From 9e476852711bca2cdb3d2e3b6ee7ca9cb6a8e91e Mon Sep 17 00:00:00 2001
From: Mike Farah <mikefarah@gmail.com>
Date: Mon, 3 Feb 2020 13:59:16 +1100
Subject: [PATCH] Compare first cut

---
 cmd/compare.go | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++
 cmd/root.go    |  1 +
 cmd/utils.go   | 10 +++----
 go.mod         |  1 +
 go.sum         |  2 ++
 5 files changed, 81 insertions(+), 5 deletions(-)
 create mode 100644 cmd/compare.go

diff --git a/cmd/compare.go b/cmd/compare.go
new file mode 100644
index 00000000..211c668e
--- /dev/null
+++ b/cmd/compare.go
@@ -0,0 +1,72 @@
+package cmd
+
+import (
+	"bufio"
+	"bytes"
+
+	"github.com/kylelemons/godebug/diff"
+	errors "github.com/pkg/errors"
+	"github.com/spf13/cobra"
+	yaml "gopkg.in/yaml.v3"
+)
+
+func createCompareCmd() *cobra.Command {
+	var cmdCompare = &cobra.Command{
+		Use:     "compare [yaml_file_a] [yaml_file_b]",
+		Aliases: []string{"x"},
+		Short:   "yq x data1.yml data2.yml",
+		Example: `
+yq x - data2.yml # reads from stdin
+`,
+		Long: "Compares two yaml files, prints the difference",
+		RunE: compareDocuments,
+	}
+	cmdCompare.PersistentFlags().StringVarP(&docIndex, "doc", "d", "0", "process document index number (0 based)")
+	cmdCompare.PersistentFlags().BoolVarP(&prettyPrint, "prettyPrint", "P", false, "pretty print (does not have an affect with json output)")
+	return cmdCompare
+}
+
+func compareDocuments(cmd *cobra.Command, args []string) error {
+	if len(args) != 2 {
+		return errors.New("Must provide at 2 yaml files")
+	}
+	if docIndex == "*" {
+		return errors.New("Document splat for compare not yet supported")
+	}
+
+	var _, docIndexInt, errorParsingDocIndex = parseDocumentIndex()
+	if errorParsingDocIndex != nil {
+		return errorParsingDocIndex
+	}
+
+	var dataBucketA yaml.Node
+	var dataBucketB yaml.Node
+	var errorReadingStream error
+	errorReadingStream = readData(args[0], docIndexInt, &dataBucketA)
+	if errorReadingStream != nil {
+		return errorReadingStream
+	}
+
+	errorReadingStream = readData(args[1], docIndexInt, &dataBucketB)
+	if errorReadingStream != nil {
+		return errorReadingStream
+	}
+
+	if prettyPrint {
+		updateStyleOfNode(&dataBucketA, 0)
+		updateStyleOfNode(&dataBucketB, 0)
+	}
+
+	if errorReadingStream != nil {
+		return errorReadingStream
+	}
+
+	var dataBufferA bytes.Buffer
+	printNode(&dataBucketA, bufio.NewWriter(&dataBufferA))
+
+	var dataBufferB bytes.Buffer
+	printNode(&dataBucketB, bufio.NewWriter(&dataBufferB))
+
+	cmd.Print(diff.Diff(dataBufferA.String(), dataBufferB.String()))
+	return nil
+}
diff --git a/cmd/root.go b/cmd/root.go
index f8eb8f63..e435b6af 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -44,6 +44,7 @@ func New() *cobra.Command {
 
 	rootCmd.AddCommand(
 		createReadCmd(),
+		createCompareCmd(),
 		createValidateCmd(),
 		createWriteCmd(),
 		createPrefixCmd(),
diff --git a/cmd/utils.go b/cmd/utils.go
index 878f0dee..ed6cf532 100644
--- a/cmd/utils.go
+++ b/cmd/utils.go
@@ -71,8 +71,11 @@ func printValue(node *yaml.Node, cmd *cobra.Command) error {
 		cmd.Print(node.Value)
 		return nil
 	}
+	return printNode(node, cmd.OutOrStdout())
+}
 
-	bufferedWriter := bufio.NewWriter(cmd.OutOrStdout())
+func printNode(node *yaml.Node, writer io.Writer) error {
+	bufferedWriter := bufio.NewWriter(writer)
 	defer safelyFlush(bufferedWriter)
 
 	var encoder yqlib.Encoder
@@ -81,10 +84,7 @@ func printValue(node *yaml.Node, cmd *cobra.Command) error {
 	} else {
 		encoder = yqlib.NewYamlEncoder(bufferedWriter)
 	}
-	if err := encoder.Encode(node); err != nil {
-		return err
-	}
-	return nil
+	return encoder.Encode(node)
 }
 
 func setStyle(matchingNodes []*yqlib.NodeContext, style yaml.Style) {
diff --git a/go.mod b/go.mod
index b6863a43..ef0a88db 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,7 @@
 module github.com/mikefarah/yq/v3
 
 require (
+	github.com/kylelemons/godebug v1.1.0
 	github.com/pkg/errors v0.8.1
 	github.com/spf13/cobra v0.0.5
 	golang.org/x/tools v0.0.0-20191213221258-04c2e8eff935 // indirect
diff --git a/go.sum b/go.sum
index 2f045e24..9235f824 100644
--- a/go.sum
+++ b/go.sum
@@ -9,6 +9,8 @@ github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMo
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
 github.com/inconshreveable/mousetrap v1.0.0 h1:Z8tu5sraLXCXIcARxBp/8cbvlwVa7Z1NHg9XEKhtSvM=
 github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
 github.com/mikefarah/yaml v2.1.0+incompatible h1:nu2cqmzk4WlWJNgnevY88faMcdrDzYGcsUjYFxEpB7Y=
 github.com/mikefarah/yaml/v2 v2.4.0 h1:eYqfooY0BnvKTJxr7+ABJs13n3dg9n347GScDaU2Lww=