package diffstore

import (
	"encoding/json"
	"fmt"
	"image"
	"image/png"
	"io"
	"os"
	"path"

	"github.com/boltdb/bolt"
	"go.skia.org/infra/go/fileutil"
	"go.skia.org/infra/go/util"
	"go.skia.org/infra/golden/go/diff"
)

const (
	// IMG_EXTENSION is the default extension of images.
	IMG_EXTENSION = "png"

	// GS_PREFIX is the prefix of an imageID that indicates that it is corresponds
	// to a storage location in GCS.
	GS_PREFIX = "gs"
)

// saveFile writes the given file to disk.
func saveFile(targetPath string, r io.Reader) error {
	f, err := os.Create(targetPath)
	if err != nil {
		return err
	}
	defer util.Close(f)

	_, err = io.Copy(f, r)
	return err
}

// loadImg loads an image from disk.
func loadImg(sourcePath string) (*image.NRGBA, error) {
	f, err := os.Open(sourcePath)
	if err != nil {
		return nil, err
	}
	defer util.Close(f)
	return decodeImg(f)
}

// encodeImg encodes the given image as a PNG and writes the result to the
// given writer.
func encodeImg(w io.Writer, img *image.NRGBA) error {
	encoder := png.Encoder{CompressionLevel: png.BestSpeed}
	if err := encoder.Encode(w, img); err != nil {
		return err
	}
	return nil
}

// decodeImg decodes an image from the given reader and returns it as a NRGBA image.
func decodeImg(reader io.Reader) (*image.NRGBA, error) {
	im, err := png.Decode(reader)
	if err != nil {
		return nil, err
	}
	return diff.GetNRGBA(im), nil
}

// getDigestImageFileName returns the image name based on the digest.
func getDigestImageFileName(digest string) string {
	return fmt.Sprintf("%s.%s", digest, IMG_EXTENSION)
}

// openBoltDB opens a boltDB in the given given directory with the given name.
func openBoltDB(baseDir, name string) (*bolt.DB, error) {
	baseDir, err := fileutil.EnsureDirExists(baseDir)
	if err != nil {
		return nil, err
	}

	return bolt.Open(path.Join(baseDir, name), 0600, nil)
}

// saveFilePath saves the given buffer in path.
func saveFilePath(path string, r io.Reader) error {
	err := fileutil.EnsureDirPathExists(path)
	if err != nil {
		return fmt.Errorf("Unable to create path for %s: %s", path, err)
	}

	if err := saveFile(path, r); err != nil {
		return fmt.Errorf("Unable to save file %s. Got error: %s", path, err)
	}
	return nil
}

// MetricMapCodec implements the util.LRUCodec interface by serializing and
// deserializing generic diff result structs, instances of map[string]interface{}
type MetricMapCodec struct{}

// See util.LRUCodec interface
func (m MetricMapCodec) Encode(data interface{}) ([]byte, error) {
	return json.Marshal(data)
}

// See util.LRUCodec interface
func (m MetricMapCodec) Decode(byteData []byte) (interface{}, error) {
	dm := map[string]*diff.DiffMetrics{}
	err := json.Unmarshal(byteData, &dm)
	if err != nil {
		return nil, err
	}

	// Must make result of deserialization generic in order to propagate
	ret := make(map[string]interface{}, len(dm))
	for k, metric := range dm {
		ret[k] = metric
	}
	return ret, nil
}