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

use loggers::Logger;
use symbols::Symbol;

#[derive(Debug)]
pub enum SymbolRunError {
  Symbol(Box<Error>),
  ExecuteDidNotReach(())
}

impl Error for SymbolRunError {
  fn description(&self) -> &str {
    match self {
      &SymbolRunError::Symbol(_) => "Symbol execution error",
      &SymbolRunError::ExecuteDidNotReach(_) => "Target not reached after executing symbol"
    }
  }
  fn cause(&self) -> Option<&Error> {
    match self {
      &SymbolRunError::Symbol(ref e) => Some(&**e),
      &SymbolRunError::ExecuteDidNotReach(_) => None
    }
  }
}

impl fmt::Display for SymbolRunError {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    match self {
      &SymbolRunError::Symbol(ref e) => write!(f, "{}", e),
      &SymbolRunError::ExecuteDidNotReach(_) => write!(f, "{}", self.description())
    }
  }
}

pub trait SymbolRunner {
  fn run_symbol<S: ?Sized + Symbol + fmt::Display>(&self, logger: &mut Logger, symbol: &S) -> Result<(), Box<Error>>;
}

pub struct InitializingSymbolRunner;

impl SymbolRunner for InitializingSymbolRunner {
  fn run_symbol<S: ?Sized + Symbol + fmt::Display>(&self, logger: &mut Logger, symbol: &S) -> Result<(), Box<Error>>
  {
    let target_reached = try!(symbol.target_reached());
    if target_reached {
      logger.write(format!("{} already reached", symbol).as_str());
    } else {
      logger.debug(format!("Symbol reports target_reached: {:?}", target_reached).as_str());
      logger.write(format!("Executing {}", symbol).as_str());
      try!(symbol.execute());
      let target_reached = try!(symbol.target_reached());
      logger.debug(format!("Symbol reports target_reached: {:?} (should be true)", target_reached).as_str());
      if !target_reached {
        return Err(Box::new(SymbolRunError::ExecuteDidNotReach(())));
      }
    }
    Ok(())
  }
}

pub struct DrySymbolRunner;

impl SymbolRunner for DrySymbolRunner {
  fn run_symbol<S: ?Sized + Symbol + fmt::Display>(&self, logger: &mut Logger, symbol: &S) -> Result<(), Box<Error>>
  {
    let target_reached = try!(symbol.target_reached());
    logger.debug(format!("Symbol reports target_reached: {:?}", target_reached).as_str());
    if !target_reached {
      logger.write(format!("Would execute {}", symbol).as_str());
    }
    Ok(())
  }
}

// FIXME: Add ExpectingSymbolRunner

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

  use loggers::Logger;
  use symbols::Symbol;
  use schema::SymbolRunner;
  use schema::InitializingSymbolRunner;

  #[derive(Debug, PartialEq, Clone)]
  enum DummySymbolError {
    Error(())
  }

  impl Error for DummySymbolError {
    fn description(&self) -> &str {
      return "Description";
    }
  }

  impl fmt::Display for DummySymbolError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
      write!(f, "Dummy symbol error")
    }
  }

  struct DummySymbol<'a> {
    _execute: &'a Fn() -> Result<(), Box<Error>>,
    _target_reached: &'a Fn() -> Result<bool, Box<Error>>
  }

  impl<'a> Symbol for DummySymbol<'a> {
    fn target_reached(&self) -> Result<bool, Box<Error>> {
      (self._target_reached)()
    }
    fn execute(&self) -> Result<(), Box<Error>> {
      (self._execute)()
    }
  }

  impl<'a> fmt::Display for DummySymbol<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
      write!(f, "Dummy symbol")
    }
  }

  impl<'a> DummySymbol<'a> {
    fn new(target_reached: &'a Fn() -> Result<bool, Box<Error>>, execute: &'a Fn() -> Result<(), Box<Error>>) -> DummySymbol<'a> {
      DummySymbol { _target_reached: target_reached, _execute: execute }
    }
  }

  struct DummyLogger {
    log: Vec<String>
  }

  impl DummyLogger {
    fn new() -> DummyLogger {
      DummyLogger { log: Vec::new() }
    }
  }

  impl Logger for DummyLogger {
    fn write(&mut self, line: &str) {
      self.log.push(From::from(line));
    }
    fn debug(&mut self, line: &str) {
      self.log.push(From::from(line));
    }
  }

  #[test]
  fn nothing_needed_to_be_done() {
    let result = InitializingSymbolRunner.run_symbol( &mut DummyLogger::new(), &DummySymbol::new(&|| Ok(true), &|| Ok(())) );
    assert!(result.is_ok());
  }

  #[test]
  fn everything_is_ok() {
    let first = RefCell::new(true);
    let result = InitializingSymbolRunner.run_symbol( &mut DummyLogger::new(), &DummySymbol::new(&|| {
      let mut _first = first.borrow_mut();
      Ok(if *_first {
        *_first = false;
        true
      } else {
        false
      })
    }, &|| Ok(())) );
    assert!(result.is_ok());
  }

  #[test]
  fn executing_did_not_change_state() {
    let result = InitializingSymbolRunner.run_symbol( &mut DummyLogger::new(), &DummySymbol::new(&|| Ok(false), &|| Ok(())));
    assert_eq!(
      result.unwrap_err().description(),
      "Target not reached after executing symbol"
    );
  }

  #[test]
  fn executing_did_not_work() {
    let err = InitializingSymbolRunner.run_symbol( &mut DummyLogger::new(), &DummySymbol::new(&|| Ok(false), &|| Err(Box::new(DummySymbolError::Error(()))) )).unwrap_err();
    assert_eq!(err.description(), "Description");
  }
}