yq/pkg/yqlib/path_postfix.go

93 lines
3.1 KiB
Go

package yqlib
import (
"errors"
logging "gopkg.in/op/go-logging.v1"
)
type PathPostFixer interface {
ConvertToPostfix([]*Token) ([]*Operation, error)
}
type pathPostFixer struct {
}
func NewPathPostFixer() PathPostFixer {
return &pathPostFixer{}
}
func popOpToResult(opStack []*Token, result []*Operation) ([]*Token, []*Operation) {
var newOp *Token
opStack, newOp = opStack[0:len(opStack)-1], opStack[len(opStack)-1]
return opStack, append(result, newOp.Operation)
}
func (p *pathPostFixer) ConvertToPostfix(infixTokens []*Token) ([]*Operation, error) {
var result []*Operation
// surround the whole thing with quotes
var opStack = []*Token{&Token{TokenType: OpenBracket}}
var tokens = append(infixTokens, &Token{TokenType: CloseBracket})
for _, token := range tokens {
log.Debugf("postfix processing token %v, %v", token.toString(), token.Operation)
switch token.TokenType {
case OpenBracket, OpenCollect, OpenCollectObject:
opStack = append(opStack, token)
case CloseCollect, CloseCollectObject:
var opener TokenType = OpenCollect
var collectOperator *OperationType = Collect
if token.TokenType == CloseCollectObject {
opener = OpenCollectObject
collectOperator = CollectObject
}
itemsInMiddle := false
for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != opener {
opStack, result = popOpToResult(opStack, result)
itemsInMiddle = true
}
if !itemsInMiddle {
// must be an empty collection, add the empty object as a LHS parameter
result = append(result, &Operation{OperationType: Empty})
}
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]
//and append a collect to the opStack
opStack = append(opStack, &Token{TokenType: OperationToken, Operation: &Operation{OperationType: ShortPipe}})
opStack = append(opStack, &Token{TokenType: OperationToken, Operation: &Operation{OperationType: collectOperator}})
case CloseBracket:
for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != OpenBracket {
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 = token.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, token)
}
}
if log.IsEnabledFor(logging.DEBUG) {
log.Debugf("PostFix Result:")
for _, token := range result {
log.Debugf("> %v", token.toString())
}
}
return result, nil
}