package http

import (
	"bytes"
	"embed"
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"log/slog"
	"net"
	"net/http"
	"os"
	"path/filepath"

	_ "embed"

	"github.com/dschmidt/go-layerfs"
	"github.com/pkg/errors"
)

//go:embed templates
var embeddedTemplates embed.FS

//go:embed assets
var embeddedAssets embed.FS

type Server struct {
	http      *http.Server
	opts      *Options
	templates template.Template
}

var templateFuncs = template.FuncMap{
	"humanSize": func(b float64) string {
		const unit = 1000
		if b < unit {
			return fmt.Sprintf("%d B", int64(b))
		}

		div, exp := int64(unit), 0

		for n := b / unit; n >= unit; n /= unit {
			div *= unit
			exp++
		}

		return fmt.Sprintf("%.1f %cB",
			float64(b)/float64(div), "kMGTPE"[exp])
	},
}

func (s *Server) serveHomepage(w http.ResponseWriter, r *http.Request) {
	stats, err := s.opts.Stats.Snapshot()
	if err != nil {
		slog.Error("could not make stats snapshot", slog.Any("error", errors.WithStack(err)))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	data := struct {
		TemplateData
		Stats map[string]float64
	}{
		TemplateData: *s.opts.TemplateData,
		Stats:        stats,
	}

	s.opts.Stats.Add(StatTotalPageView, 1, 0)

	s.renderTemplate(w, "index", data)
}

func (s *Server) Serve(l net.Listener) error {
	templatesFilesystem, err := s.getCustomizedFilesystem(embeddedTemplates)
	if err != nil {
		return errors.WithStack(err)
	}

	if err := s.parseTemplates(templatesFilesystem); err != nil {
		return errors.WithStack(err)
	}

	assetsFilesystem, err := s.getCustomizedFilesystem(embeddedAssets)
	if err != nil {
		return errors.WithStack(err)
	}

	mux := http.NewServeMux()

	mux.Handle("/assets/", http.FileServer(http.FS(assetsFilesystem)))
	mux.HandleFunc("/", s.serveHomepage)

	httpServer := &http.Server{
		Handler: mux,
	}

	s.http = httpServer

	if err := s.http.Serve(l); err != nil {
		return errors.WithStack(err)
	}

	return nil
}

func (s *Server) parseTemplates(fs fs.FS) error {
	templates, err := template.New("").Funcs(templateFuncs).ParseFS(fs, "templates/*.html")
	if err != nil {
		return errors.WithStack(err)
	}

	s.templates = *templates

	return nil
}

func (s *Server) renderTemplate(w http.ResponseWriter, name string, data any) {
	var buff bytes.Buffer

	if err := s.templates.ExecuteTemplate(&buff, name, data); err != nil {
		s.log("[ERROR] %+s", errors.WithStack(err))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}

	if _, err := io.Copy(w, &buff); err != nil {
		s.log("[ERROR] %+s", errors.WithStack(err))
	}
}

func (s *Server) log(message string, args ...any) {
	s.opts.Logger(message, args...)
}

func (s *Server) getCustomizedFilesystem(base fs.FS) (fs.FS, error) {
	filesystems := []fs.FS{}

	if s.opts.CustomDir != "" {
		absPath, err := filepath.Abs(s.opts.CustomDir)
		if err != nil {
			return nil, errors.WithStack(err)
		}

		filesystems = append(filesystems, os.DirFS(absPath))
	}

	filesystems = append(filesystems, base)

	return layerfs.New(filesystems...), nil
}

func NewServer(funcs ...OptionFunc) *Server {
	opts := DefaultOptions()
	for _, fn := range funcs {
		fn(opts)
	}

	return &Server{
		opts: opts,
	}
}