//! Structures and utilities used for compressing/encoding data into the Zstd format.

pub(crate) mod block_header;
pub(crate) mod blocks;
pub(crate) mod frame_header;
pub(crate) mod match_generator;
pub(crate) mod util;

mod frame_compressor;
mod levels;
pub use frame_compressor::FrameCompressor;

use crate::io::{Read, Write};
use alloc::vec::Vec;

/// Convenience function to compress some source into a target without reusing any resources of the compressor
/// ```rust
/// use ruzstd::encoding::{compress, CompressionLevel};
/// let data: &[u8] = &[0,0,0,0,0,0,0,0,0,0,0,0];
/// let mut target = Vec::new();
/// compress(data, &mut target, CompressionLevel::Fastest);
/// ```
pub fn compress<R: Read, W: Write>(source: R, target: W, level: CompressionLevel) {
    let mut frame_enc = FrameCompressor::new(level);
    frame_enc.set_source(source);
    frame_enc.set_drain(target);
    frame_enc.compress();
}

/// Convenience function to compress some source into a Vec without reusing any resources of the compressor
/// ```rust
/// use ruzstd::encoding::{compress_to_vec, CompressionLevel};
/// let data: &[u8] = &[0,0,0,0,0,0,0,0,0,0,0,0];
/// let compressed = compress_to_vec(data, CompressionLevel::Fastest);
/// ```
pub fn compress_to_vec<R: Read>(source: R, level: CompressionLevel) -> Vec<u8> {
    let mut vec = Vec::new();
    compress(source, &mut vec, level);
    vec
}

/// The compression mode used impacts the speed of compression,
/// and resulting compression ratios. Faster compression will result
/// in worse compression ratios, and vice versa.
#[derive(Copy, Clone)]
pub enum CompressionLevel {
    /// This level does not compress the data at all, and simply wraps
    /// it in a Zstandard frame.
    Uncompressed,
    /// This level is roughly equivalent to Zstd compression level 1
    Fastest,
    /// This level is roughly equivalent to Zstd level 3,
    /// or the one used by the official compressor when no level
    /// is specified.
    ///
    /// UNIMPLEMENTED
    Default,
    /// This level is roughly equivalent to Zstd level 7.
    ///
    /// UNIMPLEMENTED
    Better,
    /// This level is roughly equivalent to Zstd level 11.
    ///
    /// UNIMPLEMENTED
    Best,
}

/// Trait used by the encoder that users can use to extend the matching facilities with their own algorithm
/// making their own tradeoffs between runtime, memory usage and compression ratio
///
/// This trait operates on buffers that represent the chunks of data the matching algorithm wants to work on.
/// Each one of these buffers is referred to as a *space*. One or more of these buffers represent the window
/// the decoder will need to decode the data again.
///
/// This library asks the Matcher for a new buffer using `get_next_space` to allow reusing of allocated buffers when they are no longer part of the
/// window of data that is being used for matching.
///
/// The library fills the buffer with data that is to be compressed and commits them back to the matcher using `commit_space`.
///
/// Then it will either call `start_matching` or, if the space is deemed not worth compressing, `skip_matching` is called.
///
/// This is repeated until no more data is left to be compressed.
pub trait Matcher {
    /// Get a space where we can put data to be matched on. Will be encoded as one block. The maximum allowed size is 128 kB.
    fn get_next_space(&mut self) -> alloc::vec::Vec<u8>;
    /// Get a reference to the last commited space
    fn get_last_space(&mut self) -> &[u8];
    /// Commit a space to the matcher so it can be matched against
    fn commit_space(&mut self, space: alloc::vec::Vec<u8>);
    /// Just process the data in the last commited space for future matching
    fn skip_matching(&mut self);
    /// Process the data in the last commited space for future matching AND generate matches for the data
    fn start_matching(&mut self, handle_sequence: impl for<'a> FnMut(Sequence<'a>));
    /// Reset this matcher so it can be used for the next new frame
    fn reset(&mut self, level: CompressionLevel);
    /// The size of the window the decoder will need to execute all sequences produced by this matcher
    ///
    /// May change after a call to reset with a different compression level
    fn window_size(&self) -> u64;
}

#[derive(PartialEq, Eq, Debug)]
/// Sequences that a [`Matcher`] can produce
pub enum Sequence<'data> {
    /// Is encoded as a sequence for the decoder sequence execution.
    ///
    /// First the literals will be copied to the decoded data,
    /// then `match_len` bytes are copied from `offset` bytes back in the buffer
    Triple {
        literals: &'data [u8],
        offset: usize,
        match_len: usize,
    },
    /// This is returned as the last sequence in a block
    ///
    /// These literals will just be copied at the end of the sequence execution by the decoder
    Literals { literals: &'data [u8] },
}