package calendar

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

var ErrNotFound = errors.New("calendar: not found")

type Store struct {
	db *pgxpool.Pool
}

func NewStore(db *pgxpool.Pool) *Store {
	return &Store{db: db}
}

func (s *Store) ListCalendars(ctx context.Context, ownerID uuid.UUID) ([]Calendar, error) {
	rows, err := s.db.Query(ctx,
		`SELECT id, owner_id, name, color, description, supports_todo, timezone, ctag, created_at
		   FROM cal_calendars WHERE owner_id = $1 ORDER BY created_at`,
		ownerID,
	)
	if err != nil {
		return nil, fmt.Errorf("query calendars: %w", err)
	}
	defer rows.Close()

	var out []Calendar
	for rows.Next() {
		var c Calendar
		if err := rows.Scan(&c.ID, &c.OwnerID, &c.Name, &c.Color, &c.Description, &c.SupportsTodo, &c.TimeZone, &c.CTag, &c.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan calendar: %w", err)
		}
		out = append(out, c)
	}
	return out, rows.Err()
}

func (s *Store) GetCalendar(ctx context.Context, ownerID, id uuid.UUID) (*Calendar, error) {
	var c Calendar
	err := s.db.QueryRow(ctx,
		`SELECT id, owner_id, name, color, description, supports_todo, timezone, ctag, created_at
		   FROM cal_calendars WHERE owner_id = $1 AND id = $2`,
		ownerID, id,
	).Scan(&c.ID, &c.OwnerID, &c.Name, &c.Color, &c.Description, &c.SupportsTodo, &c.TimeZone, &c.CTag, &c.CreatedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("query calendar: %w", err)
	}
	return &c, nil
}

// EnsureDefaultCalendar liefert den ersten Kalender des Nutzers, legt bei
// Bedarf "Persönlich" an. So findet ein frisch eingerichteter Client sofort
// ein Ziel vor, statt erst ein MKCALENDAR schicken zu müssen – nicht jeder
// CalDAV-Client kann das.
func (s *Store) EnsureDefaultCalendar(ctx context.Context, ownerID uuid.UUID) (*Calendar, error) {
	cals, err := s.ListCalendars(ctx, ownerID)
	if err != nil {
		return nil, err
	}
	if len(cals) > 0 {
		return &cals[0], nil
	}
	return s.CreateCalendar(ctx, ownerID, "Persönlich", "#4285f4", "")
}

func (s *Store) CreateCalendar(ctx context.Context, ownerID uuid.UUID, name, color, description string) (*Calendar, error) {
	if color == "" {
		color = "#4285f4"
	}
	var c Calendar
	err := s.db.QueryRow(ctx,
		`INSERT INTO cal_calendars (owner_id, name, color, description)
		 VALUES ($1, $2, $3, $4)
		 RETURNING id, owner_id, name, color, description, supports_todo, timezone, ctag, created_at`,
		ownerID, name, color, description,
	).Scan(&c.ID, &c.OwnerID, &c.Name, &c.Color, &c.Description, &c.SupportsTodo, &c.TimeZone, &c.CTag, &c.CreatedAt)
	if err != nil {
		return nil, fmt.Errorf("insert calendar: %w", err)
	}
	return &c, nil
}

// UpdateCalendar ändert Name/Farbe/Beschreibung/Zeitzone. Ein nil-Feld lässt
// die bestehende Spalte unangetastet – so kann der Aufrufer nur das Feld
// schicken, das sich wirklich ändert, ohne vorher den ganzen Datensatz zu
// laden.
func (s *Store) UpdateCalendar(ctx context.Context, ownerID, id uuid.UUID, name, color, description, timezone *string) (*Calendar, error) {
	var c Calendar
	err := s.db.QueryRow(ctx,
		`UPDATE cal_calendars SET
		   name        = COALESCE($3, name),
		   color       = COALESCE($4, color),
		   description = COALESCE($5, description),
		   timezone    = COALESCE($6, timezone)
		 WHERE owner_id = $1 AND id = $2
		 RETURNING id, owner_id, name, color, description, supports_todo, timezone, ctag, created_at`,
		ownerID, id, name, color, description, timezone,
	).Scan(&c.ID, &c.OwnerID, &c.Name, &c.Color, &c.Description, &c.SupportsTodo, &c.TimeZone, &c.CTag, &c.CreatedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("update calendar: %w", err)
	}
	return &c, nil
}

func (s *Store) DeleteCalendar(ctx context.Context, ownerID, id uuid.UUID) error {
	tag, err := s.db.Exec(ctx, `DELETE FROM cal_calendars WHERE owner_id = $1 AND id = $2`, ownerID, id)
	if err != nil {
		return fmt.Errorf("delete calendar: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

func (s *Store) ListObjects(ctx context.Context, calendarID uuid.UUID) ([]Object, error) {
	rows, err := s.db.Query(ctx,
		`SELECT id, calendar_id, uid, component, data, etag, dtstart, dtend, created_at, updated_at
		   FROM cal_objects WHERE calendar_id = $1 ORDER BY uid`,
		calendarID,
	)
	if err != nil {
		return nil, fmt.Errorf("query objects: %w", err)
	}
	defer rows.Close()

	var out []Object
	for rows.Next() {
		o, err := scanObject(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, o)
	}
	return out, rows.Err()
}

func (s *Store) GetObjectByUID(ctx context.Context, calendarID uuid.UUID, uid string) (*Object, error) {
	row := s.db.QueryRow(ctx,
		`SELECT id, calendar_id, uid, component, data, etag, dtstart, dtend, created_at, updated_at
		   FROM cal_objects WHERE calendar_id = $1 AND uid = $2`,
		calendarID, uid,
	)
	o, err := scanObject(row)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return &o, nil
}

type rowScanner interface {
	Scan(dest ...any) error
}

func scanObject(row rowScanner) (Object, error) {
	var o Object
	err := row.Scan(&o.ID, &o.CalendarID, &o.UID, &o.Component, &o.Data, &o.ETag, &o.DTStart, &o.DTEnd, &o.CreatedAt, &o.UpdatedAt)
	if err != nil {
		return Object{}, fmt.Errorf("scan object: %w", err)
	}
	return o, nil
}

// PutObject legt ein Objekt an oder ersetzt es (gleiche UID im selben
// Kalender). Die ETag-Vorbedingungen (If-Match/If-None-Match) prüft der
// Aufrufer vorher – hier zählt nur noch das Schreiben selbst.
func (s *Store) PutObject(ctx context.Context, calendarID uuid.UUID, uid, component, data, etag string, dtstart, dtend *time.Time) (*Object, error) {
	tx, err := s.db.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin tx: %w", err)
	}
	defer tx.Rollback(ctx)

	var o Object
	err = tx.QueryRow(ctx,
		`INSERT INTO cal_objects (calendar_id, uid, component, data, etag, dtstart, dtend, updated_at)
		 VALUES ($1, $2, $3, $4, $5, $6, $7, now())
		 ON CONFLICT (calendar_id, uid) DO UPDATE
		   SET component = EXCLUDED.component, data = EXCLUDED.data, etag = EXCLUDED.etag,
		       dtstart = EXCLUDED.dtstart, dtend = EXCLUDED.dtend, updated_at = now()
		 RETURNING id, calendar_id, uid, component, data, etag, dtstart, dtend, created_at, updated_at`,
		calendarID, uid, component, data, etag, dtstart, dtend,
	).Scan(&o.ID, &o.CalendarID, &o.UID, &o.Component, &o.Data, &o.ETag, &o.DTStart, &o.DTEnd, &o.CreatedAt, &o.UpdatedAt)
	if err != nil {
		return nil, fmt.Errorf("upsert object: %w", err)
	}

	if _, err := tx.Exec(ctx, `UPDATE cal_calendars SET ctag = ctag + 1 WHERE id = $1`, calendarID); err != nil {
		return nil, fmt.Errorf("bump ctag: %w", err)
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit tx: %w", err)
	}
	return &o, nil
}

func (s *Store) DeleteObject(ctx context.Context, calendarID uuid.UUID, uid string) error {
	tx, err := s.db.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin tx: %w", err)
	}
	defer tx.Rollback(ctx)

	tag, err := tx.Exec(ctx, `DELETE FROM cal_objects WHERE calendar_id = $1 AND uid = $2`, calendarID, uid)
	if err != nil {
		return fmt.Errorf("delete object: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	if _, err := tx.Exec(ctx, `UPDATE cal_calendars SET ctag = ctag + 1 WHERE id = $1`, calendarID); err != nil {
		return fmt.Errorf("bump ctag: %w", err)
	}
	return tx.Commit(ctx)
}