package zntg

import (
	"encoding/json"
	"image"
	_ "image/gif"  // decoding of GIF
	_ "image/jpeg" // decoding of JPEG
	"image/png"
	"io"
	"os"
)

// CreateJSONDecoder create a new a generic JSON decoder for the specified value.
func CreateJSONDecoder(value interface{}) DecoderFn {
	return func(r io.Reader) (interface{}, error) {
		decoder := json.NewDecoder(r)
		return value, decoder.Decode(value)
	}
}

// DecoderFn describes a generic decoder.
type DecoderFn func(io.Reader) (interface{}, error)

// DecodeFile is a generic decode method to decode content from disk.
func DecodeFile(path string, decoder func(io.Reader) (interface{}, error)) (interface{}, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return decoder(f)
}

// DecodeImage tries to decode a file to an image.
func DecodeImage(path string) (image.Image, error) {
	value, err := DecodeFile(path, ImageDecoder)
	if err != nil {
		return nil, err
	}
	return value.(image.Image), nil
}

// DecodeJSON tries to decode a file to specifed value.
func DecodeJSON(path string, value interface{}) error {
	_, err := DecodeFile(path, CreateJSONDecoder(value))
	return err
}

// EncoderFn describes a generic encoder.
type EncoderFn func(io.Writer, interface{}) error

// EncodeFile is a generic encode method to encode content to disk.
func EncodeFile(path string, value interface{}, encoder EncoderFn) error {
	dst, err := os.Create(path)
	if err != nil {
		return err
	}
	defer dst.Close()
	return encoder(dst, value)
}

// EncodeJSON encodes a JSON struct to a file.
func EncodeJSON(path string, value interface{}) error {
	return EncodeFile(path, value, JSONEncoder)
}

// EncodePNG encodes an image to a file.
func EncodePNG(path string, im image.Image) error {
	return EncodeFile(path, im, PNGEncoder)
}

var _ DecoderFn = ImageDecoder

// ImageDecoder is a generic image decoder.
func ImageDecoder(r io.Reader) (interface{}, error) {
	im, _, err := image.Decode(r)
	return im, err
}

var _ EncoderFn = JSONEncoder

// JSONEncoder is a generic JSON encoder.
func JSONEncoder(w io.Writer, value interface{}) error {
	encoder := json.NewEncoder(w)
	return encoder.Encode(value)
}

var _ EncoderFn = PNGEncoder

// PNGEncoder is a generic PNG encoder.
func PNGEncoder(w io.Writer, value interface{}) error { return png.Encode(w, value.(image.Image)) }