// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use ethcore::snapshot::{ManifestData, SnapshotService};
use ethereum_types::H256;
use hash::keccak;

use std::{collections::HashSet, iter::FromIterator};

#[derive(PartialEq, Eq, Debug)]
pub enum ChunkType {
    State(H256),
    Block(H256),
}

pub struct Snapshot {
    pending_state_chunks: Vec<H256>,
    pending_block_chunks: Vec<H256>,
    downloading_chunks: HashSet<H256>,
    completed_chunks: HashSet<H256>,
    snapshot_hash: Option<H256>,
    bad_hashes: HashSet<H256>,
    initialized: bool,
}

impl Snapshot {
    /// Create a new instance.
    pub fn new() -> Snapshot {
        Snapshot {
            pending_state_chunks: Vec::new(),
            pending_block_chunks: Vec::new(),
            downloading_chunks: HashSet::new(),
            completed_chunks: HashSet::new(),
            snapshot_hash: None,
            bad_hashes: HashSet::new(),
            initialized: false,
        }
    }

    /// Sync the Snapshot completed chunks with the Snapshot Service
    pub fn initialize(&mut self, snapshot_service: &dyn SnapshotService) {
        if self.initialized {
            return;
        }

        if let Some(completed_chunks) = snapshot_service.completed_chunks() {
            self.completed_chunks = HashSet::from_iter(completed_chunks);
        }

        trace!(
            target: "snapshot",
            "Snapshot is now initialized with {} completed chunks.",
            self.completed_chunks.len(),
        );

        self.initialized = true;
    }

    /// Clear everything.
    pub fn clear(&mut self) {
        self.pending_state_chunks.clear();
        self.pending_block_chunks.clear();
        self.downloading_chunks.clear();
        self.completed_chunks.clear();
        self.snapshot_hash = None;
        self.initialized = false;
    }

    /// Check if currently downloading a snapshot.
    pub fn have_manifest(&self) -> bool {
        self.snapshot_hash.is_some()
    }

    /// Reset collection for a manifest RLP
    pub fn reset_to(&mut self, manifest: &ManifestData, hash: &H256) {
        self.clear();
        self.pending_state_chunks = manifest.state_hashes.clone();
        self.pending_block_chunks = manifest.block_hashes.clone();
        self.snapshot_hash = Some(hash.clone());
    }

    /// Validate chunk and mark it as downloaded
    pub fn validate_chunk(&mut self, chunk: &[u8]) -> Result<ChunkType, ()> {
        let hash = keccak(chunk);
        if self.completed_chunks.contains(&hash) {
            trace!(target: "sync", "Ignored proccessed chunk: {:x}", hash);
            return Err(());
        }
        self.downloading_chunks.remove(&hash);
        if self.pending_block_chunks.iter().any(|h| h == &hash) {
            self.completed_chunks.insert(hash.clone());
            return Ok(ChunkType::Block(hash));
        }
        if self.pending_state_chunks.iter().any(|h| h == &hash) {
            self.completed_chunks.insert(hash.clone());
            return Ok(ChunkType::State(hash));
        }
        trace!(target: "sync", "Ignored unknown chunk: {:x}", hash);
        Err(())
    }

    /// Find a chunk to download
    pub fn needed_chunk(&mut self) -> Option<H256> {
        // Find next needed chunk: first block, then state chunks
        let chunk = {
            let chunk_filter =
                |h| !self.downloading_chunks.contains(h) && !self.completed_chunks.contains(h);

            let needed_block_chunk = self
                .pending_block_chunks
                .iter()
                .filter(|&h| chunk_filter(h))
                .map(|h| *h)
                .next();

            // If no block chunks to download, get the state chunks
            if needed_block_chunk.is_none() {
                self.pending_state_chunks
                    .iter()
                    .filter(|&h| chunk_filter(h))
                    .map(|h| *h)
                    .next()
            } else {
                needed_block_chunk
            }
        };

        if let Some(hash) = chunk {
            self.downloading_chunks.insert(hash.clone());
        }
        chunk
    }

    pub fn clear_chunk_download(&mut self, hash: &H256) {
        self.downloading_chunks.remove(hash);
    }

    // note snapshot hash as bad.
    pub fn note_bad(&mut self, hash: H256) {
        self.bad_hashes.insert(hash);
    }

    // whether snapshot hash is known to be bad.
    pub fn is_known_bad(&self, hash: &H256) -> bool {
        self.bad_hashes.contains(hash)
    }

    pub fn snapshot_hash(&self) -> Option<H256> {
        self.snapshot_hash
    }

    pub fn total_chunks(&self) -> usize {
        self.pending_block_chunks.len() + self.pending_state_chunks.len()
    }

    pub fn done_chunks(&self) -> usize {
        self.completed_chunks.len()
    }

    pub fn is_complete(&self) -> bool {
        self.total_chunks() == self.completed_chunks.len()
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use bytes::Bytes;
    use ethcore::snapshot::ManifestData;
    use hash::keccak;

    fn is_empty(snapshot: &Snapshot) -> bool {
        snapshot.pending_block_chunks.is_empty()
            && snapshot.pending_state_chunks.is_empty()
            && snapshot.completed_chunks.is_empty()
            && snapshot.downloading_chunks.is_empty()
            && snapshot.snapshot_hash.is_none()
    }

    fn test_manifest() -> (ManifestData, H256, Vec<Bytes>, Vec<Bytes>) {
        let state_chunks: Vec<Bytes> = (0..20).map(|_| H256::random().to_vec()).collect();
        let block_chunks: Vec<Bytes> = (0..20).map(|_| H256::random().to_vec()).collect();
        let manifest = ManifestData {
            version: 2,
            state_hashes: state_chunks.iter().map(|data| keccak(data)).collect(),
            block_hashes: block_chunks.iter().map(|data| keccak(data)).collect(),
            state_root: H256::new(),
            block_number: 42,
            block_hash: H256::new(),
        };
        let mhash = keccak(manifest.clone().into_rlp());
        (manifest, mhash, state_chunks, block_chunks)
    }

    #[test]
    fn create_clear() {
        let mut snapshot = Snapshot::new();
        assert!(is_empty(&snapshot));
        let (manifest, mhash, _, _) = test_manifest();
        snapshot.reset_to(&manifest, &mhash);
        assert!(!is_empty(&snapshot));
        snapshot.clear();
        assert!(is_empty(&snapshot));
    }

    #[test]
    fn validate_chunks() {
        let mut snapshot = Snapshot::new();
        let (manifest, mhash, state_chunks, block_chunks) = test_manifest();
        snapshot.reset_to(&manifest, &mhash);
        assert_eq!(snapshot.done_chunks(), 0);
        assert!(snapshot.validate_chunk(&H256::random().to_vec()).is_err());

        let requested: Vec<H256> = (0..40).map(|_| snapshot.needed_chunk().unwrap()).collect();
        assert!(snapshot.needed_chunk().is_none());

        let requested_all_block_chunks = manifest
            .block_hashes
            .iter()
            .all(|h| requested.iter().any(|rh| rh == h));
        assert!(requested_all_block_chunks);

        let requested_all_state_chunks = manifest
            .state_hashes
            .iter()
            .all(|h| requested.iter().any(|rh| rh == h));
        assert!(requested_all_state_chunks);

        assert_eq!(snapshot.downloading_chunks.len(), 40);

        assert_eq!(
            snapshot.validate_chunk(&state_chunks[4]),
            Ok(ChunkType::State(manifest.state_hashes[4].clone()))
        );
        assert_eq!(snapshot.completed_chunks.len(), 1);
        assert_eq!(snapshot.downloading_chunks.len(), 39);

        assert_eq!(
            snapshot.validate_chunk(&block_chunks[10]),
            Ok(ChunkType::Block(manifest.block_hashes[10].clone()))
        );
        assert_eq!(snapshot.completed_chunks.len(), 2);
        assert_eq!(snapshot.downloading_chunks.len(), 38);

        for (i, data) in state_chunks.iter().enumerate() {
            if i != 4 {
                assert!(snapshot.validate_chunk(data).is_ok());
            }
        }

        for (i, data) in block_chunks.iter().enumerate() {
            if i != 10 {
                assert!(snapshot.validate_chunk(data).is_ok());
            }
        }

        assert!(snapshot.is_complete());
        assert_eq!(snapshot.done_chunks(), 40);
        assert_eq!(snapshot.done_chunks(), snapshot.total_chunks());
        assert_eq!(snapshot.snapshot_hash(), Some(keccak(manifest.into_rlp())));
    }

    #[test]
    fn tracks_known_bad() {
        let mut snapshot = Snapshot::new();
        let hash = H256::random();

        assert_eq!(snapshot.is_known_bad(&hash), false);
        snapshot.note_bad(hash);
        assert_eq!(snapshot.is_known_bad(&hash), true);
    }
}