todogo/main.go

package main

import (
	"embed"
	"html/template"
	"io"
	"log"
	"math/rand"
	"net/http"
	"strconv"
)

//go:embed views/*.html
var tmplFS embed.FS

//go:embed public/*
var publicFS embed.FS

type Template struct {
	templates *template.Template
}

func New() *Template {
	templates := template.Must(template.New("").ParseFS(tmplFS, "views/*.html"))

	return &Template{
		templates: templates,
	}
}

func (t *Template) Render(w io.Writer, name string, data any) error {
	tmpl := template.Must(t.templates.Clone())
	tmpl = template.Must(tmpl.ParseFS(tmplFS, "views/"+name))
	return tmpl.ExecuteTemplate(w, "layout.html", data)
}

type Todo struct {
	Id        string
	Title     string
	Completed bool
}

type ViewModel struct {
	Todos      []Todo
	Only       string
	Incomplete int
}

func filterSlice[T any](xs []T, pred func(T) bool) []T {
	result := make([]T, 0, len(xs))
	for _, element := range xs {
		if pred(element) {
			result = append(result, element)
		}

	}

	return result
}

func countSlice[T any](xs []T, pred func(T) bool) int {
	count := 0
	for _, element := range xs {
		if pred(element) {
			count += 1
		}
	}

	return count
}

func main() {
	todos := make([]Todo, 0, 10)

	t := New()
	http.Handle("/public/", http.FileServer(http.FS(publicFS)))
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		q := r.URL.Query()
		renderTodos := todos
		only := q.Get("only")

		if only == "active" {
			renderTodos = filterSlice(todos, func(todo Todo) bool { return !todo.Completed })
		}

		if only == "completed" {
			renderTodos = filterSlice(todos, func(todo Todo) bool { return todo.Completed })
		}

		incomplete := countSlice(todos, func(todo Todo) bool { return !todo.Completed })

		vm := ViewModel{
			Todos:      renderTodos,
			Only:       only,
			Incomplete: incomplete,
		}
		err := t.Render(w, "list.html", vm)
		if err != nil {
			log.Println(err)
		}
	})
	http.HandleFunc("/todo", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != "POST" {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}

		if err := r.ParseForm(); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		title := r.Form.Get("title")
		todos = append(todos, Todo{
			Id:    strconv.Itoa(rand.Int()),
			Title: title,
		})

		w.Header().Set("Location", "/")
		w.WriteHeader(http.StatusSeeOther)
	})

	http.HandleFunc("/toggle", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != "POST" {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}

		if err := r.ParseForm(); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		id := r.Form.Get("id")
		for i, todo := range todos {
			if todo.Id == id {
				todo.Completed = !todo.Completed
				todos[i] = todo
			}
		}

		w.Header().Set("Location", "/")
		w.WriteHeader(http.StatusSeeOther)
	})

	http.HandleFunc("/destroy", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != "POST" {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}

		if err := r.ParseForm(); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		id := r.Form.Get("id")
		todos = filterSlice(todos, func(t Todo) bool { return t.Id != id })

		w.Header().Set("Location", "/")
		w.WriteHeader(http.StatusSeeOther)
	})

	http.HandleFunc("/clear", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != "POST" {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}

		if err := r.ParseForm(); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		todos = filterSlice(todos, func(t Todo) bool { return !t.Completed })

		w.Header().Set("Location", "/")
		w.WriteHeader(http.StatusSeeOther)
	})

	log.Print("Running on 8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}