// Copyright (c) 2014 Conformal Systems LLC.
// Copyright (c) 2015-2020 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package schnorr

// ErrorKind identifies a kind of error.  It has full support for errors.Is
// and errors.As, so the caller can directly check against an error kind
// when determining the reason for an error.
type ErrorKind string

// These constants are used to identify a specific RuleError.
const (
	// ErrInvalidHashLen indicates that the input hash to sign or verify is not
	// the required length.
	ErrInvalidHashLen = ErrorKind("ErrInvalidHashLen")

	// ErrPrivateKeyIsZero indicates an attempt was made to sign a message with
	// a private key that is equal to zero.
	ErrPrivateKeyIsZero = ErrorKind("ErrPrivateKeyIsZero")

	// ErrSchnorrHashValue indicates that the hash of (R || m) was too large and
	// so a new nonce should be used.
	ErrSchnorrHashValue = ErrorKind("ErrSchnorrHashValue")

	// ErrPubKeyNotOnCurve indicates that a point was not on the given elliptic
	// curve.
	ErrPubKeyNotOnCurve = ErrorKind("ErrPubKeyNotOnCurve")

	// ErrSigRYIsOdd indicates that the calculated Y value of R was odd.
	ErrSigRYIsOdd = ErrorKind("ErrSigRYIsOdd")

	// ErrSigRNotOnCurve indicates that the calculated or given point R for some
	// signature was not on the curve.
	ErrSigRNotOnCurve = ErrorKind("ErrSigRNotOnCurve")

	// ErrUnequalRValues indicates that the calculated point R for some
	// signature was not the same as the given R value for the signature.
	ErrUnequalRValues = ErrorKind("ErrUnequalRValues")

	// ErrSigTooShort is returned when a signature that should be a Schnorr
	// signature is too short.
	ErrSigTooShort = ErrorKind("ErrSigTooShort")

	// ErrSigTooLong is returned when a signature that should be a Schnorr
	// signature is too long.
	ErrSigTooLong = ErrorKind("ErrSigTooLong")

	// ErrSigRTooBig is returned when a signature has r with a value that is
	// greater than or equal to the prime of the field underlying the group.
	ErrSigRTooBig = ErrorKind("ErrSigRTooBig")

	// ErrSigSTooBig is returned when a signature has s with a value that is
	// greater than or equal to the group order.
	ErrSigSTooBig = ErrorKind("ErrSigSTooBig")
)

// Error satisfies the error interface and prints human-readable errors.
func (e ErrorKind) Error() string {
	return string(e)
}

// Error identifies an error related to a schnorr signature. It has full
// support for errors.Is and errors.As, so the caller can ascertain the
// specific reason for the error by checking the underlying error.
type Error struct {
	Err         error
	Description string
}

// Error satisfies the error interface and prints human-readable errors.
func (e Error) Error() string {
	return e.Description
}

// Unwrap returns the underlying wrapped error.
func (e Error) Unwrap() error {
	return e.Err
}

// signatureError creates an Error given a set of arguments.
func signatureError(kind ErrorKind, desc string) Error {
	return Error{Err: kind, Description: desc}
}