public class DispatcherServlet extends HttpServlet {

    private Properties contextConfig = new Properties();

    private List<String> classNames = new ArrayList<>();

    private Map<String, Object> ioc = new HashMap<>();

    private Map<String,Method> handlerMapping = new HashMap<>();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //執行階段，根據使用者請求的URL進行自動分發和排程
        try {
            doDispatch(req,resp);
        } catch (Exception e) {
            e.printStackTrace();
            resp.getWriter().write("500 Detail:" + Arrays.toString(e.getStackTrace()));
        }
    }

    private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        if(this.handlerMapping.isEmpty()){
            return;
        }
        //絕對路徑
        String url  = req.getRequestURI();
        //處理成相對路徑
        String contextPath = req.getContextPath();
        url = url.replace(contextPath, "").replaceAll("/+", "/");
        if(!this.handlerMapping.containsKey(url)){
            resp.getWriter().write("404 Not found");
            return;
        }

        Method method = this.handlerMapping.get(url);
        //如何拿到例項？
        //唯一的方式從IOC容器中拿
        //繼續投機取巧
        String beanName =  lowerFirstCase(method.getDeclaringClass().getSimpleName());
        System.out.println("beanName:" + beanName);
        Map<String,String[]> params = req.getParameterMap();

        method.invoke(ioc.get(beanName), new Object[]{req, resp,params.get("name")[0]});


       // System.out.println(method);
    }


    @Override
    public void init(ServletConfig config) throws ServletException {
        //1、載入配置檔案
        doLoadConfig(config.getInitParameter("contextConfigLocation"));

        //2. 掃描所有相關的類
        doScanner(contextConfig.getProperty("scanPackage"));

        //3.初始化剛剛掃描到所有相關的類，並且把它儲存在IOC容器中
        doInstance();

        //4. 實現依賴注入 DI 自動賦值
        doAutowired();

        //5. 初始化handlerMapping
        initHandleMapping();

        System.out.println("Spring is init");
    }

    private void initHandleMapping() {
        if(ioc.isEmpty()){
            return;
        }

        for(Map.Entry<String, Object> entry: ioc.entrySet()) {
            Class<?> clazz = entry.getValue().getClass();
            if(!clazz.isAnnotationPresent(Controller.class)){
                continue;
            }

            String baseUrl = "";
            if(clazz.isAnnotationPresent(RequestMapping.class)){
                RequestMapping requestMapping = clazz.getAnnotation(RequestMapping.class);
                baseUrl =  requestMapping.value();
            }

            Method[] methods = clazz.getMethods(); //只認public的方法
            for(Method method : methods){
                if(!method.isAnnotationPresent(RequestMapping.class)){
                    continue;
                }
                RequestMapping requestMapping =  method.getAnnotation(RequestMapping.class);
               String url = ("/" + baseUrl + "/" + requestMapping.value()).replaceAll("/+", "/");
                handlerMapping.put(url,method);
                System.out.println("Mapped:" + url +"," + method);
            }

            Field[] fields = entry.getValue().getClass().getDeclaredFields();
            for (Field field : fields) {
                if (!field.isAnnotationPresent(Autowired.class)) {
                    continue;
                }
            }
        }
    }

    private void doAutowired() {
        if(ioc.isEmpty()){
            return;
        }

        for(Map.Entry<String, Object> entry: ioc.entrySet()){
           Field[] fields = entry.getValue().getClass().getDeclaredFields();
           for(Field field: fields){
               if(!field.isAnnotationPresent(Autowired.class)){
                   continue;
               }

              Autowired autowired =  field.getAnnotation(Autowired.class);
              String beanName = autowired.value().trim();
              if("".equals(beanName)){
                  beanName = field.getType().getName();
              }

              field.setAccessible(true); //強制暴力訪問
               try {
                   field.set(entry.getValue(), ioc.get(beanName));
               } catch (IllegalAccessException e) {
                   e.printStackTrace();
                   continue;
               }

           }
        }
    }

    private void doInstance() {
        if(classNames.isEmpty()){
            return;
        }

        try{
            for (String className: classNames) {
               Class<?> clazz =  Class.forName(className);
               //例項化，把例項化的物件儲存到IOC容器之中

                if(clazz.isAnnotationPresent(Controller.class)){
                    Object instance = clazz.newInstance();
                    String beanName = lowerFirstCase(clazz.getSimpleName());
                    ioc.put(beanName, instance);
                } else if(clazz.isAnnotationPresent(Service.class)){
                    //因為Service有可能注入的不是它本身，有可能是它的實現類
                    //1、預設類名首字母小寫

                    //2、自定義的beanName
                    Service service = clazz.getAnnotation(Service.class);
                    String beanName = service.value();
                    if("".equals(beanName)){
                         beanName = lowerFirstCase(clazz.getSimpleName());
                    }
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);

                    //3、如果是介面，投機取巧的方式，用它的介面型別作為key
                    Class<?>[] interfaces = clazz.getInterfaces();
                    for(Class<?> i : interfaces){
                        if(ioc.containsKey(i.getName())){
                            throw  new Exception("The beanName is exists");
                        }
                        ioc.put(i.getName(), instance);
                    }

                }else{
                    continue;
                }

            }
        }catch (Exception e){
            e.printStackTrace();
        }

    }

    /**
     * 類名首字母小寫
     */
    private String lowerFirstCase(String simpleName) {
        char[] chars = simpleName.toCharArray();
        chars[0] += 32;
        return  String.valueOf(chars);
    }

    private void doScanner(String scanPackage) {
        URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.", "/"));
        File classDir = new File(url.getFile());
        for(File file : classDir.listFiles()){
            if(file.isDirectory()){
                doScanner(scanPackage + "." + file.getName());
            }else{
                if(file.getName().endsWith(".class")){
                    String classname = (scanPackage + "." +file.getName()).replace(".class","");
                    classNames.add(classname);
                }
            }
        }
    }

    private void doLoadConfig(String contextConfigLocation) {
        InputStream is = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
        try {
            contextConfig.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(is != null){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}