package handlers

import (
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/flatrender/payment-svc/internal/config"
	"github.com/flatrender/payment-svc/internal/db"
	"github.com/flatrender/payment-svc/internal/middleware"
	"github.com/flatrender/payment-svc/internal/models"
	"github.com/flatrender/payment-svc/internal/signing"
	"github.com/flatrender/payment-svc/internal/zarinpal"
	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
)

const minAmountRial = 1000 // ZarinPal minimum (= 100 Toman)

type PayHandler struct {
	store *db.Store
	zp    *zarinpal.Client
	disp  *Dispatcher
	cfg   config.Config
}

func NewPayHandler(store *db.Store, zp *zarinpal.Client, disp *Dispatcher, cfg config.Config) *PayHandler {
	return &PayHandler{store: store, zp: zp, disp: disp, cfg: cfg}
}

// merchantFor resolves the ZarinPal merchant + sandbox flag for a client
// (per-client override falls back to the broker default).
func (h *PayHandler) merchantFor(client *models.ClientApp) (string, bool) {
	merchant := h.cfg.ZarinPalMerchantID
	if client.ZarinPalMerchantID != nil && *client.ZarinPalMerchantID != "" {
		merchant = *client.ZarinPalMerchantID
	}
	sandbox := h.cfg.ZarinPalSandbox
	if client.ZarinPalSandbox != nil {
		sandbox = *client.ZarinPalSandbox
	}
	return merchant, sandbox
}

// zpAmount converts canonical Rial to the unit ZarinPal expects for this broker.
func (h *PayHandler) zpAmount(amountRial int64) int64 {
	if h.cfg.ZarinPalAmountUnit == "toman" {
		return amountRial / 10
	}
	return amountRial
}

// toRial normalizes the client-supplied amount + currency to canonical Rial.
func toRial(amount int64, currency string) int64 {
	switch strings.ToUpper(strings.TrimSpace(currency)) {
	case "IRT", "TOMAN", "TMN", "TOMANS":
		return amount * 10
	default: // IRR / RIAL / empty
		return amount
	}
}

// POST /v1/pay/request   (client-authed: X-Api-Key + X-Signature)
func (h *PayHandler) Request(c *gin.Context) {
	client := middleware.GetClient(c)
	rawAny, _ := c.Get(middleware.CtxRawBody)
	raw, _ := rawAny.([]byte)

	var req models.PayRequest
	if err := json.Unmarshal(raw, &req); err != nil {
		c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: "invalid JSON body"})
		return
	}
	if req.ReturnURL == "" {
		c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: "return_url is required"})
		return
	}
	if !originAllowed(client, req.ReturnURL) {
		c.JSON(http.StatusBadRequest, models.APIError{Code: "return_url_not_allowed", Message: "return_url origin is not in the client's allowed list"})
		return
	}
	amountRial := toRial(req.Amount, req.Currency)
	if amountRial < minAmountRial {
		c.JSON(http.StatusBadRequest, models.APIError{Code: "amount_too_low", Message: fmt.Sprintf("amount must be at least %d Rial (100 Toman)", minAmountRial)})
		return
	}

	desc := req.Description
	if desc == "" {
		desc = "پرداخت آنلاین"
	}
	exp := time.Now().Add(30 * time.Minute)
	txn := &models.Transaction{
		ClientAppID: client.ID,
		Status:      models.StatusCreated,
		Gateway:     "ZarinPal",
		AmountRial:  amountRial,
		Currency:    "IRR",
		Description: &desc,
		ReturnURL:   req.ReturnURL,
		Metadata:    req.Metadata,
		ExpiresAt:   &exp,
	}
	if req.ClientRef != "" {
		txn.ClientRef = &req.ClientRef
	}
	if req.Mobile != "" {
		txn.PayerMobile = &req.Mobile
	}
	if req.Email != "" {
		txn.PayerEmail = &req.Email
	}

	created, err := h.store.CreateTransaction(c.Request.Context(), txn)
	if err != nil {
		c.JSON(http.StatusInternalServerError, models.APIError{Code: "db_error", Message: "could not create transaction"})
		return
	}

	merchant, sandbox := h.merchantFor(client)
	if merchant == "" {
		c.JSON(http.StatusServiceUnavailable, models.APIError{Code: "gateway_unconfigured", Message: "ZarinPal merchant id is not configured"})
		return
	}

	res, err := h.zp.Request(c.Request.Context(), sandbox, merchant, h.zpAmount(amountRial),
		h.cfg.CallbackURL(), desc, map[string]string{"order_id": created.ID.String()})
	if err != nil {
		_, _ = h.store.MarkFailed(c.Request.Context(), created.ID, err.Error(), nil)
		c.JSON(http.StatusBadGateway, models.APIError{Code: "gateway_error", Message: err.Error()})
		return
	}

	if err := h.store.SetAuthority(c.Request.Context(), created.ID, res.Authority); err != nil {
		c.JSON(http.StatusInternalServerError, models.APIError{Code: "db_error", Message: "could not persist authority"})
		return
	}

	c.JSON(http.StatusOK, models.PayResponse{
		ID:         created.ID,
		Status:     models.StatusPending,
		PaymentURL: res.StartPay,
		Authority:  res.Authority,
		AmountRial: amountRial,
	})
}

// GET /callback/zarinpal?Authority=..&Status=OK|NOK   (PUBLIC — ZarinPal hits this)
func (h *PayHandler) Callback(c *gin.Context) {
	authority := c.Query("Authority")
	status := c.Query("Status")
	if authority == "" {
		c.String(http.StatusBadRequest, "missing Authority")
		return
	}

	txn, err := h.store.GetTransactionByAuthority(c.Request.Context(), authority)
	if err != nil {
		c.String(http.StatusNotFound, "transaction not found")
		return
	}
	client, err := h.store.GetClientApp(c.Request.Context(), txn.ClientAppID)
	if err != nil {
		c.String(http.StatusInternalServerError, "client not found")
		return
	}
	// Re-fetch with secret for signing the redirect/webhook.
	client, _ = h.store.GetClientByAPIKey(c.Request.Context(), client.APIKey)

	now := time.Now().Unix()

	// User cancelled / bank declined before verify.
	if status != "OK" {
		failed, _ := h.store.MarkFailed(c.Request.Context(), txn.ID, "user cancelled or status NOK", nil)
		if failed != nil {
			h.disp.Enqueue(c.Request.Context(), client, failed, now)
			h.redirectBack(c, client, failed)
		} else {
			h.redirectBack(c, client, txn)
		}
		return
	}

	merchant, sandbox := h.merchantFor(client)
	vr, err := h.zp.Verify(c.Request.Context(), sandbox, merchant, h.zpAmount(txn.AmountRial), authority)
	if err != nil {
		failed, _ := h.store.MarkFailed(c.Request.Context(), txn.ID, "verify error: "+err.Error(), rawJSON(vr))
		final := pick(failed, txn)
		h.disp.Enqueue(c.Request.Context(), client, final, now)
		h.redirectBack(c, client, final)
		return
	}

	if vr.Code == 100 || vr.Code == 101 {
		paid, perr := h.store.MarkPaid(c.Request.Context(), txn.ID, vr.RefID, vr.CardPan, vr.Fee, rawJSON(vr))
		if perr != nil {
			// Already terminal (duplicate callback) — just bounce the user back with current state.
			cur, _ := h.store.GetTransaction(c.Request.Context(), txn.ID)
			h.redirectBack(c, client, pick(cur, txn))
			return
		}
		h.disp.Enqueue(c.Request.Context(), client, paid, now)
		h.redirectBack(c, client, paid)
		return
	}

	failed, _ := h.store.MarkFailed(c.Request.Context(), txn.ID, fmt.Sprintf("zarinpal verify code %d", vr.Code), rawJSON(vr))
	final := pick(failed, txn)
	h.disp.Enqueue(c.Request.Context(), client, final, now)
	h.redirectBack(c, client, final)
}

// redirectBack bounces the user to the client's return_url with a signed result.
// Signature canonical string: "{id}.{status}.{ref_id}.{amount_rial}".
func (h *PayHandler) redirectBack(c *gin.Context, client *models.ClientApp, t *models.Transaction) {
	ref := ""
	if t.RefID != nil {
		ref = *t.RefID
	}
	canonical := fmt.Sprintf("%s.%s.%s.%d", t.ID, t.Status, ref, t.AmountRial)
	sign := signing.Sign(client.Secret, []byte(canonical))

	u, err := url.Parse(t.ReturnURL)
	if err != nil {
		c.String(http.StatusOK, "payment %s (ref %s)", t.Status, ref)
		return
	}
	q := u.Query()
	q.Set("status", t.Status)
	q.Set("id", t.ID.String())
	q.Set("ref_id", ref)
	q.Set("sign", sign)
	u.RawQuery = q.Encode()
	c.Redirect(http.StatusFound, u.String())
}

// POST /v1/pay/inquiry   (client-authed)  body: { "id": "<txn uuid>" }
// Authoritative server-side status check — clients should NOT trust the redirect alone.
func (h *PayHandler) Inquiry(c *gin.Context) {
	client := middleware.GetClient(c)
	rawAny, _ := c.Get(middleware.CtxRawBody)
	raw, _ := rawAny.([]byte)

	var body struct {
		ID        string `json:"id"`
		ClientRef string `json:"client_ref"`
	}
	_ = json.Unmarshal(raw, &body)

	var txn *models.Transaction
	var err error
	if body.ID != "" {
		id, perr := uuid.Parse(body.ID)
		if perr != nil {
			c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: "invalid id"})
			return
		}
		txn, err = h.store.GetTransaction(c.Request.Context(), id)
	} else {
		c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: "id is required"})
		return
	}
	if err != nil || txn.ClientAppID != client.ID {
		c.JSON(http.StatusNotFound, models.APIError{Code: "not_found", Message: "transaction not found"})
		return
	}
	c.JSON(http.StatusOK, txn)
}

// ── helpers ──────────────────────────────────────────────────────────────────

func originAllowed(client *models.ClientApp, returnURL string) bool {
	if len(client.AllowedReturnOrigins) == 0 {
		return true // no allow-list configured → permissive
	}
	u, err := url.Parse(returnURL)
	if err != nil || u.Host == "" {
		return false
	}
	origin := strings.ToLower(u.Scheme + "://" + u.Host)
	for _, o := range client.AllowedReturnOrigins {
		if strings.ToLower(strings.TrimRight(o, "/")) == origin {
			return true
		}
	}
	return false
}

func rawJSON(vr *zarinpal.VerifyResult) []byte {
	if vr == nil {
		return nil
	}
	return vr.Raw
}

func pick(primary, fallback *models.Transaction) *models.Transaction {
	if primary != nil {
		return primary
	}
	return fallback
}