// Package matrixbot provides Matrix state storage utilities.
package matrixbot

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"

	_ "modernc.org/sqlite"

	"maunium.net/go/mautrix/id"
)

const (
	defaultEventTTL = 24 * time.Hour
)

// StateStore persists sync tokens and processed event IDs.
type StateStore struct {
	db          *sql.DB
	mu          sync.Mutex
	dedupeTTL   time.Duration
	lastCleanup time.Time
}

// NewStateStore opens or creates the state store database.
func NewStateStore(path string) (*StateStore, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, fmt.Errorf("create state store dir: %w", err)
	}

	db, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, fmt.Errorf("open state store: %w", err)
	}

	store := &StateStore{db: db, dedupeTTL: defaultEventTTL}
	if err := store.init(); err != nil {
		_ = db.Close()
		return nil, err
	}

	return store, nil
}

func (s *StateStore) init() error {
	stmts := []string{
		`CREATE TABLE IF NOT EXISTS sync_tokens (
			user_id TEXT PRIMARY KEY,
			filter_id TEXT,
			next_batch TEXT
		);`,
		`CREATE TABLE IF NOT EXISTS processed_events (
			event_id TEXT PRIMARY KEY,
			processed_at INTEGER NOT NULL
		);`,
	}
	for _, stmt := range stmts {
		if _, err := s.db.Exec(stmt); err != nil {
			return fmt.Errorf("init state store: %w", err)
		}
	}
	return nil
}

// Close closes the state store database.
func (s *StateStore) Close() error {
	return s.db.Close()
}

// SaveFilterID stores the filter ID for the given user.
func (s *StateStore) SaveFilterID(ctx context.Context, userID id.UserID, filterID string) error {
	_, err := s.db.ExecContext(ctx,
		`INSERT INTO sync_tokens (user_id, filter_id) VALUES (?, ?)
		ON CONFLICT(user_id) DO UPDATE SET filter_id = excluded.filter_id`,
		userID.String(), filterID,
	)
	return err
}

// LoadFilterID loads the filter ID for the given user.
func (s *StateStore) LoadFilterID(ctx context.Context, userID id.UserID) (string, error) {
	var filterID sql.NullString
	err := s.db.QueryRowContext(ctx,
		`SELECT filter_id FROM sync_tokens WHERE user_id = ?`,
		userID.String(),
	).Scan(&filterID)
	if err == sql.ErrNoRows {
		return "", nil
	}
	if err != nil {
		return "", err
	}
	if filterID.Valid {
		return filterID.String, nil
	}
	return "", nil
}

// SaveNextBatch stores the next batch token for the given user.
func (s *StateStore) SaveNextBatch(ctx context.Context, userID id.UserID, nextBatchToken string) error {
	_, err := s.db.ExecContext(ctx,
		`INSERT INTO sync_tokens (user_id, next_batch) VALUES (?, ?)
		ON CONFLICT(user_id) DO UPDATE SET next_batch = excluded.next_batch`,
		userID.String(), nextBatchToken,
	)
	return err
}

// LoadNextBatch loads the next batch token for the given user.
func (s *StateStore) LoadNextBatch(ctx context.Context, userID id.UserID) (string, error) {
	var nextBatch sql.NullString
	err := s.db.QueryRowContext(ctx,
		`SELECT next_batch FROM sync_tokens WHERE user_id = ?`,
		userID.String(),
	).Scan(&nextBatch)
	if err == sql.ErrNoRows {
		return "", nil
	}
	if err != nil {
		return "", err
	}
	if nextBatch.Valid {
		return nextBatch.String, nil
	}
	return "", nil
}

// WasEventProcessed checks whether an event ID has already been recorded.
func (s *StateStore) WasEventProcessed(ctx context.Context, eventID string) (bool, error) {
	var exists bool
	err := s.db.QueryRowContext(ctx,
		`SELECT 1 FROM processed_events WHERE event_id = ?`,
		eventID,
	).Scan(&exists)
	if err == sql.ErrNoRows {
		return false, nil
	}
	if err != nil {
		return false, err
	}
	return true, nil
}

// MarkEventProcessed records a processed event. Returns true if newly recorded.
func (s *StateStore) MarkEventProcessed(ctx context.Context, eventID string) (bool, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	now := time.Now()
	if s.lastCleanup.IsZero() || now.Sub(s.lastCleanup) > s.dedupeTTL {
		if err := s.cleanupLocked(ctx, now); err != nil {
			return false, err
		}
		s.lastCleanup = now
	}

	res, err := s.db.ExecContext(ctx,
		`INSERT OR IGNORE INTO processed_events (event_id, processed_at) VALUES (?, ?)`,
		eventID, now.Unix(),
	)
	if err != nil {
		return false, err
	}

	affected, err := res.RowsAffected()
	if err != nil {
		return false, err
	}
	return affected > 0, nil
}

func (s *StateStore) cleanupLocked(ctx context.Context, now time.Time) error {
	cutoff := now.Add(-s.dedupeTTL).Unix()
	_, err := s.db.ExecContext(ctx,
		`DELETE FROM processed_events WHERE processed_at < ?`,
		cutoff,
	)
	return err
}