yq/pkg/yqlib/expression_postfix.go

137 lines
4.7 KiB
Go

package yqlib
import (
"errors"
"fmt"
logging "gopkg.in/op/go-logging.v1"
)
type expressionPostFixer interface {
ConvertToPostfix([]*token) ([]*Operation, error)
}
type expressionPostFixerImpl struct {
}
func newExpressionPostFixer() expressionPostFixer {
return &expressionPostFixerImpl{}
}
func popOpToResult(opStack []*token, result []*Operation) ([]*token, []*Operation) {
var newOp *token
opStack, newOp = opStack[0:len(opStack)-1], opStack[len(opStack)-1]
log.Debugf("popped %v from opstack to results", newOp.toString(true))
return opStack, append(result, newOp.Operation)
}
func validateNoOpenTokens(token *token) error {
if token.TokenType == openCollect {
return fmt.Errorf(("Bad expression, could not find matching `]`"))
} else if token.TokenType == openCollectObject {
return fmt.Errorf(("Bad expression, could not find matching `}`"))
} else if token.TokenType == openBracket {
return fmt.Errorf(("Bad expression, could not find matching `)`"))
}
return nil
}
func (p *expressionPostFixerImpl) ConvertToPostfix(infixTokens []*token) ([]*Operation, error) {
var result []*Operation
// surround the whole thing with brackets
var opStack = []*token{{TokenType: openBracket}}
var tokens = append(infixTokens, &token{TokenType: closeBracket})
for _, currentToken := range tokens {
log.Debugf("postfix processing currentToken %v", currentToken.toString(true))
switch currentToken.TokenType {
case openBracket, openCollect, openCollectObject:
opStack = append(opStack, currentToken)
log.Debugf("put %v onto the opstack", currentToken.toString(true))
case closeCollect, closeCollectObject:
var opener tokenType = openCollect
var collectOperator *operationType = collectOpType
if currentToken.TokenType == closeCollectObject {
opener = openCollectObject
collectOperator = collectObjectOpType
}
for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != opener {
missingClosingTokenErr := validateNoOpenTokens(opStack[len(opStack)-1])
if missingClosingTokenErr != nil {
return nil, missingClosingTokenErr
}
opStack, result = popOpToResult(opStack, result)
}
if len(opStack) == 0 {
return nil, errors.New("Bad path expression, got close collect brackets without matching opening bracket")
}
// now we should have [ as the last element on the opStack, get rid of it
opStack = opStack[0 : len(opStack)-1]
log.Debugf("deleting open bracket from opstack")
//and append a collect to the result
// hack - see if there's the optional traverse flag
// on the close op - move it to the traverse array op
// allows for .["cat"]?
prefs := traversePreferences{}
closeTokenMatch := string(currentToken.Match.Bytes)
if closeTokenMatch[len(closeTokenMatch)-1:] == "?" {
prefs.OptionalTraverse = true
}
result = append(result, &Operation{OperationType: collectOperator})
log.Debugf("put collect onto the result")
if opener != openCollect {
result = append(result, &Operation{OperationType: shortPipeOpType})
log.Debugf("put shortpipe onto the result")
}
//traverseArrayCollect is a sneaky op that needs to be included too
//when closing a ]
if len(opStack) > 0 && opStack[len(opStack)-1].Operation != nil && opStack[len(opStack)-1].Operation.OperationType == traverseArrayOpType {
opStack[len(opStack)-1].Operation.Preferences = prefs
opStack, result = popOpToResult(opStack, result)
}
case closeBracket:
for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != openBracket {
missingClosingTokenErr := validateNoOpenTokens(opStack[len(opStack)-1])
if missingClosingTokenErr != nil {
return nil, missingClosingTokenErr
}
opStack, result = popOpToResult(opStack, result)
}
if len(opStack) == 0 {
return nil, errors.New("Bad path expression, got close brackets without matching opening bracket")
}
// now we should have ( as the last element on the opStack, get rid of it
opStack = opStack[0 : len(opStack)-1]
default:
var currentPrecedence = currentToken.Operation.OperationType.Precedence
// pop off higher precedent operators onto the result
for len(opStack) > 0 &&
opStack[len(opStack)-1].TokenType == operationToken &&
opStack[len(opStack)-1].Operation.OperationType.Precedence > currentPrecedence {
opStack, result = popOpToResult(opStack, result)
}
// add this operator to the opStack
opStack = append(opStack, currentToken)
log.Debugf("put %v onto the opstack", currentToken.toString(true))
}
}
log.Debugf("opstackLen: %v", len(opStack))
if log.IsEnabledFor(logging.DEBUG) {
log.Debugf("PostFix Result:")
for _, currentToken := range result {
log.Debugf("> %v", currentToken.toString())
}
}
return result, nil
}