Getting there

src/main/java/eu/simstadt/regionchooser/RegionChooserCommandLineInterface.java

 package eu.simstadt.regionchooser;
 
-import java.io.BufferedWriter;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.List;
+import java.nio.file.Paths;
 import java.util.Scanner;
 import java.util.concurrent.Callable;
 import picocli.CommandLine;
@@ -16,7 +16,7 @@ class RegionChooserCommandLineInterface implements Callable<Integer>
 {
 	@Option(names = { "-i",
 			"--input" }, required = true, split = ",", description = "Citygml files to extract from", paramLabel = "input.gml")
-	List<Path> citygmls;
+	Path[] citygmls;
 
 	@Option(names = { "-o",
 			"--output" }, required = true, description = "Output file", paramLabel = "output.gml")
@@ -25,40 +25,43 @@ class RegionChooserCommandLineInterface implements Callable<Integer>
 	@Option(names = { "-e", "--epsg" }, description = "EPSG id for coordinate reference system", paramLabel = "31467")
 	Integer espgId;
 
+	//TODO: Add possibility to choose wgs84 or local_crs
+
 	@Option(names = { "-w",
 			"--wkt" }, description = "File containing WKT polygon, or - for stdin", paramLabel = "polygon.wkt")
 	String wktFile = "-";
 
 	@Override
-	public Integer call() throws Exception { // your business logic goes here...
-		System.out.println("Should extract from :");
-		for (Path input_citygml : citygmls) {
-			System.out.println("  " + input_citygml);
-		}
-		System.out.print("And write to : ");
-		System.out.println(outputCityGML);
-		try (BufferedWriter bf = Files.newBufferedWriter(outputCityGML)) {
-			bf.write("HELLO THERE!");
-		}
+	public Integer call() throws Exception {
+		String srsName;
+
 		if (espgId == null) {
-			System.out.println("coordinates from " + citygmls.get(0));
+			srsName = RegionChooserUtils.crsFromCityGMLHeader(citygmls[0]).toString();
 		} else {
-			System.out.print("in EPSG:");
-			System.out.println(espgId + " coordinates.");
+			srsName = "EPSG:" + espgId;
 		}
 
+		String wktPolygon = "unknown";
+
 		if (wktFile.equals("-")) {
 			if (System.in.available() == 0) {
-				System.out.println("OH NOEs, NO INPUT!");
+				throw new IllegalArgumentException("Please provide \"POLYGON((x1 y1, x2 y2, ...))\" to standard input.");
 			} else {
-				System.out.println("Here's standard input:");
-				System.out.println(getInput());
-				System.out.println("Done");
+				wktPolygon = getInput();
 			}
 		} else {
-			System.out.println("Try to read from " + wktFile);
+			wktPolygon = new String(Files.readAllBytes(Paths.get(wktFile)), StandardCharsets.UTF_8);
+			if (wktPolygon.isEmpty()) {
+				throw new IllegalArgumentException("Please write \"POLYGON((x1 y1, x2 y2, ...))\" inside " + wktFile);
+			}
 		}
 
+		System.out.println("WKT Polygon : " + wktPolygon);
+
+		StringBuilder sb = RegionExtractor.selectRegionDirectlyFromCityGML(wktPolygon, srsName, citygmls);
+
+		RegionChooserUtils.writeStringBuilderToFile(sb, outputCityGML);
+
 		return 0;
 	}