armature-compression 0.1.0

//! Streaming Compression - Compress chunks as they're generated
//!
//! This module provides streaming compression that compresses data incrementally
//! as it's produced, rather than buffering the entire response.
//!
//! # Features
//!
//! - Incremental compression for streaming responses
//! - Multiple algorithm support (gzip, brotli, zstd)
//! - Configurable flush intervals
//! - Integration with SSE and chunked responses
//!
//! # Example
//!
//! ```rust,ignore
//! use armature_compression::streaming::{StreamingCompressor, StreamingConfig};
//!
//! let config = StreamingConfig::new()
//!     .algorithm(CompressionAlgorithm::Gzip)
//!     .flush_interval(1024);
//!
//! let mut compressor = StreamingCompressor::new(config)?;
//!
//! // Compress chunks as they arrive
//! let compressed = compressor.compress_chunk(data)?;
//!
//! // Finish compression
//! let final_chunk = compressor.finish()?;
//! ```

use crate::{CompressionAlgorithm, CompressionError, Result};
use bytes::{Bytes, BytesMut};

#[cfg(feature = "gzip")]
use flate2::Compression as GzipCompression;
#[cfg(feature = "gzip")]
use flate2::write::GzEncoder;

#[cfg(feature = "brotli")]
use brotli::CompressorWriter as BrotliEncoder;

#[cfg(feature = "zstd")]
use zstd::stream::write::Encoder as ZstdEncoder;

use std::io::Write;

/// Configuration for streaming compression.
#[derive(Debug, Clone)]
pub struct StreamingConfig {
    /// Compression algorithm to use
    pub algorithm: CompressionAlgorithm,
    /// Compression level (algorithm-specific)
    pub level: u32,
    /// Flush after this many bytes (0 = auto)
    pub flush_interval: usize,
    /// Minimum chunk size before compressing
    pub min_chunk_size: usize,
    /// Buffer size for compression output
    pub buffer_size: usize,
}

impl Default for StreamingConfig {
    fn default() -> Self {
        Self {
            algorithm: CompressionAlgorithm::Auto,
            level: 6,
            flush_interval: 4096,
            min_chunk_size: 64,
            buffer_size: 8192,
        }
    }
}

impl StreamingConfig {
    /// Create new streaming config.
    pub fn new() -> Self {
        Self::default()
    }

    /// Set compression algorithm.
    pub fn algorithm(mut self, algorithm: CompressionAlgorithm) -> Self {
        self.algorithm = algorithm;
        self
    }

    /// Set compression level.
    pub fn level(mut self, level: u32) -> Self {
        self.level = level;
        self
    }

    /// Set flush interval (bytes).
    pub fn flush_interval(mut self, interval: usize) -> Self {
        self.flush_interval = interval;
        self
    }

    /// Set minimum chunk size.
    pub fn min_chunk_size(mut self, size: usize) -> Self {
        self.min_chunk_size = size;
        self
    }

    /// Set buffer size.
    pub fn buffer_size(mut self, size: usize) -> Self {
        self.buffer_size = size;
        self
    }

    /// Create config optimized for low latency streaming.
    pub fn low_latency() -> Self {
        Self {
            algorithm: CompressionAlgorithm::Auto,
            level: 1,            // Fastest
            flush_interval: 256, // Frequent flushes
            min_chunk_size: 16,
            buffer_size: 1024,
        }
    }

    /// Create config optimized for high compression ratio.
    pub fn high_compression() -> Self {
        Self {
            algorithm: CompressionAlgorithm::Auto,
            level: 9,              // Best compression
            flush_interval: 16384, // Less frequent flushes
            min_chunk_size: 1024,
            buffer_size: 32768,
        }
    }
}

/// Internal encoder state.
#[allow(clippy::large_enum_variant)] // Boxing adds complexity, variant is stack-allocated once
enum EncoderState {
    None,
    #[cfg(feature = "gzip")]
    Gzip(GzEncoder<Vec<u8>>),
    #[cfg(feature = "brotli")]
    Brotli(BrotliEncoder<Vec<u8>>),
    #[cfg(feature = "zstd")]
    Zstd(ZstdEncoder<'static, Vec<u8>>),
}

/// Streaming compressor that compresses chunks incrementally.
pub struct StreamingCompressor {
    config: StreamingConfig,
    encoder: EncoderState,
    bytes_in: u64,
    bytes_out: u64,
    unflushed_bytes: usize,
    finished: bool,
}

impl StreamingCompressor {
    /// Create a new streaming compressor.
    pub fn new(config: StreamingConfig) -> Result<Self> {
        let encoder = Self::create_encoder(&config)?;

        Ok(Self {
            config,
            encoder,
            bytes_in: 0,
            bytes_out: 0,
            unflushed_bytes: 0,
            finished: false,
        })
    }

    /// Create with specific algorithm selected from Accept-Encoding.
    pub fn from_accept_encoding(accept_encoding: &str, config: StreamingConfig) -> Result<Self> {
        let algorithm = CompressionAlgorithm::select_from_accept_encoding(accept_encoding);
        let config = StreamingConfig {
            algorithm,
            ..config
        };
        Self::new(config)
    }

    fn create_encoder(config: &StreamingConfig) -> Result<EncoderState> {
        let algorithm = match config.algorithm {
            CompressionAlgorithm::Auto => {
                // Default to gzip for streaming (best compatibility)
                #[cfg(feature = "gzip")]
                {
                    CompressionAlgorithm::Gzip
                }
                #[cfg(not(feature = "gzip"))]
                {
                    CompressionAlgorithm::None
                }
            }
            other => other,
        };

        match algorithm {
            CompressionAlgorithm::None | CompressionAlgorithm::Auto => Ok(EncoderState::None),

            #[cfg(feature = "gzip")]
            CompressionAlgorithm::Gzip => {
                let level = config.level.clamp(1, 9);
                let encoder = GzEncoder::new(
                    Vec::with_capacity(config.buffer_size),
                    GzipCompression::new(level),
                );
                Ok(EncoderState::Gzip(encoder))
            }

            #[cfg(feature = "brotli")]
            CompressionAlgorithm::Brotli => {
                let level = config.level.clamp(0, 11);
                let encoder = BrotliEncoder::new(
                    Vec::with_capacity(config.buffer_size),
                    config.buffer_size,
                    level,
                    22, // lgwin
                );
                Ok(EncoderState::Brotli(encoder))
            }

            #[cfg(feature = "zstd")]
            CompressionAlgorithm::Zstd => {
                let level = config.level.clamp(1, 22) as i32;
                let encoder = ZstdEncoder::new(Vec::with_capacity(config.buffer_size), level)
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                Ok(EncoderState::Zstd(encoder))
            }

            #[allow(unreachable_patterns)]
            _ => Err(CompressionError::UnsupportedAlgorithm(format!(
                "{:?} not available",
                algorithm
            ))),
        }
    }

    /// Get the Content-Encoding value for this compressor.
    pub fn encoding(&self) -> Option<&'static str> {
        match &self.encoder {
            EncoderState::None => None,
            #[cfg(feature = "gzip")]
            EncoderState::Gzip(_) => Some("gzip"),
            #[cfg(feature = "brotli")]
            EncoderState::Brotli(_) => Some("br"),
            #[cfg(feature = "zstd")]
            EncoderState::Zstd(_) => Some("zstd"),
        }
    }

    /// Compress a chunk of data.
    ///
    /// Returns compressed bytes. May return empty if data is being buffered.
    pub fn compress_chunk(&mut self, data: &[u8]) -> Result<Bytes> {
        if self.finished {
            return Err(CompressionError::CompressionFailed(
                "Compressor already finished".to_string(),
            ));
        }

        if data.is_empty() {
            return Ok(Bytes::new());
        }

        self.bytes_in += data.len() as u64;
        self.unflushed_bytes += data.len();

        match &mut self.encoder {
            EncoderState::None => {
                // Pass through
                self.bytes_out += data.len() as u64;
                Ok(Bytes::copy_from_slice(data))
            }

            #[cfg(feature = "gzip")]
            EncoderState::Gzip(encoder) => {
                encoder
                    .write_all(data)
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;

                // Flush if we've accumulated enough
                if self.unflushed_bytes >= self.config.flush_interval {
                    self.flush_internal()
                } else {
                    Ok(Bytes::new())
                }
            }

            #[cfg(feature = "brotli")]
            EncoderState::Brotli(encoder) => {
                encoder
                    .write_all(data)
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;

                if self.unflushed_bytes >= self.config.flush_interval {
                    self.flush_internal()
                } else {
                    Ok(Bytes::new())
                }
            }

            #[cfg(feature = "zstd")]
            EncoderState::Zstd(encoder) => {
                encoder
                    .write_all(data)
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;

                if self.unflushed_bytes >= self.config.flush_interval {
                    self.flush_internal()
                } else {
                    Ok(Bytes::new())
                }
            }
        }
    }

    /// Flush compressed data without finishing.
    pub fn flush(&mut self) -> Result<Bytes> {
        self.flush_internal()
    }

    fn flush_internal(&mut self) -> Result<Bytes> {
        self.unflushed_bytes = 0;

        match &mut self.encoder {
            EncoderState::None => Ok(Bytes::new()),

            #[cfg(feature = "gzip")]
            EncoderState::Gzip(encoder) => {
                encoder
                    .flush()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                let inner = encoder.get_mut();
                if inner.is_empty() {
                    return Ok(Bytes::new());
                }
                let output = std::mem::take(inner);
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }

            #[cfg(feature = "brotli")]
            EncoderState::Brotli(encoder) => {
                encoder
                    .flush()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                let inner = encoder.get_mut();
                if inner.is_empty() {
                    return Ok(Bytes::new());
                }
                let output = std::mem::take(inner);
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }

            #[cfg(feature = "zstd")]
            EncoderState::Zstd(encoder) => {
                encoder
                    .flush()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                let inner = encoder.get_mut();
                if inner.is_empty() {
                    return Ok(Bytes::new());
                }
                let output = std::mem::take(inner);
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }
        }
    }

    /// Finish compression and return final bytes.
    pub fn finish(mut self) -> Result<Bytes> {
        if self.finished {
            return Ok(Bytes::new());
        }
        self.finished = true;

        match self.encoder {
            EncoderState::None => Ok(Bytes::new()),

            #[cfg(feature = "gzip")]
            EncoderState::Gzip(encoder) => {
                let output = encoder
                    .finish()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }

            #[cfg(feature = "brotli")]
            EncoderState::Brotli(mut encoder) => {
                encoder
                    .flush()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                let output = encoder.into_inner();
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }

            #[cfg(feature = "zstd")]
            EncoderState::Zstd(encoder) => {
                let output = encoder
                    .finish()
                    .map_err(|e| CompressionError::CompressionFailed(e.to_string()))?;
                self.bytes_out += output.len() as u64;
                Ok(Bytes::from(output))
            }
        }
    }

    /// Get compression statistics.
    pub fn stats(&self) -> CompressionStats {
        CompressionStats {
            bytes_in: self.bytes_in,
            bytes_out: self.bytes_out,
            ratio: if self.bytes_in > 0 {
                self.bytes_out as f64 / self.bytes_in as f64
            } else {
                1.0
            },
        }
    }
}

/// Compression statistics.
#[derive(Debug, Clone, Copy)]
pub struct CompressionStats {
    /// Total bytes before compression
    pub bytes_in: u64,
    /// Total bytes after compression
    pub bytes_out: u64,
    /// Compression ratio (out/in, lower is better)
    pub ratio: f64,
}

impl CompressionStats {
    /// Get space savings as percentage (0-100).
    pub fn savings_percent(&self) -> f64 {
        if self.bytes_in == 0 {
            return 0.0;
        }
        (1.0 - self.ratio) * 100.0
    }
}

/// Async streaming compressor wrapper.
///
/// Wraps a StreamingCompressor for use with async streams.
pub struct AsyncStreamingCompressor {
    inner: StreamingCompressor,
    #[allow(dead_code)] // Reserved for buffering partial data
    pending: BytesMut,
}

impl AsyncStreamingCompressor {
    /// Create a new async streaming compressor.
    pub fn new(config: StreamingConfig) -> Result<Self> {
        Ok(Self {
            inner: StreamingCompressor::new(config)?,
            pending: BytesMut::with_capacity(8192),
        })
    }

    /// Get the Content-Encoding header value.
    pub fn encoding(&self) -> Option<&'static str> {
        self.inner.encoding()
    }

    /// Process a chunk and return compressed data.
    pub async fn process(&mut self, chunk: Bytes) -> Result<Bytes> {
        self.inner.compress_chunk(&chunk)
    }

    /// Flush any pending compressed data.
    pub async fn flush(&mut self) -> Result<Bytes> {
        self.inner.flush()
    }

    /// Finish compression.
    pub fn finish(self) -> Result<Bytes> {
        self.inner.finish()
    }

    /// Get compression statistics.
    pub fn stats(&self) -> CompressionStats {
        self.inner.stats()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_streaming_config() {
        let config = StreamingConfig::new()
            .algorithm(CompressionAlgorithm::None)
            .level(6)
            .flush_interval(1024);

        assert_eq!(config.level, 6);
        assert_eq!(config.flush_interval, 1024);
    }

    #[test]
    fn test_passthrough_compressor() {
        let config = StreamingConfig::new().algorithm(CompressionAlgorithm::None);

        let mut compressor = StreamingCompressor::new(config).unwrap();

        let data = b"Hello, World!";
        let compressed = compressor.compress_chunk(data).unwrap();

        assert_eq!(compressed.as_ref(), data);

        let final_chunk = compressor.finish().unwrap();
        assert!(final_chunk.is_empty());
    }

    #[test]
    #[cfg(feature = "gzip")]
    fn test_gzip_streaming() {
        let config = StreamingConfig::new()
            .algorithm(CompressionAlgorithm::Gzip)
            .flush_interval(10); // Flush frequently for test

        let mut compressor = StreamingCompressor::new(config).unwrap();

        let mut total_compressed = BytesMut::new();

        // Send multiple chunks
        for _ in 0..10 {
            let data = b"Hello, World! This is a test chunk.\n";
            let compressed = compressor.compress_chunk(data).unwrap();
            total_compressed.extend_from_slice(&compressed);
        }

        // Get stats before finishing (finish consumes self)
        let stats = compressor.stats();
        assert_eq!(stats.bytes_in, 10 * 36);

        // Finish
        let final_chunk = compressor.finish().unwrap();
        total_compressed.extend_from_slice(&final_chunk);

        // Should be smaller than original
        let original_size = 10 * 36; // 10 chunks * 36 bytes each
        assert!(total_compressed.len() < original_size);
    }

    #[test]
    fn test_compression_stats() {
        let stats = CompressionStats {
            bytes_in: 1000,
            bytes_out: 400,
            ratio: 0.4,
        };

        assert_eq!(stats.savings_percent(), 60.0);
    }

    #[test]
    fn test_low_latency_config() {
        let config = StreamingConfig::low_latency();
        assert_eq!(config.level, 1);
        assert_eq!(config.flush_interval, 256);
    }

    #[test]
    fn test_high_compression_config() {
        let config = StreamingConfig::high_compression();
        assert_eq!(config.level, 9);
        assert!(config.flush_interval > 1024);
    }
}