Allow project-specific CommentCreator taking into account the existing header

README.md

@@ -117,6 +117,27 @@ To override the configuration for Scala/Java files or add a configuration for so
 headerMappings := headerMappings.value + (HeaderFileType.scala -> HeaderCommentStyle.cppStyleLineComment)
 ```
 
+#### Custom comment creators
+
+You can customize how content gets created by providing your own
+`CommentCreator`. For example, this would be a (crude) way to preserve the
+copyright year in existing headers but still update the rest:
+
+    CommentStyle.cStyleBlockComment.copy(commentCreator = new CommentCreator() {
+      val Pattern = "(?s).*?(\\d{4}(-\\d{4})?).*".r
+      def findYear(header: String): Option[String] = header match {
+       case Pattern(years, _) => Some(years)
+        case _                 => None
+      }
+      override def apply(text: String, existingText: Option[String]): String = {
+        val newText = CommentStyle.cStyleBlockComment.commentCreator.apply(text, existingText)
+        existingText
+          .flatMap(findYear)
+          .map(year => newText.replace("2017", year))
+          .getOrElse(newText)
+      }
+    })
+
 ### Excluding files
 
 To exclude some files, use the [sbt's file filters](http://www.scala-sbt.org/0.13/docs/Howto-Customizing-Paths.html#Include%2Fexclude+files+in+the+source+directory):

src/main/scala/de/heikoseeberger/sbtheader/CommentStyle.scala

@@ -27,15 +27,23 @@ import scala.util.matching.Regex
   */
 final case class CommentStyle(commentCreator: CommentCreator, pattern: Regex) {
 
+  def apply(licenseText: String, existingHeader: Option[String]): String =
+    commentCreator(licenseText, existingHeader) + newLine + newLine
+
+  def apply(license: License, existingHeader: Option[String]): String =
+    apply(license.text, existingHeader)
+
   def apply(licenseText: String): String =
-    commentCreator(licenseText) + newLine + newLine
+    apply(licenseText, None)
 
   def apply(license: License): String =
     apply(license.text)
 }
 
-sealed trait CommentCreator {
-  def apply(text: String): String
+trait CommentCreator {
+  def apply(text: String, existingText: Option[String] = None): String
+
+  def apply(text: String): String = apply(text, None)
 }
 
 object CommentStyle {
@@ -60,7 +68,7 @@ object CommentStyle {
 
 object TwirlStyleFramedBlockCommentCreator extends CommentCreator {
 
-  def apply(text: String): String = {
+  def apply(text: String, existingText: Option[String]): String = {
     val maxLineLength = text.lines.map(_.length).max
 
     def fillLine(line: String) =
@@ -80,7 +88,7 @@ object TwirlStyleFramedBlockCommentCreator extends CommentCreator {
 
 final class LineCommentCreator(linePrefix: String) extends CommentCreator {
 
-  override def apply(text: String): String = {
+  override def apply(text: String, existingText: Option[String]): String = {
     def prependWithLinePrefix(s: String) =
       s match {
         case ""   => if (!linePrefix.trim.isEmpty) linePrefix else ""
@@ -96,10 +104,10 @@ final class CommentBlockCreator(blockPrefix: String, linePrefix: String, blockSu
 
   private val lineCommentCreator = new LineCommentCreator(linePrefix)
 
-  def apply(text: String): String =
+  def apply(text: String, existingText: Option[String]): String =
     blockPrefix + newLine + lineCommentCreator(text) + newLine + blockSuffix
 }
 
 object IdentityCommentCreator extends CommentCreator {
-  override def apply(text: String) = text
+  override def apply(text: String, existingText: Option[String]) = text
 }

src/main/scala/de/heikoseeberger/sbtheader/HeaderCreator.scala

@@ -38,7 +38,6 @@ final class HeaderCreator private (fileType: FileType,
 
   private val crlf          = """(?s)(?:.*)(\r\n)(?:.*)""".r
   private val cr            = """(?s)(?:.*)(\r)(?:.*)""".r
-  private val headerText    = commentStyle(license)
   private val headerPattern = commentStyle.pattern
 
   private val (firstLine, text) = {
@@ -67,21 +66,26 @@ final class HeaderCreator private (fileType: FileType,
       case _       => "\n"
     }
 
-  private val headerNewLine =
-    headerText match {
-      case crlf(_) => "\r\n"
-      case cr(_)   => "\r"
-      case _       => "\n"
-    }
-
-  private val newHeaderText = headerText.replace(headerNewLine, fileNewLine)
+  private def newHeaderText(existingHeader: Option[String]) = {
+    val headerText = commentStyle(license, existingHeader)
+    val headerNewLine =
+      headerText match {
+        case crlf(_) => "\r\n"
+        case cr(_)   => "\r"
+        case _       => "\n"
+      }
+    headerText.replace(headerNewLine, fileNewLine)
+  }
 
   private val modifiedText =
     text match {
-      case headerPattern(`headerText`, _) => None
-      case headerPattern(_, body)         => Some(firstLine + newHeaderText + body)
-      case body if body.isEmpty           => None
-      case body                           => Some(firstLine + newHeaderText + body.replaceAll("""^\s+""", "")) // Trim left
+      case headerPattern(existingText, body) =>
+        val newText = newHeaderText(Some(existingText))
+        if (newText == existingText) None
+        else Some(firstLine + newText + body.replaceAll("""^\s+""", "")) // Trim left
+      case body if body.isEmpty => None
+      case body =>
+        Some(firstLine + newHeaderText(None) + body.replaceAll("""^\s+""", "")) // Trim left
     }
   log.debug(s"Modified text of file is:$newLine$modifiedText")
 

src/test/scala/de/heikoseeberger/sbtheader/HeaderCreatorSpec.scala

@@ -179,12 +179,51 @@ final class HeaderCreatorSpec extends WordSpec with Matchers {
         )
       }
     }
+
+    "given a file with an existing copyright year" should {
+      val yearPreservingStyle =
+        CommentStyle.cStyleBlockComment.copy(commentCreator = new CommentCreator() {
+          val Pattern = "(?s).*?(\\d{4}(-\\d{4})?).*".r
+          def findYear(header: String): Option[String] = header match {
+            case Pattern(years, _) => Some(years)
+            case _                 => None
+          }
+          override def apply(text: String, existingText: Option[String]): String = {
+            val newText = CommentStyle.cStyleBlockComment.commentCreator.apply(text, existingText)
+            existingText
+              .flatMap(findYear)
+              .map(year => newText.replace("2017", year))
+              .getOrElse(newText)
+          }
+        })
+      val licenseText = "Copyright 2017 MyCorp, Inc <https://mycorp.com>"
+
+      "allow updating the header retaining the copyright year" in {
+        val fileContent = """/*
+        | * Copyright 2016 MyCorp http://mycorp.com
+        | */
+        |This is the file content
+        |""".stripMargin
+
+        createHeader(fileContent, licenseText, commentCreator = yearPreservingStyle) shouldBe Some(
+          """/*
+          | * Copyright 2016 MyCorp, Inc <https://mycorp.com>
+          | */
+          |
+          |This is the file content
+          |""".stripMargin
+        )
+      }
+    }
   }
 
-  private def createHeader(fileContent: String, header: String, fileType: FileType = FileType.sh) =
+  private def createHeader(fileContent: String,
+                           header: String,
+                           fileType: FileType = FileType.sh,
+                           commentCreator: CommentStyle = hashLineComment) =
     HeaderCreator(
       fileType,
-      hashLineComment,
+      commentCreator,
       Custom(header),
       new StubLogger,
       new ByteArrayInputStream(fileContent.getBytes)