// Package watcher polls TronGrid for incoming USDT and marks paid orders.
// It only reads the chain and flips order state — it never holds keys or moves
// funds (sweeping is a separate offline step).
package watcher

import (
	"context"
	"log/slog"
	"time"

	"github.com/wangjia/pangolin/pay/internal/store"
	"github.com/wangjia/pangolin/pay/internal/tron"
)

type Watcher struct {
	st   *store.Store
	tron tron.Fetcher
	log  *slog.Logger
	now  func() time.Time
}

func New(st *store.Store, f tron.Fetcher, log *slog.Logger) *Watcher {
	if log == nil {
		log = slog.Default()
	}
	return &Watcher{st: st, tron: f, log: log, now: time.Now}
}

// Tick: (1) expire overdue pending orders; (2) for each still-pending order,
// look for a confirmed incoming transfer >= the expected amount on its unique
// address and mark it paid. Idempotent — a transfer seen twice flips the order
// at most once (MarkPaid only affects a still-pending row).
func (w *Watcher) Tick(ctx context.Context) error {
	if n, err := w.st.MarkExpired(ctx, w.now()); err != nil {
		return err
	} else if n > 0 {
		w.log.Info("orders expired", "count", n)
	}

	pending, err := w.st.ListPending(ctx)
	if err != nil {
		return err
	}
	for _, o := range pending {
		transfers, err := w.tron.IncomingTransfers(ctx, o.Address)
		if err != nil {
			// Transient (rate limit / network): log and move on; retried next tick.
			w.log.Warn("fetch transfers failed", "order", o.OrderNo, "err", err)
			continue
		}
		for _, t := range transfers {
			if t.Value < o.ExpectAmount {
				continue
			}
			ok, err := w.st.MarkPaid(ctx, o.OrderNo, t.TxID)
			if err != nil {
				w.log.Error("mark paid", "order", o.OrderNo, "err", err)
				break
			}
			if ok {
				w.log.Info("order paid", "order", o.OrderNo, "tx", t.TxID, "value", t.Value, "address", o.Address)
			}
			break
		}
	}
	return nil
}

// Loop runs Tick every interval until ctx is cancelled.
func (w *Watcher) Loop(ctx context.Context, interval time.Duration) {
	t := time.NewTicker(interval)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			if err := w.Tick(ctx); err != nil {
				w.log.Error("watcher tick", "err", err)
			}
		}
	}
}