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// Package httpserver assembles ori's HTTP surface: the embedded single-page
// application, a health check, and (from later steps) the WebSocket bridge to
// the ACP agent.
package httpserver

import (
	"io/fs"
	"net/http"
)

// Handler builds the root http.Handler of the ori server.
//
// uiFS is the root of the built SPA (index.html at its root, see ui.Dist).
// extra maps additional route patterns (http.ServeMux syntax) to handlers and
// is how the WebSocket endpoint plugs in without this package importing it.
//
// Example:
//
//	h := httpserver.Handler(ui.Dist(), map[string]http.Handler{
//		"GET /ws": wsHandler,
//	})
//	log.Fatal(http.ListenAndServe(":8888", h))
func Handler(uiFS fs.FS, extra map[string]http.Handler) http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, _ *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		_, _ = w.Write([]byte(`{"status":"ok"}`))
	})
	for pattern, handler := range extra {
		mux.Handle(pattern, handler)
	}
	mux.Handle("/", spaHandler(uiFS))
	return mux
}

// spaHandler serves the static files of the SPA and falls back to index.html
// for any unknown path, so client-side routes deep-link correctly.
func spaHandler(uiFS fs.FS) http.Handler {
	fileServer := http.FileServerFS(uiFS)
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if _, err := fs.Stat(uiFS, "index.html"); err != nil {
			http.Error(w, "UI not built: run `make build-ui` and rebuild the server", http.StatusServiceUnavailable)
			return
		}
		path := r.URL.Path
		if path != "/" {
			if _, err := fs.Stat(uiFS, path[1:]); err != nil {
				// Unknown path: let the SPA router handle it.
				r.URL.Path = "/"
			}
		}
		fileServer.ServeHTTP(w, r)
	})
}