package web

import (
	"context"
	"log"
	"net/http"
	"regexp"
	"time"
)

// CoverFetcher retrieves one kagane cover by image id. Satisfied by
// latest.BrowserFetcher, and nil when BROWSER_WS_URL is unset — which leaves
// kagane covers exactly as unavailable as they were before this endpoint
// existed, rather than hanging a request on a fetcher that cannot run.
type CoverFetcher interface {
	Image(ctx context.Context, imageID string) (body []byte, contentType string, err error)
}

// coverIDRe matches the request path segment that becomes part of an outbound
// URL. The proxy is session-gated, but the id still reaches a headless browser,
// so it is validated at the boundary rather than passed through.
var coverIDRe = regexp.MustCompile(`^[0-9a-f-]{36}$`)

// coverTypes is the set of content types the proxy will echo back. A response
// header sourced from a third party is not repeated verbatim: anything outside
// this set is treated as "not a cover".
var coverTypes = map[string]bool{
	"image/webp": true,
	"image/jpeg": true,
	"image/png":  true,
	"image/avif": true,
	"image/gif":  true,
}

// coverTimeout bounds one proxied cover. Shorter than the fetcher's own
// challenge budget on purpose: a browser page is waiting on this, and a cover
// that has not arrived by now is better left as a broken slot than as a request
// holding a connection open.
const coverTimeout = 20 * time.Second

// kaganeCover serves a kagane cover from the backend's own origin.
//
// kagane answers image requests with a Cloudflare challenge and
// `cross-origin-resource-policy: same-origin`, so the web UI cannot render one
// directly under any combination of referrer policy or crossorigin attribute
// (verified 2026-08-08). Fetching it through the headless browser that already
// clears the challenge, and re-serving it here, is what puts the bytes on an
// origin the page may load from.
func (h *Handler) kaganeCover(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if !coverIDRe.MatchString(id) {
		http.NotFound(w, r)
		return
	}
	if body, contentType, ok, err := h.store.GetKaganeCover(id); err != nil {
		log.Printf("read kagane cover %s: %v", id, err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	} else if ok {
		writeCover(w, body, contentType)
		return
	}
	if h.covers == nil {
		http.NotFound(w, r)
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), coverTimeout)
	defer cancel()
	body, contentType, err := h.covers.Image(ctx, id)
	if err != nil {
		log.Printf("kagane cover %s: %v", id, err)
		http.NotFound(w, r)
		return
	}
	if !coverTypes[contentType] {
		log.Printf("kagane cover %s: unexpected content type %q", id, contentType)
		http.NotFound(w, r)
		return
	}
	if err := h.store.PutKaganeCover(id, body, contentType); err != nil {
		log.Printf("persist kagane cover %s: %v", id, err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	writeCover(w, body, contentType)
}

// writeCover sends the bytes with a long cache life: an image id names one
// immutable rendering, so a client that has it never needs to ask again.
func writeCover(w http.ResponseWriter, body []byte, contentType string) {
	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Cache-Control", "private, max-age=604800, immutable")
	w.Write(body)
}