package tasks

import (
	"fmt"
	"os/exec"
	"strings"
)

// mergeEXRFiles averages multiple linear EXR renders into one (Monte Carlo accumulation).
func mergeEXRFiles(output string, inputs []string) error {
	if len(inputs) == 0 {
		return fmt.Errorf("no input EXR files to merge")
	}
	if len(inputs) == 1 {
		return copyFile(inputs[0], output)
	}

	args := append([]string{}, inputs...)
	args = append(args, "-evaluate-sequence", "mean", output)

	if path, err := exec.LookPath("magick"); err == nil {
		cmd := exec.Command(path, args...)
		if out, err := cmd.CombinedOutput(); err != nil {
			return fmt.Errorf("magick merge failed: %w (%s)", err, strings.TrimSpace(string(out)))
		}
		return nil
	}

	if path, err := exec.LookPath("convert"); err == nil {
		cmd := exec.Command(path, args...)
		if out, err := cmd.CombinedOutput(); err != nil {
			return fmt.Errorf("convert merge failed: %w (%s)", err, strings.TrimSpace(string(out)))
		}
		return nil
	}

	return fmt.Errorf("ImageMagick (magick or convert) required to merge batched EXR renders")
}

func copyFile(src, dst string) error {
	cmd := exec.Command("cp", "-f", src, dst)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("copy %s to %s: %w (%s)", src, dst, err, strings.TrimSpace(string(out)))
	}
	return nil
}