package auth

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"path/filepath"
	"strings"
	"time"

	"github.com/google/uuid"

	"git.librete.ch/public/librenotes/internal/storage"
)

// nowFn is overridable in tests.
var nowFn = func() time.Time { return time.Now().UTC() }

// Service orchestrates the magic-link login flow: request a link by
// email and verify a returned link to issue a JWT session.
type Service struct {
	users   *storage.UserStore
	tokens  *TokenStore
	limiter *RateLimiter
	mailer  Mailer
	signer  *Signer
	baseURL string
	dataDir string
}

// Config bundles dependencies for NewService.
type Config struct {
	Users   *storage.UserStore
	Tokens  *TokenStore
	Limiter *RateLimiter
	Mailer  Mailer
	Signer  *Signer
	// BaseURL is the public origin used to build verification links,
	// e.g. "https://librenot.es".
	BaseURL string
	// DataDir is the parent directory under which per-user note
	// directories are created on first login.
	DataDir string
}

// NewService validates and assembles a Service.
func NewService(c Config) (*Service, error) {
	if c.Users == nil || c.Tokens == nil || c.Limiter == nil || c.Mailer == nil || c.Signer == nil {
		return nil, fmt.Errorf("auth: missing dependency")
	}
	if c.BaseURL == "" {
		return nil, fmt.Errorf("auth: BaseURL required")
	}
	if c.DataDir == "" {
		return nil, fmt.Errorf("auth: DataDir required")
	}
	return &Service{
		users:   c.Users,
		tokens:  c.Tokens,
		limiter: c.Limiter,
		mailer:  c.Mailer,
		signer:  c.Signer,
		baseURL: strings.TrimRight(c.BaseURL, "/"),
		dataDir: c.DataDir,
	}, nil
}

// RequestLogin generates a magic link and emails it. The user is
// auto-created on first login. Returns ErrRateLimited if the email has
// exceeded the limiter window.
func (s *Service) RequestLogin(ctx context.Context, email string) error {
	email = strings.ToLower(strings.TrimSpace(email))
	if !looksLikeEmail(email) {
		return fmt.Errorf("invalid email")
	}
	if err := s.limiter.Check(ctx, email); err != nil {
		return err
	}

	user, err := s.users.GetByEmail(ctx, email)
	if errors.Is(err, storage.ErrNotFound) {
		id := uuid.NewString()
		path := filepath.Join(s.dataDir, id)
		created, cerr := s.users.Create(ctx, storage.User{
			ID:          id,
			Email:       email,
			StoragePath: path,
		})
		if cerr != nil {
			return fmt.Errorf("create user: %w", cerr)
		}
		user = created
	} else if err != nil {
		return fmt.Errorf("lookup user: %w", err)
	}

	plaintext, err := s.tokens.Issue(ctx, user.ID, email)
	if err != nil {
		return err
	}
	link := s.baseURL + "/auth/verify?token=" + url.QueryEscape(plaintext)
	if err := s.mailer.SendMagicLink(ctx, email, link); err != nil {
		return fmt.Errorf("send mail: %w", err)
	}
	return nil
}

// VerifyResult holds the outcome of a successful magic-link verification.
type VerifyResult struct {
	JWT  string
	User storage.User
}

// Verify consumes a magic-link token and returns a signed session JWT.
func (s *Service) Verify(ctx context.Context, token string) (VerifyResult, error) {
	userID, err := s.tokens.Consume(ctx, token)
	if err != nil {
		return VerifyResult{}, err
	}
	user, err := s.users.GetByID(ctx, userID)
	if err != nil {
		return VerifyResult{}, fmt.Errorf("load user: %w", err)
	}
	now := nowFn()
	if err := s.users.UpdateLastLogin(ctx, user.ID, now); err != nil {
		return VerifyResult{}, fmt.Errorf("update last login: %w", err)
	}
	jwtStr, err := s.signer.Issue(user.ID, user.Email)
	if err != nil {
		return VerifyResult{}, err
	}
	return VerifyResult{JWT: jwtStr, User: user}, nil
}

// looksLikeEmail does a minimal sanity check; full validation is left
// to the SMTP server. We just want to reject obvious garbage.
func looksLikeEmail(s string) bool {
	at := strings.IndexByte(s, '@')
	if at <= 0 || at == len(s)-1 {
		return false
	}
	if strings.ContainsAny(s, " \t\r\n") {
		return false
	}
	return strings.IndexByte(s[at+1:], '.') >= 0
}