package auth

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/redis/go-redis/v9"

	"github.com/wangjia/pangolin/server/internal/apierr"
)

// ═══════════════ App → 网页免登录（一次性换票，magic-link）═══════════════
//
// The app (already holding a valid JWT) mints a one-time ticket via
// IssueWebTicket and opens the system browser at .../sso?t=<ticket>. The web
// user-center exchanges the ticket via LoginWithWebTicket for a normal token
// pair — same shape as /auth/login — without ever seeing the app's own tokens.
//
// Storage: Redis only (no DB row). Tickets are single-instance, ephemeral
// (60s TTL) credentials — a DB table would need its own cleanup job for what
// Redis already gives for free via key expiry. Consumption uses GETDEL, which
// is atomic server-side: a replayed/concurrent second exchange always loses
// the race and gets redis.Nil, so single-use is enforced without a CAS dance.

const (
	// webTicketTTL is the ticket lifetime: long enough for the system browser
	// to open and hit the exchange endpoint, short enough to bound replay risk.
	webTicketTTL = 60 * time.Second
	// webTicketPrefix namespaces ticket keys in Redis.
	webTicketPrefix = "auth:webticket:"
	// scopeWebTicket is the rate-limit scope for ticket issuance (1/sec/user).
	scopeWebTicket = "webticket"
)

func webTicketKey(ticket string) string { return webTicketPrefix + ticket }

// genWebTicket returns a fresh, cryptographically random one-time ticket. 32
// bytes (256 bits) of entropy makes guessing infeasible within the 60s TTL.
func genWebTicket() (string, error) {
	buf := make([]byte, 32)
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("auth: gen web ticket: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(buf), nil
}

// IssueWebTicket mints a one-time ticket for an already-authenticated user
// (userID/userUUID come from the caller's validated JWT claims — see
// Handler.WebTicket). Rate-limited to 1/sec/user as a rebuff-abuse backstop
// (the endpoint already requires login). The ticket value itself never
// carries a real token — only enough to look the user up on exchange.
func (s *Service) IssueWebTicket(ctx context.Context, userID int64, userUUID string) (ticket string, ttlSeconds int, retryAfter time.Duration, apiErr *apierr.Error) {
	ok, ra, err := s.rl.Allow(ctx, scopeWebTicket, strconv.FormatInt(userID, 10), 1, time.Second)
	if err != nil {
		return "", 0, 0, ErrInternal
	}
	if !ok {
		return "", 0, ra, ErrRateLimited
	}

	tk, err := genWebTicket()
	if err != nil {
		return "", 0, 0, ErrInternal
	}
	val := userID2UUID(userID, userUUID)
	if err := s.rdb.Set(ctx, webTicketKey(tk), val, webTicketTTL).Err(); err != nil {
		return "", 0, 0, ErrInternal
	}
	return tk, int(webTicketTTL.Seconds()), 0, nil
}

// LoginWithWebTicket validates+atomically-consumes a one-time ticket and
// issues a fresh token pair for its user, registering the device exactly like
// a normal Login (best-effort — see recordLogin). Any invalid/expired/
// already-used ticket collapses to ErrTicketInvalid (no distinguishing info
// leaked).
func (s *Service) LoginWithWebTicket(ctx context.Context, ticket, ip string, device DeviceMeta) (*TokenPair, *DeviceLimit, *apierr.Error) {
	if ticket == "" {
		return nil, nil, ErrTicketInvalid
	}

	// GETDEL is atomic: concurrent/replayed exchanges of the same ticket race
	// on a single Redis command, so exactly one caller ever sees the value.
	val, err := s.rdb.GetDel(ctx, webTicketKey(ticket)).Result()
	if errors.Is(err, redis.Nil) {
		return nil, nil, ErrTicketInvalid
	}
	if err != nil {
		return nil, nil, ErrInternal
	}

	userID, userUUID, ok := splitUserID2UUID(val)
	if !ok {
		// Our own format, corrupt only via a Redis-level anomaly — never surface
		// internals to the (unauthenticated) caller.
		return nil, nil, ErrInternal
	}

	pair, jti, err := s.tokens.IssueWithJTI(ctx, userID, userUUID)
	if err != nil {
		return nil, nil, ErrInternal
	}
	dl := s.recordLogin(ctx, userID, jti, ip, device)
	return pair, dl, nil
}

// userID2UUID / splitUserID2UUID encode the ticket's Redis value as
// "<userID>:<userUUID>". UUIDs are hyphenated hex (no ':'), so a single
// SplitN(2) round-trips unambiguously.
func userID2UUID(userID int64, userUUID string) string {
	return strconv.FormatInt(userID, 10) + ":" + userUUID
}

func splitUserID2UUID(val string) (userID int64, userUUID string, ok bool) {
	parts := strings.SplitN(val, ":", 2)
	if len(parts) != 2 || parts[1] == "" {
		return 0, "", false
	}
	id, err := strconv.ParseInt(parts[0], 10, 64)
	if err != nil || id == 0 {
		return 0, "", false
	}
	return id, parts[1], true
}