package testusers

import (
	"bytes"
	"fmt"
	"image/png"
	"os"
	"path/filepath"
)

// CopyAvatars validates all sources and destination collisions before copying.
// Existing identical assets are reused. Existing different files are not replaced.
func CopyAvatars(sourceDir, mediaDir string) error {
	if sourceDir == "" || mediaDir == "" {
		return fmt.Errorf("both avatar source and media directories are required")
	}
	assets := make(map[string][]byte)
	for _, name := range Avatars() {
		data, err := os.ReadFile(filepath.Join(sourceDir, name))
		if err != nil {
			return err
		}
		cfg, err := png.DecodeConfig(bytes.NewReader(data))
		if err != nil || cfg.Width < 256 || cfg.Height < 256 {
			return fmt.Errorf("invalid or undersized PNG avatar: %s", name)
		}
		existing, err := os.ReadFile(filepath.Join(mediaDir, name))
		if err == nil {
			if !bytes.Equal(existing, data) {
				return fmt.Errorf("refusing to overwrite different existing avatar: %s", name)
			}
			continue
		}
		if !os.IsNotExist(err) {
			return err
		}
		assets[name] = data
	}
	if err := os.MkdirAll(mediaDir, 0755); err != nil {
		return err
	}
	for name, data := range assets {
		file, err := os.OpenFile(filepath.Join(mediaDir, name), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
		if err != nil {
			return err
		}
		_, writeErr := file.Write(data)
		closeErr := file.Close()
		if writeErr != nil {
			return writeErr
		}
		if closeErr != nil {
			return closeErr
		}
	}
	return nil
}