// -*- mode: rust; -*-
//
// This file is part of ed25519-dalek.
// Copyright (c) 2017-2019 isis lovecruft
// See LICENSE for licensing information.
//
// Authors:
// - isis agora lovecruft <isis@patternsinthevoid.net>

//! Errors which may occur when parsing keys and/or signatures to or from wire formats.

// rustc seems to think the typenames in match statements (e.g. in
// Display) should be snake cased, for some reason.
#![allow(non_snake_case)]

use core::fmt;
use core::fmt::Display;

#[cfg(feature = "std")]
use std::error::Error;

/// Internal errors.  Most application-level developers will likely not
/// need to pay any attention to these.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
pub(crate) enum InternalError {
    PointDecompressionError,
    ScalarFormatError,
    /// An error in the length of bytes handed to a constructor.
    ///
    /// To use this, pass a string specifying the `name` of the type which is
    /// returning the error, and the `length` in bytes which its constructor
    /// expects.
    BytesLengthError {
        name: &'static str,
        length: usize,
    },
    /// The verification equation wasn't satisfied
    VerifyError,
    /// Two arrays did not match in size, making the called signature
    /// verification method impossible.
    ArrayLengthError{ name_a: &'static str, length_a: usize,
                      name_b: &'static str, length_b: usize,
                      name_c: &'static str, length_c: usize, },
}

impl Display for InternalError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            InternalError::PointDecompressionError
                => write!(f, "Cannot decompress Edwards point"),
            InternalError::ScalarFormatError
                => write!(f, "Cannot use scalar with high-bit set"),
            InternalError::BytesLengthError{ name: n, length: l}
                => write!(f, "{} must be {} bytes in length", n, l),
            InternalError::VerifyError
                => write!(f, "Verification equation was not satisfied"),
            InternalError::ArrayLengthError{ name_a: na, length_a: la,
                                             name_b: nb, length_b: lb,
                                             name_c: nc, length_c: lc, }
                => write!(f, "Arrays must be the same length: {} has length {},
                              {} has length {}, {} has length {}.", na, la, nb, lb, nc, lc),
        }
    }
}

#[cfg(feature = "std")]
impl Error for InternalError { }

/// Errors which may occur while processing signatures and keypairs.
///
/// This error may arise due to:
///
/// * Being given bytes with a length different to what was expected.
///
/// * A problem decompressing `r`, a curve point, in the `Signature`, or the
///   curve point for a `PublicKey`.
///
/// * A problem with the format of `s`, a scalar, in the `Signature`.  This
///   is only raised if the high-bit of the scalar was set.  (Scalars must
///   only be constructed from 255-bit integers.)
///
/// * Failure of a signature to satisfy the verification equation.
#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug)]
pub struct SignatureError(pub(crate) InternalError);

impl Display for SignatureError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.0)
    }
}

#[cfg(feature = "std")]
impl Error for SignatureError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&self.0)
    }
}