// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum 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.

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

use std::{
    fs, io,
    io::{Read, Seek, SeekFrom, Write},
    path::Path,
};

use ethbloom;

/// Autoresizable file containing blooms.
pub struct File {
    /// Backing file.
    file: fs::File,
    /// Current file len.
    len: u64,
}

impl File {
    /// Opens database file. Creates new file if database file does not exist.
    pub fn open<P>(path: P) -> io::Result<File>
    where
        P: AsRef<Path>,
    {
        let file = fs::OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            // appending is done manually by calling `ensure_space_for_write`
            .append(false)
            .open(path)?;
        let len = file.metadata()?.len();

        let file = File { file, len };

        Ok(file)
    }

    /// Resizes the file if there is not enough space to write bloom at given position.
    fn ensure_space_for_write(&mut self, pos: u64) -> io::Result<()> {
        // position to write + 256 bytes
        let required_space = (pos + 1) * 256;
        if required_space > self.len {
            self.file.set_len(required_space)?;
            self.len = required_space;
        }
        Ok(())
    }

    /// Read bloom at given position.
    pub fn read_bloom(&self, pos: u64) -> io::Result<ethbloom::Bloom> {
        let mut file_ref = &self.file;
        file_ref.seek(SeekFrom::Start(pos * 256))?;
        let mut bloom = ethbloom::Bloom::default();
        file_ref.read_exact(bloom.as_bytes_mut())?;
        Ok(bloom)
    }

    /// Accrue bloom into bloom at given position.
    pub fn accrue_bloom<'a, B>(&mut self, pos: u64, bloom: B) -> io::Result<()>
    where
        ethbloom::BloomRef<'a>: From<B>,
    {
        self.ensure_space_for_write(pos)?;
        let mut old_bloom: ethbloom::Bloom = self.read_bloom(pos)?;
        old_bloom.accrue_bloom(bloom);
        let mut file_ref = &self.file;
        file_ref.seek(SeekFrom::Start(pos * 256))?;
        file_ref.write_all(old_bloom.as_bytes())
    }

    /// Replace bloom at given position with a new one.
    pub fn replace_bloom<'a, B>(&mut self, pos: u64, bloom: B) -> io::Result<()>
    where
        ethbloom::BloomRef<'a>: From<B>,
    {
        self.ensure_space_for_write(pos)?;
        let mut file_ref = &self.file;
        file_ref.seek(SeekFrom::Start(pos * 256))?;
        file_ref.write_all(ethbloom::BloomRef::from(bloom).data())
    }

    /// Returns an iterator over file.
    ///
    /// This function needs to be mutable `fs::File` is just a shared reference a system file handle.
    /// https://users.rust-lang.org/t/how-to-handle-match-with-irrelevant-ok--/6291/15
    pub fn iterator_from(&mut self, pos: u64) -> io::Result<FileIterator> {
        let start = std::cmp::min(self.len, pos * 256);
        let mut buf_reader = io::BufReader::new(&self.file);
        buf_reader.seek(SeekFrom::Start(start))?;

        let iter = FileIterator { file: buf_reader };

        Ok(iter)
    }

    /// Flush outstanding modifications to the disk
    pub fn flush(&mut self) -> io::Result<()> {
        self.file.flush()
    }
}

/// Iterator over blooms of a single file.
pub struct FileIterator<'a> {
    /// Backing file.
    file: io::BufReader<&'a fs::File>,
}

impl<'a> FileIterator<'a> {
    /// Advance file by n blooms
    pub fn advance(&mut self, n: u64) -> io::Result<()> {
        self.file.seek(SeekFrom::Current(n as i64 * 256))?;
        Ok(())
    }
}

impl<'a> Iterator for FileIterator<'a> {
    type Item = io::Result<ethbloom::Bloom>;

    fn next(&mut self) -> Option<Self::Item> {
        let mut bloom = ethbloom::Bloom::default();
        match self.file.read_exact(bloom.as_bytes_mut()) {
            Ok(_) => Some(Ok(bloom)),
            Err(ref err) if err.kind() == io::ErrorKind::UnexpectedEof => None,
            Err(err) => Some(Err(err)),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::File;
    use ethbloom::Bloom;
    use tempdir::TempDir;

    #[test]
    fn test_file() {
        let tempdir = TempDir::new("").unwrap();
        let mut file = File::open(tempdir.path().join("file")).unwrap();
        file.accrue_bloom(0, &Bloom::from_low_u64_be(1)).unwrap();
        file.flush().unwrap();
        assert_eq!(file.read_bloom(0).unwrap(), Bloom::from_low_u64_be(1));
    }
}