package staticimages

import (
	"io"
	"io/fs"
	"net/http"
	"os"
	"path"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
)

const cacheControl = "public, max-age=31536000, immutable"
const svgContentSecurityPolicy = "default-src 'none'; style-src 'unsafe-inline'; sandbox"
const fallbackContentType = "application/octet-stream"

var contentTypeExtensions = map[string]string{
	".png":  "image/png",
	".jpeg": "image/jpeg",
	".webp": "image/webp",
	".svg":  "image/svg+xml",
}

type Handler struct {
	uploadDir fs.FS
	modTime   time.Time
}

func NewHandler(uploadDir string) *Handler {
	return &Handler{
		uploadDir: os.DirFS(uploadDir),
		modTime:   time.Now(),
	}
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("X-Content-Type-Options", "nosniff")

	cleaned := cleanPath(requestedPath(r))
	file, stat, ok := h.openFile(cleaned)
	if !ok {
		http.NotFound(w, r)
		return
	}
	defer file.Close()

	content, ok := file.(io.ReadSeeker)
	if !ok {
		http.Error(w, "File not seekable", http.StatusInternalServerError)
		return
	}

	contentType := contentTypeFor(cleaned)
	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Cache-Control", cacheControl)
	if contentType == "image/svg+xml" {
		w.Header().Set("Content-Security-Policy", svgContentSecurityPolicy)
	}

	http.ServeContent(w, r, cleaned, stat.ModTime(), content)
}

func requestedPath(r *http.Request) string {
	if rctx := chi.RouteContext(r.Context()); rctx != nil && rctx.RoutePath != "" {
		return rctx.RoutePath
	}
	return r.URL.Path
}

func cleanPath(p string) string {
	return strings.TrimPrefix(path.Clean("/"+p), "/")
}

func (h *Handler) openFile(p string) (fs.File, fs.FileInfo, bool) {
	if p == "" || p == "." {
		return nil, nil, false
	}
	file, err := h.uploadDir.Open(p)
	if err != nil {
		return nil, nil, false
	}
	stat, err := file.Stat()
	if err != nil || stat.IsDir() {
		file.Close()
		return nil, nil, false
	}
	return file, stat, true
}

func contentTypeFor(p string) string {
	ext := path.Ext(p)
	if contentType, ok := contentTypeExtensions[ext]; ok {
		return contentType
	}
	return fallbackContentType
}