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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity 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 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.  If not, see <http://www.gnu.org/licenses/>.

    //! Snapshot i/o.
    //! Ways of writing and reading snapshots. This module supports writing and reading
    //! snapshots of two different formats: packed and loose.
    //! Packed snapshots are written to a single file, and loose snapshots are
    //! written to multiple files in one directory.

    use std::collections::HashMap;
    use std::io::{self, Read, Seek, SeekFrom, Write};
    use std::fs::{self, File};
    use std::path::{Path, PathBuf};

    use util::Bytes;
    use util::hash::H256;
    use rlp::{self, Encodable, RlpStream, UntrustedRlp, Stream, View};

    use super::ManifestData;

    /// Something which can write snapshots.
    /// Writing the same chunk multiple times will lead to implementation-defined
    /// behavior, and is not advised.
    pub trait SnapshotWriter {
    	/// Write a compressed state chunk.
    	fn write_state_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()>;

    	/// Write a compressed block chunk.
    	fn write_block_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()>;

    	/// Complete writing. The manifest's chunk lists must be consistent
    	/// with the chunks written.
    	fn finish(self, manifest: ManifestData) -> io::Result<()> where Self: Sized;
    }

    // (hash, len, offset)
    struct ChunkInfo(H256, u64, u64);

    impl Encodable for ChunkInfo {
    	fn rlp_append(&self, s: &mut RlpStream) {
    		s.begin_list(3);
    		s.append(&self.0).append(&self.1).append(&self.2);
    	}
    }

    impl rlp::Decodable for ChunkInfo {
    	fn decode<D: rlp::Decoder>(decoder: &D) -> Result<Self, rlp::DecoderError> {
    		let d = decoder.as_rlp();

    		let hash = d.val_at(0)?;
    		let len = d.val_at(1)?;
    		let off = d.val_at(2)?;
    		Ok(ChunkInfo(hash, len, off))
    	}
    }

    /// A packed snapshot writer. This writes snapshots to a single concatenated file.
    ///
    /// The file format is very simple and consists of three parts:
    /// 	[Concatenated chunk data]
    /// 	[manifest as RLP]
    ///     [manifest start offset (8 bytes little-endian)]
    ///
    /// The manifest contains all the same information as a standard `ManifestData`,
    /// but also maps chunk hashes to their lengths and offsets in the file
    /// for easy reading.
    pub struct PackedWriter {
    	file: File,
    	state_hashes: Vec<ChunkInfo>,
    	block_hashes: Vec<ChunkInfo>,
    	cur_len: u64,
    }

    impl PackedWriter {
    	/// Create a new "PackedWriter", to write into the file at the given path.
    	pub fn new(path: &Path) -> io::Result<Self> {
    		Ok(PackedWriter {
    			file: File::create(path)?,
    			state_hashes: Vec::new(),
    			block_hashes: Vec::new(),
    			cur_len: 0,
    		})
    	}
    }

    impl SnapshotWriter for PackedWriter {
    	fn write_state_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()> {
    		self.file.write_all(chunk)?;

    		let len = chunk.len() as u64;
    		self.state_hashes.push(ChunkInfo(hash, len, self.cur_len));

    		self.cur_len += len;
    		Ok(())
    	}

    	fn write_block_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()> {
    		self.file.write_all(chunk)?;

    		let len = chunk.len() as u64;
    		self.block_hashes.push(ChunkInfo(hash, len, self.cur_len));

    		self.cur_len += len;
    		Ok(())
    	}

    	fn finish(mut self, manifest: ManifestData) -> io::Result<()> {
    		// we ignore the hashes fields of the manifest under the assumption that
    		// they are consistent with ours.
    		let mut stream = RlpStream::new_list(5);
    		stream
    			.append(&self.state_hashes)
    			.append(&self.block_hashes)
    			.append(&manifest.state_root)
    			.append(&manifest.block_number)
    			.append(&manifest.block_hash);

    		let manifest_rlp = stream.out();

    		self.file.write_all(&manifest_rlp)?;
    		let off = self.cur_len;
    		trace!(target: "snapshot_io", "writing manifest of len {} to offset {}", manifest_rlp.len(), off);

    		let off_bytes: [u8; 8] =
    			[
    				off as u8,
    				(off >> 8) as u8,
    				(off >> 16) as u8,
    				(off >> 24) as u8,
    				(off >> 32) as u8,
    				(off >> 40) as u8,
    				(off >> 48) as u8,
    				(off >> 56) as u8,
    			];

    		self.file.write_all(&off_bytes[..])?;

    		Ok(())
    	}
    }

    /// A "loose" writer writes chunk files into a directory.
    pub struct LooseWriter {
    	dir: PathBuf,
    }

    impl LooseWriter {
    	/// Create a new LooseWriter which will write into the given directory,
    	/// creating it if it doesn't exist.
    	pub fn new(path: PathBuf) -> io::Result<Self> {
    		fs::create_dir_all(&path)?;

    		Ok(LooseWriter {
    			dir: path,
    		})
    	}

    	// writing logic is the same for both kinds of chunks.
    	fn write_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()> {
    		let mut file_path = self.dir.clone();
    		file_path.push(hash.hex());

    		let mut file = File::create(file_path)?;
    		file.write_all(chunk)?;

    		Ok(())
    	}
    }

    impl SnapshotWriter for LooseWriter {
    	fn write_state_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()> {
    		self.write_chunk(hash, chunk)
    	}

    	fn write_block_chunk(&mut self, hash: H256, chunk: &[u8]) -> io::Result<()> {
    		self.write_chunk(hash, chunk)
    	}

    	fn finish(self, manifest: ManifestData) -> io::Result<()> {
    		let rlp = manifest.into_rlp();
    		let mut path = self.dir.clone();
    		path.push("MANIFEST");

    		let mut file = File::create(path)?;
    		file.write_all(&rlp[..])?;

    		Ok(())
    	}
    }

    /// Something which can read compressed snapshots.
    pub trait SnapshotReader {
    	/// Get the manifest data for this snapshot.
    	fn manifest(&self) -> &ManifestData;

    	/// Get raw chunk data by hash. implementation defined behavior
    	/// if a chunk not in the manifest is requested.
    	fn chunk(&self, hash: H256) -> io::Result<Bytes>;
    }

    /// Packed snapshot reader.
    pub struct PackedReader {
    	file: File,
    	state_hashes: HashMap<H256, (u64, u64)>, // len, offset
    	block_hashes: HashMap<H256, (u64, u64)>, // len, offset
    	manifest: ManifestData,
    }

    impl PackedReader {
    	/// Create a new `PackedReader` for the file at the given path.
    	/// This will fail if any io errors are encountered or the file
    	/// is not a valid packed snapshot.
    	pub fn new(path: &Path) -> Result<Option<Self>, ::error::Error> {
    		let mut file = File::open(path)?;
    		let file_len = file.metadata()?.len();
    		if file_len < 8 {
    			// ensure we don't seek before beginning.
    			return Ok(None);
    		}

    		file.seek(SeekFrom::End(-8))?;
    		let mut off_bytes = [0u8; 8];

    		file.read_exact(&mut off_bytes[..])?;

    		let manifest_off: u64 =
    			((off_bytes[7] as u64) << 56) +
    			((off_bytes[6] as u64) << 48) +
    			((off_bytes[5] as u64) << 40) +
    			((off_bytes[4] as u64) << 32) +
    			((off_bytes[3] as u64) << 24) +
    			((off_bytes[2] as u64) << 16) +
    			((off_bytes[1] as u64) << 8) +
    			(off_bytes[0] as u64);

    		let manifest_len = file_len - manifest_off - 8;
    		trace!(target: "snapshot", "loading manifest of length {} from offset {}", manifest_len, manifest_off);

    		let	mut manifest_buf = vec![0; manifest_len as usize];

    		file.seek(SeekFrom::Start(manifest_off))?;
    		file.read_exact(&mut manifest_buf)?;

    		let rlp = UntrustedRlp::new(&manifest_buf);

    		let state: Vec<ChunkInfo> = rlp.val_at(0)?;
    		let blocks: Vec<ChunkInfo> = rlp.val_at(1)?;

    		let manifest = ManifestData {
    			state_hashes: state.iter().map(|c| c.0).collect(),
    			block_hashes: blocks.iter().map(|c| c.0).collect(),
    			state_root: rlp.val_at(2)?,
    			block_number: rlp.val_at(3)?,
    			block_hash: rlp.val_at(4)?,
    		};

    		Ok(Some(PackedReader {
    			file: file,
    			state_hashes: state.into_iter().map(|c| (c.0, (c.1, c.2))).collect(),
    			block_hashes: blocks.into_iter().map(|c| (c.0, (c.1, c.2))).collect(),
    			manifest: manifest
    		}))
    	}
    }

    impl SnapshotReader for PackedReader {
    	fn manifest(&self) -> &ManifestData {
    		&self.manifest
    	}

    	fn chunk(&self, hash: H256) -> io::Result<Bytes> {
    		let &(len, off) = self.state_hashes.get(&hash).or_else(|| self.block_hashes.get(&hash))
    			.expect("only chunks in the manifest can be requested; qed");

    		let mut file = &self.file;

    		file.seek(SeekFrom::Start(off))?;
    		let mut buf = vec![0; len as usize];

    		file.read_exact(&mut buf[..])?;

    		Ok(buf)
    	}
    }

    /// reader for "loose" snapshots
    pub struct LooseReader {
    	dir: PathBuf,
    	manifest: ManifestData,
    }

    impl LooseReader {
    	/// Create a new `LooseReader` which will read the manifest and chunk data from
    	/// the given directory.
    	pub fn new(mut dir: PathBuf) -> Result<Self, ::error::Error> {
    		let mut manifest_buf = Vec::new();

    		dir.push("MANIFEST");
    		let mut manifest_file = File::open(&dir)?;
    		manifest_file.read_to_end(&mut manifest_buf)?;

    		let manifest = ManifestData::from_rlp(&manifest_buf[..])?;

    		dir.pop();

    		Ok(LooseReader {
    			dir: dir,
    			manifest: manifest,
    		})
    	}
    }

    impl SnapshotReader for LooseReader {
    	fn manifest(&self) -> &ManifestData {
    		&self.manifest
    	}

    	fn chunk(&self, hash: H256) -> io::Result<Bytes> {
    		let mut path = self.dir.clone();
    		path.push(hash.hex());

    		let mut buf = Vec::new();
    		let mut file = File::open(&path)?;

    		file.read_to_end(&mut buf)?;

    		Ok(buf)
    	}
    }

    #[cfg(test)]
    mod tests {
    	use devtools::RandomTempPath;
    	use util::sha3::Hashable;

    	use snapshot::ManifestData;
    	use super::{SnapshotWriter, SnapshotReader, PackedWriter, PackedReader, LooseWriter, LooseReader};

    	const STATE_CHUNKS: &'static [&'static [u8]] = &[b"dog", b"cat", b"hello world", b"hi", b"notarealchunk"];
    	const BLOCK_CHUNKS: &'static [&'static [u8]] = &[b"hello!", b"goodbye!", b"abcdefg", b"hijklmnop", b"qrstuvwxy", b"and", b"z"];

    	#[test]
    	fn packed_write_and_read() {
    		let path = RandomTempPath::new();
    		let mut writer = PackedWriter::new(path.as_path()).unwrap();

    		let mut state_hashes = Vec::new();
    		let mut block_hashes = Vec::new();

    		for chunk in STATE_CHUNKS {
    			let hash = chunk.sha3();
    			state_hashes.push(hash.clone());
    			writer.write_state_chunk(hash, chunk).unwrap();
    		}

    		for chunk in BLOCK_CHUNKS {
    			let hash = chunk.sha3();
    			block_hashes.push(hash.clone());
    			writer.write_block_chunk(chunk.sha3(), chunk).unwrap();
    		}

    		let manifest = ManifestData {
    			state_hashes: state_hashes,
    			block_hashes: block_hashes,
    			state_root: b"notarealroot".sha3(),
    			block_number: 12345678987654321,
    			block_hash: b"notarealblock".sha3(),
    		};

    		writer.finish(manifest.clone()).unwrap();

    		let reader = PackedReader::new(path.as_path()).unwrap().unwrap();
    		assert_eq!(reader.manifest(), &manifest);

    		for hash in manifest.state_hashes.iter().chain(&manifest.block_hashes) {
    			reader.chunk(hash.clone()).unwrap();
    		}
    	}

    	#[test]
    	fn loose_write_and_read() {
    		let path = RandomTempPath::new();
    		let mut writer = LooseWriter::new(path.as_path().into()).unwrap();

    		let mut state_hashes = Vec::new();
    		let mut block_hashes = Vec::new();

    		for chunk in STATE_CHUNKS {
    			let hash = chunk.sha3();
    			state_hashes.push(hash.clone());
    			writer.write_state_chunk(hash, chunk).unwrap();
    		}

    		for chunk in BLOCK_CHUNKS {
    			let hash = chunk.sha3();
    			block_hashes.push(hash.clone());
    			writer.write_block_chunk(chunk.sha3(), chunk).unwrap();
    		}

    		let manifest = ManifestData {
    			state_hashes: state_hashes,
    			block_hashes: block_hashes,
    			state_root: b"notarealroot".sha3(),
    			block_number: 12345678987654321,
    			block_hash: b"notarealblock".sha3(),
    		};

    		writer.finish(manifest.clone()).unwrap();

    		let reader = LooseReader::new(path.as_path().into()).unwrap();
    		assert_eq!(reader.manifest(), &manifest);

    		for hash in manifest.state_hashes.iter().chain(&manifest.block_hashes) {
    			reader.chunk(hash.clone()).unwrap();
    		}
    	}
    }

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