//go:build ignore

// Re-encode an opaque icon as RGB PNG; Chromium may retain an unused alpha channel.
package main

import (
	"bytes"
	"fmt"
	"image/png"
	"io"
	"os"
)

func main() {
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func run() error {
	raw, err := io.ReadAll(io.LimitReader(os.Stdin, 8<<20))
	if err != nil || len(raw) == 8<<20 {
		return fmt.Errorf("icon PNG exceeds input limit")
	}
	cfg, err := png.DecodeConfig(bytes.NewReader(raw))
	if err != nil || cfg.Width != 1024 || cfg.Height != 1024 {
		return fmt.Errorf("icon must be a 1024-pixel PNG")
	}
	img, err := png.Decode(bytes.NewReader(raw))
	if err != nil {
		return err
	}
	opaque, ok := img.(interface{ Opaque() bool })
	if !ok || !opaque.Opaque() {
		return fmt.Errorf("iPhone icon must be fully opaque")
	}
	// The standard encoder omits alpha when every pixel is opaque.
	return png.Encode(os.Stdout, img)
}