// Copyright (c) 2013-2017 The btcsuite developers
// 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 txscript

import (
	"errors"
)

// ErrorKind identifies a kind of script error.
type ErrorKind string

// These constants are used to identify a specific ErrorKind.
const (
	// ---------------------------------------
	// Failures related to improper API usage.
	// ---------------------------------------

	// ErrInvalidIndex is returned when an out-of-bounds index is passed to
	// a function.
	ErrInvalidIndex = ErrorKind("ErrInvalidIndex")

	// ErrInvalidSigHashSingleIndex is returned when an attempt is
	// made to sign an input with the SigHashSingle hash type and an
	// index that is greater than or equal to the number of outputs.
	ErrInvalidSigHashSingleIndex = ErrorKind("ErrInvalidSigHashSingleIndex")

	// ErrUnsupportedScriptVersion is returned when an unsupported script
	// version is passed to a function which deals with script analysis.
	ErrUnsupportedScriptVersion = ErrorKind("ErrUnsupportedScriptVersion")

	// ------------------------------------------
	// Failures related to final execution state.
	// ------------------------------------------

	// ErrEarlyReturn is returned when OP_RETURN is executed in the script.
	ErrEarlyReturn = ErrorKind("ErrEarlyReturn")

	// ErrEmptyStack is returned when the script evaluated without error,
	// but terminated with an empty top stack element.
	ErrEmptyStack = ErrorKind("ErrEmptyStack")

	// ErrEvalFalse is returned when the script evaluated without error but
	// terminated with a false top stack element.
	ErrEvalFalse = ErrorKind("ErrEvalFalse")

	// ErrScriptUnfinished is returned when CheckErrorCondition is called on
	// a script that has not finished executing.
	ErrScriptUnfinished = ErrorKind("ErrScriptUnfinished")

	// ErrScriptDone is returned when an attempt to execute an opcode is
	// made once all of them have already been executed.  This can happen
	// due to things such as a second call to Execute or calling Step after
	// all opcodes have already been executed.
	ErrInvalidProgramCounter = ErrorKind("ErrInvalidProgramCounter")

	// -----------------------------------------------------
	// Failures related to exceeding maximum allowed limits.
	// -----------------------------------------------------

	// ErrScriptTooBig is returned if a script is larger than MaxScriptSize.
	ErrScriptTooBig = ErrorKind("ErrScriptTooBig")

	// ErrElementTooBig is returned if the size of an element to be pushed
	// to the stack is over MaxScriptElementSize.
	ErrElementTooBig = ErrorKind("ErrElementTooBig")

	// ErrTooManyOperations is returned if a script has more than
	// MaxOpsPerScript opcodes that do not push data.
	ErrTooManyOperations = ErrorKind("ErrTooManyOperations")

	// ErrStackOverflow is returned when stack and altstack combined depth
	// is over the limit.
	ErrStackOverflow = ErrorKind("ErrStackOverflow")

	// ErrInvalidPubKeyCount is returned when the number of public keys
	// specified for a multsig is either negative or greater than
	// MaxPubKeysPerMultiSig.
	ErrInvalidPubKeyCount = ErrorKind("ErrInvalidPubKeyCount")

	// ErrInvalidSignatureCount is returned when the number of signatures
	// specified for a multisig is either negative or greater than the
	// number of public keys.
	ErrInvalidSignatureCount = ErrorKind("ErrInvalidSignatureCount")

	// ErrNumOutOfRange is returned when the argument for an opcode that
	// expects numeric input is larger than the expected maximum number of
	// bytes.  For the most part, opcodes that deal with stack manipulation
	// via offsets, arithmetic, numeric comparison, and boolean logic are
	// those that this applies to.  However, any opcode that expects numeric
	// input may fail with this error.
	ErrNumOutOfRange = ErrorKind("ErrNumOutOfRange")

	// --------------------------------------------
	// Failures related to verification operations.
	// --------------------------------------------

	// ErrVerify is returned when OP_VERIFY is encountered in a script and
	// the top item on the data stack does not evaluate to true.
	ErrVerify = ErrorKind("ErrVerify")

	// ErrEqualVerify is returned when OP_EQUALVERIFY is encountered in a
	// script and the top item on the data stack does not evaluate to true.
	ErrEqualVerify = ErrorKind("ErrEqualVerify")

	// ErrNumEqualVerify is returned when OP_NUMEQUALVERIFY is encountered
	// in a script and the top item on the data stack does not evaluate to
	// true.
	ErrNumEqualVerify = ErrorKind("ErrNumEqualVerify")

	// ErrCheckSigVerify is returned when OP_CHECKSIGVERIFY is encountered
	// in a script and the top item on the data stack does not evaluate to
	// true.
	ErrCheckSigVerify = ErrorKind("ErrCheckSigVerify")

	// ErrCheckSigVerify is returned when OP_CHECKMULTISIGVERIFY is
	// encountered in a script and the top item on the data stack does not
	// evaluate to true.
	ErrCheckMultiSigVerify = ErrorKind("ErrCheckMultiSigVerify")

	// ErrCheckSigAltVerify is returned when OP_CHECKSIGALTVERIFY is
	// encountered in a script and the top item on the data stack does not
	// evaluate to true.
	ErrCheckSigAltVerify = ErrorKind("ErrCheckSigAltVerify")

	// --------------------------------------------
	// Failures related to improper use of opcodes.
	// --------------------------------------------

	// ErrP2SHStakeOpCodes is returned when one or more stake opcodes are
	// found in the redeem script of a pay-to-script-hash script.
	ErrP2SHStakeOpCodes = ErrorKind("ErrP2SHStakeOpCodes")

	// ErrDisabledOpcode is returned when a disabled opcode is encountered
	// in a script.
	ErrDisabledOpcode = ErrorKind("ErrDisabledOpcode")

	// ErrReservedOpcode is returned when an opcode marked as reserved
	// is encountered in a script.
	ErrReservedOpcode = ErrorKind("ErrReservedOpcode")

	// ErrMalformedPush is returned when a data push opcode tries to push
	// more bytes than are left in the script.
	ErrMalformedPush = ErrorKind("ErrMalformedPush")

	// ErrInvalidStackOperation is returned when a stack operation is
	// attempted with a number that is invalid for the current stack size.
	ErrInvalidStackOperation = ErrorKind("ErrInvalidStackOperation")

	// ErrUnbalancedConditional is returned when an OP_ELSE or OP_ENDIF is
	// encountered in a script without first having an OP_IF or OP_NOTIF or
	// the end of script is reached without encountering an OP_ENDIF when
	// an OP_IF or OP_NOTIF was previously encountered.
	ErrUnbalancedConditional = ErrorKind("ErrUnbalancedConditional")

	// ErrNegativeSubstrIdx is returned when an OP_SUBSTR, OP_LEFT, or
	// OP_RIGHT opcode encounters a negative index.
	ErrNegativeSubstrIdx = ErrorKind("ErrNegativeSubstrIdx")

	// ErrOverflowSubstrIdx is returned when an OP_SUBSTR, OP_LEFT, or
	// OP_RIGHT opcode encounters an index that is larger than the max
	// allowed index that can operate on the string or the start index
	// is greater than the end index for OP_SUBSTR.
	ErrOverflowSubstrIdx = ErrorKind("ErrOverflowSubstrIdx")

	// ErrNegativeRotation is returned when an OP_ROTL or OP_ROTR attempts
	// to perform a rotation with a negative rotation count.
	ErrNegativeRotation = ErrorKind("ErrNegativeRotation")

	// ErrOverflowRotation is returned when an OP_ROTL or OP_ROTR opcode
	// encounters a rotation count that is larger than the maximum allowed
	// value for a uint32 bit rotation.
	ErrOverflowRotation = ErrorKind("ErrOverflowRotation")

	// ErrDivideByZero is returned when an OP_DIV of OP_MOD attempts to
	// divide by zero.
	ErrDivideByZero = ErrorKind("ErrDivideByZero")

	// ErrNegativeRotation is returned when an OP_LSHIFT or OP_RSHIFT opcode
	// attempts to perform a shift with a negative count.
	ErrNegativeShift = ErrorKind("ErrNegativeShift")

	// ErrOverflowShift is returned when an OP_LSHIFT or OP_RSHIFT opcode
	// encounters a shift count that is larger than the maximum allowed value
	// for a shift.
	ErrOverflowShift = ErrorKind("ErrOverflowShift")

	// ErrP2SHTreasuryOpCodes is returned when one or more treasury opcodes
	// are found in the redeem script of a pay-to-script-hash script.
	ErrP2SHTreasuryOpCodes = ErrorKind("ErrP2SHTreasuryOpCodes")

	// ---------------------------------
	// Failures related to malleability.
	// ---------------------------------

	// ErrMinimalData is returned when the script contains push operations
	// that do not use the minimal opcode required.
	ErrMinimalData = ErrorKind("ErrMinimalData")

	// ErrInvalidSigHashType is returned when a signature hash type is not
	// one of the supported types.
	ErrInvalidSigHashType = ErrorKind("ErrInvalidSigHashType")

	// ErrSigTooShort is returned when a signature that should be a
	// canonically-encoded DER signature is too short.
	ErrSigTooShort = ErrorKind("ErrSigTooShort")

	// ErrSigTooLong is returned when a signature that should be a
	// canonically-encoded DER signature is too long.
	ErrSigTooLong = ErrorKind("ErrSigTooLong")

	// ErrSigInvalidSeqID is returned when a signature that should be a
	// canonically-encoded DER signature does not have the expected ASN.1
	// sequence ID.
	ErrSigInvalidSeqID = ErrorKind("ErrSigInvalidSeqID")

	// ErrSigInvalidDataLen is returned when a signature that should be a
	// canonically-encoded DER signature does not specify the correct number
	// of remaining bytes for the R and S portions.
	ErrSigInvalidDataLen = ErrorKind("ErrSigInvalidDataLen")

	// ErrSigMissingSTypeID is returned when a signature that should be a
	// canonically-encoded DER signature does not provide the ASN.1 type ID
	// for S.
	ErrSigMissingSTypeID = ErrorKind("ErrSigMissingSTypeID")

	// ErrSigMissingSLen is returned when a signature that should be a
	// canonically-encoded DER signature does not provide the length of S.
	ErrSigMissingSLen = ErrorKind("ErrSigMissingSLen")

	// ErrSigInvalidSLen is returned when a signature that should be a
	// canonically-encoded DER signature does not specify the correct number
	// of bytes for the S portion.
	ErrSigInvalidSLen = ErrorKind("ErrSigInvalidSLen")

	// ErrSigInvalidRIntID is returned when a signature that should be a
	// canonically-encoded DER signature does not have the expected ASN.1
	// integer ID for R.
	ErrSigInvalidRIntID = ErrorKind("ErrSigInvalidRIntID")

	// ErrSigZeroRLen is returned when a signature that should be a
	// canonically-encoded DER signature has an R length of zero.
	ErrSigZeroRLen = ErrorKind("ErrSigZeroRLen")

	// ErrSigNegativeR is returned when a signature that should be a
	// canonically-encoded DER signature has a negative value for R.
	ErrSigNegativeR = ErrorKind("ErrSigNegativeR")

	// ErrSigTooMuchRPadding is returned when a signature that should be a
	// canonically-encoded DER signature has too much padding for R.
	ErrSigTooMuchRPadding = ErrorKind("ErrSigTooMuchRPadding")

	// ErrSigInvalidSIntID is returned when a signature that should be a
	// canonically-encoded DER signature does not have the expected ASN.1
	// integer ID for S.
	ErrSigInvalidSIntID = ErrorKind("ErrSigInvalidSIntID")

	// ErrSigZeroSLen is returned when a signature that should be a
	// canonically-encoded DER signature has an S length of zero.
	ErrSigZeroSLen = ErrorKind("ErrSigZeroSLen")

	// ErrSigNegativeS is returned when a signature that should be a
	// canonically-encoded DER signature has a negative value for S.
	ErrSigNegativeS = ErrorKind("ErrSigNegativeS")

	// ErrSigTooMuchSPadding is returned when a signature that should be a
	// canonically-encoded DER signature has too much padding for S.
	ErrSigTooMuchSPadding = ErrorKind("ErrSigTooMuchSPadding")

	// ErrSigHighS is returned when a signature that should be a
	// canonically-encoded DER signature has an S value that is higher than
	// the curve half order.
	ErrSigHighS = ErrorKind("ErrSigHighS")

	// ErrNotPushOnly is returned when a script that is required to only
	// push data to the stack performs other operations.  A couple of cases
	// where this applies is for a pay-to-script-hash signature script when
	// bip16 is active and when the ScriptVerifySigPushOnly flag is set.
	ErrNotPushOnly = ErrorKind("ErrNotPushOnly")

	// ErrPubKeyType is returned when the script contains invalid public keys.
	ErrPubKeyType = ErrorKind("ErrPubKeyType")

	// ErrCleanStack is returned when the ScriptVerifyCleanStack flag
	// is set, and after evaluation, the stack does not contain only a
	// single element.
	ErrCleanStack = ErrorKind("ErrCleanStack")

	// -------------------------------
	// Failures related to soft forks.
	// -------------------------------

	// ErrDiscourageUpgradableNOPs is returned when the
	// ScriptDiscourageUpgradableNops flag is set and a NOP opcode is
	// encountered in a script.
	ErrDiscourageUpgradableNOPs = ErrorKind("ErrDiscourageUpgradableNOPs")

	// ErrNegativeLockTime is returned when a script contains an opcode that
	// interprets a negative lock time.
	ErrNegativeLockTime = ErrorKind("ErrNegativeLockTime")

	// ErrUnsatisfiedLockTime is returned when a script contains an opcode
	// that involves a lock time and the required lock time has not been
	// reached.
	ErrUnsatisfiedLockTime = ErrorKind("ErrUnsatisfiedLockTime")
)

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

// Error identifies a script-related error.  It is used to indicate three
// classes of errors:
// 1) Script execution failures due to violating one of the many requirements
//    imposed by the script engine or evaluating to false
// 2) Improper API usage by callers
// 3) Internal consistency check failures
//
// 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
}

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

// IsDERSigError returns whether or not the provided error is one of the error
// kinds which are caused due to encountering a signature that is not a
// canonically-encoded DER signature.
func IsDERSigError(err error) bool {
	var kind ErrorKind
	if !errors.As(err, &kind) {
		return false
	}

	switch kind {
	case ErrSigTooShort, ErrSigTooLong, ErrSigInvalidSeqID,
		ErrSigInvalidDataLen, ErrSigMissingSTypeID, ErrSigMissingSLen,
		ErrSigInvalidSLen, ErrSigInvalidRIntID, ErrSigZeroRLen, ErrSigNegativeR,
		ErrSigTooMuchRPadding, ErrSigInvalidSIntID, ErrSigZeroSLen,
		ErrSigNegativeS, ErrSigTooMuchSPadding, ErrSigHighS:

		return true
	}

	return false
}