nix-amer/internal/cnf/json.go

package cnf

import (
	lib "encoding/json"
	"io"
	"strings"
)

type json struct {
	data   interface{}
	parsed bool
}

// ReadFrom implements io.ReaderFrom
func (d *json) ReadFrom(_reader io.Reader) (int64, error) {

	// 1. get json decoder
	decoder := lib.NewDecoder(_reader)
	err := decoder.Decode(&d.data)
	if err != nil {
		return 0, err
	}

	d.parsed = true
	return 0, nil

}

// WriteTo implements io.WriterTo
func (d *json) WriteTo(_writer io.Writer) (int64, error) {
	encoder := lib.NewEncoder(_writer)
	encoder.SetIndent("", "\t")
	return 0, encoder.Encode(&d.data)
}

// browse returns the target of a dot-separated path (as an interface{} chain where the last is the target if found)
func (d *json) browse(_path string) ([]interface{}, bool) {

	// 1. extract path
	path := strings.Split(_path, ".")

	// 2. init output chain
	current := d.data
	chain := make([]interface{}, 0, len(path)+1)
	chain = append(chain, current)

	// 3. iterate over path / nested fields
	for _, field := range path {
		fmap, ok := current.(map[string]interface{})
		if !ok { // incomplete path
			return chain, false
		}

		child, ok := fmap[field]
		if !ok { // incomplete path
			return chain, false
		}

		current = child
		chain = append(chain, current)
	}

	return chain, true
}

// Get returns the value of a dot-separated path, and if it exists
func (d *json) Get(_path string) (string, bool) {

	// 1. browse path
	chain, found := d.browse(_path)
	if !found {
		return "", false
	}

	// 2. return if string value
	value, ok := chain[len(chain)-1].(string)
	return value, ok

}

// Set the value of a dot-separated path, and creates it if not found
func (d *json) Set(_path, _value string) bool {

	// 1. browse path + create it if does not exist
	path := strings.Split(_path, ".")
	lp := len(path)
	chain, found := d.browse(_path)

	// 2. if found -> set value
	if found {
		mapWrapper, ok := chain[len(chain)-2].(map[string]interface{})
		if !ok { // impossible
			return false
		}
		key := path[lp-1]
		mapWrapper[key] = _value
		return true
	}

	// 3. create path until the end to set value
	root := make(map[string]interface{})
	current := root

	// create children until second to last
	for i, l := len(chain)-1, lp-1; i < l; i++ {
		child := make(map[string]interface{})
		current[path[i]] = child
		current = child
	}

	// set value
	current[path[lp-1]] = _value

	// replace whole object if empty
	if len(chain) < 2 {
		wrapper, ok := d.data.(map[string]interface{})
		if !ok { // impossible
			return false
		}
		key := path[0]
		wrapper[key] = root[key] // store with key ; eitherway it will erase all brother keys
		return true
	}

	// update last found object to add the value
	wrapper, ok := chain[len(chain)-1].(map[string]interface{})
	if !ok { // impossible
		return false
	}

	// add each subkey
	for subkey, subvalue := range root {
		wrapper[subkey] = subvalue
	}
	return true

}