package mempool

import (
	"github.com/p9c/p9/pkg/blockchain"
	"github.com/p9c/p9/pkg/wire"
)

// RuleError identifies a rule violation. It is used to indicate that processing of a transaction failed due to one of
// the many validation rules. The caller can use type assertions to determine if a failure was specifically due to a
// rule violation and use the Err field to access the underlying error, which will be either a TxRuleError or a
// blockchain. RuleError.
type RuleError struct {
	Err error
}

// Error satisfies the error interface and prints human-readable errors.
func (e RuleError) Error() string {
	if e.Err == nil {
		return "<nil>"
	}
	return e.Err.Error()
}

// TxRuleError identifies a rule violation. It is used to indicate that processing of a transaction failed due to one of
// the many validation rules. The caller can use type assertions to determine if a failure was specifically due to a
// rule violation and access the ErrorCode field to ascertain the specific reason for the rule violation.
type TxRuleError struct {
	RejectCode  wire.RejectCode // The code to send with reject messages
	Description string          // Human readable description of the issue
}

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

// txRuleError creates an underlying TxRuleError with the given a set of arguments and returns a RuleError that
// encapsulates it.
func txRuleError(c wire.RejectCode, desc string) RuleError {
	return RuleError{
		Err: TxRuleError{RejectCode: c, Description: desc},
	}
}

// chainRuleError returns a RuleError that encapsulates the given blockchain. RuleError.
func chainRuleError(chainErr blockchain.RuleError) RuleError {
	return RuleError{
		Err: chainErr,
	}
}

// extractRejectCode attempts to return a relevant reject code for a given error by examining the error for known types.
// It will return true if a code was successfully extracted.
func extractRejectCode(e error) (wire.RejectCode, bool) {
	// Pull the underlying error out of a RuleError.
	if rerr, ok := e.(RuleError); ok {
		e = rerr.Err
	}
	switch er := e.(type) {
	case blockchain.RuleError:
		// Convert the chain error to a reject code.
		var code wire.RejectCode
		switch er.ErrorCode {
		// Rejected due to duplicate.
		case blockchain.ErrDuplicateBlock:
			code = wire.RejectDuplicate
		// Rejected due to obsolete version.
		case blockchain.ErrBlockVersionTooOld:
			code = wire.RejectObsolete
		// Rejected due to checkpoint.
		case blockchain.ErrCheckpointTimeTooOld:
			fallthrough
		case blockchain.ErrDifficultyTooLow:
			fallthrough
		case blockchain.ErrBadCheckpoint:
			fallthrough
		case blockchain.ErrForkTooOld:
			code = wire.RejectCheckpoint
		// Everything else is due to the block or transaction being invalid.
		default:
			code = wire.RejectInvalid
		}
		return code, true
	case TxRuleError:
		return er.RejectCode, true
	case nil:
		return wire.RejectInvalid, false
	}
	return wire.RejectInvalid, false
}

// ErrToRejectErr examines the underlying type of the error and returns a reject code and string appropriate to be sent
// in a wire.MsgReject message.
func ErrToRejectErr(e error) (wire.RejectCode, string) {
	// Return the reject code along with the error text if it can be
	// extracted from the error.
	rejectCode, found := extractRejectCode(e)
	if found {
		return rejectCode, e.Error()
	}
	// Return a generic rejected string if there is no error. This really should not happen unless the code elsewhere is
	// not setting an error as it should be but it's best to be safe and simply return a generic string rather than
	// allowing the following code that dereferences the err to panic.
	if e == nil {
		return wire.RejectInvalid, "rejected"
	}
	// When the underlying error is not one of the above cases, just return wire.RejectInvalid with a generic rejected
	// string plus the error text.
	return wire.RejectInvalid, "rejected: " + e.Error()
}