From 3a6a913ef2a648f6897202e6e44905a7778c9ed5 Mon Sep 17 00:00:00 2001
From: Erik Brakkee <erik@brakkee.org>
Date: Tue, 24 Dec 2024 22:39:09 +0100
Subject: [PATCH] yamldiff re-implementation in go

---
 cmd/yamldiff/yamldiff.go | 99 ++++++++++++++++++++++++++++++++++++++++
 go.mod                   |  2 +
 2 files changed, 101 insertions(+)
 create mode 100644 cmd/yamldiff/yamldiff.go

diff --git a/cmd/yamldiff/yamldiff.go b/cmd/yamldiff/yamldiff.go
new file mode 100644
index 0000000..0a2255c
--- /dev/null
+++ b/cmd/yamldiff/yamldiff.go
@@ -0,0 +1,99 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	yaml "github.com/goccy/go-yaml"
+	"os"
+	"reflect"
+)
+
+func read(file string) []byte {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		panic(err)
+	}
+	return data
+}
+
+func parse(data []byte) yaml.MapSlice {
+	var result yaml.MapSlice
+	decoder := yaml.NewDecoder(bytes.NewReader(data),
+		yaml.UseOrderedMap())
+	err := decoder.Decode(&result)
+	if err != nil {
+		panic(err)
+	}
+	return result
+}
+
+type TypeId int
+
+const (
+	Map TypeId = iota
+	Slice
+	Scalar
+)
+
+func Type(elem any) TypeId {
+	switch elem.(type) {
+	case yaml.MapSlice:
+		return Map
+	case []any:
+		return Slice
+	default:
+		return Scalar
+	}
+}
+
+func subtract(yaml1 yaml.MapSlice, yaml2 yaml.MapSlice) yaml.MapSlice {
+	res := make(yaml.MapSlice, 0)
+	for _, item := range yaml2 {
+		k := item.Key
+		v1 := item.Value
+		v2 := yaml1.ToMap()[k]
+		switch {
+		case reflect.DeepEqual(v1, v2):
+			// delete is implicit by not copying to the output
+		case Type(v1) == Map && Type(v2) == Map:
+			diff := subtract(v2.(yaml.MapSlice), v1.(yaml.MapSlice))
+			if len(diff) > 0 {
+				res = append(res, item)
+			}
+		case Type(v1) == Slice && Type(v2) == Slice:
+			if !reflect.DeepEqual(v1, v2) {
+				res = append(res, item)
+			}
+		default:
+			res = append(res, item)
+		}
+	}
+	return res
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		fmt.Fprintf(os.Stderr, `
+Usage: yamldiff <file1> <file2>")
+  Shows changes and additions made in <file2> w.r.t. <file1> 
+`)
+	}
+	file1 := os.Args[1]
+	file2 := os.Args[2]
+
+	yaml1 := parse(read(file1))
+	yaml2 := parse(read(file2))
+
+	subtract(yaml2, yaml1)
+
+	enc := yaml.NewEncoder(os.Stdout,
+		yaml.UseLiteralStyleIfMultiline(true),
+		yaml.Indent(2), // Set indentation
+		//yaml.UseOrderedMap(), // Preserve map order
+	)
+	err := enc.Encode(yaml2)
+	if err != nil {
+		panic(err)
+	}
+
+}
diff --git a/go.mod b/go.mod
index 67b9e4c..9212ccf 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module git.wamblee.org/public/gotools
 
 go 1.23.3
+
+require github.com/goccy/go-yaml v1.15.13