// Copyright (c) 2025, s0up and the autobrr contributors.
// SPDX-License-Identifier: GPL-2.0-or-later

// Package web web/build.go
package web

import (
	"embed"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
)

var (
	//go:embed all:dist
	Dist embed.FS

	DistDirFS = MustSubFS(Dist, "dist")
)

type defaultFS struct {
	prefix string
	fs     fs.FS
}

func (fs defaultFS) Open(name string) (fs.File, error) {
	if fs.fs == nil {
		return os.Open(name)
	}
	return fs.fs.Open(name)
}

// MustSubFS creates sub FS from current filesystem or panic on failure.
// Panic happens when `fsRoot` contains invalid path according to `fs.ValidPath` rules.
//
// MustSubFS is helpful when dealing with `embed.FS` because for example `//go:embed assets/images` embeds files with
// paths including `assets/images` as their prefix. In that case use `fs := MustSubFS(fs, "rootDirectory") to
// create sub fs which uses necessary prefix for directory path.
func MustSubFS(currentFs fs.FS, fsRoot string) fs.FS {
	subFs, err := subFS(currentFs, fsRoot)
	if err != nil {
		panic(fmt.Errorf("can not create sub FS, invalid root given, err: %w", err))
	}
	return subFs
}

func subFS(currentFs fs.FS, root string) (fs.FS, error) {
	root = filepath.ToSlash(filepath.Clean(root)) // note: fs.FS operates only with slashes. `ToSlash` is necessary for Windows
	if dFS, ok := currentFs.(*defaultFS); ok {
		// we need to make exception for `defaultFS` instances as it interprets root prefix differently from fs.FS.
		// fs.Fs.Open does not like relative paths ("./", "../") and absolute paths.
		if !filepath.IsAbs(root) {
			root = filepath.Join(dFS.prefix, root)
		}
		return &defaultFS{
			prefix: root,
			fs:     os.DirFS(root),
		}, nil
	}
	return fs.Sub(currentFs, root)
}
