use blake2_rfc::blake2b::Blake2b;
use std::io::{self, Read};

/// Abstraction over a reader which hashes the data being read.
pub struct HashReader<R: Read> {
    reader: R,
    hasher: Blake2b,
}

impl<R: Read> HashReader<R> {
    /// Construct a new `HashReader` given an existing `reader` by value.
    pub fn new(reader: R) -> Self {
        HashReader {
            reader: reader,
            hasher: Blake2b::new(64),
        }
    }

    /// Destroy this reader and return the hash of what was read.
    pub fn into_hash(self) -> String {
        let hash = self.hasher.finalize();

        let mut s = String::new();
        for c in hash.as_bytes().iter() {
            s += &format!("{:02x}", c);
        }

        s
    }
}

impl<R: Read> Read for HashReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let bytes = self.reader.read(buf)?;

        if bytes > 0 {
            self.hasher.update(&buf[0..bytes]);
        }

        Ok(bytes)
    }
}