// permission.go 实现 ACP fs/* method 的路径安全校验。
//
// 规则（spec §5.6）：
//  1. 路径必须以 cwd_path 为前缀（防 ../../etc/passwd）
//  2. 解析 symlink 后的真实路径必须仍在 cwd_path 下（防 symlink 逃逸）
//
// 三重校验：filepath.Abs + strings.HasPrefix + filepath.EvalSymlinks。
package acp

import (
	"path/filepath"
	"strings"

	"github.com/yan1h/agent-coding-workflow/internal/infra/errs"
)

// ResolveSafePath 校验 requested 是否安全（在 cwd 内）。
// cwd 必须是绝对路径；requested 可以是绝对或相对（相对时基于 cwd 解析）。
// 返回校验通过后的绝对路径（含 symlink 解析）；失败返回 CodeAcpFsPathOutsideWorktree。
func ResolveSafePath(cwd, requested string) (string, error) {
	if !filepath.IsAbs(cwd) {
		return "", errs.New(errs.CodeAcpFsPathOutsideWorktree, "cwd must be absolute")
	}
	cleanCwd := filepath.Clean(cwd)

	var abs string
	if filepath.IsAbs(requested) {
		abs = filepath.Clean(requested)
	} else {
		abs = filepath.Clean(filepath.Join(cleanCwd, requested))
	}

	if !hasPathPrefix(abs, cleanCwd) {
		return "", errs.New(errs.CodeAcpFsPathOutsideWorktree, "path outside worktree")
	}

	real, err := filepath.EvalSymlinks(abs)
	if err == nil {
		if !hasPathPrefix(real, cleanCwd) {
			return "", errs.New(errs.CodeAcpFsPathOutsideWorktree, "path resolves outside worktree via symlink")
		}
	}
	return abs, nil
}

// hasPathPrefix reports whether abs is equal to base or under base. Trailing
// separator handling is critical: we want "/foo/bar" to be inside "/foo" but
// NOT inside "/fo".
func hasPathPrefix(abs, base string) bool {
	if abs == base {
		return true
	}
	sep := string(filepath.Separator)
	return strings.HasPrefix(abs, base+sep)
}