package store

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"regexp"
	"strings"
)

// vanityRe is deliberately narrow: lowercase alphanumerics plus dot, dash and
// underscore, starting with an alphanumeric, 2-64 characters. Anything that
// could be mistaken for a path element, a dotfile or a traversal is excluded.
var vanityRe = regexp.MustCompile(`^[a-z0-9][a-z0-9._-]{1,63}$`)

// reserved names would shadow a route or a well-known file if they were ever
// allowed into the object namespace.
var reserved = map[string]bool{
	"d": true, "i": true, "api": true, "static": true, "admin": true,
	"login": true, "logout": true, "upload": true,
	"favicon.ico": true, "robots.txt": true, "index.html": true,
	"sitemap.xml": true, "tokens.json": true, "objects": true,
}

var ErrBadID = errors.New("invalid name")

// CleanID validates an id arriving from a URL or from a vanity request and
// returns its canonical form. IDs are lowercased so that a case-insensitive
// filesystem cannot be tricked into treating two distinct names as one object.
//
// This is the *only* function permitted to turn caller input into a path
// element; every filesystem path in this package is built from its output.
func CleanID(s string) (string, error) {
	s = strings.ToLower(strings.TrimSpace(s))
	if !vanityRe.MatchString(s) {
		return "", ErrBadID
	}
	// The regexp permits interior dots; a doubled dot or a trailing dot is
	// still refused so no spelling of a traversal survives.
	if strings.Contains(s, "..") || strings.HasSuffix(s, ".") {
		return "", ErrBadID
	}
	if reserved[s] {
		return "", ErrBadID
	}
	return s, nil
}

// NewUUID returns a random RFC 4122 version 4 UUID.
func NewUUID() (string, error) {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		return "", err
	}
	b[6] = (b[6] & 0x0f) | 0x40 // version 4
	b[8] = (b[8] & 0x3f) | 0x80 // variant 10
	h := hex.EncodeToString(b[:])
	return h[:8] + "-" + h[8:12] + "-" + h[12:16] + "-" + h[16:20] + "-" + h[20:], nil
}

// NewSecret returns a high-entropy URL-safe secret, used for both API tokens
// and per-object delete tokens.
func NewSecret() (string, error) {
	var b [32]byte
	if _, err := rand.Read(b[:]); err != nil {
		return "", err
	}
	return hex.EncodeToString(b[:]), nil
}