package auth

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"

	"golang.org/x/crypto/bcrypt"
)

// sessionTokenBytes is the raw entropy per session token. 32 bytes of
// crypto/rand gives ~256 bits; after base64 url-safe encoding the cookie
// value is 43 chars with no padding.
const sessionTokenBytes = 32

// MintSessionToken returns a freshly-generated, url-safe opaque token.
// The token is what the client carries; the DB only ever sees its sha256.
func MintSessionToken() (string, error) {
	b := make([]byte, sessionTokenBytes)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(b), nil
}

// HashSessionToken is the single source of truth for mapping a raw token to
// the `sessions.token_hash` column. sha256 is fine here — we're not guarding
// against offline brute force (the token has 256 bits of entropy); we only
// want "leaked DB row can't be replayed without also having the raw token."
func HashSessionToken(token string) []byte {
	sum := sha256.Sum256([]byte(token))
	return sum[:]
}

// VerifyPassword is the canonical bcrypt comparison. Returns false on a
// malformed hash so callers don't need to distinguish "hash invalid" from
// "password wrong" — both are auth failures from the client's perspective.
func VerifyPassword(hash, plaintext string) bool {
	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(plaintext)) == nil
}