package zntg

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

// 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
}

// Dir is a convenience struct for representing a path to a directory.
type Dir struct {
	Path string
}

// FilePath returns the path of a file with the specified name in the directory.
func (d *Dir) FilePath(name string) string {
	return filepath.Join(d.Path, name)
}

// Write writes the content of the reader into a file with the specified name.
func (d *Dir) Write(name string, r io.Reader) error {
	path := d.FilePath(name)
	dir := filepath.Dir(path)
	os.MkdirAll(dir, 0777)
	return EncodeFile(path, r, CopyReader)
}

// Destroy removes the directory.
func (d *Dir) Destroy() error {
	return os.RemoveAll(d.Path)
}

// 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)
}

// FileExists returns if file exists on specified path.
func FileExists(path string) bool {
	if _, err := os.Stat(path); os.IsNotExist(err) {
		return false
	}
	return true
}

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)) }

// NewTempDir creates a temporary directory.
func NewTempDir(prefix string) (*Dir, error) {
	path, err := ioutil.TempDir("", prefix)
	if nil != err {
		return nil, err
	}
	return &Dir{path}, nil
}

// UserCacheDir gives back the user configuration directory with given name.
func UserCacheDir(name string) (string, error) {
	config, err := os.UserCacheDir()
	if err != nil {
		return "", err
	}
	dir := filepath.Join(config, name)
	err = os.MkdirAll(dir, 0777)
	if err != nil {
		return "", err
	}
	return dir, nil
}

// UserCacheFile gives back the path to the file with the specified name and the directory named app.
func UserCacheFile(app, name string) (string, error) {
	dir, err := UserCacheDir(app)
	if err != nil {
		return "", err
	}
	return filepath.Join(dir, name), nil
}

// UserConfigDir gives back the user configuration directory with given name.
func UserConfigDir(name string) (string, error) {
	config, err := os.UserConfigDir()
	if err != nil {
		return "", err
	}
	dir := filepath.Join(config, name)
	err = os.MkdirAll(dir, 0777)
	if err != nil {
		return "", err
	}
	return dir, nil
}

// UserConfigFile gives back the path to the file with the specified name and the directory named app.
func UserConfigFile(app, name string) (string, error) {
	dir, err := UserConfigDir(app)
	if err != nil {
		return "", err
	}
	return filepath.Join(dir, name), nil
}

var _ EncoderFn = CopyReader

// CopyReader copies the provided value to the output.
func CopyReader(w io.Writer, value interface{}) error {
	_, err := io.Copy(w, value.(io.Reader))
	return err
}