package resize

import (
	"bytes"
	"github.com/anthonynsimon/bild/transform"
	"image"
	"image/jpeg"
	"image/png"
	"io"
)

var mimeTypes = map[string]string{
	"image/jpg":  "image/jpg",
	"image/jpeg": "image/jpeg",
	"image/png":  "image/png",
}

func IsResizable(mimeType string) bool {
	_, present := mimeTypes[mimeType]
	return present
}

type ResizeType int

const (
	// Cover - resize preserving image aspect
	//       - resizes to the smallest image where both width and height are larger or equal to given size
	Cover ResizeType = iota
	// Contain - resize preserving image aspect
	//       - resizes to the largest image where both width and height are smaller or equal to given size
	Contain ResizeType = iota
	// ExactHeight - resize preserving image aspect
	//       - resizes to the image with given height
	ExactHeight ResizeType = iota
	// ExactWidth - resize preserving image aspect
	//       - resizes to the image with given width
	ExactWidth ResizeType = iota
	// Exact - resize without preserving image aspect
	//       - resizes to exact size defined in request
	Exact ResizeType = iota
)

type Resize struct {
	Height int
	Width  int
	Type   ResizeType
}

func ResizeImage(imageBytes []byte, resize Resize) ([]byte, error) {
	img, format, err := image.Decode(bytes.NewReader(imageBytes))
	if err != nil {
		return nil, err
	}
	var buffer bytes.Buffer
	writer := io.Writer(&buffer)

	resizeWidth, resizeHeight := calculateResizedDimensions(img.Bounds(), resize)

	img = transform.Resize(img, resizeWidth, resizeHeight, transform.Gaussian)
	switch format {
	case "png":
		err = png.Encode(writer, img)
	case "jpeg":
		err = jpeg.Encode(writer, img, nil)
	default:
		err = jpeg.Encode(writer, img, nil)
	}
	if err != nil {
		return nil, err
	}
	return buffer.Bytes(), nil
}

func calculateResizedDimensions(bounds image.Rectangle, resize Resize) (width int, height int) {
	width = bounds.Dx()
	height = bounds.Dy()

	switch resize.Type {
	case Cover:
		rWidth := resize.Height * width / height
		if rWidth >= resize.Width {
			return rWidth, resize.Height
		}
		rHeight := resize.Width * height / width
		if rHeight >= resize.Height {
			return resize.Width, rHeight
		}
	case Contain:
		rWidth := resize.Height * width / height
		if rWidth <= resize.Width {
			return rWidth, resize.Height
		}
		rHeight := resize.Width * height / width
		if rHeight <= resize.Height {
			return resize.Width, rHeight
		}
	case ExactHeight:
		rWidth := resize.Height * width / height
		return rWidth, resize.Height
	case ExactWidth:
		rHeight := resize.Width * height / width
		return resize.Width, rHeight
	}
	return
}