// SPDX-License-Identifier: AGPL-3.0-or-later

package store

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"log/slog"
	"time"

	"kode.naiv.no/olemd/favoritter/internal/model"
)

var ErrSessionNotFound = errors.New("session not found")

type SessionStore struct {
	db       *sql.DB
	lifetime time.Duration
}

func NewSessionStore(db *sql.DB) *SessionStore {
	return &SessionStore{db: db, lifetime: 720 * time.Hour} // default 30 days
}

// SetLifetime configures the session lifetime.
func (s *SessionStore) SetLifetime(d time.Duration) {
	s.lifetime = d
}

// Create generates a new session token for the given user.
func (s *SessionStore) Create(userID int64) (string, error) {
	tokenBytes := make([]byte, 32)
	if _, err := rand.Read(tokenBytes); err != nil {
		return "", fmt.Errorf("generate session token: %w", err)
	}
	token := hex.EncodeToString(tokenBytes)

	expiresAt := time.Now().UTC().Add(s.lifetime)
	_, err := s.db.Exec(
		`INSERT INTO sessions (token, user_id, expires_at) VALUES (?, ?, ?)`,
		token, userID, expiresAt.Format(time.RFC3339),
	)
	if err != nil {
		return "", fmt.Errorf("insert session: %w", err)
	}

	return token, nil
}

// Validate checks if a session token is valid and not expired.
// Returns the session if valid.
func (s *SessionStore) Validate(token string) (*model.Session, error) {
	var session model.Session
	var expiresAt, createdAt string
	err := s.db.QueryRow(
		`SELECT token, user_id, expires_at, created_at
		FROM sessions WHERE token = ?`, token,
	).Scan(&session.Token, &session.UserID, &expiresAt, &createdAt)

	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrSessionNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("query session: %w", err)
	}

	session.ExpiresAt, _ = time.Parse(time.RFC3339, expiresAt)
	session.CreatedAt, _ = time.Parse(time.RFC3339, createdAt)

	if time.Now().UTC().After(session.ExpiresAt) {
		// Session has expired — delete it.
		s.Delete(token)
		return nil, ErrSessionNotFound
	}

	return &session, nil
}

// Delete removes a session by its token.
func (s *SessionStore) Delete(token string) error {
	_, err := s.db.Exec("DELETE FROM sessions WHERE token = ?", token)
	return err
}

// DeleteAllForUser removes all sessions for a given user (e.g., on password change).
func (s *SessionStore) DeleteAllForUser(userID int64) error {
	_, err := s.db.Exec("DELETE FROM sessions WHERE user_id = ?", userID)
	return err
}

// CleanupLoop periodically removes expired sessions. It runs until the
// context is canceled.
func (s *SessionStore) CleanupLoop(ctx context.Context, interval time.Duration) {
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			result, err := s.db.Exec(
				`DELETE FROM sessions WHERE expires_at < strftime('%Y-%m-%dT%H:%M:%SZ', 'now')`,
			)
			if err != nil {
				slog.Error("session cleanup failed", "error", err)
				continue
			}
			n, _ := result.RowsAffected()
			if n > 0 {
				slog.Info("cleaned up expired sessions", "count", n)
			}
		}
	}
}