package http

import (
	"bytes"
	"embed"
	"errors"
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"net/http"
	"net/url"
	"path/filepath"
	"strings"

	"dev.mediocregopher.com/mediocre-blog.git/src/http/apiutil"
	"dev.mediocregopher.com/mediocre-blog.git/src/post"
	"dev.mediocregopher.com/mediocre-blog.git/src/render"
)

//go:embed tpl
var tplFS embed.FS

func mustReadTplFile(fileName string) string {
	path := filepath.Join("tpl", fileName)

	b, err := fs.ReadFile(tplFS, path)
	if err != nil {
		panic(fmt.Errorf("reading file %q from tplFS: %w", path, err))
	}

	return string(b)
}

func (a *api) blogURL(base *url.URL, path string, abs bool) string {
	// filepath.Join strips trailing slash, but we want to keep it
	trailingSlash := strings.HasSuffix(path, "/")

	path = filepath.Join("/", base.Path, path)

	if trailingSlash && path != "/" {
		path += "/"
	}

	if !abs {
		return path
	}

	u := *base
	u.Path = path
	return u.String()
}

func (a *api) postURL(id string, abs bool) string {
	path := filepath.Join("posts", id)
	return a.blogURL(a.params.PublicURL, path, abs)
}

func (a *api) editPostURL(id string, abs bool) string {
	return a.postURL(id, abs) + "?method=edit"
}

func (a *api) managePostsURL(abs bool) string {
	return a.blogURL(a.params.PublicURL, "posts?method=manage", abs)
}

func (a *api) manageAssetsURL(abs bool) string {
	return a.blogURL(a.params.PublicURL, "assets?method=manage", abs)
}

func (a *api) assetURL(id string, abs bool) string {
	path := filepath.Join("assets", id)
	return a.blogURL(a.params.PublicURL, path, false)
}

func (a *api) draftPostURL(id string, abs bool) string {
	path := filepath.Join("drafts", id)
	return a.blogURL(a.params.PublicURL, path, abs)
}

func (a *api) editDraftPostURL(id string, abs bool) string {
	return a.draftPostURL(id, abs) + "?method=edit"
}

func (a *api) manageDraftPostsURL(abs bool) string {
	return a.blogURL(a.params.PublicURL, "drafts", abs) + "?method=manage"
}

func (a *api) draftsURL(abs bool) string {
	return a.blogURL(a.params.PublicURL, "drafts", abs)
}

func mustParseTpl(tpl *template.Template, name string) *template.Template {
	return template.Must(tpl.New(name).Parse(mustReadTplFile(name)))
}

func (a *api) mustParseBasedTpl(name string) *template.Template {
	tpl := template.New("")
	tpl = mustParseTpl(tpl, "gemini-cta.html")
	tpl = mustParseTpl(tpl, "base.html")
	tpl = mustParseTpl(tpl, name)
	return tpl
}

type tplData struct {
	*render.Methods
	Payload interface{}
	Title   string
}

// WithTitlePrefix returns a copy of tplData but with the given string prefixed
// to the page title. This is intended for use within templates, when nesting
// the base template.
func (d tplData) WithTitlePrefix(prefix string) tplData {
	d.Title = prefix + " - " + d.Title
	return d
}

func (a *api) newTPLData(r *http.Request, payload interface{}) tplData {
	return tplData{
		Methods: render.NewMethods(
			r.Context(),
			r.URL,
			a.params.PublicURL,
			a.params.PublicURL, // httpURL
			a.params.GeminiPublicURL,
			a.params.GeminiGatewayURL,
			a.params.PostStore,
			a.params.PostAssetStore,
			a.params.PostDraftStore,
			a.postPreprocessFuncs(),
		),
		Payload: payload,
		Title:   "mediocregopher's lil web corner",
	}
}

// executeTemplate expects to be the final action in an http.Handler
func (a *api) executeTemplate(
	rw http.ResponseWriter,
	r *http.Request,
	tpl *template.Template,
	payload interface{},
) {

	tplData := a.newTPLData(r, payload)

	buf := new(bytes.Buffer)

	err := tpl.Execute(buf, tplData)
	if errors.Is(err, post.ErrPostNotFound) {
		http.Error(rw, "Post not found", 404)
		return
	} else if err != nil {
		apiutil.InternalServerError(
			rw, r, fmt.Errorf("rendering template: %w", err),
		)
		return
	}

	io.Copy(rw, buf)
}

func (a *api) executeRedirectTpl(
	rw http.ResponseWriter, r *http.Request, url string,
) {
	a.executeTemplate(rw, r, a.redirectTpl, struct {
		URL string
	}{
		URL: url,
	})
}

func (a *api) renderDumbTplHandler(tplName string) http.Handler {

	tpl := a.mustParseBasedTpl(tplName)

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		tplData := a.newTPLData(r, nil)

		if err := tpl.Execute(rw, tplData); err != nil {
			apiutil.InternalServerError(
				rw, r, fmt.Errorf("rendering %q: %w", tplName, err),
			)
			return
		}
	})
}