Gradle script creating a changelog out of git commit messages

changelog.gradle

buildscript {
	repositories {
		maven {
			url "https://plugins.gradle.org/m2/"
		}
	}

	dependencies {
		classpath "org.ajoberstar:grgit:+"
	}
}

import org.ajoberstar.grgit.*

task generateChangelog {
	doLast {
		def grgit = Grgit.open(dir: '.')
		def fileChangelog = new File('CHANGELOG.md')
		def excludeCommitters = ['Jenkins']
		def skipEmptyVersion = true

		// if we build a release we do not need to look at the HEAD (only until the tag which is built)
		def tags = (project.version.endsWith('-SNAPSHOT')) ? ["HEAD"] : []
		grgit.tag.list().reverse().each{ t ->
			tags += t.getName()
		}
		fileChangelog.delete()

		def builder
		def commits
		def numTags = tags.size()
		for (int i = 0; i < numTags; ++i) {
			if (tags[i+1] == null) {
				commits = grgit.log(includes: [tags[i]])
			} else {
				commits = grgit.log {
					range tags[i+1], tags[i];
				}
			}

			commits = commits.grep { commit -> 
				!excludeCommitters*.toLowerCase().contains(commit.committer.name.toLowerCase())
			}

			if (skipEmptyVersion && commits.isEmpty()) {
				continue
			}

			builder = new StringBuilder()
			builder.append("Version ${tags[i]}:\n".replaceAll('Version HEAD', 'Upcoming version'))
			def tagLength = builder.size() - 1 // -1 because of newline character
			for (int j = 0; j < tagLength; ++j) {
				builder.append('-')
			}
			builder.append('\n')

			commits.inject(builder) { bldr, commit ->
				bldr.append('  - ')
				bldr.append(commit.shortMessage.trim().replaceAll('  ', ' '))
				bldr.append(' (' + commit.committer.name + ')')
				bldr.append('\n')
			}
			builder.append('\n')
		    fileChangelog << builder.toString()
		}
	}
}

task commitChangelog(dependsOn: [generateChangelog]) {
	doLast {
		def fileChangelog = new File('CHANGELOG.md')
		def grgit = Grgit.open(dir: '.')
		def status = grgit.status();
		def staged = status.staged
		def unstaged = status.unstaged

		def allChanges = staged.added + staged.modified + staged.removed + unstaged.added + unstaged.modified + unstaged.removed
		if (allChanges.contains(fileChangelog.name)) {
			println "Commiting $fileChangelog.name"

			def msgCommit = (project.version.endsWith('-SNAPSHOT')) ? 'Updating changelog' : "Releasing new version ${project.version}"
			grgit.add(patterns: [fileChangelog.name])
			grgit.commit(message: msgCommit, amend: false)
		}
	}
}