ADD download functionality

src/main/java/com/ddf/vodsystem/services/DownloadService.java

@@ -0,0 +1,38 @@
+package com.ddf.vodsystem.services;
+
+import com.ddf.vodsystem.entities.JobStatus;
+import com.ddf.vodsystem.exceptions.JobNotFinished;
+import com.ddf.vodsystem.exceptions.JobNotFound;
+import com.ddf.vodsystem.tools.Job;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
+import org.springframework.stereotype.Service;
+
+import java.io.File;
+
+@Service
+public class DownloadService {
+
+    private final JobService jobService;
+
+    @Autowired
+    public DownloadService(JobService jobService) {
+        this.jobService = jobService;
+    }
+
+    public Resource download(String uuid) {
+        Job job = jobService.get(uuid);
+
+        if (job == null) {
+            throw new JobNotFound("Job doesn't exist");
+        }
+
+        if (job.getStatus() != JobStatus.FINISHED) {
+            throw new JobNotFinished("Job is not finished");
+        }
+
+        File file = job.getOutputFile();
+        return new FileSystemResource(file);
+    }
+}