package main

import (
    "bytes"
    "fmt"
    "image"
    "image/color"
    "image/draw"
    "image/jpeg"
    "io/ioutil"
    "log"
    "os"
)

func main() {
    f, err := os.Open("resources/image.jpg")
    if err != nil {
        log.Fatal(err)
    }

    img, str, err := image.Decode(f)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(str)

    resImg := resize(img, 3)
    fmt.Println(resImg)

    imgBytes := imgToBytes(resImg)
    fmt.Println(imgBytes)

    err = ioutil.WriteFile("resources/test.jpg", imgBytes, 0777)
    if err != nil {
        log.Fatal(err)
    }
}

func resize(img image.Image, scale int) image.Image {
    imgRect := image.Rect(img.Bounds().Min.X/scale, img.Bounds().Min.Y/scale, img.Bounds().Max.X/scale, img.Bounds().Max.Y/scale)
    resImg := image.NewRGBA(imgRect)
    draw.Draw(resImg, resImg.Bounds(), &image.Uniform{C: color.White}, image.ZP, draw.Src)
    for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y += scale {
        for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x += scale {
            resImg.Set(x/scale, y/scale, img.At(x, y))
        }
    }

    return resImg
}

func imgToBytes(img image.Image) []byte {
    var opt jpeg.Options
    opt.Quality = 80

    buff := bytes.NewBuffer(nil)
    err := jpeg.Encode(buff, img, &opt) // put quality to 80%
    if err != nil {
        log.Fatal(err)
    }

    return buff.Bytes()
}