use crate::crc::{crc24, crc32};
use crate::frame::{
    COMPRESSED_FRAME_HEADER_LENGTH, FRAME_TRAILER_LENGTH, PAYLOAD_SIZE_LIMIT,
    UNCOMPRESSED_FRAME_HEADER_LENGTH,
};
use lz4_flex::block::get_maximum_output_size;
use lz4_flex::{compress, compress_into};

#[inline]
fn put3b(buffer: &mut [u8], value: i32) {
    let value = value.to_le_bytes();
    buffer[0] = value[0];
    buffer[1] = value[1];
    buffer[2] = value[2];
}

#[inline]
fn add_trailer(buffer: &mut Vec<u8>, payload_start: usize) {
    buffer.reserve(4);

    let crc = crc32(&buffer[payload_start..]).to_le_bytes();

    buffer.push(crc[0]);
    buffer.push(crc[1]);
    buffer.push(crc[2]);
    buffer.push(crc[3]);
}

/// An encoder for frames. Since protocol *v5*, frames became "envelopes" and a frame now can contain
/// multiple complete envelopes (self-contained frame) or a part of one bigger envelope.
///
/// Encoders are stateful and can either:
/// 1. Have multiple self-contained envelopes added.
/// 2. Have a single non self-contained envelope added.
///
/// In either case, the encoder is assumed to have the buffer ready to accept envelopes before
/// adding the first one or after calling [`reset_buffer`]. At some point, the frame can become
/// finalized (which is the only possible case when adding a non self-contained envelope) and the
/// returned buffer is assumed to be immutable and ready to be sent.  
pub trait FrameEncoder {
    /// Determines if payload of given size can fit in current frame buffer.
    fn can_fit(&self, len: usize) -> bool;

    /// Resets the internal state and prepares it for encoding envelopes.
    fn reset(&mut self);

    /// Adds a self-contained envelope to current frame.
    fn add_envelope(&mut self, envelope: Vec<u8>);

    /// Finalizes a self-contained encoded frame in the buffer.
    fn finalize_self_contained(&mut self) -> &[u8];

    /// Appends a large envelope and finalizes non self-contained encoded frame in the buffer.
    /// Copies as much envelope data as possible and returns new envelope buffer start.
    fn finalize_non_self_contained(&mut self, envelope: &[u8]) -> (usize, &[u8]);

    /// Checks if current frame contains any envelopes.
    fn has_envelopes(&self) -> bool;
}

/// Pre-V5 frame encoder which simply encodes one envelope directly in the buffer.
#[derive(Clone, Debug, Default)]
pub struct LegacyFrameEncoder {
    buffer: Vec<u8>,
}

impl FrameEncoder for LegacyFrameEncoder {
    #[inline]
    fn can_fit(&self, _len: usize) -> bool {
        // we support only one envelope per frame
        self.buffer.is_empty()
    }

    #[inline]
    fn reset(&mut self) {
        self.buffer.clear();
    }

    #[inline]
    fn add_envelope(&mut self, envelope: Vec<u8>) {
        self.buffer = envelope;
    }

    #[inline]
    fn finalize_self_contained(&mut self) -> &[u8] {
        &self.buffer
    }

    #[inline]
    fn finalize_non_self_contained(&mut self, envelope: &[u8]) -> (usize, &[u8]) {
        // attempting to finalize a non self-contained frame via the legacy encoder - while this
        // will work, the legacy encoder doesn't distinguish such frames and all are considered
        // self-contained

        self.buffer.clear();
        self.buffer.extend_from_slice(envelope);

        (envelope.len(), &self.buffer)
    }

    #[inline]
    fn has_envelopes(&self) -> bool {
        !self.buffer.is_empty()
    }
}

/// Post-V5 encoder with support for envelope frames with CRC checksum.
#[derive(Clone, Debug)]
pub struct UncompressedFrameEncoder {
    buffer: Vec<u8>,
}

impl FrameEncoder for UncompressedFrameEncoder {
    #[inline]
    fn can_fit(&self, len: usize) -> bool {
        (self.buffer.len() - UNCOMPRESSED_FRAME_HEADER_LENGTH).saturating_add(len)
            < PAYLOAD_SIZE_LIMIT
    }

    #[inline]
    fn reset(&mut self) {
        self.buffer.truncate(UNCOMPRESSED_FRAME_HEADER_LENGTH);
    }

    #[inline]
    fn add_envelope(&mut self, mut envelope: Vec<u8>) {
        self.buffer.append(&mut envelope);
    }

    fn finalize_self_contained(&mut self) -> &[u8] {
        self.write_header(true);
        add_trailer(&mut self.buffer, UNCOMPRESSED_FRAME_HEADER_LENGTH);

        &self.buffer
    }

    fn finalize_non_self_contained(&mut self, envelope: &[u8]) -> (usize, &[u8]) {
        let max_size = envelope.len().min(PAYLOAD_SIZE_LIMIT - 1);

        self.buffer.extend_from_slice(&envelope[..max_size]);
        self.buffer.reserve(FRAME_TRAILER_LENGTH);

        self.write_header(false);
        add_trailer(&mut self.buffer, UNCOMPRESSED_FRAME_HEADER_LENGTH);

        (max_size, &self.buffer)
    }

    #[inline]
    fn has_envelopes(&self) -> bool {
        self.buffer.len() > UNCOMPRESSED_FRAME_HEADER_LENGTH
    }
}

impl Default for UncompressedFrameEncoder {
    fn default() -> Self {
        let mut buffer = vec![];
        buffer.resize(UNCOMPRESSED_FRAME_HEADER_LENGTH, 0);

        Self { buffer }
    }
}

impl UncompressedFrameEncoder {
    fn write_header(&mut self, self_contained: bool) {
        let len = self.buffer.len();
        debug_assert!(
            len < (PAYLOAD_SIZE_LIMIT + UNCOMPRESSED_FRAME_HEADER_LENGTH),
            "len: {} max: {}",
            len,
            PAYLOAD_SIZE_LIMIT + UNCOMPRESSED_FRAME_HEADER_LENGTH
        );

        let mut len = (len - UNCOMPRESSED_FRAME_HEADER_LENGTH) as u64;
        if self_contained {
            len |= 1 << 17;
        }

        put3b(self.buffer.as_mut_slice(), len as i32);
        put3b(&mut self.buffer[3..], crc24(&len.to_le_bytes()[..3]));
    }
}

/// Post-V5 Lz4 encoder with support for envelope frames with CRC checksum.
#[derive(Clone, Debug)]
pub struct Lz4FrameEncoder {
    buffer: Vec<u8>,
}

impl FrameEncoder for Lz4FrameEncoder {
    #[inline]
    fn can_fit(&self, len: usize) -> bool {
        // we don't know the whole compressed payload size, so we need to be conservative and expect
        // the worst case
        get_maximum_output_size(
            (self.buffer.len() - COMPRESSED_FRAME_HEADER_LENGTH).saturating_add(len),
        ) < PAYLOAD_SIZE_LIMIT
    }

    #[inline]
    fn reset(&mut self) {
        self.buffer.truncate(COMPRESSED_FRAME_HEADER_LENGTH);
    }

    #[inline]
    fn add_envelope(&mut self, mut envelope: Vec<u8>) {
        self.buffer.append(&mut envelope);
    }

    fn finalize_self_contained(&mut self) -> &[u8] {
        let uncompressed_size = self.buffer.len() - COMPRESSED_FRAME_HEADER_LENGTH;
        let mut compressed_payload = compress(&self.buffer[COMPRESSED_FRAME_HEADER_LENGTH..]);

        self.buffer.truncate(COMPRESSED_FRAME_HEADER_LENGTH);
        self.buffer.append(&mut compressed_payload);

        self.write_header(uncompressed_size, true);
        add_trailer(&mut self.buffer, COMPRESSED_FRAME_HEADER_LENGTH);

        &self.buffer
    }

    fn finalize_non_self_contained(&mut self, envelope: &[u8]) -> (usize, &[u8]) {
        let mut uncompressed_size = envelope.len().min(PAYLOAD_SIZE_LIMIT - 1);
        let offset = uncompressed_size;

        self.buffer.resize(
            get_maximum_output_size(uncompressed_size)
                + COMPRESSED_FRAME_HEADER_LENGTH
                + FRAME_TRAILER_LENGTH, // add space for trailer, so we don't allocate later
            0,
        );

        let mut compressed_size = compress_into(
            &envelope[..uncompressed_size],
            &mut self.buffer[COMPRESSED_FRAME_HEADER_LENGTH..],
        )
        .unwrap(); // we can safely unwrap, since we have at least the amount of space needed

        if compressed_size >= PAYLOAD_SIZE_LIMIT {
            // compressed size can exceed source size, therefore can exceed max payload size
            // Java driver simply ignores compression at this point, so ¯\_(ツ)_/¯
            self.buffer[COMPRESSED_FRAME_HEADER_LENGTH
                ..(COMPRESSED_FRAME_HEADER_LENGTH + uncompressed_size)]
                .copy_from_slice(&envelope[..uncompressed_size]);

            compressed_size = uncompressed_size;
            uncompressed_size = 0; // compressed size of 0 means no compression
        }

        self.buffer
            .truncate(COMPRESSED_FRAME_HEADER_LENGTH + compressed_size);

        self.write_header(uncompressed_size, false);
        add_trailer(&mut self.buffer, COMPRESSED_FRAME_HEADER_LENGTH);

        (offset, &self.buffer)
    }

    #[inline]
    fn has_envelopes(&self) -> bool {
        self.buffer.len() > COMPRESSED_FRAME_HEADER_LENGTH
    }
}

impl Default for Lz4FrameEncoder {
    fn default() -> Self {
        let mut buffer = vec![];
        buffer.resize(COMPRESSED_FRAME_HEADER_LENGTH, 0);

        Self { buffer }
    }
}

impl Lz4FrameEncoder {
    fn write_header(&mut self, uncompressed_size: usize, self_contained: bool) {
        let len = self.buffer.len();
        debug_assert!(len < (PAYLOAD_SIZE_LIMIT + COMPRESSED_FRAME_HEADER_LENGTH));

        let mut header =
            (len - COMPRESSED_FRAME_HEADER_LENGTH) as u64 | ((uncompressed_size as u64) << 17);

        if self_contained {
            header |= 1 << 34;
        }

        let crc = crc24(&header.to_le_bytes()[..5]) as u64;

        let header = header | (crc << 40);
        self.buffer[..8].copy_from_slice(&header.to_le_bytes());
    }
}