package image

import (
	"bytes"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"mime/multipart"
	"os"
)

// CompressImage 壓縮圖片至指定位置
func CompressImage(input interface{}, output string) (err error) {
	var file io.Reader
	var fileToClose io.Closer

	switch v := input.(type) {
	case string:
		f, err := os.Open(v)
		if err != nil {
			return err
		}

		file = f
		fileToClose = f
		defer func() {
			if fileToClose != nil {
				_ = fileToClose.Close()
			}
			_ = os.Remove(v)
		}()
	case *multipart.FileHeader:
		f, err := v.Open()
		if err != nil {
			return err
		}
		file = f
		fileToClose = f
		defer func() {
			if fileToClose != nil {
				_ = fileToClose.Close()
			}
		}()
	}

	var buf bytes.Buffer
	if _, err = io.Copy(&buf, file); err != nil {
		return err
	}
	bs := buf.Bytes()

	var ext string
	if _, err = jpeg.Decode(bytes.NewReader(bs)); err == nil {
		ext = "jpg"
	} else if _, err = png.Decode(bytes.NewReader(bs)); err == nil {
		ext = "png"
	} else if _, err = gif.Decode(bytes.NewReader(bs)); err == nil {
		ext = "gif"
	}

	outputFile, err := os.Create(output)
	if err != nil {
		return err
	}
	defer func() {
		if outputFile != nil {
			_ = outputFile.Close()
		}
	}()

	switch ext {
	case "jpg":
		img, err := jpeg.Decode(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		return jpeg.Encode(outputFile, img, &jpeg.Options{Quality: 70})
	case "png":
		img, err := png.Decode(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		encoder := png.Encoder{CompressionLevel: png.BestCompression}
		return encoder.Encode(outputFile, img)
	case "gif":
		img, err := gif.DecodeAll(bytes.NewReader(bs))
		if err != nil {
			return err
		}
		return gif.EncodeAll(outputFile, img)
	default:
		_, err = outputFile.Write(bs)
		return err
	}
}