package shares

import (
	"sort"
	"strconv"
	"strings"
)

// pseudoFS are filesystem types that never hold user data.
var pseudoFS = map[string]bool{
	"proc": true, "sysfs": true, "tmpfs": true, "devtmpfs": true, "devpts": true, "cgroup": true, "cgroup2": true,
	"securityfs": true, "pstore": true, "bpf": true, "debugfs": true, "tracefs": true, "configfs": true,
	"fusectl": true, "mqueue": true, "hugetlbfs": true, "autofs": true, "binfmt_misc": true, "nsfs": true,
	"overlay": true, "squashfs": true, "efivarfs": true, "rpc_pipefs": true, "nfsd": true, "ramfs": true,
}

// ParseMounts extracts shareable mountpoints from /proc/self/mounts content:
// real filesystems outside system directories, sorted and de-duplicated.
func ParseMounts(data string) []string {
	seen := map[string]bool{}
	var out []string
	for _, line := range strings.Split(data, "\n") {
		f := strings.Fields(line)
		if len(f) < 3 || pseudoFS[f[2]] {
			continue
		}
		mp := unescapeMount(f[1])
		if !strings.HasPrefix(mp, "/") || ValidateNotSystem(mp) != nil || seen[mp] {
			continue
		}
		seen[mp] = true
		out = append(out, mp)
	}
	sort.Strings(out)
	return out
}

// unescapeMount decodes the octal escapes (\040 etc.) the kernel uses in mounts.
func unescapeMount(s string) string {
	if !strings.Contains(s, `\`) {
		return s
	}
	var b strings.Builder
	for i := 0; i < len(s); i++ {
		if s[i] == '\\' && i+4 <= len(s) {
			if n, err := strconv.ParseUint(s[i+1:i+4], 8, 8); err == nil {
				b.WriteByte(byte(n))
				i += 3
				continue
			}
		}
		b.WriteByte(s[i])
	}
	return b.String()
}