package router

import (
  "net/http"
  "html/template"
  "regexp"
  "log"
  "strconv"
  "strings"
  "path"
  "os"
  "errors"
  "context"
)

type Router struct {
  /* This is the template for error pages */
  Fallback template.Template
  /* Routes are only filled by using the appropriate methods. */
  routes []Route
  /* StaticPaths can be filled from outside when constructing the Router.
   * key = uri
   * value = file path
   */
  StaticPaths map[string]string
}

type Route struct {
  path *regexp.Regexp
  handlerMap map[string]http.Handler
}

/* This represents what the server should do with a given request. */
type ServerTask struct {
  /* template and apiFmt are mutually exclusive. */
  template *template.Template
  apiFmt string

  /* doWork represents serverside work to fulfill the request.
   * This function can be composed any way you see fit when creating
   * a route.
   */
  doWork func(http.ResponseWriter, *http.Request)
}

func (self *Router) Get(path string, h http.Handler) {
  self.AddRoute("GET", path, h)
}

func (self *Router) Post(path string, h http.Handler) {
  self.AddRoute("POST", path, h)
}

func (self *Router) Put(path string,  h http.Handler) {
  self.AddRoute("PUT", path, h)
}

func (self *Router) Delete(path string, h http.Handler) {
  self.AddRoute("DELETE", path, h)
}

func (self *Router) AddRoute(method string, path string, h http.Handler) {

  exactPath := regexp.MustCompile("^" + path + "$")

  /* If the route already exists, try to add this method to the ServerTask map. */
  for _, r := range self.routes {
    if r.path == exactPath {
      r.handlerMap[method] = h
      return
    }
  }

  /* Otherwise add a new route */
  self.routes = append(self.routes, Route{
    path: exactPath,
    handlerMap: map[string]http.Handler{method: h},
  })

}

func (self *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
  /* Show the 500 error page if we panic */
  defer func() {
    if r := recover(); r != nil {
      log.Println("ERROR:", r)
      self.ErrorPage(w, req, 500, "There was an error on the server.")
    }
  }()

  /* If the request matches any our StaticPaths, try to serve a file. */
  for uri, dir := range self.StaticPaths {
    if req.Method == "GET" && strings.HasPrefix(req.URL.Path, uri) {
      restOfUri := strings.TrimPrefix(req.URL.Path, uri)
      p := path.Join(dir, restOfUri)
      p = path.Clean(p)

      /* If the file exists, try to serve it. */
      info, err := os.Stat(p);
      if err == nil && !info.IsDir() {
        http.ServeFile(w, req, p)
      /* Handle the common errors */
      } else if errors.Is(err, os.ErrNotExist) || errors.Is(err, os.ErrExist) {
        self.ErrorPage(w, req, 404, "The requested file does not exist")
      } else if errors.Is(err, os.ErrPermission) || info.IsDir() {
        self.ErrorPage(w, req, 403, "Access forbidden")
      /* If it's some weird error, serve a 500. */
      } else {
        self.ErrorPage(w, req, 500, "Internal server error")
      }

      return
    }
  }

  /* Otherwise, this is a normal route */
  for _, r := range self.routes {

    /* Pull the params out of the regex;
     * If the path doesn't match the regex, params will be nil.
     */
    params := r.Match(req)
    if params == nil {
      continue
    }
    for method, handler := range r.handlerMap {
      if method == req.Method {
        /* Parse the form and add the params to the context */
        req.ParseForm()
        ProcessParams(req, params)
        /* handle the request! */
        handler.ServeHTTP(w, req);
        return
      }
    }
  }
  self.ErrorPage(w, req, 404, "The page you requested does not exist!")
}

/*******************
 * Utility Methods *
 *******************/

func ProcessParams(req *http.Request, params map[string]string) {
  *req = *req.WithContext(context.WithValue(req.Context(), "params", params))
}

func (self *Route) Match(r *http.Request) map[string]string {
  match := self.path.FindStringSubmatch(r.URL.Path)
  if match == nil {
    return nil
  }

  params := map[string]string{}
  groupNames := self.path.SubexpNames()

  for i, group := range match {
    params[groupNames[i]] = group
  }

  return params
}

func (self *Router) ErrorPage(w http.ResponseWriter, req *http.Request, code int, errMsg string) {
  w.WriteHeader(code)
  params := map[string]string{
    "ErrorCode": strconv.Itoa(code),
    "ErrorMessage": errMsg,
  }
  ProcessParams(req, params)
  self.Fallback.Execute(w, req)
}