MrixsCraft-launcher/internal/java/java.go

// package java manages portable JRE downloads and detection.
package java

import (
	"fmt"
	"os"
	"path/filepath"
	"runtime"

	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/config"
)

// ExecutableName returns the platform-specific Java executable name.
func ExecutableName() string {
	if runtime.GOOS == "windows" {
		return "java.exe"
	}
	return "java"
}

// IsInstalled checks whether the given Java version is available locally.
func IsInstalled(version int) (string, error) {
	dir, err := config.JavaDir(version)
	if err != nil {
		return "", err
	}
	bin := filepath.Join(dir, "bin", ExecutableName())
	if _, err := os.Stat(bin); err != nil {
		if os.IsNotExist(err) {
			return "", nil // not installed
		}
		return "", fmt.Errorf("checking %s: %w", bin, err)
	}
	return bin, nil
}

// Find searches for the required Java version, downloading it if necessary.
// Returns the path to the java binary.
func Find(version int) (string, error) {
	bin, err := IsInstalled(version)
	if err != nil {
		return "", err
	}
	if bin != "" {
		return bin, nil
	}

	// TODO: Download and extract JRE for the requested version.
	// For now, return an error with instructions.
	return "", fmt.Errorf(
		"Java %d is not installed. Please wait for auto-download feature "+
			"(planned) or manually place JRE in %s",
		version,
		must(config.JavaDir(version)),
	)
}

// must panics on error — only used for error messages where the dir is already known valid.
func must(s string, err error) string {
	if err != nil {
		panic(err)
	}
	return s
}