package admin

import (
	"os"
	"path/filepath"
	"strconv"
)

func nextRoomIDInDir(dataDir string, fromRoomID int) (int, string, error) {
	base := filepath.Join(dataDir, "rooms")
	subdir, err := findRoomSubdir(base, fromRoomID)
	if err != nil {
		subdir = base
	}
	used := map[int]bool{}
	scanDir(subdir, used)
	if len(used) == 0 {
		return 1, subdir, nil
	}
	minID := 1<<31 - 1
	for id := range used {
		if id < minID {
			minID = id
		}
	}
	id := minID
	for used[id] {
		id++
	}
	return id, subdir, nil
}

func findRoomSubdir(base string, roomID int) (string, error) {
	fileName := strconv.Itoa(roomID) + ".yaml"
	var found string
	filepath.WalkDir(base, func(path string, d os.DirEntry, err error) error {
		if err != nil || found != "" {
			return nil
		}
		if !d.IsDir() && d.Name() == fileName {
			found = filepath.Dir(path)
		}
		return nil
	})
	if found == "" {
		return "", os.ErrNotExist
	}
	return found, nil
}

func scanDir(dir string, used map[int]bool) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return
	}
	for _, e := range entries {
		if !e.IsDir() && filepath.Ext(e.Name()) == ".yaml" {
			idStr := e.Name()[:len(e.Name())-5]
			if id, err := strconv.Atoi(idStr); err == nil && id > 0 {
				used[id] = true
			}
		}
	}
}