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use event::request::InvokeArgument;

pub trait Destructurable: Sized {
  fn destructure<T: FromInvokeArg>(self) -> Result<T, T::Err>;
}

impl Destructurable for InvokeArgument {
  fn destructure<T: FromInvokeArg>(self) -> Result<T, T::Err> {
    T::from_invoke_arg(self)
  }
}

pub trait FromInvokeArg: Sized {
  type Err;
  fn from_invoke_arg(InvokeArgument) -> Result<Self, Self::Err>;
}

#[derive(Debug, Clone, PartialEq)]
pub struct ImproperInvokeArgError {
  _priv: (),
}

// NOTE: This is a stopgap for impl specialization
//   The underlying issue is that FromInvokeArg can't be impld for all FromStr
//   because it creates a conflicting implementation with String
//   Issue: https://github.com/rust-lang/rust/issues/31844
macro_rules! impl_for_from_str {
  ($t: ty) => {
    impl FromInvokeArg for $t {
      type Err = ImproperInvokeArgError;

      fn from_invoke_arg(arg: InvokeArgument) -> Result<$t, ImproperInvokeArgError> {
        match arg {
          InvokeArgument::String(val) => {
            val.parse().map_err(|_| ImproperInvokeArgError { _priv: ()})
          },
          _ => Err(ImproperInvokeArgError { _priv: () })
        }
      }
    }
  }
}

impl<T> FromInvokeArg for Option<T>
  where T: FromInvokeArg
{
  type Err = ImproperInvokeArgError;

  fn from_invoke_arg(arg: InvokeArgument) -> Result<Option<T>, ImproperInvokeArgError> {
    match arg {
      InvokeArgument::None => Ok(None),
      e @ InvokeArgument::String(_) => {
        T::from_invoke_arg(e)
          .map(|r| Some(r))
          .map_err(|_| ImproperInvokeArgError { _priv: () })
      },
      _ => Err(ImproperInvokeArgError { _priv: () }),
    }
  }
}

impl_for_from_str!(f32);
impl_for_from_str!(f64);
impl_for_from_str!(isize);
impl_for_from_str!(i16);
impl_for_from_str!(i32);
impl_for_from_str!(i64);
impl_for_from_str!(usize);
impl_for_from_str!(u8);
impl_for_from_str!(u16);
impl_for_from_str!(u32);

impl FromInvokeArg for String {
  type Err = ImproperInvokeArgError;

  fn from_invoke_arg(arg: InvokeArgument) -> Result<String, ImproperInvokeArgError> {
    match arg {
      InvokeArgument::String(val) => Ok(val),
      _ => Err(ImproperInvokeArgError { _priv: () }),
    }
  }
}

// NOTE: Rules for booleans are a bit unconventional to facilitiate easy use of
// optional captures:
impl FromInvokeArg for bool {
  type Err = ImproperInvokeArgError;

  fn from_invoke_arg(arg: InvokeArgument) -> Result<bool, ImproperInvokeArgError> {
    match arg {
      InvokeArgument::None => Ok(false),
      InvokeArgument::String(val) => {
        match val.as_ref() {
          "false" => Ok(false),
          _ => Ok(true),
        }
      },
      _ => Err(ImproperInvokeArgError { _priv: () }),
    }
  }
}

impl FromInvokeArg for Vec<Vec<String>> {
  type Err = ImproperInvokeArgError;

  fn from_invoke_arg(arg: InvokeArgument) -> Result<Vec<Vec<String>>, ImproperInvokeArgError> {
    match arg {
      InvokeArgument::Table(val) => Ok(val),
      _ => Err(ImproperInvokeArgError { _priv: () }),
    }
  }
}

#[cfg(test)]
mod test {
  pub use super::*;
  pub use event::request::InvokeArgument;

  #[test]
  fn wrong_type_destructure_fails_correctly() {
    let res: Result<u32, ImproperInvokeArgError> = InvokeArgument::String("hello".to_owned())
      .destructure();

    assert_eq!(res, Err(ImproperInvokeArgError { _priv: () }));
  }

  #[test]
  fn string_can_be_destructured() {
    let res: String = InvokeArgument::String("hello".to_owned()).destructure().unwrap();

    assert_eq!(&res, "hello");
  }

  #[test]
  fn table_can_be_destructured() {
    let res: Vec<Vec<String>> =
      InvokeArgument::Table(vec![vec!["hello".to_owned()]]).destructure().unwrap();

    assert_eq!(res, vec![vec!["hello".to_owned()]]);
  }

  mod bool {
    use super::*;

    #[test]
    fn bool_doesnt_parse_from_table() {
      let res: Result<bool, ImproperInvokeArgError> =
        InvokeArgument::Table(vec![vec!["hello".to_owned()]]).destructure();

      assert_eq!(res, Err(ImproperInvokeArgError { _priv: () }));
    }

    #[test]
    fn bool_is_false_from_none() {
      let res: bool = InvokeArgument::None.destructure().unwrap();

      assert_eq!(res, false);
    }

    #[test]
    fn bool_is_false_string_false() {
      let res: bool = InvokeArgument::String("false".to_owned()).destructure().unwrap();

      assert_eq!(res, false);
    }

    #[test]
    fn bool_is_true_from_other_strings() {
      let res: bool = InvokeArgument::String("true".to_owned()).destructure().unwrap();
      assert_eq!(res, true);

      let res: bool = InvokeArgument::String("hello".to_owned()).destructure().unwrap();
      assert_eq!(res, true);
    }
  }

}