package modweb

import (
	"net/http"
	"strings"
)

type JoinedFilesystem struct {
	DefaultSystem http.FileSystem
	Systems map[string]http.FileSystem
}

func (s *JoinedFilesystem) Open(filename string) (http.File, error) {
	for prefix, fs := range s.Systems {
		if strings.HasPrefix(filename, prefix) {
			file, err := fs.Open(filename)
			if err == nil {
				return file, nil
			}
		}
	}
	return s.DefaultSystem.Open(filename)
}

func (s *JoinedFilesystem) Register(prefix string, system http.FileSystem) {
	s.Systems[prefix] = system
}

func JoinedFS(def http.FileSystem) *JoinedFilesystem {
	return &JoinedFilesystem{DefaultSystem: def}
}