package db

import (
	"database/sql"
	"errors"
	"time"

	_ "modernc.org/sqlite"
)

var ErrNotFound = errors.New("nicht gefunden")

type DB struct {
	*sql.DB
}

type User struct {
	ID           int64
	Email        string
	Name         string
	PasswordHash string
	Slug         string
	Timezone     string
	SlotMinutes  int
	DayStartMin  int
	DayEndMin    int
	HorizonDays  int
	Durations    string
	Weekdays     string
	CreatedTs    int64
}

type Connection struct {
	ID           int64
	UserID       int64
	Provider     string // google | caldav | ics
	DisplayName  string
	ConfigEnc    string
	LastSyncedTs sql.NullInt64
	LastError    sql.NullString
	CreatedTs    int64
}

type BusySlot struct {
	ID           int64
	UserID       int64
	ConnectionID sql.NullInt64
	StartTs      int64
	EndTs        int64
	BookingID    sql.NullInt64
}

type Booking struct {
	ID             int64
	UserID         int64
	StartTs        int64
	EndTs          int64
	RequesterName  string
	RequesterEmail string
	Message        string
	Status         string // pending | accepted | declined
	CreatedTs      int64
}

func Open(path string) (*DB, error) {
	d, err := sql.Open("sqlite", "file:"+path+"?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)&_pragma=foreign_keys(1)")
	if err != nil {
		return nil, err
	}
	// SQLite verträgt parallele Writer nicht gut – ein Writer reicht hier.
	d.SetMaxOpenConns(1)
	if err := d.Ping(); err != nil {
		return nil, err
	}
	dbase := &DB{d}
	if err := dbase.migrate(); err != nil {
		return nil, err
	}
	return dbase, nil
}

func (d *DB) migrate() error {
	stmts := []string{
		`CREATE TABLE IF NOT EXISTS users (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			email TEXT NOT NULL UNIQUE,
			name TEXT NOT NULL,
			password_hash TEXT NOT NULL,
			slug TEXT NOT NULL UNIQUE,
			timezone TEXT NOT NULL DEFAULT 'Europe/Berlin',
			slot_minutes INTEGER NOT NULL DEFAULT 30,
			day_start_min INTEGER NOT NULL DEFAULT 540,
			day_end_min INTEGER NOT NULL DEFAULT 1080,
			horizon_days INTEGER NOT NULL DEFAULT 21,
			durations TEXT NOT NULL DEFAULT '15,30,60,120',
			weekdays TEXT NOT NULL DEFAULT '1,2,3,4,5',
			created_ts INTEGER NOT NULL
		)`,
		`CREATE TABLE IF NOT EXISTS calendar_connections (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
			provider TEXT NOT NULL,
			display_name TEXT NOT NULL,
			config_enc TEXT NOT NULL,
			last_synced_ts INTEGER,
			last_error TEXT,
			created_ts INTEGER NOT NULL
		)`,
		`CREATE TABLE IF NOT EXISTS busy_slots (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
			connection_id INTEGER REFERENCES calendar_connections(id) ON DELETE CASCADE,
			booking_id INTEGER,
			start_ts INTEGER NOT NULL,
			end_ts INTEGER NOT NULL
		)`,
		`CREATE INDEX IF NOT EXISTS idx_busy_user_time ON busy_slots(user_id, start_ts)`,
		`CREATE INDEX IF NOT EXISTS idx_busy_booking ON busy_slots(booking_id)`,
		`CREATE TABLE IF NOT EXISTS booking_requests (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
			start_ts INTEGER NOT NULL,
			end_ts INTEGER NOT NULL,
			requester_name TEXT NOT NULL,
			requester_email TEXT NOT NULL,
			message TEXT NOT NULL DEFAULT '',
			status TEXT NOT NULL DEFAULT 'pending',
			created_ts INTEGER NOT NULL
		)`,
		`CREATE INDEX IF NOT EXISTS idx_bookings_user ON booking_requests(user_id, created_ts)`,
	}
	for _, s := range stmts {
		if _, err := d.Exec(s); err != nil {
			return err
		}
	}
	return nil
}

// --- Users ---

func (d *DB) CreateUser(u *User) error {
	return d.QueryRow(
		`INSERT INTO users (email, name, password_hash, slug, timezone, created_ts)
		 VALUES (?, ?, ?, ?, ?, ?) RETURNING id`,
		u.Email, u.Name, u.PasswordHash, u.Slug, u.Timezone, time.Now().Unix(),
	).Scan(&u.ID)
}

const userCols = `id, email, name, password_hash, slug, timezone, slot_minutes, day_start_min, day_end_min, horizon_days, durations, weekdays, created_ts`

func scanUser(row interface{ Scan(...any) error }) (*User, error) {
	u := &User{}
	err := row.Scan(&u.ID, &u.Email, &u.Name, &u.PasswordHash, &u.Slug, &u.Timezone,
		&u.SlotMinutes, &u.DayStartMin, &u.DayEndMin, &u.HorizonDays, &u.Durations, &u.Weekdays, &u.CreatedTs)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return u, nil
}

func (d *DB) UserByEmail(email string) (*User, error) {
	return scanUser(d.QueryRow(`SELECT `+userCols+` FROM users WHERE email = ?`, email))
}

func (d *DB) UserByID(id int64) (*User, error) {
	return scanUser(d.QueryRow(`SELECT `+userCols+` FROM users WHERE id = ?`, id))
}

func (d *DB) UserBySlug(slug string) (*User, error) {
	return scanUser(d.QueryRow(`SELECT `+userCols+` FROM users WHERE slug = ?`, slug))
}

func (d *DB) SlugExists(slug string) (bool, error) {
	var one int
	err := d.QueryRow(`SELECT 1 FROM users WHERE slug = ?`, slug).Scan(&one)
	if errors.Is(err, sql.ErrNoRows) {
		return false, nil
	}
	return err == nil, err
}

func (d *DB) UpdateUserSettings(u *User) error {
	_, err := d.Exec(`UPDATE users SET name=?, timezone=?, slot_minutes=?, day_start_min=?, day_end_min=?, horizon_days=?, durations=?, weekdays=? WHERE id=?`,
		u.Name, u.Timezone, u.SlotMinutes, u.DayStartMin, u.DayEndMin, u.HorizonDays, u.Durations, u.Weekdays, u.ID)
	return err
}

func (d *DB) UpdateUserSlug(id int64, slug string) error {
	_, err := d.Exec(`UPDATE users SET slug=? WHERE id=?`, slug, id)
	return err
}

// --- Connections ---

func (d *DB) CreateConnection(userID int64, provider, displayName, configEnc string) (int64, error) {
	var id int64
	err := d.QueryRow(
		`INSERT INTO calendar_connections (user_id, provider, display_name, config_enc, created_ts)
		 VALUES (?, ?, ?, ?, ?) RETURNING id`,
		userID, provider, displayName, configEnc, time.Now().Unix(),
	).Scan(&id)
	return id, err
}

const connCols = `id, user_id, provider, display_name, config_enc, last_synced_ts, last_error, created_ts`

func (d *DB) ConnectionsForUser(userID int64) ([]*Connection, error) {
	rows, err := d.Query(`SELECT `+connCols+` FROM calendar_connections WHERE user_id = ? ORDER BY created_ts`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []*Connection
	for rows.Next() {
		c := &Connection{}
		if err := rows.Scan(&c.ID, &c.UserID, &c.Provider, &c.DisplayName, &c.ConfigEnc, &c.LastSyncedTs, &c.LastError, &c.CreatedTs); err != nil {
			return nil, err
		}
		out = append(out, c)
	}
	return out, rows.Err()
}

func (d *DB) ConnectionByID(id, userID int64) (*Connection, error) {
	c := &Connection{}
	err := d.QueryRow(`SELECT `+connCols+` FROM calendar_connections WHERE id = ? AND user_id = ?`, id, userID).
		Scan(&c.ID, &c.UserID, &c.Provider, &c.DisplayName, &c.ConfigEnc, &c.LastSyncedTs, &c.LastError, &c.CreatedTs)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return c, nil
}

func (d *DB) DeleteConnection(id, userID int64) error {
	_, err := d.Exec(`DELETE FROM calendar_connections WHERE id = ? AND user_id = ?`, id, userID)
	return err
}

func (d *DB) SetConnectionState(id int64, synced bool, errMsg string) error {
	var syncedTs any
	if synced {
		syncedTs = time.Now().Unix()
	}
	_, err := d.Exec(`UPDATE calendar_connections SET last_synced_ts = ?, last_error = ? WHERE id = ?`, syncedTs, errMsg, id)
	return err
}

func (d *DB) UpdateConnectionConfig(id int64, configEnc string) error {
	_, err := d.Exec(`UPDATE calendar_connections SET config_enc = ? WHERE id = ?`, configEnc, id)
	return err
}

// --- Busy slots ---

func (d *DB) ReplaceBusyForConnection(connID, userID int64, slots []BusySlot) error {
	tx, err := d.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()
	if _, err := tx.Exec(`DELETE FROM busy_slots WHERE connection_id = ?`, connID); err != nil {
		return err
	}
	for _, s := range slots {
		if _, err := tx.Exec(`INSERT INTO busy_slots (user_id, connection_id, start_ts, end_ts) VALUES (?, ?, ?, ?)`,
			userID, connID, s.StartTs, s.EndTs); err != nil {
			return err
		}
	}
	return tx.Commit()
}

func (d *DB) BusyForUser(userID, fromTs, toTs int64) ([]BusySlot, error) {
	rows, err := d.Query(`SELECT id, user_id, connection_id, start_ts, end_ts, booking_id FROM busy_slots
		WHERE user_id = ? AND end_ts > ? AND start_ts < ? ORDER BY start_ts`, userID, fromTs, toTs)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []BusySlot
	for rows.Next() {
		var s BusySlot
		if err := rows.Scan(&s.ID, &s.UserID, &s.ConnectionID, &s.StartTs, &s.EndTs, &s.BookingID); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// --- Bookings ---

func (d *DB) CreateBooking(b *Booking) error {
	return d.QueryRow(
		`INSERT INTO booking_requests (user_id, start_ts, end_ts, requester_name, requester_email, message, status, created_ts)
		 VALUES (?, ?, ?, ?, ?, ?, 'pending', ?) RETURNING id`,
		b.UserID, b.StartTs, b.EndTs, b.RequesterName, b.RequesterEmail, b.Message, time.Now().Unix(),
	).Scan(&b.ID)
}

const bookingCols = `id, user_id, start_ts, end_ts, requester_name, requester_email, message, status, created_ts`

func (d *DB) BookingsForUser(userID int64) ([]*Booking, error) {
	rows, err := d.Query(`SELECT `+bookingCols+` FROM booking_requests WHERE user_id = ? ORDER BY (status='pending') DESC, start_ts ASC`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []*Booking
	for rows.Next() {
		b := &Booking{}
		if err := rows.Scan(&b.ID, &b.UserID, &b.StartTs, &b.EndTs, &b.RequesterName, &b.RequesterEmail, &b.Message, &b.Status, &b.CreatedTs); err != nil {
			return nil, err
		}
		out = append(out, b)
	}
	return out, rows.Err()
}

func (d *DB) BookingByID(id, userID int64) (*Booking, error) {
	b := &Booking{}
	err := d.QueryRow(`SELECT `+bookingCols+` FROM booking_requests WHERE id = ? AND user_id = ?`, id, userID).
		Scan(&b.ID, &b.UserID, &b.StartTs, &b.EndTs, &b.RequesterName, &b.RequesterEmail, &b.Message, &b.Status, &b.CreatedTs)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return b, nil
}

func (d *DB) SetBookingStatus(id int64, status string) error {
	_, err := d.Exec(`UPDATE booking_requests SET status = ? WHERE id = ?`, status, id)
	return err
}

func (d *DB) InsertBusyForBooking(b *Booking) error {
	_, err := d.Exec(`INSERT INTO busy_slots (user_id, booking_id, start_ts, end_ts) VALUES (?, ?, ?, ?)`,
		b.UserID, b.ID, b.StartTs, b.EndTs)
	return err
}

func (d *DB) DeleteBusyByBooking(bookingID int64) error {
	_, err := d.Exec(`DELETE FROM busy_slots WHERE booking_id = ?`, bookingID)
	return err
}