schematics/src/symbols/if_already_present.rs

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

use resources::Resource;
use symbols::Symbol;

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

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

impl<A, B> Symbol for IfAlreadyPresent<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>> {
    // Execute a & b if a is not reached
    // Execute b if a was reached and b isn't
    if !try!(self.a.target_reached()) {
      try!(self.a.execute());
      self.b.execute()
    } else if !try!(self.b.target_reached()) {
      self.b.execute()
    } else {
      Ok(())
    }
  }

  fn get_prerequisites(&self) -> Vec<Resource> {
    let mut r = vec![];
    r.extend(self.a.get_prerequisites().into_iter());
    r.extend(self.b.get_prerequisites().into_iter());
    r
  }

  fn provides(&self) -> Option<Vec<Resource>> {
    let mut r = vec![];
    if let Some(provides) = self.a.provides() {
      r.extend(provides.into_iter());
    }
    if let Some(provides) = self.b.provides() {
      r.extend(provides.into_iter());
    }
    if r.len() > 0 { Some(r) } else { None }
  }
}

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

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

  use symbols::Symbol;
  use symbols::if_already_present::IfAlreadyPresent;

  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 = IfAlreadyPresent::new(ErrSymbol("first".into()), ErrSymbol("second".into())).target_reached();
    assert_eq!(res.unwrap_err().description(), "first");
  }

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

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

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

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

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

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

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

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