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use std;

use json::JsonError;

/// The result type for this procedural macro.
pub type Result<T> = std::result::Result<T, Error>;

/// Represents errors that may be encountered in
/// invokations of this procedural macro.
#[derive(Debug)]
pub struct Error {
	/// The kind of this error.
	kind: ErrorKind,
}

/// Kinds of errors that may be encountered in invokations
/// of this procedural macro.
#[derive(Debug)]
pub enum ErrorKind {
	/// An error that occured upon a JSON operation.
	JsonError(JsonError),
	/// When there was an invalid number of arguments passed to `eth_abi`.
	InvalidNumberOfArguments {
		/// The number of found arguments.
		found: usize,
	},
	/// When there is a malformatted argument passed to `eth_abi`.
	MalformattedArgument {
		/// The index of the malformatted argument.
		index: usize,
	},
}

impl From<JsonError> for Error {
	fn from(json_err: JsonError) -> Self {
		Error::from_kind(ErrorKind::JsonError(json_err))
	}
}

impl Error {
	/// Create an error from the given kind.
	///
	/// # Note
	///
	/// Just a private convenience constructor.
	fn from_kind(kind: ErrorKind) -> Self {
		Error { kind }
	}

	/// Returns the error kind of `self`.
	fn kind(&self) -> &ErrorKind {
		&self.kind
	}

	/// Returns an error representing that an invalid number of
	/// arguments passed to `eth_abi` have been found.
	pub fn invalid_number_of_arguments(found: usize) -> Self {
		assert!(found != 1 && found != 2);
		Error::from_kind(ErrorKind::InvalidNumberOfArguments { found })
	}

	/// Returns an error representing a malformatted argument passed to
	/// `eth_abi` has been found at the given index.
	pub fn malformatted_argument(index: usize) -> Self {
		assert!(index <= 1);
		Error::from_kind(ErrorKind::MalformattedArgument { index })
	}
}

impl std::fmt::Display for Error {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::result::Result<(), std::fmt::Error> {
		match self.kind() {
			ErrorKind::JsonError(err) => write!(f, "{}", err),
			ErrorKind::InvalidNumberOfArguments { found } => write!(
				f,
				"found {} arguments passed to eth_abi but expected 1 or 2",
				found
			),
			ErrorKind::MalformattedArgument { index } => write!(
				f,
				"found non-identifier argument at index {} passed to eth_abi",
				index
			),
		}
	}
}

impl std::error::Error for Error {
	fn description(&self) -> &str {
		match self.kind() {
            ErrorKind::JsonError(err) => err.description(),
			ErrorKind::InvalidNumberOfArguments{ .. } => {
				"encountered an invalid number of arguments passed to eth_abi: expected 1 or 2"
			},
			ErrorKind::MalformattedArgument{ .. } => {
				"encountered malformatted argument passed to eth_abi: expected identifier (e.g. `Foo`))"
			}
		}
	}
}