nomux.go

// inspired by https://blog.merovius.de/2017/06/18/how-not-to-use-an-http-router.html
package main

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

func GETRoot(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Root")
}

func GETTag(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Tag")
}

func GETCustomers(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Customers")
}

func GETCustomer(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Customer %d", c.CustId)
}

func GETOrders(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Orders for Customer %d", c.CustId)
}

func GETOrder(w http.ResponseWriter, r *http.Request, c *Context) {
	fmt.Fprintf(w, "GET Order %d for Customer %d", c.OrderId, c.CustId)
}

type Path struct {
	Parts []string
	Index int
}

func (p *Path) Next() (next string) {
	if !p.Done() {
		next = p.Parts[p.Index]
		p.Index++
	}
	return
}

func (p *Path) This() (this string) {
	if p.Index > 0 {
		this = p.Parts[p.Index-1]
	}
	return
}

func (p *Path) Done() bool {
	return p.Index == len(p.Parts)
}

type Handler func(w http.ResponseWriter, r *http.Request, c *Context)

type Endpoint struct {
	GET    Handler
	POST   Handler
	PUT    Handler
	DELETE Handler
}

func Dispatch(w http.ResponseWriter, r *http.Request, c *Context, e *Endpoint) {
	var h Handler
	switch r.Method {
	case "GET":
		h = e.GET
	case "POST":
		h = e.POST
	case "PUT":
		h = e.PUT
	case "DELETE":
		h = e.DELETE
	}
	if h != nil {
		h(w, r, c) // middleware here
	} else {
		http.Error(w, "Not Allowed", http.StatusMethodNotAllowed)
	}
}

type Context struct {
	CustId  int
	OrderId int
}

func Route(w http.ResponseWriter, r *http.Request) {
	pth := Path{strings.Split(strings.Trim(path.Clean(r.URL.Path), "/"), "/"), 0}
	cxt := Context{}
	switch pth.Next() {
	case "":
		Dispatch(w, r, &cxt, &Endpoint{GET: GETRoot})
	case "tag":
		Dispatch(w, r, &cxt, &Endpoint{GET: GETTag})
	case "customers":
		switch pth.Next() {
		case "":
			Dispatch(w, r, &cxt, &Endpoint{GET: GETCustomers})
		default:
			i, err := strconv.Atoi(pth.This())
			if err != nil {
				goto notfound
			}
			cxt.CustId = i
			switch pth.Next() {
			case "":
				Dispatch(w, r, &cxt, &Endpoint{GET: GETCustomer})
			case "orders":
				switch pth.Next() {
				case "":
					Dispatch(w, r, &cxt, &Endpoint{GET: GETOrders})
				default:
					i, err = strconv.Atoi(pth.This())
					if err != nil {
						goto notfound
					}
					cxt.OrderId = i
					Dispatch(w, r, &cxt, &Endpoint{GET: GETOrder})
				}
			}
		}
	}
	return
notfound:
	http.Error(w, "Not Found", http.StatusNotFound)
}

type API struct{}

func (a *API) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	Route(w, r)
}

func main() {
	http.ListenAndServe(":8000", &API{})
}