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// Copyright 2021 Parity Technologies
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Error type, descriptive or undescriptive depending on features.

use crate::alloc::borrow::Cow;
#[cfg(feature = "chain-error")]
use crate::alloc::boxed::Box;

/// Error type.
///
/// Descriptive on `std` environment, with chaining error on `chain-error` environment,
/// underscriptive otherwise.
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct Error {
	#[cfg(feature = "chain-error")]
	cause: Option<Box<Error>>,
	#[cfg(feature = "chain-error")]
	desc: Cow<'static, str>,
}

impl Error {
	/// Chain error message with description.
	///
	/// When compiled with `chain-error` feature, the description is chained, otherwise the
	/// description is ditched.
	pub fn chain(self, desc: impl Into<Cow<'static, str>>) -> Self {
		#[cfg(feature = "chain-error")]
		{
			Self { desc: desc.into(), cause: Some(Box::new(self)) }
		}

		#[cfg(not(feature = "chain-error"))]
		{
			let _ = desc;
			self
		}
	}

	/// Display error with indentation.
	#[cfg(feature = "chain-error")]
	fn display_with_indent(&self, indent: u32, f: &mut core::fmt::Formatter) -> core::fmt::Result {
		for _ in 0..indent {
			f.write_str("\t")?;
		}
		f.write_str(&self.desc)?;
		if let Some(cause) = &self.cause {
			f.write_str(":")?;
			f.write_str("\n")?;
			cause.display_with_indent(indent + 1, f)
		} else {
			// Only return to new line if the error has been displayed with some indent,
			// i.e. if the error has some causes.
			if indent != 0 {
				f.write_str("\n")?;
			}
			Ok(())
		}
	}
}

impl core::fmt::Display for Error {
	fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
		#[cfg(feature = "chain-error")]
		{
			self.display_with_indent(0, f)
		}

		#[cfg(not(feature = "chain-error"))]
		{
			f.write_str("Codec error")
		}
	}
}

impl From<&'static str> for Error {
	fn from(desc: &'static str) -> Error {
		#[cfg(feature = "chain-error")]
		{
			Error { desc: desc.into(), cause: None }
		}

		#[cfg(not(feature = "chain-error"))]
		{
			let _ = desc;
			Error {}
		}
	}
}

#[cfg(feature = "std")]
impl std::error::Error for Error {
	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
		#[cfg(feature = "chain-error")]
		{
			self.cause.as_ref().map(|e| e as &(dyn std::error::Error + 'static))
		}

		#[cfg(not(feature = "chain-error"))]
		{
			None
		}
	}
}

#[cfg(test)]
mod tests {
	use crate::Error;

	#[test]
	fn test_full_error() {
		let msg: &str = "final type:\n\twrap cause:\n\t\troot cause\n";

		let error = Error::from("root cause").chain("wrap cause").chain("final type");

		assert_eq!(&error.to_string(), msg);
	}

	#[test]
	fn impl_std_error() {
		use std::error::Error as _;

		let error = Error::from("root cause").chain("wrap cause").chain("final type");
		let s = error.source().unwrap();

		assert_eq!(&s.to_string(), "wrap cause:\n\troot cause\n");
	}
}