use failure::{Context, Fail};
use failure::ResultExt;

/// Extension methods for failure `Result`.
pub trait ResultContext<T, E> {
	/// Wraps the error type in a context type generated by looking at the
	/// error value. This is very similar to `with_context` but much more
	/// concise.
	fn ctx(self, s: &str) -> Result<T, Context<String>>;
}

impl<T, E> ResultContext<T, E> for Result<T, E> where E: Fail {
	fn ctx(self, s: &str) -> Result<T, Context<String>> {
		self.map_err(|failure| {
			let context = format!("{}: {}", s, failure);
			failure.context(context)
		})
	}
}

pub fn foo() -> Result<i32, failure::Error> {
    Ok(5i32)
}

pub fn main() -> Result<(), failure::Error> {
    // This works.
    let _ = foo().with_context(|_| "foo".to_string())?;
    // This doesn't.
    foo().ctx("foo")?
}