// Package webui embeds the built frontend SPA (frontend/web/dist) into the
// single Cyrene binary and exposes it as a filesystem. It is the default asset
// source for the gateway's static server; a deployer may still drop an external
// dist directory next to the process to override it (see internal/services/
// gateway and cmd/cyrene).
//
// The embedded tree is rooted at the dist directory, so index.html and
// assets/* appear at the filesystem root. Build the frontend with
// `cd frontend/web && npm run build` (which also syncs dist into this package)
// before running `go build ./...`; the //go:embed directive fails to compile
// when the dist directory is absent.
package webui

import (
	"embed"
	"io/fs"
)

// dist holds the built SPA. It is generated by the frontend build and must
// exist for the package to compile.
//
//go:embed all:dist
var dist embed.FS

// Assets returns the embedded dist as an fs.FS rooted at the dist directory.
// The returned FS is read-only and safe for concurrent use.
func Assets() fs.FS {
	sub, err := fs.Sub(dist, "dist")
	if err != nil {
		// The embed directive guarantees dist exists, so this cannot fail; a
		// panic here is a programming error, not a runtime condition.
		panic("webui: dist embed missing: " + err.Error())
	}
	return sub
}

// Open opens a file under the dist root by its slash-separated (or
// filesystem) name. It is a convenience over Assets().Open.
func Open(name string) (fs.File, error) {
	return Assets().Open(name)
}

// Exists reports whether a file or directory exists within the embedded dist.
func Exists(path string) bool {
	_, err := fs.Stat(Assets(), path)
	return err == nil
}