eyros 2.0.0

multi-dimensional interval database
Documentation 
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use random_access_storage::RandomAccess;
use std::io::Write;

#[derive(Debug,Clone)]
pub struct WriteCache<S> where S: RandomAccess {
  store: S,
  queue: Vec<(u64,Vec<u8>)>,
  length: u64,
  enabled: bool
}

impl<S> WriteCache<S> where S: RandomAccess {
  pub fn open (store: S) -> Result<Self,S::Error> {
    let length = store.len()?;
    Ok(Self {
      store,
      queue: vec![],
      length,
      enabled: true
    })
  }
}

impl<S> RandomAccess for WriteCache<S> where S: RandomAccess {
  type Error = S::Error;
  fn write (&mut self, offset: u64, data: &[u8]) -> Result<(),Self::Error> {
    if !self.enabled { return self.store.write(offset, data) }

    let new_range = (offset,offset+(data.len() as u64));
    let overlapping: Vec<usize> = (0..self.queue.len()).filter(|i| {
      let q = &self.queue[*i];
      overlaps(new_range, (q.0,q.0+((q.1).len() as u64)))
    }).collect();

    let mut start = new_range.0;
    let mut end = new_range.1;
    for i in overlapping.iter() {
      let q = &self.queue[*i];
      start = start.min(q.0);
      end = end.max(q.0 + ((q.1).len() as u64));
    }
    let mut merged = (start,vec![0;(end-start) as usize]);
    for i in overlapping.iter() {
      let q = &self.queue[*i];
      merged.1[(q.0-start) as usize..(q.0-start+(q.1.len() as u64)) as usize]
        .copy_from_slice(&q.1.as_slice());
    }
    merged.1[(new_range.0-start) as usize
      .. (new_range.0-start+(data.len() as u64)) as usize
    ].copy_from_slice(data);
 
    for (i,ov) in overlapping.iter().enumerate() {
      self.queue.remove(ov-i);
    }
    if overlapping.is_empty() {
      let mut j = 0;
      for i in 0..self.queue.len() {
        let q = &self.queue[i];
        if merged.0 < q.0 { break }
        j = i+1;
      }
      self.queue.insert(j, merged);
    } else {
      self.queue.insert(overlapping[0], merged);
    }
    self.length = self.length.max(end);
    Ok(())
  }
  fn read (&mut self, offset: u64, length: u64)
  -> Result<Vec<u8>,Self::Error> {
    if !self.enabled { return self.store.read(offset, length) }
    // TODO: analysis to know when to skip the read()
    let range = (offset,offset+length);
    let mut data = {
      let slen = self.store.len()?;
      let mut d = if slen < offset { vec![] }
        else { self.store.read(offset, (slen-offset).min(length))? };
      let dlen = d.len() as u64;
      if dlen < length {
        d.extend(vec![0;(length-dlen) as usize]);
      }
      d
    };
    // TODO: turn these asserts into ensure_eq!
    assert_eq![data.len() as u64, length, "insufficient length"];
    for q in self.queue.iter() {
      if overlaps(range,(q.0,q.0+(q.1.len() as u64))) {
        let q1 = q.0 + (q.1.len() as u64);
        let dstart = (q.0.max(range.0) - range.0) as usize;
        let dend = (q1.min(range.1) - range.0) as usize;
        let qstart = (q.0.max(range.0) - q.0) as usize;
        let qend = (q1.min(range.1) - q.0) as usize;
        assert_eq![dend-dstart, qend-qstart, "data and range length mismatch"];
        data[dstart..dend].copy_from_slice(&q.1[qstart..qend]);
      }
    }
    assert_eq![length, data.len() as u64,
      "requested read of {} bytes, returned {} bytes instead",
      length, data.len()];
    /*
    ensure_eq![length, data.len(),
      "requested read of {} bytes, returned {} bytes instead",
      length, data.len()];
    */
    Ok(data)
  }
  fn read_to_writer (&mut self, _offset: u64, _length: u64,
  _buf: &mut impl Write) -> Result<(),Self::Error> {
    unimplemented![];
  }
  fn del (&mut self, offset: u64, length: u64) -> Result<(),Self::Error> {
    self.store.del(offset, length)
  }
  fn truncate (&mut self, length: u64) -> Result<(),Self::Error> {
    if !self.enabled { return self.store.truncate(length) }
    let mut i = 0;
    while i < self.queue.len() {
      let q0 = self.queue[i].0;
      let qlen = self.queue[i].1.len() as u64;
      if q0 < length {
        self.queue.remove(i);
      } else if q0 + qlen < length {
        self.queue[i].1.truncate((length - q0 as u64) as usize);
        i += 1;
      } else {
        i += 1;
      }
    }
    self.store.truncate(length)?;
    self.length = length;
    Ok(())
  }
  fn len (&self) -> Result<u64,Self::Error> {
    if self.enabled { Ok(self.length) }
    else { self.store.len() }
  }
  fn is_empty (&mut self) -> Result<bool,Self::Error> {
    if self.enabled { Ok(self.length == 0) }
    else { self.store.is_empty() }
  }
  fn sync_all (&mut self) -> Result<(),S::Error> {
    for q in self.queue.iter() {
      self.store.write(q.0, &q.1)?;
    }
    self.queue.clear();
    Ok(())
  }
}

fn overlaps<T> (a: (T,T), b: (T,T)) -> bool where T: PartialOrd {
  a.0 <= b.1 && b.0 <= a.1
}