ConfigLoader.java

package com.demcha.compose;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
import lombok.extern.slf4j.Slf4j;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

@Slf4j
public final class ConfigLoader {


    private ConfigLoader() {
    }

    /**
     * Load YAML or JSON from a classpath resource into the given class.
     * Supports running from IDE and from a fat JAR.
     * Optionally resolves {@code ${ENV}} or {@code ${ENV:default}} placeholders
     * from environment variables.
     *
     * <p><strong>Optional dependency:</strong> the YAML path requires
     * {@code com.fasterxml.jackson.dataformat:jackson-dataformat-yaml} on
     * the classpath. GraphCompose declares it as an optional Maven
     * dependency since {@code v1.6.7}; applications that load YAML
     * configs through this helper must add the artifact to their own
     * build. JSON configs work without it.
     *
     * @throws java.lang.NoClassDefFoundError if {@code fileName} ends with
     *         {@code .yaml} / {@code .yml} and
     *         {@code jackson-dataformat-yaml} is not on the classpath.
     */
    public static <T> T loadConfigWithEnv(String fileName, Class<T> clazz, boolean resolveEnv) {
        log.info("Initializing variables from '{}'", fileName);
        ObjectMapper mapper;
        if (fileName == null || fileName.isBlank()) throw new RuntimeException("fileName can`t be null or blank");

        if (fileName.endsWith("yaml") || fileName.endsWith("yml")) {
            mapper = new ObjectMapper(new YAMLFactory());
        } else {
            mapper = new ObjectMapper();

        }

        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        if (cl == null) cl = ConfigLoader.class.getClassLoader();

        URL resource = cl.getResource(fileName);
        if (resource == null) {
            throw new IllegalArgumentException("Config resource not found on classpath: " + fileName + "Url: " + resource);
        }
        log.info("Reading config from '{}'", resource);

        String raw;
        try (InputStream is = resource.openStream();
             BufferedReader br = new BufferedReader(new InputStreamReader(is, StandardCharsets.UTF_8))) {

            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null) sb.append(line).append('\n');
            raw = sb.toString();
        } catch (Exception e) {
            log.error("Failed to read config '{}': {}", fileName, e.toString(), e);
            throw new RuntimeException("Failed to read config: " + fileName, e);
        }

        String resolved = resolveEnv ? replaceEnvVariables(raw) : raw;


        log.info("Creating a config YAML object '{}'", clazz.getSimpleName());
        try {
            log.info("Parsing config '{}'", fileName);
          return   mapper.readValue(resolved, clazz);
        } catch (JsonProcessingException e) {
            log.error("Failed to parse config '{}': {}", fileName, e.toString(), e);
            throw new RuntimeException( "Failed to parse config: " + fileName, e);
        }
    }

    /**
     * Replace ${ENV} or ${ENV:default} with values from SystemECS.getenv().
     * Unknown vars without default → empty string.
     */
    private static String replaceEnvVariables(String text) {
        // ${VAR} or ${VAR:default value}
        Pattern p = Pattern.compile("\\$\\{([A-Za-z_][A-Za-z0-9_]*) (?:: ([^}]*))?\\}", Pattern.COMMENTS);
        Matcher m = p.matcher(text);
        StringBuffer out = new StringBuffer();

        while (m.find()) {
            String var = m.group(1);
            String def = m.group(2); // may be null
            String val = System.getenv(var);
            if (val == null) val = (def != null ? def : "");
            // Escape backslashes and dollars for appendReplacement
            m.appendReplacement(out, Matcher.quoteReplacement(val));
        }
        m.appendTail(out);
        return out.toString();
    }
}