// Copyright (c) 2013-2017 The btcsuite developers
// Copyright (c) 2015-2018 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 (
	"fmt"
)

// ErrorCode identifies a kind of script error.
type ErrorCode int

// These constants are used to identify a specific Error.
const (
	// ErrInternal is returned if internal consistency checks fail.  In
	// practice this error should never be seen as it would mean there is an
	// error in the engine logic.
	ErrInternal ErrorCode = iota

	// ---------------------------------------
	// Failures related to improper API usage.
	// ---------------------------------------

	// ErrInvalidIndex is returned when an out-of-bounds index is passed to
	// a function.
	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

	// ErrUnsupportedAddress is returned when a concrete type that
	// implements a dcrutil.Address is not a supported type.
	ErrUnsupportedAddress

	// ErrNotMultisigScript is returned from CalcMultiSigStats when the
	// provided script is not a multisig script.
	ErrNotMultisigScript

	// ErrTooManyRequiredSigs is returned from MultiSigScript when the
	// specified number of required signatures is larger than the number of
	// provided public keys.
	ErrTooManyRequiredSigs

	// ErrMalformedCoinbaseNullData is returned when the nulldata output
	// of a coinbase transaction that is used to ensure the coinbase has a
	// unique hash is not properly formed.
	ErrMalformedCoinbaseNullData

	// ErrTooMuchNullData is returned from NullDataScript when the length of
	// the provided data exceeds MaxDataCarrierSize.
	ErrTooMuchNullData

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

	// ErrEarlyReturn is returned when OP_RETURN is executed in the script.
	ErrEarlyReturn

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

	// ErrEvalFalse is returned when the script evaluated without error but
	// terminated with a false top stack element.
	ErrEvalFalse

	// ErrScriptUnfinished is returned when CheckErrorCondition is called on
	// a script that has not finished executing.
	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

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

	// ErrScriptTooBig is returned if a script is larger than MaxScriptSize.
	ErrScriptTooBig

	// ErrElementTooBig is returned if the size of an element to be pushed
	// to the stack is over MaxScriptElementSize.
	ErrElementTooBig

	// ErrTooManyOperations is returned if a script has more than
	// MaxOpsPerScript opcodes that do not push data.
	ErrTooManyOperations

	// ErrStackOverflow is returned when stack and altstack combined depth
	// is over the limit.
	ErrStackOverflow

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

	// 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 code.
	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

	// 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

	// 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

	// 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

	// 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

	// --------------------------------------------
	// 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

	// ErrDisabledOpcode is returned when a disabled opcode is encountered
	// in a script.
	ErrDisabledOpcode

	// ErrReservedOpcode is returned when an opcode marked as reserved
	// is encountered in a script.
	ErrReservedOpcode

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

	// ErrInvalidStackOperation is returned when a stack operation is
	// attempted with a number that is invalid for the current stack size.
	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

	// ErrNegativeSubstrIdx is returned when an OP_SUBSTR, OP_LEFT, or
	// OP_RIGHT opcode encounters a negative index.
	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

	// ErrNegativeRotation is returned when an OP_ROTL or OP_ROTR attempts
	// to perform a rotation with a negative rotation count.
	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

	// ErrDivideByZero is returned when an OP_DIV of OP_MOD attempts to
	// divide by zero.
	ErrDivideByZero

	// ErrNegativeRotation is returned when an OP_LSHIFT or OP_RSHIFT opcode
	// attempts to perform a shift with a negative count.
	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

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

	// ErrMinimalData is returned when the ScriptVerifyMinimalData flag
	// is set and the script contains push operations that do not use
	// the minimal opcode required.
	ErrMinimalData

	// ErrInvalidSigHashType is returned when a signature hash type is not
	// one of the supported types.
	ErrInvalidSigHashType

	// ErrSigTooShort is returned when the ScriptVerifyDERSignatures flag is
	// set and a signature that should be a canonically-encoded DER
	// signature is too short.
	ErrSigTooShort

	// ErrSigTooLong is returned when the ScriptVerifyDERSignatures flag is
	// set and a signature that should be a canonically-encoded DER
	// signature is too long.
	ErrSigTooLong

	// ErrSigInvalidSeqID is returned when the ScriptVerifyDERSignatures
	// flag is set and a signature that should be a canonically-encoded DER
	// signature does not have the expected ASN.1 sequence ID.
	ErrSigInvalidSeqID

	// ErrSigInvalidDataLen is returned when the ScriptVerifyDERSignatures
	// flag is set and 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

	// ErrSigMissingSTypeID is returned when the ScriptVerifyDERSignatures
	// flag is set and a signature that should be a canonically-encoded DER
	// signature does not provide the ASN.1 type ID for S.
	ErrSigMissingSTypeID

	// ErrSigMissingSLen is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature does not provide the length of S.
	ErrSigMissingSLen

	// ErrSigInvalidSLen is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature does not specify the correct number of bytes for the S
	// portion.
	ErrSigInvalidSLen

	// ErrSigInvalidRIntID is returned when the ScriptVerifyDERSignatures
	// flag is set and a signature that should be a canonically-encoded DER
	// signature does not have the expected ASN.1 integer ID for R.
	ErrSigInvalidRIntID

	// ErrSigZeroRLen is returned when the ScriptVerifyDERSignatures flag is
	// set and a signature that should be a canonically-encoded DER
	// signature has an R length of zero.
	ErrSigZeroRLen

	// ErrSigNegativeR is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature has a negative value for R.
	ErrSigNegativeR

	// ErrSigTooMuchRPadding is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature has too much padding for R.
	ErrSigTooMuchRPadding

	// ErrSigInvalidSIntID is returned when the ScriptVerifyDERSignatures
	// flag is set and a signature that should be a canonically-encoded DER
	// signature does not have the expected ASN.1 integer ID for S.
	ErrSigInvalidSIntID

	// ErrSigZeroSLen is returned when the ScriptVerifyDERSignatures flag is
	// set and a signature that should be a canonically-encoded DER
	// signature has an S length of zero.
	ErrSigZeroSLen

	// ErrSigNegativeS is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature has a negative value for S.
	ErrSigNegativeS

	// ErrSigTooMuchSPadding is returned when the ScriptVerifyDERSignatures flag
	// is set and a signature that should be a canonically-encoded DER
	// signature has too much padding for S.
	ErrSigTooMuchSPadding

	// ErrSigHighS is returned when the ScriptVerifyDERSignatures flag is
	// set and a signature that should be a canonically-encoded DER signature
	// has an S value that is higher than the curve half order.
	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

	// ErrPubKeyType is returned when the ScriptVerifyStrictEncoding
	// flag is set and the script contains invalid public keys.
	ErrPubKeyType

	// ErrCleanStack is returned when the ScriptVerifyCleanStack flag
	// is set, and after evalution, the stack does not contain only a
	// single element.
	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

	// ErrNegativeLockTime is returned when a script contains an opcode that
	// interprets a negative lock time.
	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

	// numErrorCodes is the maximum error code number used in tests.  This
	// entry MUST be the last entry in the enum.
	numErrorCodes
)

// Map of ErrorCode values back to their constant names for pretty printing.
var errorCodeStrings = map[ErrorCode]string{
	ErrInternal:                  "ErrInternal",
	ErrInvalidIndex:              "ErrInvalidIndex",
	ErrInvalidSigHashSingleIndex: "ErrInvalidSigHashSingleIndex",
	ErrUnsupportedAddress:        "ErrUnsupportedAddress",
	ErrNotMultisigScript:         "ErrNotMultisigScript",
	ErrTooManyRequiredSigs:       "ErrTooManyRequiredSigs",
	ErrMalformedCoinbaseNullData: "ErrMalformedCoinbaseNullData",
	ErrTooMuchNullData:           "ErrTooMuchNullData",
	ErrEarlyReturn:               "ErrEarlyReturn",
	ErrEmptyStack:                "ErrEmptyStack",
	ErrEvalFalse:                 "ErrEvalFalse",
	ErrScriptUnfinished:          "ErrScriptUnfinished",
	ErrInvalidProgramCounter:     "ErrInvalidProgramCounter",
	ErrScriptTooBig:              "ErrScriptTooBig",
	ErrElementTooBig:             "ErrElementTooBig",
	ErrTooManyOperations:         "ErrTooManyOperations",
	ErrStackOverflow:             "ErrStackOverflow",
	ErrInvalidPubKeyCount:        "ErrInvalidPubKeyCount",
	ErrInvalidSignatureCount:     "ErrInvalidSignatureCount",
	ErrNumOutOfRange:             "ErrNumOutOfRange",
	ErrVerify:                    "ErrVerify",
	ErrEqualVerify:               "ErrEqualVerify",
	ErrNumEqualVerify:            "ErrNumEqualVerify",
	ErrCheckSigVerify:            "ErrCheckSigVerify",
	ErrCheckMultiSigVerify:       "ErrCheckMultiSigVerify",
	ErrP2SHStakeOpCodes:          "ErrP2SHStakeOpCodes",
	ErrDisabledOpcode:            "ErrDisabledOpcode",
	ErrReservedOpcode:            "ErrReservedOpcode",
	ErrMalformedPush:             "ErrMalformedPush",
	ErrInvalidStackOperation:     "ErrInvalidStackOperation",
	ErrUnbalancedConditional:     "ErrUnbalancedConditional",
	ErrNegativeSubstrIdx:         "ErrNegativeSubstrIdx",
	ErrSigTooMuchSPadding:        "ErrSigTooMuchSPadding",
	ErrOverflowSubstrIdx:         "ErrOverflowSubstrIdx",
	ErrNegativeRotation:          "ErrNegativeRotation",
	ErrOverflowRotation:          "ErrOverflowRotation",
	ErrDivideByZero:              "ErrDivideByZero",
	ErrNegativeShift:             "ErrNegativeShift",
	ErrOverflowShift:             "ErrOverflowShift",
	ErrMinimalData:               "ErrMinimalData",
	ErrInvalidSigHashType:        "ErrInvalidSigHashType",
	ErrSigTooShort:               "ErrSigTooShort",
	ErrSigTooLong:                "ErrSigTooLong",
	ErrSigInvalidSeqID:           "ErrSigInvalidSeqID",
	ErrSigInvalidDataLen:         "ErrSigInvalidDataLen",
	ErrSigMissingSTypeID:         "ErrSigMissingSTypeID",
	ErrSigMissingSLen:            "ErrSigMissingSLen",
	ErrSigInvalidSLen:            "ErrSigInvalidSLen",
	ErrSigInvalidRIntID:          "ErrSigInvalidRIntID",
	ErrSigZeroRLen:               "ErrSigZeroRLen",
	ErrSigNegativeR:              "ErrSigNegativeR",
	ErrSigTooMuchRPadding:        "ErrSigTooMuchRPadding",
	ErrSigInvalidSIntID:          "ErrSigInvalidSIntID",
	ErrSigZeroSLen:               "ErrSigZeroSLen",
	ErrSigNegativeS:              "ErrSigNegativeS",
	ErrSigHighS:                  "ErrSigHighS",
	ErrNotPushOnly:               "ErrNotPushOnly",
	ErrPubKeyType:                "ErrPubKeyType",
	ErrCleanStack:                "ErrCleanStack",
	ErrDiscourageUpgradableNOPs:  "ErrDiscourageUpgradableNOPs",
	ErrNegativeLockTime:          "ErrNegativeLockTime",
	ErrUnsatisfiedLockTime:       "ErrUnsatisfiedLockTime",
}

// String returns the ErrorCode as a human-readable name.
func (e ErrorCode) String() string {
	if s := errorCodeStrings[e]; s != "" {
		return s
	}
	return fmt.Sprintf("Unknown ErrorCode (%d)", int(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
//
// The caller can use type assertions on the returned errors to access the
// ErrorCode field to ascertain the specific reason for the error.  As an
// additional convenience, the caller may make use of the IsErrorCode function
// to check for a specific error code.
type Error struct {
	ErrorCode   ErrorCode
	Description string
}

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

// scriptError creates an Error given a set of arguments.
func scriptError(c ErrorCode, desc string) Error {
	return Error{ErrorCode: c, Description: desc}
}

// IsErrorCode returns whether or not the provided error is a script error with
// the provided error code.
func IsErrorCode(err error, c ErrorCode) bool {
	serr, ok := err.(Error)
	return ok && serr.ErrorCode == c
}

// IsDERSigError returns whether or not the provided error is a script error
// with one of the error codes which are caused due to encountering a signature
// that is not a canonically-encoded DER signature.
//
// Note that the strict DER signature checks are only performed if scripts
// are executed with the ScriptVerifyDERSignatures flag.
func IsDERSigError(err error) bool {
	serr, ok := err.(Error)
	if !ok {
		return false
	}

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

		return true
	}

	return false
}