henwen/http/server.go

package main

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"io"
	"log"
	"math/big"
	"net/http"
	"time"

	h "gitlab.codemonkeysoftware.net/b/hatmill"
	a "gitlab.codemonkeysoftware.net/b/hatmill/attribute"
	e "gitlab.codemonkeysoftware.net/b/hatmill/element"
	"gitlab.codemonkeysoftware.net/b/henwen"
	_ "gitlab.codemonkeysoftware.net/b/henwen"
)

const Addr = ":8080"
const Title = "Henwen"
const baseURL = "http://localhost:8080"
const dbFileName = "./henwen.db"

const (
	PathRoot     = "/"
	PathCreate   = "/create"
	PathDoCreate = "/create/do"
)

var store *henwen.Store

func writePage(w io.Writer, contents h.Term) error {
	page := e.Html()(
		e.Head()(
			e.Title()(h.Text(Title)),
		),
		e.Body()(
			e.H1()(h.Text(Title)),
			e.Div()(contents),
		),
	)
	_, err := h.WriteDocument(w, page)
	return err
}

func pageRoot() h.Term {
	return h.Terms{
		e.H2()(h.Text("Welcome!")),
		e.A(a.Href(PathCreate))(
			h.Text("Create event"),
		),
	}
}

const (
	fieldNameEarliest  = "earliestDate"
	fieldNameLatest    = "latestDate"
	fieldNameEventName = "eventName"
)

func pageCreate() h.Term {
	return h.Terms{
		e.H2()(h.Text("Create an event")),
		e.Form(a.Action(PathDoCreate), a.Method("POST"))(
			e.Label(a.For(fieldNameEventName))(h.Text("Event name")),
			e.Input(a.Name(fieldNameEventName)),

			e.Label(a.For(fieldNameEarliest))(h.Text("Earliest date")),
			e.Input(a.Name(fieldNameEarliest), a.Type("date")),

			e.Label(a.For(fieldNameLatest))(h.Text("Latest date")),
			e.Input(a.Name(fieldNameLatest), a.Type("date")),

			e.Input(a.Type("submit")),
		),
	}
}

func makeAdminURL(eventID, adminCode string) string {
	return fmt.Sprintf("%s/%s/admin/%s", baseURL, eventID, adminCode)
}

func pageDoCreate(name string, earliest, latest time.Time) h.Term {
	id, err := genString()
	if err != nil {
		return h.Text(err.Error())
	}
	adminCode, err := genString()
	if err != nil {
		return h.Text(err.Error())
	}
	adminURL := makeAdminURL(id, adminCode)

	return h.Terms{
		e.H2()(h.Text("Created event!")),
		e.P()(
			h.Text("You can find it again at "),
			e.A(a.Href(adminURL))(h.Text(adminURL)),
			h.Text("."),
		),

		e.H3()(h.Text("Name")),
		h.Text(name),

		e.H3()(h.Text("Earliest date")),
		h.Text(earliest.Format(time.ANSIC)),

		e.H3()(h.Text("Latest date")),
		h.Text(latest.Format(time.ANSIC)),
	}
}

var chars = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")

func genString() (string, error) {
	const length = 10
	charsLength := big.NewInt(int64(len(chars)))
	var maxN big.Int
	maxN.Exp(charsLength, big.NewInt(length), nil)
	n, err := rand.Int(rand.Reader, &maxN)
	if err != nil {
		return "", err
	}

	var buf bytes.Buffer
	for n.Cmp(&big.Int{}) == 1 {
		var charIdx big.Int
		n.DivMod(n, charsLength, &charIdx)
		_ = buf.WriteByte(chars[charIdx.Int64()])
	}
	return buf.String(), nil
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc(PathRoot, func(w http.ResponseWriter, r *http.Request) {
		_ = writePage(w, pageRoot())
	})
	mux.HandleFunc(PathCreate, func(w http.ResponseWriter, r *http.Request) {
		_ = writePage(w, pageCreate())
	})
	mux.HandleFunc(PathDoCreate, func(w http.ResponseWriter, r *http.Request) {
		const dateFmt = "2006-01-02"
		earliest, err := time.Parse(dateFmt, r.FormValue(fieldNameEarliest))
		if err != nil {
			fmt.Fprint(w, "bad earliest date")
			return
		}
		latest, err := time.Parse(dateFmt, r.FormValue(fieldNameLatest))
		if err != nil {
			fmt.Fprint(w, "bad latest date")
			return
		}
		eventName := r.FormValue(fieldNameEventName)
		if eventName == "" {
			fmt.Fprint(w, "event name is required")
			return
		}

		_ = writePage(w, pageDoCreate(eventName, earliest, latest))
	})

	srv := http.Server{
		Addr:    Addr,
		Handler: mux,
	}
	log.Println(srv.ListenAndServe())
}