use std::{
    error,
    fmt,
};

#[derive(Debug)]
pub struct PrefixedError<T>
where T: error::Error + 'static
{
    prefix: String,
    internal: T,
}
impl<T> std::error::Error for PrefixedError<T>
where T: error::Error + 'static
{
    fn source(&self) -> Option<&(dyn error::Error + 'static)>
    {
	Some(&self.internal)
    }
}
impl<T> std::fmt::Display for PrefixedError<T>
where T: error::Error + 'static
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "{}: {}", self.prefix, self.internal)
    }
}


impl<T>  PrefixedError<T>
where T: error::Error + 'static
{
    #[inline] pub fn into_inner(self) -> T
    {
	self.internal
    }
}

pub trait ErrorExt: Sized + error::Error
{
    fn with_prefix(self, msg: impl ToString) -> PrefixedError<Self>;
}
pub trait ResultExt<T,E>: Sized
    where E: error::Error + 'static
{
    fn with_prefix(self, msg: impl ToString) -> Result<T,PrefixedError<E>>;
}

impl<T> ErrorExt for T
where T: error::Error + 'static
{
    #[inline] fn with_prefix(self, msg: impl ToString) -> PrefixedError<Self>
    {
	PrefixedError {
	    prefix: msg.to_string(),
	    internal: self
	}
    }
}
impl<T,E> ResultExt<T,E> for Result<T,E>
where E: error::Error + 'static
{
    #[inline] fn with_prefix(self, msg: impl ToString) -> Result<T,PrefixedError<E>>
    {
	self.map_err(|e| e.with_prefix(msg))
    }
}