// Copyright (c) 2013-2017 The btcsuite developers
// Copyright (c) 2014 Conformal Systems LLC.
// Copyright (c) 2015-2021 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")
	// ErrSecretKeyIsZero indicates an attempt was made to sign a message with
	// a secret key that is equal to zero.
	ErrSecretKeyIsZero  = ErrorKind("ErrSecretKeyIsZero")
	ErrPrivateKeyIsZero = ErrSecretKeyIsZero
	// 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 (err ErrorKind) Error() string { return string(err) }

// 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 (err Error) Error() string { return err.Description }

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

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