From 20b46bc7ec05b7d4db03002b562264d8a4f81737 Mon Sep 17 00:00:00 2001
From: Tom Wright <contact@tomwright.me>
Date: Tue, 29 Aug 2023 17:05:14 +0100
Subject: [PATCH] Fix timestamp resolution in yaml

---
 CHANGELOG.md                    |  1 +
 dencoding/yaml.go               | 17 +++++++------
 dencoding/yaml_decoder.go       | 44 +++++++++++++++++++++++++++++++++
 internal/command/select_test.go | 10 ++++++++
 4 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ecac81a7..6af653eb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Resolved an issue with YAML parser that was causing strings to be read as numbers.
+- Timestamps can now be resolved as expected in YAML.
 
 ## [v2.3.4] - 2023-06-01
 
diff --git a/dencoding/yaml.go b/dencoding/yaml.go
index 7c36a4ca..7a62e512 100644
--- a/dencoding/yaml.go
+++ b/dencoding/yaml.go
@@ -1,14 +1,15 @@
 package dencoding
 
 const (
-	yamlTagString = "!!str"
-	yamlTagMap    = "!!map"
-	yamlTagArray  = "!!seq"
-	yamlTagNull   = "!!null"
-	yamlTagBinary = "!!binary"
-	yamlTagBool   = "!!bool"
-	yamlTagInt    = "!!int"
-	yamlTagFloat  = "!!float"
+	yamlTagString    = "!!str"
+	yamlTagMap       = "!!map"
+	yamlTagArray     = "!!seq"
+	yamlTagNull      = "!!null"
+	yamlTagBinary    = "!!binary"
+	yamlTagBool      = "!!bool"
+	yamlTagInt       = "!!int"
+	yamlTagFloat     = "!!float"
+	yamlTagTimestamp = "!!timestamp"
 )
 
 // YAMLEncoderOption is identifies an option that can be applied to a YAML encoder.
diff --git a/dencoding/yaml_decoder.go b/dencoding/yaml_decoder.go
index 038a38fb..48e04c36 100644
--- a/dencoding/yaml_decoder.go
+++ b/dencoding/yaml_decoder.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"reflect"
 	"strconv"
+	"time"
 )
 
 // YAMLDecoder wraps a standard yaml encoder to implement custom ordering logic.
@@ -116,6 +117,12 @@ func (decoder *YAMLDecoder) getScalarNodeValue(node *yaml.Node) (any, error) {
 		return strconv.ParseInt(node.Value, 0, 64)
 	case yamlTagString:
 		return node.Value, nil
+	case yamlTagTimestamp:
+		value, ok := parseTimestamp(node.Value)
+		if !ok {
+			return value, fmt.Errorf("could not parse timestamp: %v", node.Value)
+		}
+		return value, nil
 	default:
 		return nil, fmt.Errorf("unhandled scalar node tag: %v", node.ShortTag())
 	}
@@ -128,3 +135,40 @@ func (decoder *YAMLDecoder) nextNode() (*yaml.Node, error) {
 	}
 	return &node, nil
 }
+
+// This is a subset of the formats allowed by the regular expression
+// defined at http://yaml.org/type/timestamp.html.
+var allowedTimestampFormats = []string{
+	"2006-1-2T15:4:5.999999999Z07:00", // RCF3339Nano with short date fields.
+	"2006-1-2t15:4:5.999999999Z07:00", // RFC3339Nano with short date fields and lower-case "t".
+	"2006-1-2 15:4:5.999999999",       // space separated with no time zone
+	"2006-1-2",                        // date only
+	// Notable exception: time.Parse cannot handle: "2001-12-14 21:59:43.10 -5"
+	// from the set of examples.
+}
+
+// parseTimestamp parses s as a timestamp string and
+// returns the timestamp and reports whether it succeeded.
+// Timestamp formats are defined at http://yaml.org/type/timestamp.html
+// Copied from yaml.v3.
+func parseTimestamp(s string) (time.Time, bool) {
+	// TODO write code to check all the formats supported by
+	// http://yaml.org/type/timestamp.html instead of using time.Parse.
+
+	// Quick check: all date formats start with YYYY-.
+	i := 0
+	for ; i < len(s); i++ {
+		if c := s[i]; c < '0' || c > '9' {
+			break
+		}
+	}
+	if i != 4 || i == len(s) || s[i] != '-' {
+		return time.Time{}, false
+	}
+	for _, format := range allowedTimestampFormats {
+		if t, err := time.Parse(format, s); err == nil {
+			return t, true
+		}
+	}
+	return time.Time{}, false
+}
diff --git a/internal/command/select_test.go b/internal/command/select_test.go
index 98ef143b..8dbbd3e3 100644
--- a/internal/command/select_test.go
+++ b/internal/command/select_test.go
@@ -218,4 +218,14 @@ octal: 8`)),
 		nil,
 	))
 
+	t.Run("Issue331 - YAML to JSON", runTest(
+		[]string{"-r", "yaml", "-w", "json"},
+		[]byte(`createdAt: 2023-06-13T20:19:48.531620935Z`),
+		newline([]byte(`{
+  "createdAt": "2023-06-13T20:19:48.531620935Z"
+}`)),
+		nil,
+		nil,
+	))
+
 }