use std::io;

use std::io::{ErrorKind, Write};

#[derive(Debug)]

pub struct Ui {

    stdout: std::io::Stdout,

    stderr: std::io::Stderr,

}

/// The kind of user interface error

pub enum UiError {

    /// The standard output stream cannot be written to

    StdoutError(io::Error),

    /// The standard error stream cannot be written to

    StderrError(io::Error),

}

/// The commandline user interface

impl Ui {

    pub fn new() -> Self {

        Ui {

            stdout: std::io::stdout(),

            stderr: std::io::stderr(),

        }

    }

    /// Returns a buffered handle on stdout for faster batch printing

    /// operations.

    pub fn stdout_buffer(&self) -> StdoutBuffer<std::io::StdoutLock> {

        StdoutBuffer::new(self.stdout.lock())

    }

    /// Write bytes to stdout

    pub fn write_stdout(&self, bytes: &[u8]) -> Result<(), UiError> {

        let mut stdout = self.stdout.lock();

        stdout.write_all(bytes).or_else(handle_stdout_error)?;

        stdout.flush().or_else(handle_stdout_error)

    }

    /// Write bytes to stderr

    pub fn write_stderr(&self, bytes: &[u8]) -> Result<(), UiError> {

        let mut stderr = self.stderr.lock();

        stderr.write_all(bytes).or_else(handle_stderr_error)?;

        stderr.flush().or_else(handle_stderr_error)

    }

    /// Write string line to stderr

    pub fn writeln_stderr_str(&self, s: &str) -> Result<(), UiError> {

        self.write_stderr(&format!("{}\n", s).as_bytes())

    }

}

/// A buffered stdout writer for faster batch printing operations.

pub struct StdoutBuffer<W: Write> {

    buf: io::BufWriter<W>,

}

impl<W: Write> StdoutBuffer<W> {

    pub fn new(writer: W) -> Self {

        let buf = io::BufWriter::new(writer);

        Self { buf }

    }

    /// Write bytes to stdout buffer

    pub fn write_all(&mut self, bytes: &[u8]) -> Result<(), UiError> {

        self.buf.write_all(bytes).or_else(handle_stdout_error)

    }

    /// Flush bytes to stdout

    pub fn flush(&mut self) -> Result<(), UiError> {

        self.buf.flush().or_else(handle_stdout_error)

    }

}

/// Sometimes writing to stdout is not possible, try writing to stderr to

/// signal that failure, otherwise just bail.

fn handle_stdout_error(error: io::Error) -> Result<(), UiError> {

    if let ErrorKind::BrokenPipe = error.kind() {

        // This makes `| head` work for example

        return Ok(());

    }

    let mut stderr = io::stderr();

    stderr

        .write_all(&[b"abort: ", error.to_string().as_bytes(), b"\n"].concat())

        .map_err(UiError::StderrError)?;

    stderr.flush().map_err(UiError::StderrError)?;

    Err(UiError::StdoutError(error))

}

/// Sometimes writing to stderr is not possible.

fn handle_stderr_error(error: io::Error) -> Result<(), UiError> {

    // A broken pipe should not result in a error

    // like with `| head` for example

    if let ErrorKind::BrokenPipe = error.kind() {

        return Ok(());

    }

    Err(UiError::StdoutError(error))

}