// Copyright 2018-2019 Martin Riedl
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package gohttprouter

import (
	"fmt"
	"net/http"
	"strings"
)

// Router is the main struct for the whole routing logic.
type Router struct {
	registry map[string]*route
}

// RouteHandler is the function construct called by this framework.
type RouteHandler func(http.ResponseWriter, *http.Request, RoutingInfo)

// RoutingInfo is returned for each web server method call and includes details abount the execution.
type RoutingInfo struct {
	Parameters map[string]string
}

// Handler interface that must be implemented by custom structs.
type Handler interface {
	ServeHTTP(http.ResponseWriter, *http.Request, RoutingInfo)
}

type defaultHandler struct {
	Func RouteHandler
}

func (handler defaultHandler) ServeHTTP(response http.ResponseWriter, request *http.Request, routingInfo RoutingInfo) {
	handler.Func(response, request, routingInfo)
}

// New creates a new router instance.
func New() *Router {
	return &Router{
		registry: make(map[string]*route),
	}
}

// Handle registers a new handler using method and path for execution.
func (router *Router) Handle(method string, path string, handler Handler) error {
	return router.addRoute(method, path, handler)
}

// HandleFunc registers a new handler function using method and path for execution.
func (router *Router) HandleFunc(method string, path string, handler RouteHandler) error {
	newHandler := defaultHandler{Func: handler}
	return router.addRoute(method, path, newHandler)
}

func (router *Router) addRoute(method string, path string, handler Handler) error {
	if err := router.validateRoute(path); err != nil {
		return err
	}

	// parse path and set new handler
	route, created, _ := router.findRoute(method, path, true)
	if !created {
		return fmt.Errorf("there is already a handler registered for the path %s", path)
	}
	route.handler = handler
	return nil
}

func (router *Router) findRoute(method string, path string, create bool) (route *route, created bool, parameter map[string]string) {
	methodUpper := strings.ToUpper(method)

	// add method, if not already existing
	methodRoute, ok := router.registry[methodUpper]
	if !ok && !create {
		return nil, false, nil
	} else if !ok && create {
		methodRoute = newRoute()
		router.registry[methodUpper] = methodRoute
		created = true
	}

	// parse path and set new handler
	route, pathCreated, parameter := methodRoute.parsePath(path, create)
	created = created || pathCreated
	return
}

func (router *Router) validateRoute(path string) error {
	// path must start with a slash
	if strings.Index(path, "/") != 0 {
		return fmt.Errorf("URL path must start with a slash (/)")
	}

	// path must not end with a slash
	if len(path) > 1 && path[len(path)-1] == '/' {
		return fmt.Errorf("URL path must not end with a slash (/)")
	}

	return nil
}

func (router *Router) ServeHTTP(response http.ResponseWriter, request *http.Request) {
	// check for exact matching
	route, _, parameter := router.findRoute(request.Method, request.URL.Path, false)
	if route != nil && route.handler != nil {
		route.handler.ServeHTTP(response, request, RoutingInfo{Parameters: parameter})
		return
	}

	// nothing found
	http.NotFound(response, request)
}

// Must is a wrapper that panics if an error was returned.
func Must(err error) {
	if err != nil {
		panic(err)
	}
}