schematics/src/symbols/hook.rs

use std::error::Error;
use std::fmt;

use symbols::Symbol;

pub struct Hook<A, B> where A: Symbol, B: Symbol {
  a: A,
  b: B
}

impl<A, B> Hook<A, B> where A: Symbol, B: Symbol {
  pub fn new(a: A, b: B) -> Self {
    Hook { a: a, b: b }
  }
}

impl<A, B> Symbol for Hook<A, B> where A: Symbol, B: Symbol {
  fn target_reached(&self) -> Result<bool, Box<Error>> {
    self.a.target_reached().and_then(|reached| if reached { self.b.target_reached() } else { Ok(reached) })
  }

  fn execute(&self) -> Result<(), Box<Error>> {
    try!(self.a.execute());
    self.b.execute()
  }
}

impl<A, B> fmt::Display for Hook<A, B> where A: Symbol, B: Symbol {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error>{
    write!(f, "Hook {} and then {}", self.a, self.b)
  }
}

#[cfg(test)]
mod test {
  use std::error::Error;
  use std::fmt;

  use symbols::Symbol;
  use symbols::hook::Hook;

  struct ErrSymbol(String);
  impl Symbol for ErrSymbol {
    fn target_reached(&self) -> Result<bool, Box<Error>> { Err(self.0.clone().into()) }
    fn execute(&self) -> Result<(), Box<Error>> { Err(self.0.clone().into()) }
  }
  impl fmt::Display for ErrSymbol { fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error>{ write!(f, "") } }

  struct OkSymbol(bool);
  impl Symbol for OkSymbol {
    fn target_reached(&self) -> Result<bool, Box<Error>> { Ok(self.0) }
    fn execute(&self) -> Result<(), Box<Error>> { Ok(()) }
  }
  impl fmt::Display for OkSymbol { fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error>{ write!(f, "") } }

  #[test]
  fn first_target_reached_fails() {
    let res = Hook::new(ErrSymbol("first".into()), ErrSymbol("second".into())).target_reached();
    assert_eq!(res.unwrap_err().description(), "first");
  }

  #[test]
  fn first_target_not_reached() {
    let res = Hook::new(OkSymbol(false), ErrSymbol("second".into())).target_reached();
    assert_eq!(res.unwrap(), false);
  }

  #[test]
  fn second_target_reached_fails() {
    let res = Hook::new(OkSymbol(true), ErrSymbol("second".into())).target_reached();
    assert_eq!(res.unwrap_err().description(), "second");
  }

  #[test]
  fn second_target_not_reached() {
    let res = Hook::new(OkSymbol(true), OkSymbol(false)).target_reached();
    assert_eq!(res.unwrap(), false);
  }

  #[test]
  fn everything_reached() {
    let res = Hook::new(OkSymbol(true), OkSymbol(true)).target_reached();
    assert_eq!(res.unwrap(), true);
  }

  #[test]
  fn first_execute_fails() {
    let res = Hook::new(ErrSymbol("first".into()), ErrSymbol("second".into())).execute();
    assert_eq!(res.unwrap_err().description(), "first");
  }

  #[test]
  fn second_execute_fails() {
    let res = Hook::new(OkSymbol(true), ErrSymbol("second".into())).execute();
    assert_eq!(res.unwrap_err().description(), "second");
  }

  #[test]
  fn everything_executes() {
    let res = Hook::new(OkSymbol(true), OkSymbol(true)).execute();
    assert_eq!(res.unwrap(), ());
  }
}