@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ApiVersion {

  /**
   * 版本。x.y.z格式
   *
   * @return
   */
  String value() default "1.0.0";
}

/**
 * 是否開啟API版本控制
 */
@Target(ElementType.TYPE)
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Import(ApiAutoConfiguration.class)
public @interface EnableApiVersion {
}

@Data
public class ApiItem implements Comparable<ApiItem> {
  private int high = 1;

  private int mid = 0;

  private int low = 0;

  public static final ApiItem API_ITEM_DEFAULT = ApiConverter.convert(ApiVersionConstant.DEFAULT_VERSION);

  public ApiItem() {
  }

  @Override
  public int compareTo(ApiItem right) {
    if (this.getHigh() > right.getHigh()) {
      return 1;
    } else if (this.getHigh() < right.getHigh()) {
      return -1;
    }

    if (this.getMid() > right.getMid()) {
      return 1;
    } else if (this.getMid() < right.getMid()) {
      return -1;
    }
    if (this.getLow() > right.getLow()) {
      return 1;
    } else if (this.getLow() < right.getLow()) {
      return -1;
    }
    
    return 0;
  }

}

public class ApiConverter {

  public static ApiItem convert(String api) {
    ApiItem apiItem = new ApiItem();
    if (StringUtils.isBlank(api)) {
      return apiItem;
    }

    String[] cells = StringUtils.split(api, ".");
    apiItem.setHigh(Integer.parseInt(cells[0]));
    if (cells.length > 1) {
      apiItem.setMid(Integer.parseInt(cells[1]));
    }

    if (cells.length > 2) {
      apiItem.setLow(Integer.parseInt(cells[2]));
    }
    
    return apiItem;
  }

}

public class ApiVersionConstant {
  /**
   * header 指定版本號請求頭
   */
  public static final String API_VERSION = "x-api-version";

  /**
   * 默認版本號
   */
  public static final String DEFAULT_VERSION = "1.0.0";
}

public interface RequestCondition<T> {

 /**
 * 方法和類上都存在相同的條件時的處理方法
 */
 T combine(T other);

 /**
 * 判斷是否符合當前請求，返回null表示不符合
 */
 @Nullable
 T getMatchingCondition(HttpServletRequest request);

 /**
 *如果存在多個符合條件的接口，則會根據(jù)這個來排序，然后用集合的第一個元素來處理
 */
 int compareTo(T other, HttpServletRequest request);

@Slf4j
public class ApiCondition implements RequestCondition<ApiCondition> {

  public static ApiCondition empty = new ApiCondition(ApiConverter.convert(ApiVersionConstant.DEFAULT_VERSION));

  private ApiItem version;

  private boolean NULL;

  public ApiCondition(ApiItem item) {
    this.version = item;
  }

  public ApiCondition(ApiItem item, boolean NULL) {
    this.version = item;
    this.NULL = NULL;
  }

  /**
   * <pre>
   *   Spring先掃描方法再掃描類，然后調(diào)用{@link #combine}
   *   按照方法上的注解優(yōu)先級大于類上注解的原則處理，但是要注意如果方法上不定義注解的情況。
   *   如果方法或者類上不定義注解，我們會給一個默認的值{@code empty},{@link ApiHandlerMapping}
   * </pre>
   * @param other 方法掃描封裝結果
   * @return
   */
  @Override
  public ApiCondition combine(ApiCondition other) {
    // 選擇版本最大的接口
    if (other.NULL) {
      return this;
    }
    return other;
  }

  @Override
  public ApiCondition getMatchingCondition(HttpServletRequest request) {
    if (CorsUtils.isPreFlightRequest(request)) {
      return empty;
    }
    String version = request.getHeader(ApiVersionConstant.API_VERSION);
    // 獲取所有小于等于版本的接口;如果前端不指定版本號，則默認請求1.0.0版本的接口
    if (StringUtils.isBlank(version)) {
      log.warn("未指定版本，使用默認1.0.0版本。");
      version = ApiVersionConstant.DEFAULT_VERSION;
    }
    ApiItem item = ApiConverter.convert(version);
    if (item.compareTo(ApiItem.API_ITEM_DEFAULT) < 0) {
      throw new IllegalArgumentException(String.format("API版本[%s]錯誤，最低版本[%s]", version, ApiVersionConstant.DEFAULT_VERSION));
    }
    if (item.compareTo(this.version) >= 0) {
      return this;
    }
    return null;
  }

  @Override
  public int compareTo(ApiCondition other, HttpServletRequest request) {
    // 獲取到多個符合條件的接口后，會按照這個排序，然后get(0)獲取最大版本對應的接口.自定義條件會最后比較
    int compare = other.version.compareTo(this.version);
    if (compare == 0) {
      log.warn("RequestMappingInfo相同，請檢查！version:{}", other.version);
    }
    return compare;
  }

}

public class ApiHandlerMapping extends RequestMappingHandlerMapping {
  @Override
  protected RequestCondition<?> getCustomTypeCondition(Class<?> handlerType) {
    return buildFrom(AnnotationUtils.findAnnotation(handlerType, ApiVersion.class));
  }

  @Override
  protected RequestCondition<?> getCustomMethodCondition(Method method) {
    return buildFrom(AnnotationUtils.findAnnotation(method, ApiVersion.class));
  }

  private ApiCondition buildFrom(ApiVersion platform) {
    return platform == null ? getDefaultCondition() :
        new ApiCondition(ApiConverter.convert(platform.value()));
  }

  private ApiCondition getDefaultCondition(){
    return new ApiCondition(ApiConverter.convert(ApiVersionConstant.DEFAULT_VERSION),true);
  }
}

public class ApiAutoConfiguration implements WebMvcRegistrations {

  @Override
  public RequestMappingHandlerMapping getRequestMappingHandlerMapping() {
    return new ApiHandlerMapping();
  }

}