Various improvements

- Turn replace and interpolate into properties
- Add environment variable methods for command steps
- Add skip option for command steps
- Add some doc comments

build.gradle

@@ -43,7 +43,7 @@ publishing {
 }
 
 tasks.create('pipeline', UploadPipeline) {
-    replace true
+    replace = true
 
     commandStep {
         label ':junit: Unit tests'
@@ -57,7 +57,7 @@ tasks.create('pipeline', UploadPipeline) {
 
     commandStep {
         label ':maven: Publish JARs'
-        command './gradlew publish --continue ${GRADLE_SWITCHES}'
+        command './gradlew publish --continue $${GRADLE_SWITCHES}'
         branch '*.*.*'
         agentQueue 'builder'
         dockerComposeContainer 'gradle'

buildSrc/src/main/groovy/com/widen/plugins/UploadPipeline.groovy

@@ -6,35 +6,46 @@ import org.gradle.api.tasks.TaskAction
 
 import java.nio.file.Files
 
+/**
+ * A Gradle task that allows you to define a Buildkite pipeline dynamically and then upload it during a build.
+ */
 class UploadPipeline extends DefaultTask {
-    private boolean interpolation = true
-    private boolean replace = false
-    private steps = []
-
-    void replace(boolean replace) {
-        this.replace = replace
-    }
-
-    String k8s(String environment, String region) {
-        if (environment == 'stage' && region == 'us-east-1') {
-            return '***REMOVED***'
-        }
-        return "***REMOVED***"
-    }
-
+    private final List steps = []
+
+    /**
+     * Enable or disable variable interpolation on upload.
+     */
+    boolean interpolate = true
+
+    /**
+     * Replace the rest of the existing pipeline with the steps uploaded. Jobs that are already running are not removed.
+     */
+    boolean replace = false
+
+    /**
+     * Add a <a href="https://buildkite.com/docs/pipelines/command-step">command step</a> to the pipeline.
+     *
+     * @param closure
+     */
     void commandStep(@DelegatesTo(CommandStep) Closure closure) {
         def step = new CommandStep()
         closure = closure.rehydrate(step, this, this)
         closure.resolveStrategy = Closure.OWNER_FIRST
         closure()
-
         steps << step.model
     }
 
+    /**
+     * Add a <a href="https://buildkite.com/docs/pipelines/wait-step">wait step</a> to the pipeline.
+     */
     void waitStep() {
         steps << 'wait'
     }
 
+    /**
+     * Add a <a href="https://buildkite.com/docs/pipelines/wait-step">wait step</a> to the pipeline that continues on
+     * failure.
+     */
     void waitStepContinueOnFailure() {
         steps << [
             wait: [
@@ -43,18 +54,40 @@ class UploadPipeline extends DefaultTask {
         ]
     }
 
+    /**
+     * Helper method to return the correct Widen Kubernetes cluster endpoint for a given environment and region.
+     *
+     * @param environment
+     * @param region
+     * @return
+     */
+    String k8s(String environment, String region) {
+        if (environment == 'stage' && region == 'us-east-1') {
+            return '***REMOVED***'
+        }
+        return "***REMOVED***"
+    }
+
+    /**
+     * Get the JSON representation of the pipeline.
+     *
+     * @return A JSON string.
+     */
     String toJson() {
         return JsonOutput.toJson([
             steps: steps
         ])
     }
 
+    /**
+     * Upload the pipeline to Buildkite to be executed.
+     */
     @TaskAction
     void upload() {
         if (System.env.BUILDKITE || System.env.CI) {
             def cmd = ['buildkite-agent', 'pipeline', 'upload']
 
-            if (!interpolation) {
+            if (!interpolate) {
                 cmd << '--no-interpolation'
             }
 
@@ -75,26 +108,34 @@ class UploadPipeline extends DefaultTask {
         }
     }
 
-    class Step {
-        protected Map model = [:]
-
+    /**
+     * Base class for Buildkite step types.
+     */
+    abstract class Step {
+        protected final Map model = [:]
+
+        /**
+         * Sets the label that will be displayed in the pipeline visualisation in Buildkite.
+         *
+         * @param label
+         */
         void label(String label) {
             model.label = label
         }
 
+        /**
+         * The branch pattern defining which branches will include this step in their builds.
+         *
+         * @param branch
+         */
         void branch(String branch) {
             model.branches = branch
         }
-
-        void agentQueue(String name) {
-            model.get('agents', [:]).queue = name
-        }
-
-        void agentQueue(String name, String region) {
-            agentQueue(region == 'us-east-1' ? name : "$name-$region")
-        }
     }
 
+    /**
+     * Configuration for a Buildkite command step.
+     */
     class CommandStep extends Step {
         void command(String command) {
             model.command = command
@@ -108,6 +149,32 @@ class UploadPipeline extends DefaultTask {
             model.get('artifact_paths', []) << path
         }
 
+        void agentQueue(String name) {
+            model.get('agents', [:]).queue = name
+        }
+
+        void agentQueue(String name, String region) {
+            agentQueue(region == 'us-east-1' ? name : "$name-$region")
+        }
+
+        void environment(String name, String value) {
+            model.get('env', [:]).put(name, value)
+        }
+
+        void environment(Map<String, String> variables) {
+            variables.each { name, value ->
+                environment(name, value)
+            }
+        }
+
+        void skip() {
+            model.skip = true
+        }
+
+        void skip(String reason) {
+            model.skip = reason
+        }
+
         void plugin(String name, Object config) {
             model.get('plugins', []) << [
                 (name): config