// Copyright 2024 RustFS Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::compress_index::{Index, TryGetIndex};
use pin_project_lite::pin_project;
use rustfs_utils::compress::{CompressionAlgorithm, compress_block, decompress_block};
use rustfs_utils::{put_uvarint, uvarint};
use std::cmp::min;
use std::io::{self};
use std::pin::Pin;
use std::task::{Context, Poll};
use tokio::io::{AsyncRead, ReadBuf};
// use tracing::error;

const COMPRESS_TYPE_COMPRESSED: u8 = 0x00;
const COMPRESS_TYPE_UNCOMPRESSED: u8 = 0x01;
const COMPRESS_TYPE_END: u8 = 0xFF;

const DEFAULT_BLOCK_SIZE: usize = 1 << 20; // 1MB
const HEADER_LEN: usize = 8;

pin_project! {
    #[derive(Debug)]
    /// A reader wrapper that compresses data on the fly using DEFLATE algorithm.
    pub struct CompressReader<R> {
        #[pin]
        pub inner: R,
        buffer: Vec<u8>,
        pos: usize,
        done: bool,
        block_size: usize,
        compression_algorithm: CompressionAlgorithm,
        index: Index,
        written: usize,
        uncomp_written: usize,
        temp_buffer: Vec<u8>,
        read_buffer: Vec<u8>,
    }
}

impl<R> CompressReader<R>
where
    R: AsyncRead + Unpin + Send + Sync,
{
    pub fn new(inner: R, compression_algorithm: CompressionAlgorithm) -> Self {
        Self {
            inner,
            buffer: Vec::new(),
            pos: 0,
            done: false,
            compression_algorithm,
            block_size: DEFAULT_BLOCK_SIZE,
            index: Index::new(),
            written: 0,
            uncomp_written: 0,
            temp_buffer: Vec::with_capacity(DEFAULT_BLOCK_SIZE),
            read_buffer: vec![0u8; DEFAULT_BLOCK_SIZE],
        }
    }

    /// Optional: allow users to customize block_size
    pub fn with_block_size(inner: R, block_size: usize, compression_algorithm: CompressionAlgorithm) -> Self {
        Self {
            inner,
            buffer: Vec::new(),
            pos: 0,
            done: false,
            compression_algorithm,
            block_size,
            index: Index::new(),
            written: 0,
            uncomp_written: 0,
            temp_buffer: Vec::with_capacity(block_size),
            read_buffer: vec![0u8; block_size],
        }
    }
}

impl<R> TryGetIndex for CompressReader<R> {
    fn try_get_index(&self) -> Option<&Index> {
        Some(&self.index)
    }
}

impl<R> AsyncRead for CompressReader<R>
where
    R: AsyncRead + Unpin + Send + Sync,
{
    fn poll_read(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<io::Result<()>> {
        let mut this = self.project();
        // Copy from buffer first if available
        if *this.pos < this.buffer.len() {
            let to_copy = min(buf.remaining(), this.buffer.len() - *this.pos);
            buf.put_slice(&this.buffer[*this.pos..*this.pos + to_copy]);
            *this.pos += to_copy;
            if *this.pos == this.buffer.len() {
                this.buffer.clear();
                *this.pos = 0;
            }
            return Poll::Ready(Ok(()));
        }
        if *this.done {
            return Poll::Ready(Ok(()));
        }
        // Fill temporary buffer
        while this.temp_buffer.len() < *this.block_size {
            let remaining = *this.block_size - this.temp_buffer.len();
            let mut temp_buf = ReadBuf::new(&mut this.read_buffer[..remaining]);
            match this.inner.as_mut().poll_read(cx, &mut temp_buf) {
                Poll::Pending => {
                    if this.temp_buffer.is_empty() {
                        return Poll::Pending;
                    }
                    break;
                }
                Poll::Ready(Ok(())) => {
                    let n = temp_buf.filled().len();
                    if n == 0 {
                        if this.temp_buffer.is_empty() {
                            *this.done = true;
                            return Poll::Ready(Ok(()));
                        }
                        break;
                    }
                    this.temp_buffer.extend_from_slice(&temp_buf.filled()[..n]);
                }
                Poll::Ready(Err(e)) => {
                    // error!("CompressReader poll_read: read inner error: {e}");
                    return Poll::Ready(Err(e));
                }
            }
        }
        // Process accumulated data
        if !this.temp_buffer.is_empty() {
            let uncompressed_data = &this.temp_buffer;
            let out = build_compressed_block(uncompressed_data, *this.compression_algorithm);
            *this.written += out.len();
            *this.uncomp_written += uncompressed_data.len();
            if let Err(e) = this.index.add(*this.written as i64, *this.uncomp_written as i64) {
                // error!("CompressReader index add error: {e}");
                return Poll::Ready(Err(e));
            }
            *this.buffer = out;
            *this.pos = 0;
            this.temp_buffer.truncate(0); // More efficient way to clear
            let to_copy = min(buf.remaining(), this.buffer.len());
            buf.put_slice(&this.buffer[..to_copy]);
            *this.pos += to_copy;
            if *this.pos == this.buffer.len() {
                this.buffer.clear();
                *this.pos = 0;
            }
            Poll::Ready(Ok(()))
        } else {
            Poll::Pending
        }
    }
}

delegate_reader_capabilities_generic_no_index!(CompressReader<R>, inner);

pin_project! {
    /// A reader wrapper that decompresses data on the fly using DEFLATE algorithm.
    /// Header format:
    /// - First byte: compression type (00 = compressed, 01 = uncompressed, FF = end)
    /// - Bytes 1-3: length of compressed data (little-endian)
    /// - Bytes 4-7: CRC32 checksum of uncompressed data (little-endian)
    #[derive(Debug)]
    pub struct DecompressReader<R> {
        #[pin]
        pub inner: R,
        buffer: Vec<u8>,
        buffer_pos: usize,
        finished: bool,
        // Fields for saving header read progress across polls
        header_buf: [u8; 8],
        header_read: usize,
        header_done: bool,
        // Fields for saving compressed block read progress across polls
        compressed_buf: Vec<u8>,
        compressed_read: usize,
        compressed_len: usize,
        compression_algorithm: CompressionAlgorithm,
    }
}

impl<R> DecompressReader<R>
where
    R: AsyncRead + Unpin + Send + Sync,
{
    pub fn new(inner: R, compression_algorithm: CompressionAlgorithm) -> Self {
        Self {
            inner,
            buffer: Vec::new(),
            buffer_pos: 0,
            finished: false,
            header_buf: [0u8; 8],
            header_read: 0,
            header_done: false,
            compressed_buf: Vec::new(),
            compressed_read: 0,
            compressed_len: 0,
            compression_algorithm,
        }
    }
}

impl<R> AsyncRead for DecompressReader<R>
where
    R: AsyncRead + Unpin + Send + Sync,
{
    fn poll_read(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<io::Result<()>> {
        let mut this = self.project();
        // Copy from buffer first if available
        if *this.buffer_pos < this.buffer.len() {
            let to_copy = min(buf.remaining(), this.buffer.len() - *this.buffer_pos);
            buf.put_slice(&this.buffer[*this.buffer_pos..*this.buffer_pos + to_copy]);
            *this.buffer_pos += to_copy;
            if *this.buffer_pos == this.buffer.len() {
                this.buffer.clear();
                *this.buffer_pos = 0;
            }
            return Poll::Ready(Ok(()));
        }
        if *this.finished {
            return Poll::Ready(Ok(()));
        }
        // Read header
        while !*this.header_done && *this.header_read < HEADER_LEN {
            let mut temp = [0u8; HEADER_LEN];
            let mut temp_buf = ReadBuf::new(&mut temp[0..HEADER_LEN - *this.header_read]);
            match this.inner.as_mut().poll_read(cx, &mut temp_buf) {
                Poll::Pending => return Poll::Pending,
                Poll::Ready(Ok(())) => {
                    let n = temp_buf.filled().len();
                    if n == 0 {
                        break;
                    }
                    this.header_buf[*this.header_read..*this.header_read + n].copy_from_slice(&temp_buf.filled()[..n]);
                    *this.header_read += n;
                }
                Poll::Ready(Err(e)) => {
                    // error!("DecompressReader poll_read: read header error: {e}");
                    return Poll::Ready(Err(e));
                }
            }
            if *this.header_read < HEADER_LEN {
                return Poll::Pending;
            }
        }
        if !*this.header_done && *this.header_read == 0 {
            return Poll::Ready(Ok(()));
        }
        let typ = this.header_buf[0];
        let len = (this.header_buf[1] as usize) | ((this.header_buf[2] as usize) << 8) | ((this.header_buf[3] as usize) << 16);
        let crc = (this.header_buf[4] as u32)
            | ((this.header_buf[5] as u32) << 8)
            | ((this.header_buf[6] as u32) << 16)
            | ((this.header_buf[7] as u32) << 24);
        *this.header_read = 0;
        *this.header_done = true;

        if typ == COMPRESS_TYPE_END {
            *this.compressed_read = 0;
            *this.compressed_len = 0;
            *this.finished = true;
            return Poll::Ready(Ok(()));
        }

        if this.compressed_buf.len() < len {
            this.compressed_buf.resize(len, 0);
        }
        *this.compressed_len = len;
        *this.compressed_read = 0;

        while *this.compressed_read < *this.compressed_len {
            let mut temp_buf = ReadBuf::new(&mut this.compressed_buf[*this.compressed_read..*this.compressed_len]);
            match this.inner.as_mut().poll_read(cx, &mut temp_buf) {
                Poll::Pending => return Poll::Pending,
                Poll::Ready(Ok(())) => {
                    let n = temp_buf.filled().len();
                    if n == 0 {
                        break;
                    }
                    *this.compressed_read += n;
                }
                Poll::Ready(Err(e)) => {
                    // error!("DecompressReader poll_read: read compressed block error: {e}");
                    *this.compressed_read = 0;
                    *this.compressed_len = 0;
                    return Poll::Ready(Err(e));
                }
            }
        }
        let compressed_buf = &this.compressed_buf[..*this.compressed_len];
        // `compressed_buf`'s length comes from the untrusted 24-bit header length field, so it
        // can be shorter than 16 bytes. `uvarint` is safe on any slice length (reads at most 10
        // bytes and stops at the terminator), so pass the whole slice instead of a fixed
        // `[0..16]` index that panics on corrupted/truncated blocks shorter than 16 bytes.
        let (uncompress_len, uvarint) = uvarint(compressed_buf);
        // Reject a length prefix that could not be decoded: `uvarint <= 0` means the varint was
        // empty/unterminated (0) or overflowed (negative — as usize it would index far past the
        // buffer and panic the slice below). The `> len` bound is belt-and-suspenders (uvarint's
        // positive return is always <= buf.len()) but keeps the slice panic-free regardless.
        if uvarint <= 0 || uvarint as usize > compressed_buf.len() {
            *this.compressed_read = 0;
            *this.compressed_len = 0;
            return Poll::Ready(Err(io::Error::new(io::ErrorKind::InvalidData, "Invalid compressed block length prefix")));
        }
        let compressed_data = &compressed_buf[uvarint as usize..];
        let decompressed = if typ == COMPRESS_TYPE_COMPRESSED {
            match decompress_block(compressed_data, *this.compression_algorithm) {
                Ok(out) => out,
                Err(e) => {
                    // error!("DecompressReader decompress_block error: {e}");
                    *this.compressed_read = 0;
                    *this.compressed_len = 0;
                    return Poll::Ready(Err(e));
                }
            }
        } else if typ == COMPRESS_TYPE_UNCOMPRESSED {
            compressed_data.to_vec()
        } else {
            // error!("DecompressReader unknown compression type: {typ}");
            *this.compressed_read = 0;
            *this.compressed_len = 0;
            return Poll::Ready(Err(io::Error::new(io::ErrorKind::InvalidData, "Unknown compression type")));
        };
        if decompressed.len() != uncompress_len as usize {
            // error!("DecompressReader decompressed length mismatch: {} != {}", decompressed.len(), uncompress_len);
            *this.compressed_read = 0;
            *this.compressed_len = 0;
            return Poll::Ready(Err(io::Error::new(io::ErrorKind::InvalidData, "Decompressed length mismatch")));
        }
        let actual_crc = {
            let mut hasher = crc_fast::Digest::new(crc_fast::CrcAlgorithm::Crc32IsoHdlc);
            hasher.update(&decompressed);
            hasher.finalize() as u32
        };
        if actual_crc != crc {
            // error!("DecompressReader CRC32 mismatch: actual {actual_crc} != expected {crc}");
            *this.compressed_read = 0;
            *this.compressed_len = 0;
            return Poll::Ready(Err(io::Error::new(io::ErrorKind::InvalidData, "CRC32 mismatch")));
        }
        *this.buffer = decompressed;
        *this.buffer_pos = 0;
        *this.compressed_read = 0;
        *this.compressed_len = 0;
        *this.header_done = false;
        let to_copy = min(buf.remaining(), this.buffer.len());
        buf.put_slice(&this.buffer[..to_copy]);
        *this.buffer_pos += to_copy;
        if *this.buffer_pos == this.buffer.len() {
            this.buffer.clear();
            *this.buffer_pos = 0;
        }
        Poll::Ready(Ok(()))
    }
}

delegate_reader_capabilities_generic_no_index!(DecompressReader<R>, inner);

/// Build compressed block with header + uvarint + compressed data
fn build_compressed_block(uncompressed_data: &[u8], compression_algorithm: CompressionAlgorithm) -> Vec<u8> {
    let crc = {
        let mut hasher = crc_fast::Digest::new(crc_fast::CrcAlgorithm::Crc32IsoHdlc);
        hasher.update(uncompressed_data);
        hasher.finalize() as u32
    };
    let compressed_data = compress_block(uncompressed_data, compression_algorithm);
    let uncompressed_len = uncompressed_data.len();
    let mut uncompressed_len_buf = [0u8; 10];
    let int_len = put_uvarint(&mut uncompressed_len_buf[..], uncompressed_len as u64);
    let len = compressed_data.len() + int_len;
    let mut header = [0u8; HEADER_LEN];
    header[0] = COMPRESS_TYPE_COMPRESSED;
    header[1] = (len & 0xFF) as u8;
    header[2] = ((len >> 8) & 0xFF) as u8;
    header[3] = ((len >> 16) & 0xFF) as u8;
    header[4] = (crc & 0xFF) as u8;
    header[5] = ((crc >> 8) & 0xFF) as u8;
    header[6] = ((crc >> 16) & 0xFF) as u8;
    header[7] = ((crc >> 24) & 0xFF) as u8;
    let mut out = Vec::with_capacity(len + HEADER_LEN);
    out.extend_from_slice(&header);
    out.extend_from_slice(&uncompressed_len_buf[..int_len]);
    out.extend_from_slice(&compressed_data);
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use rand::RngExt;
    use std::io::Cursor;
    use tokio::io::{AsyncReadExt, BufReader};

    #[tokio::test]
    async fn test_compress_reader_basic() {
        let data = b"hello world, hello world, hello world!";
        let reader = Cursor::new(&data[..]);
        let mut compress_reader = CompressReader::new(reader, CompressionAlgorithm::Gzip);

        let mut compressed = Vec::new();
        compress_reader.read_to_end(&mut compressed).await.unwrap();

        // DecompressReader unpacking
        let mut decompress_reader = DecompressReader::new(Cursor::new(compressed.clone()), CompressionAlgorithm::Gzip);
        let mut decompressed = Vec::new();
        decompress_reader.read_to_end(&mut decompressed).await.unwrap();

        assert_eq!(&decompressed, data);
    }

    #[tokio::test]
    async fn test_compress_reader_basic_deflate() {
        let data = b"hello world, hello world, hello world!";
        let reader = BufReader::new(&data[..]);
        let mut compress_reader = CompressReader::new(reader, CompressionAlgorithm::Deflate);

        let mut compressed = Vec::new();
        compress_reader.read_to_end(&mut compressed).await.unwrap();

        // DecompressReader unpacking
        let mut decompress_reader = DecompressReader::new(Cursor::new(compressed.clone()), CompressionAlgorithm::Deflate);
        let mut decompressed = Vec::new();
        decompress_reader.read_to_end(&mut decompressed).await.unwrap();

        assert_eq!(&decompressed, data);
    }

    #[tokio::test]
    async fn test_compress_reader_empty() {
        let data = b"";
        let reader = BufReader::new(&data[..]);
        let mut compress_reader = CompressReader::new(reader, CompressionAlgorithm::Gzip);

        let mut compressed = Vec::new();
        compress_reader.read_to_end(&mut compressed).await.unwrap();

        let mut decompress_reader = DecompressReader::new(Cursor::new(compressed.clone()), CompressionAlgorithm::Gzip);
        let mut decompressed = Vec::new();
        decompress_reader.read_to_end(&mut decompressed).await.unwrap();

        assert_eq!(&decompressed, data);
    }

    #[tokio::test]
    async fn test_compress_reader_large() {
        // Generate 1MB of random bytes
        let mut data = vec![0u8; 1024 * 1024 * 32];
        rand::rng().fill(&mut data[..]);
        let reader = Cursor::new(data.clone());
        let mut compress_reader = CompressReader::new(reader, CompressionAlgorithm::Gzip);

        let mut compressed = Vec::new();
        compress_reader.read_to_end(&mut compressed).await.unwrap();

        let mut decompress_reader = DecompressReader::new(Cursor::new(compressed.clone()), CompressionAlgorithm::Gzip);
        let mut decompressed = Vec::new();
        decompress_reader.read_to_end(&mut decompressed).await.unwrap();

        assert_eq!(&decompressed, &data);
    }

    #[tokio::test]
    async fn test_compress_reader_large_deflate() {
        // Generate 1MB of random bytes
        let mut data = vec![0u8; 1024 * 1024 * 3 + 512];
        rand::rng().fill(&mut data[..]);
        let reader = Cursor::new(data.clone());
        let mut compress_reader = CompressReader::new(reader, CompressionAlgorithm::default());

        let mut compressed = Vec::new();
        compress_reader.read_to_end(&mut compressed).await.unwrap();

        let mut decompress_reader = DecompressReader::new(Cursor::new(compressed.clone()), CompressionAlgorithm::default());
        let mut decompressed = Vec::new();
        decompress_reader.read_to_end(&mut decompressed).await.unwrap();

        assert_eq!(&decompressed, &data);
    }

    // Regression: a corrupted block whose 24-bit length field is < 16 must not panic.
    // Header layout (HEADER_LEN = 8): [type, len_lo, len_mid, len_hi, crc0..crc3], then `len`
    // bytes of block body. Pre-fix, poll_read sliced `compressed_buf[0..16]` unconditionally,
    // panicking with "range end index 16 out of range for slice of length N" when N < 16.
    #[tokio::test]
    async fn test_decompress_reader_short_block_no_panic() {
        let len: usize = 3;
        let mut input = vec![
            COMPRESS_TYPE_COMPRESSED,
            (len & 0xFF) as u8,
            ((len >> 8) & 0xFF) as u8,
            ((len >> 16) & 0xFF) as u8,
        ];
        input.extend_from_slice(&[0u8; 4]); // bogus CRC
        // Body: a uvarint claiming uncompressed length = 127, followed by 2 bytes that are not
        // a valid compressed stream — post-fix this must surface as a clean InvalidData error.
        input.extend_from_slice(&[0x7f, 0xAB, 0xCD]);

        let mut decompress_reader = DecompressReader::new(Cursor::new(input), CompressionAlgorithm::default());
        let mut out = Vec::new();
        let res = decompress_reader.read_to_end(&mut out).await;
        assert!(res.is_err(), "corrupted short block must return an error, not panic or succeed");
        assert_eq!(res.unwrap_err().kind(), std::io::ErrorKind::InvalidData);
    }

    // Directly exercises the length-prefix guard: an unterminated varint (all continuation bytes)
    // makes `uvarint` return 0, which must be rejected as an invalid length prefix.
    #[tokio::test]
    async fn test_decompress_reader_unterminated_length_prefix_is_rejected() {
        let len: usize = 3;
        let mut input = vec![
            COMPRESS_TYPE_COMPRESSED,
            (len & 0xFF) as u8,
            ((len >> 8) & 0xFF) as u8,
            ((len >> 16) & 0xFF) as u8,
        ];
        input.extend_from_slice(&[0u8; 4]); // bogus CRC
        input.extend_from_slice(&[0x80, 0x80, 0x80]); // 3 continuation bytes, no terminator

        let mut decompress_reader = DecompressReader::new(Cursor::new(input), CompressionAlgorithm::default());
        let mut out = Vec::new();
        let err = decompress_reader
            .read_to_end(&mut out)
            .await
            .expect_err("unterminated length prefix must error");
        assert_eq!(err.kind(), std::io::ErrorKind::InvalidData);
        assert!(err.to_string().contains("length prefix"), "got: {err}");
    }
}