package io.apicurio.registry.maven;
   
   import org.apache.maven.plugin.AbstractMojo;
   import org.apache.maven.plugin.MojoExecutionException;
   import org.apache.maven.plugin.MojoFailureException;
   import org.apache.maven.plugins.annotations.Mojo;
   import org.apache.maven.plugins.annotations.Parameter;
   
   import java.io.File;
  import java.io.FileReader;
  import java.io.FileWriter;
  import java.io.Reader;
  import java.util.List;
  import java.util.Properties;
  
  @Mojo(name = "merge")
  public class MergePropertiesMojo extends AbstractMojo {
  
      /**
       * The output file location.  This is where the merged properties file will be written.
       */
      @Parameter(required = true)
      File output;
  
      /**
       * A set of input files, each one should be a valid .properties file.
       */
      @Parameter(required = true)
      List<File> inputs;
  
      /**
       * Set to 'true' if the input files should be deleted after the merge.
       */
      @Parameter(required = false, defaultValue = "false")
      Boolean deleteInputs;
  
      /**
       * @see org.apache.maven.plugin.Mojo#execute()
       */
      @Override
      public void execute() throws MojoExecutionException, MojoFailureException {
          if (output == null || !output.getParentFile().isDirectory() || output.isDirectory()) {
              throw new MojoExecutionException("Invalid 'output' file.");
          }
          if (inputs == null || inputs.isEmpty()) {
              throw new MojoExecutionException("Invalid 'inputs'.  Must be a collection of input files.");
          }
  
          Properties mergedProps = new Properties();
          // Read all the input properties files
          getLog().info("Reading " + inputs.size() + " input files.");
          for (File input : inputs) {
              if (!input.isFile()) {
                  throw new MojoExecutionException("Invalid input file: " + input.getAbsolutePath());
              }
              Properties inputProps = new Properties();
              try (Reader reader = new FileReader(input)) {
                  inputProps.load(reader);
                  mergedProps.putAll(inputProps);
                  getLog().info("Read all properties from input file: " + input.getName());
              } catch (Throwable t) {
                  throw new MojoExecutionException("Failed to load input file: " + input.getAbsolutePath(), t);
              }
              if (deleteInputs) {
                  input.delete();
                  getLog().info("Deleted input file: " + input.getName());
              }
          }
  
          // Write out the merged properties to the output file.
          if (output.isFile()) {
              output.delete();
          }
          try (FileWriter writer = new FileWriter(output)) {
              mergedProps.store(writer, "Properties merged by 'apicurio-registry-maven-plugin'");
              getLog().info("Merged properties written to: " + output.getName());
          } catch (Throwable t) {
              throw new MojoExecutionException(
                      "Failed to write merged properties to: " + output.getAbsolutePath());
          }
      }
  
  }