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: Pipe}}) 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 }