package storage

import (
	"path"
	"strings"
)

// ChunkDir 实现默认分片目录约定：<父目录>/chunks/<uploadID>。
// local/s3/webdav 三引擎共用，保持分片路径一致。
func ChunkDir(savePath, uploadID string) string {
	dir := path.Dir(savePath)
	name := path.Base(savePath)
	// 防御：savePath 非法时仍返回明确结构，具体引擎再做安全校验
	if name == "." || name == "/" {
		name = "file"
	}
	return path.Join(dir, "chunks", uploadID) + "/" + name
}

// ChunkPartPath 分片对象完整路径（相对存储根）。
func ChunkPartPath(savePath, uploadID string, index int) string {
	dir := path.Dir(savePath)
	return path.Join(dir, "chunks", uploadID, itoa(index)+".part")
}

// SanitizePath 清理相对路径：统一斜杠、去首尾斜杠、拒绝 .. 穿越。
// 返回清理后的相对路径与是否合法。
func SanitizePath(p string) (string, bool) {
	raw := strings.ReplaceAll(strings.TrimSpace(p), "\\", "/")
	raw = strings.TrimPrefix(raw, "/")
	if raw == "" {
		return "", false
	}
	cleaned := path.Clean(raw)
	if cleaned == ".." || strings.HasPrefix(cleaned, "../") || path.IsAbs(cleaned) {
		return "", false
	}
	// 拒绝任何单独的 .. 段
	for _, seg := range strings.Split(cleaned, "/") {
		if seg == ".." {
			return "", false
		}
	}
	return cleaned, true
}

// SanitizeFileName 清理文件名：剥离路径、替换非法字符、限制长度。
// 对齐参考 core/utils.py 的 sanitize_filename。
func SanitizeFileName(name string) string {
	// 剥离路径
	if idx := strings.LastIndexAny(name, "/\\"); idx >= 0 {
		name = name[idx+1:]
	}
	var b strings.Builder
	for _, r := range name {
		switch {
		case r < 0x20 || r == 0x7f:
			b.WriteByte('_')
		case strings.ContainsRune(`\*?:"<>|`, r):
			b.WriteByte('_')
		case r == ' ':
			b.WriteByte('_')
		default:
			b.WriteRune(r)
		}
	}
	cleaned := b.String()
	// 压缩连续下划线
	for strings.Contains(cleaned, "__") {
		cleaned = strings.ReplaceAll(cleaned, "__", "_")
	}
	cleaned = strings.Trim(cleaned, "._")
	if cleaned == "" {
		return "unnamed_file"
	}
	if len(cleaned) > 255 {
		cleaned = cleaned[:255]
	}
	return cleaned
}

// itoa 小整数转字符串。
func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	neg := n < 0
	if neg {
		n = -n
	}
	var buf [21]byte
	i := len(buf)
	for n > 0 {
		i--
		buf[i] = byte('0' + n%10)
		n /= 10
	}
	if neg {
		i--
		buf[i] = '-'
	}
	return string(buf[i:])
}