package image

import (
	"bytes"
	"errors"
	"github.com/nfnt/resize"
	"image"
	"image/jpeg"
	"image/png"
	"strings"
)

func CreateThumbnail(fileBytes []byte, side, width, height int) ([]byte, error) {
	img, format, err := image.Decode(bytes.NewReader(fileBytes))
	if err != nil {
		return nil, err
	}

	var thumbnailImg image.Image
	if side > 0 {
		var canvas image.Image
		s := side
		sz := img.Bounds().Size()

		if sz.X > sz.Y {
			canvas = resize.Thumbnail(uint(sz.X), uint(s), img, resize.Lanczos2)
		} else {
			canvas = resize.Thumbnail(uint(s), uint(sz.Y), img, resize.Lanczos2)
		}
		sz = canvas.Bounds().Size()
		var l, t, r, b int
		if sz.X > s {
			l = (sz.X - s) / 2
			r = l + s
		} else {
			l = 0
			r = sz.X
		}
		if sz.Y > s {
			t = (sz.Y - s) / 2
			b = t + s
		} else {
			t = 0
			b = sz.Y
		}

		if ycbcr, ok := canvas.(*image.YCbCr); ok {
			thumbnailImg = ycbcr.SubImage(image.Rect(l, t, r, b)).(*image.YCbCr)
		} else if rgba, ok := canvas.(*image.RGBA); ok {
			thumbnailImg = rgba.SubImage(image.Rect(l, t, r, b)).(*image.RGBA)
		} else {
			return nil, errors.New("未识别的图片色彩类型")
		}
	} else {
		w := width
		h := height
		if w > 0 && h > 0 {
		} else if w > 0 {
			h = img.Bounds().Dy()
		} else {
			w = img.Bounds().Dx()
		}
		thumbnailImg = resize.Thumbnail(uint(w), uint(h), img, resize.Lanczos2)
	}

	buffer := new(bytes.Buffer)
	format = strings.ToLower(format)
	if format == "jpg" || format == "jpeg" {
		if err := jpeg.Encode(buffer, thumbnailImg, nil); err != nil {
			return nil, err
		}
	} else if format == "png" {
		if err := png.Encode(buffer, thumbnailImg); err != nil {
			return nil, err
		}
	} else {
		return nil, errors.New("不支持的文件格式")
	}
	return buffer.Bytes(), nil
}