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use std::error::Error;
use std::fmt;
use std::fs::File;
use std::io::{BufRead, BufReader, Read, self};
use super::{DataLine, DataParseError, Line};

/// Representation of `/etc/hosts`.
pub struct HostsFile<R: BufRead> {
    inner: R,
}

impl HostsFile<BufReader<File>> {
    /// Loads the data from `/etc/hosts`.
    pub fn load() -> io::Result<HostsFile<BufReader<File>>> {
        Ok(HostsFile {
            inner: BufReader::new(File::open("/etc/hosts")?),
        })
    }
}
impl<R: Read> HostsFile<BufReader<R>> {
    /// Loads the data from `/etc/hosts` from a generic reader wrapped in a `BufReader`.
    pub fn read_buffered(reader: R) -> HostsFile<BufReader<R>> {
        HostsFile { inner: BufReader::new(reader) }
    }
}
impl<R: BufRead> HostsFile<R> {
    /// Loads the data from `/etc/hosts` from a generic reader.
    pub fn read(reader: R) -> HostsFile<R> {
        HostsFile { inner: reader }
    }

    /// Iterates over all lines in the file.
    pub fn lines(self) -> Lines<R> {
        Lines { inner: self.inner.lines() }
    }

    /// Iterates over the lines in the file with data.
    pub fn data_lines(self) -> DataLines<R> {
        DataLines { inner: self.inner.lines() }
    }
}

/// Error found when reading a line in `/etc/hosts`.
#[derive(Debug)]
pub enum LineReadError {
    /// The line failed to read.
    Read(io::Error),

    /// The line failed to parse.
    Parse(DataParseError),
}
impl From<io::Error> for LineReadError {
    fn from(err: io::Error) -> LineReadError {
        LineReadError::Read(err)
    }
}
impl From<DataParseError> for LineReadError {
    fn from(err: DataParseError) -> LineReadError {
        LineReadError::Parse(err)
    }
}
impl Error for LineReadError {
    fn description(&self) -> &str {
        match *self {
            LineReadError::Read(ref err) => err.description(),
            LineReadError::Parse(ref err) => err.description(),
        }
    }
    fn cause(&self) -> Option<&Error> {
        Some(match *self {
            LineReadError::Read(ref err) => err,
            LineReadError::Parse(ref err) => err
        })
    }
}
impl fmt::Display for LineReadError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            LineReadError::Read(ref err) => fmt::Display::fmt(err, f),
            LineReadError::Parse(ref err) => fmt::Display::fmt(err, f),
        }
    }
}

/// Iterator over the lines in `/etc/hosts`.
pub struct Lines<R: BufRead> {
    inner: io::Lines<R>,
}
impl<R: BufRead> Iterator for Lines<R> {
    type Item = Result<Line<'static>, LineReadError>;
    fn next(&mut self) -> Option<Result<Line<'static>, LineReadError>> {
        self.inner.next().map(|line| {
            match line {
                Err(err) => return Err(err.into()),
                Ok(line) => return line.parse().map_err(Into::into).map(Line::into_owned),
            }
        })
    }
}

/// Iterator over the lines in `/etc/hosts` with data.
pub struct DataLines<R: BufRead> {
    inner: io::Lines<R>,
}
impl<R: BufRead> Iterator for DataLines<R> {
    type Item = Result<DataLine, LineReadError>;
    fn next(&mut self) -> Option<Result<DataLine, LineReadError>> {
        for line in self.inner.by_ref() {
            match line {
                Err(err) => return Some(Err(err.into())),
                Ok(line) => {
                    match line.parse().map(Line::into_data) {
                        Ok(None) => (),
                        Ok(Some(data)) => return Some(Ok(data)),
                        Err(err) => return Some(Err(err.into())),
                    }
                }
            }
        }
        None
    }
}

#[cfg(test)]
mod tests {
    use std::fmt::Write;
    use super::*;

    static PRETTY: &str = "\
# basic ones
127.0.0.1  locahost localhost.localdomain
0.0.0.0  allzeros  # nonstandard

# others
8.8.8.8  gdns  # this is the more common one
8.8.4.4  gdns2  # this is the less common one

# comment by itself
";

    static PLAIN: &str = "\
127.0.0.1  locahost localhost.localdomain
0.0.0.0  allzeros
8.8.8.8  gdns
8.8.4.4  gdns2
";

    static BIG: &str = "\
127.0.0.1  locahost
::1  localhost.localdomain
::1  lh
127.0.0.1  lh
0.0.0.0  allzeros
8.8.8.8  gdns
0.0.0.0  lotsazeros
8.8.4.4  gdns2
8.8.8.8  google-dns
";

    static SMALL: &str = "\
0.0.0.0  allzeros lotsazeros
8.8.4.4  gdns2
8.8.8.8  gdns google-dns
127.0.0.1  lh locahost
::1  lh localhost.localdomain
";

    #[test]
    fn lines() {
        let mut rewritten = String::new();
        for line in HostsFile::read_buffered(PRETTY.as_bytes()).lines() {
            let line = line.unwrap();
            writeln!(rewritten, "{}", line).unwrap();
        }
        assert_eq!(rewritten, PRETTY);
    }

    #[test]
    fn data_lines() {
        let mut rewritten = String::new();
        for line in HostsFile::read_buffered(PRETTY.as_bytes()).data_lines() {
            let line = line.unwrap();
            writeln!(rewritten, "{}", line).unwrap();
        }
        assert_eq!(rewritten, PLAIN);
    }
}