package handlers

import (
	"bytes"
	"context"
	"encoding/json"
	"log"
	"net/http"
	"time"

	"github.com/flatrender/payment-svc/internal/db"
	"github.com/flatrender/payment-svc/internal/models"
	"github.com/flatrender/payment-svc/internal/signing"
)

// Dispatcher delivers signed webhooks to client sites with retry/backoff.
type Dispatcher struct {
	store *db.Store
	http  *http.Client
}

func NewDispatcher(store *db.Store) *Dispatcher {
	return &Dispatcher{store: store, http: &http.Client{Timeout: 15 * time.Second}}
}

// Enqueue builds the signed payload for a finished transaction and queues delivery.
// No-op if the client has no webhook_url configured.
func (d *Dispatcher) Enqueue(ctx context.Context, client *models.ClientApp, t *models.Transaction, nowUnix int64) {
	if client.WebhookURL == nil || *client.WebhookURL == "" {
		return
	}
	event := "payment.failed"
	if t.Status == models.StatusPaid {
		event = "payment.paid"
	}
	payload := models.WebhookPayload{
		Event:       event,
		ID:          t.ID,
		Status:      t.Status,
		AmountRial:  t.AmountRial,
		Currency:    t.Currency,
		Metadata:    t.Metadata,
		CreatedAtTs: nowUnix,
		PaidAt:      t.PaidAt,
	}
	if t.ClientRef != nil {
		payload.ClientRef = *t.ClientRef
	}
	if t.RefID != nil {
		payload.RefID = *t.RefID
	}
	if t.Authority != nil {
		payload.Authority = *t.Authority
	}
	if t.CardPan != nil {
		payload.CardPan = *t.CardPan
	}
	body, _ := json.Marshal(payload)
	sig := signing.Sign(client.Secret, body)
	id, err := d.store.EnqueueWebhook(ctx, t.ID, *client.WebhookURL, body, sig)
	if err != nil {
		log.Printf("webhook enqueue failed for txn %s: %v", t.ID, err)
		return
	}
	// Best-effort immediate delivery so the client credits near-instantly; the
	// retry loop (Run) still covers it if this attempt fails.
	go func() {
		bg, cancel := context.WithTimeout(context.Background(), 20*time.Second)
		defer cancel()
		if w, err := d.store.GetWebhook(bg, id); err == nil && w != nil {
			d.deliver(bg, w)
		}
	}()
}

// Run starts the delivery loop until ctx is cancelled.
func (d *Dispatcher) Run(ctx context.Context) {
	ticker := time.NewTicker(10 * time.Second)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			d.tick(ctx)
		}
	}
}

func (d *Dispatcher) tick(ctx context.Context) {
	due, err := d.store.ClaimDueWebhooks(ctx, 20)
	if err != nil {
		log.Printf("webhook claim failed: %v", err)
		return
	}
	for _, w := range due {
		d.deliver(ctx, w)
	}
}

func (d *Dispatcher) deliver(ctx context.Context, w *db.WebhookDelivery) {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, w.URL, bytes.NewReader(w.Payload))
	if err != nil {
		_ = d.store.MarkWebhookFailed(ctx, w.ID, 0, err.Error(), backoff(w.Attempts))
		return
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-FlatPay-Signature", w.Signature)
	req.Header.Set("X-FlatPay-Event", "payment")

	resp, err := d.http.Do(req)
	if err != nil {
		_ = d.store.MarkWebhookFailed(ctx, w.ID, 0, err.Error(), backoff(w.Attempts))
		return
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
		_ = d.store.MarkWebhookDelivered(ctx, w.ID, resp.StatusCode)
		return
	}
	_ = d.store.MarkWebhookFailed(ctx, w.ID, resp.StatusCode, "non-2xx response", backoff(w.Attempts))
}

// backoff: 30s, 1m, 2m, 4m, 8m, ... capped at 1h.
func backoff(attempts int) time.Duration {
	d := 30 * time.Second
	for i := 0; i < attempts; i++ {
		d *= 2
		if d >= time.Hour {
			return time.Hour
		}
	}
	return d
}