// SPDX-FileCopyrightText: 2021 Luke Granger-Brown <depot@lukegb.com>
//
// SPDX-License-Identifier: Apache-2.0

package fuphttp

import (
	"context"
	"fmt"
	"io/fs"
	"net/http"

	"github.com/google/safehtml"
	"github.com/google/safehtml/template"
	"github.com/google/safehtml/template/uncheckedconversions"
	shuncheckedconversions "github.com/google/safehtml/uncheckedconversions"
	"github.com/gorilla/mux"
	"hg.lukegb.com/lukegb/depot/web/fup/hashfs"
)

type Config struct {
	Templates  fs.FS
	Static     fs.FS
	StaticRoot safehtml.TrustedResourceURL
}

type Application struct {
	indexTmpl    *template.Template
	notFoundTmpl *template.Template
}

func (a *Application) Handler() http.Handler {
	r := mux.NewRouter()

	r.NotFoundHandler = http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
		rw.WriteHeader(http.StatusNotFound)
		a.notFoundTmpl.Execute(rw, nil)
	})

	return r
}

func parseTemplate(t *template.Template, fsys fs.FS, name string) (*template.Template, error) {
	bs, err := fs.ReadFile(fsys, name)
	if err != nil {
		return nil, fmt.Errorf("reading template %q: %w", name, err)
	}

	return t.ParseFromTrustedTemplate(
		uncheckedconversions.TrustedTemplateFromStringKnownToSatisfyTypeContract(string(bs)),
	)
}

func loadTemplate(fsys fs.FS, name string, funcs template.FuncMap) (*template.Template, error) {
	t := template.New(name).Funcs(funcs)
	var err error
	if t, err = parseTemplate(t, fsys, "base.html"); err != nil {
		return nil, fmt.Errorf("loading base template: %w", err)
	}
	if t, err = parseTemplate(t, fsys, fmt.Sprintf("%s.html", name)); err != nil {
		return nil, fmt.Errorf("loading leaf template: %w", err)
	}
	return t, nil
}

func New(ctx context.Context, cfg *Config) (*Application, error) {
	a := new(Application)

	tmpls := []struct {
		t    **template.Template
		name string
	}{
		{&a.indexTmpl, "index"},
		{&a.notFoundTmpl, "404"},
	}

	funcMap := template.FuncMap{
		"static": func(s string) safehtml.TrustedResourceURL {
			staticPath := s
			if fs, ok := cfg.Static.(*hashfs.FS); ok {
				sp, ok := fs.LookupHashedName(staticPath)
				if ok {
					staticPath = sp
				} else {
					log.Printf("warning: couldn't find static file %v", staticPath)
				}
			}
			return shuncheckedconversions.TrustedResourceURLFromStringKnownToSatisfyTypeContract(cfg.StaticRoot.String() + staticPath)
		},
	}

	for _, tmpl := range tmpls {
		t, err := loadTemplate(cfg.Templates, tmpl.name, funcMap)
		if err != nil {
			return nil, fmt.Errorf("loading template %q: %w", tmpl.name, err)
		}
		*tmpl.t = t
	}

	return a, nil
}