package main

import (
	"flag"
	"fmt"
	"image"
	"image/draw"
	_ "image/gif"
	_ "image/jpeg"
	"image/png"
	"os"
)

func main() {
	outputPath := flag.String("o", "output.png", "output spritesheet path")
	direction := flag.String("direction", "h", "join direction: h (horizontal) or v (vertical)")
	flag.Parse()

	inputPaths := flag.Args()
	if len(inputPaths) == 0 {
		fmt.Println("Usage: spritestitch -o output.png [-direction h|v] sheet1.png sheet2.png ...")
		os.Exit(1)
	}

	if *direction != "h" && *direction != "v" {
		fmt.Println("direction must be 'h' (horizontal) or 'v' (vertical)")
		os.Exit(1)
	}

	var images []image.Image
	var bounds []image.Rectangle

	for _, path := range inputPaths {
		imgFile, err := os.Open(path)
		if err != nil {
			fmt.Fprintf(os.Stderr, "failed to open %s: %v\n", path, err)
			os.Exit(1)
		}

		img, _, err := image.Decode(imgFile)
		imgFile.Close()
		if err != nil {
			fmt.Fprintf(os.Stderr, "failed to decode %s: %v\n", path, err)
			os.Exit(1)
		}

		images = append(images, img)
		bounds = append(bounds, img.Bounds())
	}

	var totalWidth, totalHeight int
	if *direction == "h" {
		maxHeight := 0
		sumWidth := 0
		for _, b := range bounds {
			w := b.Dx()
			h := b.Dy()
			sumWidth += w
			if h > maxHeight {
				maxHeight = h
			}
		}
		totalWidth = sumWidth
		totalHeight = maxHeight
	} else {
		maxWidth := 0
		sumHeight := 0
		for _, b := range bounds {
			w := b.Dx()
			h := b.Dy()
			sumHeight += h
			if w > maxWidth {
				maxWidth = w
			}
		}
		totalWidth = maxWidth
		totalHeight = sumHeight
	}

	outImg := image.NewRGBA(image.Rect(0, 0, totalWidth, totalHeight))

	offsetX, offsetY := 0, 0
	for i, img := range images {
		b := bounds[i]
		w := b.Dx()
		h := b.Dy()

		var dstRect image.Rectangle
		if *direction == "h" {
			dstRect = image.Rect(offsetX, 0, offsetX+w, h)
			offsetX += w
		} else {
			dstRect = image.Rect(0, offsetY, w, offsetY+h)
			offsetY += h
		}

		draw.Draw(outImg, dstRect, img, b.Min, draw.Over)
	}

	outFile, err := os.Create(*outputPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create output file: %v\n", err)
		os.Exit(1)
	}
	defer outFile.Close()

	if err := png.Encode(outFile, outImg); err != nil {
		fmt.Fprintf(os.Stderr, "failed to encode PNG: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Spritesheet written to %s\n", *outputPath)
}