package cn.home1.oss.lib.common.msginterpolate;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   import org.springframework.context.expression.MapAccessor;
   import org.springframework.expression.EvaluationContext;
   import org.springframework.expression.Expression;
   import org.springframework.expression.ExpressionException;
   import org.springframework.expression.ExpressionParser;
  import org.springframework.expression.common.TemplateParserContext;
  import org.springframework.expression.spel.standard.SpelExpressionParser;
  import org.springframework.expression.spel.support.StandardEvaluationContext;
  import org.springframework.util.Assert;
  
  import java.util.Map;
  
  /**
   * Implementation of the {@link MessageInterpolator} that uses the Spring Expression Language (SpEL)
   * to evaluate expressions inside a template message.
   *
   * <p>
   * SpEL expressions are delimited by {@code #{} and {@code }}. The provided variables are accessible
   * directly by name.
   * </p>
   */
  public class SpelMessageInterpolator implements MessageInterpolator {
  
    private static final Logger log = LoggerFactory.getLogger(SpelMessageInterpolator.class);
  
    private final EvaluationContext evalContext;
  
    /**
     * Creates a new instance with a custom {@link EvaluationContext}.
     *
     * @param evalContext evalContext
     */
    public SpelMessageInterpolator(final EvaluationContext evalContext) {
      Assert.notNull(evalContext, "EvaluationContext must not be null");
      this.evalContext = evalContext;
    }
  
    /**
     * Creates a new instance with {@link StandardEvaluationContext} including
     * {@link org.springframework.expression.spel.support.ReflectivePropertyAccessor
     * ReflectivePropertyAccessor} and {@link MapAccessor}.
     */
    public SpelMessageInterpolator() {
      final StandardEvaluationContext ctx = new StandardEvaluationContext();
      ctx.addPropertyAccessor(new MapAccessor());
      this.evalContext = ctx;
    }
  
    @Override
    public String interpolate(final String template, final Map<String, Object> variables) {
      Assert.notNull(template, "messageTemplate must not be null");
  
      String result;
      try {
        final Expression expression = parser().parseExpression(template, new TemplateParserContext());
        result = expression.getValue(this.evalContext, variables, String.class);
      } catch (final ExpressionException ex) {
        result = "Failed to interpolate message template, error: " + ex.getMessage(); // TODO test this
        log.warn("Failed to interpolate message template: {}, variables: {}", template, variables, ex);
      }
      return result;
    }
  
    ExpressionParser parser() {
      return new SpelExpressionParser();
    }
  }