package main

import (
  "os"
  "image"
  "log"
  "image/png"
  "github.com/disintegration/gift"
  "flag"
  "math"
  "lcthw.dev/go/jankifier/filters"
)

func LoadImage(filename string) image.Image {
  reader, err := os.Open(filename)
  if err != nil { log.Fatal(err) }
  defer reader.Close()

  img, _, err := image.Decode(reader)
  if err != nil { log.Fatal(err) }

  return img
}

func SaveImage(filename string, img image.Image) {
  out, err := os.Create(filename)
  if err != nil {
    log.Fatalf("can't write file %s: %v", filename, err)
  }
  defer out.Close()

  err = png.Encode(out, img)
  if err != nil {
    log.Fatalf("can't png encode %s: %v", filename, err)
  }
}

type Opts struct {
  InFile string
  OutFile string
  PixelWidth int
  ColorDepth int
  DitherType int
}

func ParseOpts() Opts {
  var opts Opts

  flag.StringVar(&opts.InFile, "input", "", "input file.png")
  flag.StringVar(&opts.OutFile, "output", "", "output file.png")
  flag.IntVar(&opts.PixelWidth, "pixel-width", 4, "pixel width")
  flag.IntVar(&opts.ColorDepth, "color-depth", 16, "number of colors in the palette")
  flag.IntVar(&opts.DitherType, "dither", 0, "0=none, 1=floyd, 2=atkinson")
  flag.Parse()

  if opts.ColorDepth > math.MaxUint8 {
    log.Fatalf("color-depth can't be greater than %d", math.MaxUint8);
  }

  return opts
}

func main() {
  opts := ParseOpts()

  src := LoadImage(opts.InFile)
  bounds := src.Bounds()

  resize := gift.Resize(bounds.Max.X / opts.PixelWidth, 0, gift.NearestNeighborResampling)
  posterize := filters.Posterize(uint16(opts.ColorDepth), opts.DitherType)
  upscale := filters.Upscale(bounds, opts.PixelWidth)
  sharpen := gift.UnsharpMask(1, 1, 0)

  g := gift.New(resize, posterize, upscale, sharpen)
  smaller := image.NewNRGBA(g.Bounds(bounds))
  g.Draw(smaller, src)

  SaveImage(opts.OutFile, smaller)
}