}", dict_size);

        // Unpacked size
        let unpacked_size: Option<u64> = match options.unpacked_size {
            UnpackedSize::ReadFromHeader => {
                let unpacked_size_provided = input
                    .read_u64::<LittleEndian>()
                    .map_err(error::Error::HeaderTooShort)?;
                let marker_mandatory: bool = unpacked_size_provided == 0xFFFF_FFFF_FFFF_FFFF;
                if marker_mandatory {
                    None
                } else {
                    Some(unpacked_size_provided)
                }
            }
            UnpackedSize::ReadHeaderButUseProvided(x) => {
                input
                    .read_u64::<LittleEndian>()
                    .map_err(error::Error::HeaderTooShort)?;
                x
            }
            UnpackedSize::UseProvided(x) => x,
        };

        lzma_info!("Unpacked size: {:?}", unpacked_size);

        let params = LzmaParams {
            properties: LzmaProperties { lc, lp, pb },
            dict_size,
            unpacked_size,
        };

        Ok(params)
    }
}

#[derive(Debug)]
pub(crate) struct DecoderState {
    // Buffer input data here if we need more for decompression. Up to
    // MAX_REQUIRED_INPUT bytes can be consumed during one iteration.
    partial_input_buf: std::io::Cursor<[u8; MAX_REQUIRED_INPUT]>,
    pub(crate) lzma_props: LzmaProperties,
    unpacked_size: Option<u64>,
    literal_probs: Vec2D<u16>,
    pos_slot_decoder: [BitTree; 4],
    align_decoder: BitTree,
    pos_decoders: [u16; 115],
    is_match: [u16; 192], // true = LZ, false = literal
    is_rep: [u16; 12],
    is_rep_g0: [u16; 12],
    is_rep_g1: [u16; 12],
    is_rep_g2: [u16; 12],
    is_rep_0long: [u16; 192],
    state: usize,
    rep: [usize; 4],
    len_decoder: LenDecoder,
    rep_len_decoder: LenDecoder,
}

impl DecoderState {
    pub fn new(lzma_props: LzmaProperties, unpacked_size: Option<u64>) -> Self {
        lzma_props.validate();
        DecoderState {
            partial_input_buf: std::io::Cursor::new([0; MAX_REQUIRED_INPUT]),
            lzma_props,
            unpacked_size,
            literal_probs: Vec2D::init(0x400, (1 << (lzma_props.lc + lzma_props.lp), 0x300)),
            pos_slot_decoder: [
                BitTree::new(6),
                BitTree::new(6),
                BitTree::new(6),
                BitTree::new(6),
            ],
            align_decoder: BitTree::new(4),
            pos_decoders: [0x400; 115],
            is_match: [0x400; 192],
            is_rep: [0x400; 12],
            is_rep_g0: [0x400; 12],
            is_rep_g1: [0x400; 12],
            is_rep_g2: [0x400; 12],
            is_rep_0long: [0x400; 192],
            state: 0,
            rep: [0; 4],
            len_decoder: LenDecoder::new(),
            rep_len_decoder: LenDecoder::new(),
        }
    }

    pub fn reset_state(&mut self, new_props: LzmaProperties) {
        new_props.validate();
        if self.lzma_props.lc + self.lzma_props.lp == new_props.lc + new_props.lp {
            // We can reset here by filling the existing buffer with 0x400.
            self.literal_probs.fill(0x400);
        } else {
            // We need to reallocate because of the new size of `lc+lp`.
            self.literal_probs = Vec2D::init(0x400, (1 << (new_props.lc + new_props.lp), 0x300));
        }

        self.lzma_props = new_props;
        self.pos_slot_decoder.iter_mut().for_each(|t| t.reset());
        self.align_decoder.reset();
        // For stack-allocated arrays, it was found to be faster to re-create new arrays
        // dropping the existing one, rather than using `fill` to reset the contents to zero.
        // Heap-based arrays use fill to keep their allocation rather than reallocate.
        self.pos_decoders = [0x400; 115];
        self.is_match = [0x400; 192];
        self.is_rep = [0x400; 12];
        self.is_rep_g0 = [0x400; 12];
        self.is_rep_g1 = [0x400; 12];
        self.is_rep_g2 = [0x400; 12];
        self.is_rep_0long = [0x400; 192];
        self.state = 0;
        self.rep = [0; 4];
        self.len_decoder.reset();
        self.rep_len_decoder.reset();
    }

    pub fn set_unpacked_size(&mut self, unpacked_size: Option<u64>) {
        self.unpacked_size = unpacked_size;
    }

    pub fn process<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
    ) -> error::Result<()> {
        self.process_mode(output, rangecoder, ProcessingMode::Finish)
    }

    #[cfg(feature = "stream")]
    pub fn process_stream<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
    ) -> error::Result<()> {
        self.process_mode(output, rangecoder, ProcessingMode::Partial)
    }

    /// Process the next iteration of the loop.
    ///
    /// If the update flag is true, the decoder's state will be updated.
    ///
    /// Returns `ProcessingStatus` to determine whether one should continue
    /// processing the loop.
    fn process_next_inner<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
        update: bool,
    ) -> error::Result<ProcessingStatus> {
        let pos_state = output.len() & ((1 << self.lzma_props.pb) - 1);

        // Literal
        if !rangecoder.decode_bit(
            // TODO: assumes pb = 2 ??
            &mut self.is_match[(self.state << 4) + pos_state],
            update,
        )? {
            let byte: u8 = self.decode_literal(output, rangecoder, update)?;

            if update {
                lzma_debug!("Literal: {}", byte);
                output.append_literal(byte)?;

                self.state = if self.state < 4 {
                    0
                } else if self.state < 10 {
                    self.state - 3
                } else {
                    self.state - 6
                };
            }
            return Ok(ProcessingStatus::Continue);
        }

        // LZ
        let mut len: usize;
        // Distance is repeated from LRU
        if rangecoder.decode_bit(&mut self.is_rep[self.state], update)? {
            // dist = rep[0]
            if !rangecoder.decode_bit(&mut self.is_rep_g0[self.state], update)? {
                // len = 1
                if !rangecoder.decode_bit(
                    &mut self.is_rep_0long[(self.state << 4) + pos_state],
                    update,
                )? {
                    // update state (short rep)
                    if update {
                        self.state = if self.state < 7 { 9 } else { 11 };
                        let dist = self.rep[0] + 1;
                        output.append_lz(1, dist)?;
                    }
                    return Ok(ProcessingStatus::Continue);
                }
            // dist = rep[i]
            } else {
                let idx: usize;
                if !rangecoder.decode_bit(&mut self.is_rep_g1[self.state], update)? {
                    idx = 1;
                } else if !rangecoder.decode_bit(&mut self.is_rep_g2[self.state], update)? {
                    idx = 2;
                } else {
                    idx = 3;
                }
                if update {
                    // Update LRU
                    let dist = self.rep[idx];
                    for i in (0..idx).rev() {
                        self.rep[i + 1] = self.rep[i];
                    }
                    self.rep[0] = dist
                }
            }

            len = self.rep_len_decoder.decode(rangecoder, pos_state, update)?;

            if update {
                // update state (rep)
                self.state = if self.state < 7 { 8 } else { 11 };
            }
        // New distance
        } else {
            if update {
                // Update LRU
                self.rep[3] = self.rep[2];
                self.rep[2] = self.rep[1];
                self.rep[1] = self.rep[0];
            }

            len = self.len_decoder.decode(rangecoder, pos_state, update)?;

            if update {
                // update state (match)
                self.state = if self.state < 7 { 7 } else { 10 };
            }

            let rep_0 = self.decode_distance(rangecoder, len, update)?;

            if update {
                self.rep[0] = rep_0;
                if self.rep[0] == 0xFFFF_FFFF {
                    if rangecoder.is_finished_ok()? {
                        return Ok(ProcessingStatus::Finished);
                    }
                    return Err(error::Error::LzmaError(String::from(
                        "Found end-of-stream marker but more bytes are available",
                    )));
                }
            }
        }

        if update {
            len += 2;

            let dist = self.rep[0] + 1;
            output.append_lz(len, dist)?;
        }

        Ok(ProcessingStatus::Continue)
    }

    fn process_next<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
    ) -> error::Result<ProcessingStatus> {
        self.process_next_inner(output, rangecoder, true)
    }

    /// Try to process the next iteration of the loop.
    ///
    /// This will check to see if there is enough data to consume and advance the
    /// decompressor. Needed in streaming mode to avoid corrupting the state while
    /// processing incomplete chunks of data.
    fn try_process_next<W: io::Write, LZB: LzBuffer<W>>(
        &mut self,
        output: &mut LZB,
        buf: &[u8],
        range: u32,
        code: u32,
    ) -> error::Result<()> {
        let mut temp = std::io::Cursor::new(buf);
        let mut rangecoder = RangeDecoder::from_parts(&mut temp, range, code);
        let _ = self.process_next_inner(output, &mut rangecoder, false)?;
        Ok(())
    }

    /// Utility function to read data into the partial input buffer.
    fn read_partial_input_buf<'a, R: io::BufRead>(
        &mut self,
        rangecoder: &mut RangeDecoder<'a, R>,
    ) -> error::Result<()> {
        // Fill as much of the tmp buffer as possible
        let start = self.partial_input_buf.position() as usize;
        let bytes_read =
            rangecoder.read_into(&mut self.partial_input_buf.get_mut()[start..])? as u64;
        self.partial_input_buf
            .set_position(self.partial_input_buf.position() + bytes_read);
        Ok(())
    }

    fn process_mode<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
        mode: ProcessingMode,
    ) -> error::Result<()> {
        loop {
            if let Some(unpacked_size) = self.unpacked_size {
                if output.len() as u64 >= unpacked_size {
                    break;
                }
            } else if match mode {
                ProcessingMode::Partial => {
                    rangecoder.is_eof()? && self.partial_input_buf.position() as usize == 0
                }
                ProcessingMode::Finish => {
                    rangecoder.is_finished_ok()? && self.partial_input_buf.position() as usize == 0
                }
            } {
                break;
            }

            if self.partial_input_buf.position() as usize > 0 {
                self.read_partial_input_buf(rangecoder)?;
                let tmp = *self.partial_input_buf.get_ref();

                // Check if we need more data to advance the decompressor
                if mode == ProcessingMode::Partial
                    && (self.partial_input_buf.position() as usize) < MAX_REQUIRED_INPUT
                    && self
                        .try_process_next(
                            output,
                            &tmp[..self.partial_input_buf.position() as usize],
                            rangecoder.range,
                            rangecoder.code,
                        )
                        .is_err()
                {
                    return Ok(());
                }

                // Run the decompressor on the tmp buffer
                let mut tmp_reader =
                    io::Cursor::new(&tmp[..self.partial_input_buf.position() as usize]);
                let mut tmp_rangecoder =
                    RangeDecoder::from_parts(&mut tmp_reader, rangecoder.range, rangecoder.code);
                let res = self.process_next(output, &mut tmp_rangecoder)?;

                // Update the actual rangecoder
                rangecoder.set(tmp_rangecoder.range, tmp_rangecoder.code);

                // Update tmp buffer
                let end = self.partial_input_buf.position();
                let new_len = end - tmp_reader.position();
                self.partial_input_buf.get_mut()[..new_len as usize]
                    .copy_from_slice(&tmp[tmp_reader.position() as usize..end as usize]);
                self.partial_input_buf.set_position(new_len);

                if res == ProcessingStatus::Finished {
                    break;
                };
            } else {
                let buf: &[u8] = rangecoder.stream.fill_buf()?;
                if mode == ProcessingMode::Partial
                    && buf.len() < MAX_REQUIRED_INPUT
                    && self
                        .try_process_next(output, buf, rangecoder.range, rangecoder.code)
                        .is_err()
                {
                    return self.read_partial_input_buf(rangecoder);
                }

                if self.process_next(output, rangecoder)? == ProcessingStatus::Finished {
                    break;
                };
            }
        }

        if let Some(len) = self.unpacked_size {
            if mode == ProcessingMode::Finish && len != output.len() as u64 {
                return Err(error::Error::LzmaError(format!(
                    "Expected unpacked size of {} but decompressed to {}",
                    len,
                    output.len()
                )));
            }
        }

        Ok(())
    }

    fn decode_literal<'a, W: io::Write, LZB: LzBuffer<W>, R: io::BufRead>(
        &mut self,
        output: &mut LZB,
        rangecoder: &mut RangeDecoder<'a, R>,
        update: bool,
    ) -> error::Result<u8> {
        let def_prev_byte = 0u8;
        let prev_byte = output.last_or(def_prev_byte) as usize;

        let mut result: usize = 1;
        let lit_state = ((output.len() & ((1 << self.lzma_props.lp) - 1)) << self.lzma_props.lc)
            + (prev_byte >> (8 - self.lzma_props.lc));
        let probs = &mut self.literal_probs[lit_state];

        if self.state >= 7 {
            let mut match_byte = output.last_n(self.rep[0] + 1)? as usize;

            while result < 0x100 {
                let match_bit = (match_byte >> 7) & 1;
                match_byte <<= 1;
                let bit = rangecoder
                    .decode_bit(&mut probs[((1 + match_bit) << 8) + result], update)?
                    as usize;
                result = (result << 1) ^ bit;
                if match_bit != bit {
                    break;
                }
            }
        }

        while result < 0x100 {
            result = (result << 1) ^ (rangecoder.decode_bit(&mut probs[result], update)? as usize);
        }

        Ok((result - 0x100) as u8)
    }

    fn decode_distance<'a, R: io::BufRead>(
        &mut self,
        rangecoder: &mut RangeDecoder<'a, R>,
        length: usize,
        update: bool,
    ) -> error::Result<usize> {
        let len_state = if length > 3 { 3 } else { length };

        let pos_slot = self.pos_slot_decoder[len_state].parse(rangecoder, update)? as usize;
        if pos_slot < 4 {
            return Ok(pos_slot);
        }

        let num_direct_bits = (pos_slot >> 1) - 1;
        let mut result = (2 ^ (pos_slot & 1)) << num_direct_bits;

        if pos_slot < 14 {
            result += rangecoder.parse_reverse_bit_tree(
                num_direct_bits,
                &mut self.pos_decoders,
                result - pos_slot,
                update,
            )? as usize;
        } else {
            result += (rangecoder.get(num_direct_bits - 4)? as usize) << 4;
            result += self.align_decoder.parse_reverse(rangecoder, update)? as usize;
        }

        Ok(result)
    }
}

#[derive(Debug)]
/// Raw decoder for LZMA.
pub struct LzmaDecoder {
    params: LzmaParams,
    memlimit: usize,
    state: DecoderState,
}

impl LzmaDecoder {
    /// Creates a new object ready for decompressing data that it's given for the input
    /// dict size, expected unpacked data size, and memory limit for the internal buffer.
    pub fn new(params: LzmaParams, memlimit: Option<usize>) -> error::Result<LzmaDecoder> {
        Ok(Self {
            params,
            memlimit: memlimit.unwrap_or(usize::MAX),
            state: DecoderState::new(params.properties, params.unpacked_size),
        })
    }

    /// Performs the equivalent of replacing this decompression state with a freshly allocated copy.
    ///
    /// Because the decoder state is reset, the unpacked size may optionally be re-specified. If `None`
    /// is given, the previous unpacked size that the decoder was initialized with remains unchanged.
    ///
    /// This function may not allocate memory and will attempt to reuse any previously allocated resources.
    #[cfg(feature = "raw_decoder")]
    pub fn reset(&mut self, unpacked_size: Option<Option<u64>>) {
        self.state.reset_state(self.params.properties);

        if let Some(unpacked_size) = unpacked_size {
            self.state.set_unpacked_size(unpacked_size);
        }
    }

    /// Decompresses the input data into the output, consuming only as much input as needed and writing as much output as possible.
    pub fn decompress<W: io::Write, R: io::BufRead>(
        &mut self,
        input: &mut R,
        output: &mut W,
    ) -> error::Result<()> {
        let mut output =
            LzCircularBuffer::from_stream(output, self.params.dict_size as usize, self.memlimit);

        let mut rangecoder = RangeDecoder::new(input)
            .map_err(|e| error::Error::LzmaError(format!("LZMA stream too short: {}", e)))?;
        self.state.process(&mut output, &mut rangecoder)?;
        output.finish()?;
        Ok(())
    }
}