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)
	}

}