Added StringEvaluator for evaluating string input #1266 (#1278)

pkg/yqlib/string_evaluator.go

@@ -0,0 +1,85 @@
+package yqlib
+
+import (
+	"bytes"
+	"container/list"
+	"errors"
+	"fmt"
+	"io"
+
+	yaml "gopkg.in/yaml.v3"
+)
+
+type StringEvaluator interface {
+	Evaluate(expression string, input string, encoder Encoder, leadingContentPreProcessing bool, decoder Decoder) (string, error)
+}
+
+type stringEvaluator struct {
+	treeNavigator DataTreeNavigator
+	fileIndex     int
+}
+
+func NewStringEvaluator() StringEvaluator {
+	return &stringEvaluator{
+		treeNavigator: NewDataTreeNavigator(),
+	}
+}
+
+func (s *stringEvaluator) Evaluate(expression string, input string, encoder Encoder, leadingContentPreProcessing bool, decoder Decoder) (string, error) {
+
+	// Use bytes.Buffer for output of string
+	out := new(bytes.Buffer)
+	printer := NewPrinter(encoder, NewSinglePrinterWriter(out))
+
+	InitExpressionParser()
+	node, err := ExpressionParser.ParseExpression(expression)
+	if err != nil {
+		return "", err
+	}
+
+	reader, leadingContent, err := readString(input, leadingContentPreProcessing)
+	if err != nil {
+		return "", err
+	}
+
+	var currentIndex uint
+	decoder.Init(reader)
+	for {
+		var dataBucket yaml.Node
+		errorReading := decoder.Decode(&dataBucket)
+
+		if errors.Is(errorReading, io.EOF) {
+			s.fileIndex = s.fileIndex + 1
+			return out.String(), nil
+		} else if errorReading != nil {
+			return "", fmt.Errorf("bad input '%v': %w", input, errorReading)
+		}
+
+		candidateNode := &CandidateNode{
+			Document:  currentIndex,
+			Node:      &dataBucket,
+			FileIndex: s.fileIndex,
+		}
+		// move document comments into candidate node
+		// otherwise unwrap drops them.
+		candidateNode.TrailingContent = dataBucket.FootComment
+		dataBucket.FootComment = ""
+
+		if currentIndex == 0 {
+			candidateNode.LeadingContent = leadingContent
+		}
+		inputList := list.New()
+		inputList.PushBack(candidateNode)
+
+		result, errorParsing := s.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputList}, node)
+		if errorParsing != nil {
+			return "", errorParsing
+		}
+		err = printer.PrintResults(result.MatchingNodes)
+
+		if err != nil {
+			return "", err
+		}
+		currentIndex = currentIndex + 1
+	}
+}