use crate::terminal::error::{self, TerminalError};

use std::io::{BufRead, BufReader, Read};
use std::str;


pub struct CharBufReader<R: Read> {
  byte_reader: BufReader<R>,
  char_buffer: String,
}


impl<R: Read> CharBufReader<R> {
  pub fn new(input_stream: R) -> CharBufReader<R> {
    let byte_reader = BufReader::new(input_stream);

    CharBufReader {
      byte_reader: byte_reader,
      char_buffer: String::new(),
    }
  }

  pub fn fill_buf(&mut self)
    -> std::result::Result<&str, TerminalError>
  {
    loop {
      let byte_buffer = self.byte_reader.fill_buf().map_err(error::input)?;

      match str::from_utf8(byte_buffer) {
        Err(error) => {
          let n_valid = error.valid_up_to();
          if n_valid == 0 {
            self.byte_reader.consume(1);
          } else {
            match str::from_utf8(&byte_buffer[..n_valid]) {
              Err(_) => {
                self.byte_reader.consume(1);
              },
              Ok(chars) => {
                self.char_buffer.push_str(chars);

                self.byte_reader.consume(n_valid);

                break;
              },
            }
          }
        },
        Ok(chars) => {
          self.char_buffer.push_str(chars);

          let n_to_consume = byte_buffer.len();
          self.byte_reader.consume(n_to_consume);

          break;
        }
      }
    }

    return Ok(&self.char_buffer);
  }

  pub fn consume(&mut self, amount: usize) {
    self.char_buffer.replace_range(..amount, "");
  }
}