use std::io::BufRead;
use std::io::Write;
use command::*;
use std::str::FromStr;
use std::env;

pub struct Shell<R:BufRead, W:Write> {
    pub reader: R,
    pub writer: W,
    pub should_exit: bool,
    pub name: String,
}

impl <R:BufRead, W:Write> Shell<R, W> {
    /// Creates a new Shell.
    pub fn new(input: R, output: W, name: String) -> Self {
        Shell {
            reader : input,
            writer : output,
            should_exit : false,
            name : name,
        }
    }
    /// Initializes the Shell Loop
    pub fn start(&mut self) -> Result<(), &str> {
        self.shell_loop()
    }

    /// Waits for user inputs.
    fn shell_loop(&mut self) -> Result<(),&str> {
        while !self.should_exit {
            if let Ok(line) = self.prompt() {
                Command::from_str(&line).and_then(|cmd| self.run(cmd));
            }
        }
        Ok(())
    }

    /// Prints the shell prompt.
    fn prompt (&mut self) -> Result<String, &str> {


        match env::current_dir() {
            Ok(pwd) => {
                self.writer.write(format!("{} {} > ", self.name, pwd.display()).as_bytes());
                self.writer.flush();

                let mut line: String = String::new();
                let read_result = self.reader.read_line(&mut line);
                match read_result {
                    Ok(_) => {
                        Ok(line)
                    },
                    Err(_) => {
                        Err("Error reading.")
                    },
                }
            },
            Err(_) => return Err("Path Error"),
        }
    }
    /// Runs a command.
    fn run(&mut self, command: Command) -> Result<(), CommandNotFoundError>{

        match command {
            Command::Empty => {
                self.writer.write("Command not found\n".as_bytes());
                self.writer.flush();
                return Err(CommandNotFoundError);},
            Command::Exit => self.should_exit = true,
            Command::Cd(_) => {
                command.exec_cd();
            },
        }
        Ok(())
    }

}