🚧 Start work on executing openssl commands

src/main/java/de/mlessmann/certassist/ExecutableResolver.java

@@ -0,0 +1,55 @@
+package de.mlessmann.certassist;
+
+import de.mlessmann.certassist.except.UnresolvableCLIDependency;
+import lombok.Setter;
+import org.slf4j.Logger;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Objects;
+import java.util.Optional;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+@Service
+public class ExecutableResolver {
+
+    private static final Logger LOGGER = getLogger(ExecutableResolver.class);
+
+    @Value("${openssl.path:#{null}}")
+    private String opensslPath;
+
+    public String getOpenSSLPath() throws UnresolvableCLIDependency {
+        if (opensslPath == null) {
+            LOGGER.atDebug().log("No openssl path configured, falling back to resolving by shell.");
+            var optSSLPath = searchCommandFromPath("openssl");
+            opensslPath = optSSLPath.orElseThrow(() -> new UnresolvableCLIDependency("openssl", "openssl.path"));
+        }
+
+        Path configuredPath = new File(opensslPath).toPath();
+        if (!Files.isRegularFile(configuredPath)) {
+            throw new UnresolvableCLIDependency("openssl", "openssl.path");
+        }
+
+        return opensslPath;
+    }
+
+    private Optional<String> searchCommandFromPath(String executableName) {
+        String envPath = System.getenv("PATH");
+        Objects.requireNonNull(envPath, "Environment variable 'PATH' is not set?!");
+        String[] pathEntries = envPath.split(File.pathSeparator);
+
+        for (String pathEntry : pathEntries) {
+            Path executablePath = Path.of(pathEntry, executableName);
+            if (Files.isRegularFile(executablePath) && Files.isExecutable(executablePath)) {
+                return Optional.of(executablePath.toString());
+            }
+        }
+
+        LOGGER.error("Could not find executable '{}' in PATH. Make sure that it exists on the of the directory and is executable.", executableName);
+        return Optional.empty();
+    }
+}