Date Time Ops (#1110)

* Added datetime operators

* Added date subtract support

pkg/yqlib/operator_datetime.go

@@ -0,0 +1,126 @@
+package yqlib
+
+import (
+	"container/list"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+func getStringParamter(parameterName string, d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (string, error) {
+	result, err := d.GetMatchingNodes(context.ReadOnlyClone(), expressionNode)
+
+	if err != nil {
+		return "", err
+	} else if result.MatchingNodes.Len() == 0 {
+		return "", fmt.Errorf("could not find %v for format_time", parameterName)
+	}
+
+	return result.MatchingNodes.Front().Value.(*CandidateNode).Node.Value, nil
+}
+
+func withDateTimeFormat(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	if expressionNode.RHS.Operation.OperationType == blockOpType || expressionNode.RHS.Operation.OperationType == unionOpType {
+		layout, err := getStringParamter("layout", d, context, expressionNode.RHS.LHS)
+		if err != nil {
+			return Context{}, fmt.Errorf("could not get date time format: %w", err)
+		}
+		context.SetDateTimeLayout(layout)
+		return d.GetMatchingNodes(context, expressionNode.RHS.RHS)
+
+	}
+	return Context{}, errors.New(`must provide a date time format string and an expression, e.g. with_dtf("Monday, 02-Jan-06 at 3:04PM MST"; <exp>)`)
+
+}
+
+// for unit tests
+var Now = time.Now
+
+func nowOp(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+
+	node := &yaml.Node{
+		Tag:   "!!timestamp",
+		Kind:  yaml.ScalarNode,
+		Value: Now().Format(time.RFC3339),
+	}
+
+	return context.SingleChildContext(&CandidateNode{Node: node}), nil
+
+}
+
+func formatDateTime(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	format, err := getStringParamter("format", d, context, expressionNode.RHS)
+	layout := context.GetDateTimeLayout()
+	decoder := NewYamlDecoder()
+
+	if err != nil {
+		return Context{}, err
+	}
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		parsedTime, err := time.Parse(layout, candidate.Node.Value)
+		if err != nil {
+			return Context{}, fmt.Errorf("could not parse datetime of [%v]: %w", candidate.GetNicePath(), err)
+		}
+		formattedTimeStr := parsedTime.Format(format)
+		decoder.Init(strings.NewReader(formattedTimeStr))
+		var dataBucket yaml.Node
+		errorReading := decoder.Decode(&dataBucket)
+		var node *yaml.Node
+		if errorReading != nil {
+			log.Debugf("could not parse %v - lets just leave it as a string", formattedTimeStr)
+			node = &yaml.Node{
+				Kind:  yaml.ScalarNode,
+				Tag:   "!!str",
+				Value: formattedTimeStr,
+			}
+		} else {
+			node = unwrapDoc(&dataBucket)
+		}
+
+		results.PushBack(candidate.CreateReplacement(node))
+	}
+
+	return context.ChildContext(results), nil
+}
+
+func tzOp(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	timezoneStr, err := getStringParamter("timezone", d, context, expressionNode.RHS)
+	layout := context.GetDateTimeLayout()
+
+	if err != nil {
+		return Context{}, err
+	}
+	var results = list.New()
+
+	timezone, err := time.LoadLocation(timezoneStr)
+	if err != nil {
+		return Context{}, fmt.Errorf("could not load tz [%v]: %w", timezoneStr, err)
+	}
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		parsedTime, err := time.Parse(layout, candidate.Node.Value)
+		if err != nil {
+			return Context{}, fmt.Errorf("could not parse datetime of [%v] using layout [%v]: %w", candidate.GetNicePath(), layout, err)
+		}
+		tzTime := parsedTime.In(timezone)
+
+		node := &yaml.Node{
+			Kind:  yaml.ScalarNode,
+			Tag:   candidate.Node.Tag,
+			Value: tzTime.Format(layout),
+		}
+
+		results.PushBack(candidate.CreateReplacement(node))
+	}
+
+	return context.ChildContext(results), nil
+}