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// Copyright 2015-2019 Parity Technologies (UK) Ltd.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

extern crate elastic_array;
#[macro_use]
extern crate lazy_static;
extern crate rlp;

mod common;

use common::{BLOCKS_SWAPPER, SNAPSHOT_SWAPPER};
use elastic_array::ElasticArray1024;
use rlp::{Rlp, RlpStream};
use std::{cmp, collections::HashMap};

pub fn snapshot_swapper() -> &'static Swapper<'static> {
    &SNAPSHOT_SWAPPER as &Swapper
}

pub fn blocks_swapper() -> &'static Swapper<'static> {
    &BLOCKS_SWAPPER as &Swapper
}

/// A trait used to compress rlp.
pub trait Compressor {
    /// Get compressed version of given rlp.
    fn compressed(&self, rlp: &[u8]) -> Option<&[u8]>;
}

/// A trait used to convert compressed rlp into it's original version.
pub trait Decompressor {
    /// Get decompressed rlp.
    fn decompressed(&self, compressed: &[u8]) -> Option<&[u8]>;
}

/// Call this function to compress rlp.
pub fn compress(c: &[u8], swapper: &dyn Compressor) -> ElasticArray1024<u8> {
    let rlp = Rlp::new(c);
    if rlp.is_data() {
        ElasticArray1024::from_slice(
            swapper
                .compressed(rlp.as_raw())
                .unwrap_or_else(|| rlp.as_raw()),
        )
    } else {
        map_rlp(&rlp, |r| compress(r.as_raw(), swapper))
    }
}

/// Call this function to decompress rlp.
pub fn decompress(c: &[u8], swapper: &dyn Decompressor) -> ElasticArray1024<u8> {
    let rlp = Rlp::new(c);
    if rlp.is_data() {
        ElasticArray1024::from_slice(
            swapper
                .decompressed(rlp.as_raw())
                .unwrap_or_else(|| rlp.as_raw()),
        )
    } else {
        map_rlp(&rlp, |r| decompress(r.as_raw(), swapper))
    }
}

fn map_rlp<F: Fn(&Rlp) -> ElasticArray1024<u8>>(rlp: &Rlp, f: F) -> ElasticArray1024<u8> {
    let mut stream = RlpStream::new_list(rlp.item_count().unwrap_or_default());
    for subrlp in rlp.iter() {
        stream.append_raw(&f(&subrlp), 1);
    }
    stream.drain().as_slice().into()
}

/// Stores RLPs used for compression
pub struct Swapper<'a> {
    compressed_to_rlp: HashMap<&'a [u8], &'a [u8]>,
    rlp_to_compressed: HashMap<&'a [u8], &'a [u8]>,
}

impl<'a> Swapper<'a> {
    /// Construct a swapper from a list of common RLPs
    pub fn new(rlps_to_swap: &[&'a [u8]], compressed: &[&'a [u8]]) -> Self {
        if rlps_to_swap.len() > 0x7e {
            panic!("Invalid usage, only 127 RLPs can be swappable.");
        }

        let items = cmp::min(rlps_to_swap.len(), compressed.len());
        let mut compressed_to_rlp = HashMap::with_capacity(items);
        let mut rlp_to_compressed = HashMap::with_capacity(items);

        for (&rlp, &compressed) in rlps_to_swap.iter().zip(compressed.iter()) {
            compressed_to_rlp.insert(compressed, rlp);
            rlp_to_compressed.insert(rlp, compressed);
        }

        Swapper {
            compressed_to_rlp,
            rlp_to_compressed,
        }
    }
}

impl<'a> Decompressor for Swapper<'a> {
    fn decompressed(&self, compressed: &[u8]) -> Option<&[u8]> {
        self.compressed_to_rlp.get(compressed).cloned()
    }
}

impl<'a> Compressor for Swapper<'a> {
    fn compressed(&self, rlp: &[u8]) -> Option<&[u8]> {
        self.rlp_to_compressed.get(rlp).cloned()
    }
}