// Package store persists pay orders + the HD address-derivation cursor in
// SQLite (pure-Go modernc driver, no CGO — same choice as the control plane).
package store

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

	_ "modernc.org/sqlite"
)

type Status string

const (
	StatusPending Status = "pending"
	StatusPaid    Status = "paid"
	StatusExpired Status = "expired"
)

// Order is one payment request. Amounts are in micro-USDT (1e-6), matching the
// raw integer value of a TRC20 USDT transfer (USDT has 6 decimals).
type Order struct {
	OrderNo      string
	SKU          string
	ExpectAmount int64
	AddrIndex    uint32
	Address      string
	Status       Status
	TxID         string
	CreatedAt    time.Time
	ExpiresAt    time.Time
}

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

type Store struct{ db *sql.DB }

func Open(dsn string) (*Store, error) {
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(1) // SQLite: serialize writers, avoid "database is locked"
	s := &Store{db: db}
	if err := s.migrate(); err != nil {
		_ = db.Close()
		return nil, err
	}
	return s, nil
}

func (s *Store) Close() error { return s.db.Close() }

func (s *Store) migrate() error {
	stmts := []string{
		`CREATE TABLE IF NOT EXISTS pay_orders(
  order_no TEXT PRIMARY KEY,
  sku TEXT NOT NULL,
  expect_amount INTEGER NOT NULL,
  addr_index INTEGER NOT NULL,
  address TEXT NOT NULL,
  status TEXT NOT NULL,
  tx_id TEXT NOT NULL DEFAULT '',
  created_at INTEGER NOT NULL,
  expires_at INTEGER NOT NULL
)`,
		`CREATE INDEX IF NOT EXISTS idx_orders_status ON pay_orders(status)`,
		`CREATE TABLE IF NOT EXISTS addr_cursor(id INTEGER PRIMARY KEY CHECK(id=1), next_index INTEGER NOT NULL)`,
		`INSERT OR IGNORE INTO addr_cursor(id, next_index) VALUES(1, 0)`,
	}
	for _, q := range stmts {
		if _, err := s.db.Exec(q); err != nil {
			return err
		}
	}
	return nil
}

// NextAddrIndex atomically returns the current HD index and advances the cursor.
// Addresses are never reused (avoids an old payment landing on a recycled slot).
func (s *Store) NextAddrIndex(ctx context.Context) (uint32, error) {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return 0, err
	}
	defer func() { _ = tx.Rollback() }()
	var idx uint32
	if err := tx.QueryRowContext(ctx, `SELECT next_index FROM addr_cursor WHERE id=1`).Scan(&idx); err != nil {
		return 0, err
	}
	if _, err := tx.ExecContext(ctx, `UPDATE addr_cursor SET next_index=? WHERE id=1`, idx+1); err != nil {
		return 0, err
	}
	if err := tx.Commit(); err != nil {
		return 0, err
	}
	return idx, nil
}

func (s *Store) CreateOrder(ctx context.Context, o *Order) error {
	_, err := s.db.ExecContext(ctx,
		`INSERT INTO pay_orders(order_no,sku,expect_amount,addr_index,address,status,created_at,expires_at)
		 VALUES(?,?,?,?,?,?,?,?)`,
		o.OrderNo, o.SKU, o.ExpectAmount, o.AddrIndex, o.Address, o.Status, o.CreatedAt.Unix(), o.ExpiresAt.Unix())
	return err
}

const cols = `order_no,sku,expect_amount,addr_index,address,status,tx_id,created_at,expires_at`

func scanOrder(sc interface{ Scan(...any) error }) (*Order, error) {
	o := &Order{}
	var created, expires int64
	if err := sc.Scan(&o.OrderNo, &o.SKU, &o.ExpectAmount, &o.AddrIndex, &o.Address, &o.Status, &o.TxID, &created, &expires); err != nil {
		return nil, err
	}
	o.CreatedAt = time.Unix(created, 0)
	o.ExpiresAt = time.Unix(expires, 0)
	return o, nil
}

func (s *Store) GetOrder(ctx context.Context, orderNo string) (*Order, error) {
	row := s.db.QueryRowContext(ctx, `SELECT `+cols+` FROM pay_orders WHERE order_no=?`, orderNo)
	o, err := scanOrder(row)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	return o, err
}

func (s *Store) ListPending(ctx context.Context) ([]*Order, error) {
	rows, err := s.db.QueryContext(ctx, `SELECT `+cols+` FROM pay_orders WHERE status=?`, StatusPending)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()
	var out []*Order
	for rows.Next() {
		o, err := scanOrder(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, o)
	}
	return out, rows.Err()
}

// MarkPaid transitions pending->paid, idempotently (only affects a still-pending
// row). Returns true if this call was the one that flipped it.
func (s *Store) MarkPaid(ctx context.Context, orderNo, txID string) (bool, error) {
	res, err := s.db.ExecContext(ctx,
		`UPDATE pay_orders SET status=?, tx_id=? WHERE order_no=? AND status=?`,
		StatusPaid, txID, orderNo, StatusPending)
	if err != nil {
		return false, err
	}
	n, _ := res.RowsAffected()
	return n > 0, nil
}

// MarkExpired flips pending->expired for orders past their deadline.
func (s *Store) MarkExpired(ctx context.Context, now time.Time) (int64, error) {
	res, err := s.db.ExecContext(ctx,
		`UPDATE pay_orders SET status=? WHERE status=? AND expires_at < ?`,
		StatusExpired, StatusPending, now.Unix())
	if err != nil {
		return 0, err
	}
	n, _ := res.RowsAffected()
	return n, nil
}