// Package web maps requests to bundles and writes bytes. It knows content and render, and exposes
// neither to them.
package web

import (
	"log/slog"
	"net/http"

	"khosra/internal/content"
	"khosra/internal/render"
)

// Handler serves a site.
//
// One mux entry, because URL shape is the resolver's business rather than the mux's: see resolve.
func Handler(site *content.Site, r *render.Renderer) http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /", func(w http.ResponseWriter, req *http.Request) {
		serve(w, req, site, r)
	})
	return mux
}

// serve resolves one request and writes its bundle.
func serve(w http.ResponseWriter, req *http.Request, site *content.Site, r *render.Renderer) {
	res, ok := resolve(req.URL.Path, site)
	if !ok {
		http.NotFound(w, req)
		return
	}
	// A redirect target only exists for a path that resolves, so check the bundle before sending one:
	// otherwise a nonexistent page answers 301 and confirms nothing.
	b, served, found := site.Lookup(res.key, res.lang)
	if res.redirect != "" && (found || res.key == "") {
		http.Redirect(w, req, res.redirect, http.StatusMovedPermanently)
		return
	}
	if !found {
		// An alias is a promise that an old URL keeps working, so it answers a permanent redirect to the
		// canonical one — and only for an alias that exists, so nothing can be probed by 301.
		if canonical, isAlias := site.Alias(res.key); isAlias {
			http.Redirect(w, req, content.URL(canonical, res.lang), http.StatusMovedPermanently)
			return
		}
		http.NotFound(w, req)
		return
	}
	out, err := r.Bundle(b, served, site.Variants(res.key))
	if err != nil {
		// A render failure degrades: log it and say nothing more to the client than that it failed
		// (conventions.md). It must never leak a template or filesystem detail.
		slog.Error("render failed", "key", b.Key, "err", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if _, err := w.Write(out); err != nil {
		slog.Warn("write failed", "key", b.Key, "err", err)
	}
}