pipeline {
    agent any

    environment {
        REGISTRY = 'registry.example.com/docker-images'
    }

    stages {
        stage('Detect changed images') {
            steps {
                script {
                    def base = env.CHANGE_TARGET ? "origin/${env.CHANGE_TARGET}" : "HEAD~1"

                    // returnStdout gives a String. Trim, split, and FORCE to a List.
                    def diffOutput = sh(
                        script: "git diff --name-only ${base} HEAD || true",
                        returnStdout: true
                    ).trim()

                    // 'as List' avoids the non-serializable String[] array
                    def changedFiles = diffOutput ? (diffOutput.split('\n') as List) : []

                    // Build a plain List of unique top-level dirs (Strings only)
                    def candidates = []
                    for (String f : changedFiles) {
                        def top = f.split('/')[0]
                        if (top && !candidates.contains(top)) {
                            candidates.add(top)
                        }
                    }

                    // fileExists is a pipeline STEP, so it must stay in CPS land
                    // (i.e. a normal for-loop, NOT inside @NonCPS or a findAll closure)
                    def toBuild = []
                    for (String dir : candidates) {
                        if (fileExists("${dir}/Dockerfile")) {
                            toBuild.add(dir)
                        }
                    }

                    // Store only a plain String in env
                    env.IMAGES_TO_BUILD = toBuild.join(',')
                    echo "Images to build: ${env.IMAGES_TO_BUILD ?: '(none)'}"
                }
            }
        }
        stage('Build & push') {
            when { expression { env.IMAGES_TO_BUILD } }
            steps {
                script {
                    def shortSha = env.GIT_COMMIT.take(8)
                    env.IMAGES_TO_BUILD.split(',').each { img ->
                        def tag = "${REGISTRY}/${img}"
                        sh """
                            docker build \
                              --label org.opencontainers.image.source=${env.GIT_URL} \
                              --label org.opencontainers.image.revision=${env.GIT_COMMIT} \
                              -t ${tag}:${shortSha} \
                              ${img}/
                        """
                        if (env.BRANCH_NAME == 'main') {
                            sh """
                                docker tag ${tag}:${shortSha} ${tag}:latest
                                docker push ${tag}:${shortSha}
                                docker push ${tag}:latest
                            """
                        }
                    }
                }
            }
        }
    }
}