use crate::prelude::*;
use std::collections::HashMap;
use std::collections::HashSet;
use std::io;
use std::io::prelude::*;
use std::os::unix::fs::PermissionsExt;

#[macro_use] extern crate lalrpop_util;

lalrpop_mod!(pub commandline);
pub mod error;
pub mod path;
pub mod prelude;
pub mod result;


pub enum Input {
  String(String),
  End,
}


fn main() -> Result<()> {
  std::process::exit(match repl() {
    Ok(()) => 0,
    Err(ref e) => {
      eprintln!("{}", e);
      1
    }
  })
}


fn repl() -> Result<()> {
  println!("Hello, terminal!");

  loop {
    prompt()?;

    let input = read()?;
    match input {
      Input::String(string) => execute(&string)?,
      Input::End => break,
    }
  }

  Ok(())
}


fn prompt() -> Result<()> {
  print!("$ ");
  io::stdout().flush()?;

  Ok(())
}


fn read() -> Result<Input> {
  let mut input = String::new();
  let n_bytes = io::stdin().read_line(&mut input)?;

  if n_bytes == 0 {
    Ok(Input::End)
  } else {
    Ok(Input::String(input))
  }
}


fn execute(input: &str) -> Result<()> {
  let invocation = commandline::InvocationParser::new().parse(input)?;

  match invocation.as_slice() {
    ["environment", ..] => {
      let environment = read_environment()?;
      println!("{:?}", environment);
    }
    ["which", command_name, ..] => {
      match find_executable_path(command_name)? {
        Some(executable_path) => {
          println!("{}", executable_path);
        }
        None => {
          println!("Command not found: {}", command_name);
        }
      };
    },
    [command_name, ..] => {
      match find_executable_path(command_name)? {
        Some(executable_path) => {
          println!("{}", executable_path);
        }
        None => {
          println!("Command not found: {}", command_name);
        }
      };
    },
    _ => {
      println!("invocation '{:?}'", invocation);
    }
  }

  Ok(())
}


fn read_environment() -> Result<HashMap<String,String>> {
  Ok(std::env::vars().collect())
}


fn get_environment(variable_name: &str) -> Result<Option<String>> {
  Ok(std::env::vars()
     .find(|(key, _)| key == variable_name)
     .map(|(_, value)| value))
}


fn get_search_paths() -> Result<Vec<path::AbsoluteDirectoryPath>> {
  let paths = get_environment("PATH")?.unwrap_or_default();
  let paths = path::parse_path_list(&paths)?;

  let mut result = Vec::new();
  let mut seen = HashSet::new();
  for path in paths {
    if seen.contains(&path) {
      continue;
    }

    seen.insert(path.clone());
    result.push(path);
  }

  Ok(result)
}


fn find_executable_path(command_name: &str)
  -> Result<Option<path::AbsoluteFilePath>>
{
  let file_name: path::FileName = command_name.parse()?;
  let search_paths = get_search_paths()?;

  let mut executable_path: Option<path::AbsoluteFilePath> = None;
  for search_path in &search_paths {
    let candidate_path = search_path.concat_file_name(&file_name);
    match candidate_path.to_sys_path().metadata() {
      Ok(metadata) => {
        if metadata.is_file()
          && metadata.permissions().mode() & 0o111 != 0
        {
          executable_path = Some(candidate_path);
          break;
        }
      },
      Err(_) => { },
    }
  }

  Ok(executable_path)
}