// Paddle Checkout Integration
// Simplified - uses Paddle.js for client-side checkout

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"
)

// PaddleConfig holds our Paddle configuration
// In production these come from env vars
type PaddleConfig struct {
	ClientToken string // For Paddle.js frontend
	VendorID    string // Your Paddle vendor ID
	Environment string // "production" or "sandbox"
}

func getPaddleConfig() PaddleConfig {
	return PaddleConfig{
		// Client token is PUBLIC - safe to expose in JS
		// This is different from the API key (which is secret)
		ClientToken: os.Getenv("PADDLE_CLIENT_TOKEN"),
		VendorID:    os.Getenv("PADDLE_VENDOR_ID"),
		Environment: "production",
	}
}

// Price IDs - these come from your Paddle dashboard
// You create these when you set up products/prices
var PriceIDs = map[string]string{
	"personal_yearly_usd": "pri_01knejm7ft2ska5r4qff2gm9r4",
	"personal_yearly_eur": "pri_01knejm7kfhfknjyjq3je56r19",
	"personal_yearly_gbp": "pri_01knejm7q2bkkszam05dtyrsnc",
	"family_yearly_usd":   "pri_01knejm7xs9kqt0vn61dx6q808",
	"family_yearly_eur":   "pri_01knejm811100z4xx2xxedwez6",
	"family_yearly_gbp":   "pri_01knejm85v2d1fjt998xypac2v",
	"pro_yearly_usd":      "pri_01knejm8djq4p63rmsxze7by58",
	"pro_yearly_eur":      "pri_01knejm8gjq5staaz9s7b4k8bp",
	"pro_yearly_gbp":      "pri_01knejm8kk3qwtk32kry5c607g",
	"team10_yearly_usd":   "pri_01knejm8twprj5ca4zem1g4g56",
	"team25_yearly_usd":   "pri_01knejm91d5xppcfw4w4w2tf7x",
	"team100_yearly_usd":  "pri_01knejm98a7bxvcpgtqm9aa81b",
	"team250_yearly_usd":  "pri_01knejm9fevyr7bse0hm7ym9mq",
	"team500_yearly_usd":  "pri_01knejm9nz0zbvecv0fx5d1red",
}

// CheckoutRequest - user wants to subscribe
type CheckoutRequest struct {
	PriceID    string `json:"price_id"`    // Which plan
	CustomerID string `json:"customer_id"` // Our customer ID (if exists)
	Email      string `json:"email"`       // Customer email
	VaultL0    string `json:"vault_l0"`    // Which vault this pays for
}

// CheckoutResponse - Paddle checkout URL or token
type CheckoutResponse struct {
	Success       bool   `json:"success"`
	CheckoutURL   string `json:"checkout_url,omitempty"` // For hosted checkout
	TransactionID string `json:"transaction_id,omitempty"`
	Error         string `json:"error,omitempty"`
}

// HandleCheckout creates a Paddle checkout for a new subscription
func HandleCheckout(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}

	var req CheckoutRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		respondJSON(w, CheckoutResponse{Success: false, Error: "invalid json"})
		return
	}

	// Validate price ID exists
	if req.PriceID == "" {
		respondJSON(w, CheckoutResponse{Success: false, Error: "price_id required"})
		return
	}

	// Get or create customer
	var customerID string
	if req.CustomerID != "" {
		// Use existing
		customerID = req.CustomerID
	} else {
		// Create new customer via Paddle
		if req.Email == "" {
			respondJSON(w, CheckoutResponse{Success: false, Error: "email required for new customer"})
			return
		}

		// Create in our DB + Paddle via dual-write layer
		// TODO: Implement using sync.go
		customerID = createCustomerViaPaddle(req.Email, "")
	}

	// Create transaction (invoice) in Paddle
	// For automatic collection (credit card): creates checkout
	// For manual collection (enterprise): creates invoice
	transactionID := createPaddleTransaction(customerID, req.PriceID)

	// Store the link between transaction and vault
	// So when webhook says "paid", we know which vault to activate
	storePendingSubscription(customerID, req.VaultL0, transactionID, req.PriceID)

	// Get checkout URL from Paddle
	checkoutURL := getPaddleCheckoutURL(transactionID)

	respondJSON(w, CheckoutResponse{
		Success:       true,
		CheckoutURL:   checkoutURL,
		TransactionID: transactionID,
	})
}

// HandleCheckoutSuccess - Paddle redirects here after successful payment
func HandleCheckoutSuccess(w http.ResponseWriter, r *http.Request) {
	// Paddle redirects to: /checkout/success?transaction_id=txn_xxx&subscription_id=sub_xxx
	transactionID := r.URL.Query().Get("transaction_id")
	subscriptionID := r.URL.Query().Get("subscription_id")

	if transactionID == "" {
		http.Error(w, "Missing transaction_id", http.StatusBadRequest)
		return
	}

	// Look up which vault this is for
	vaultL0 := getVaultForTransaction(transactionID)
	if vaultL0 == "" {
		http.Error(w, "Unknown transaction", http.StatusNotFound)
		return
	}

	// Update our records
	activateVaultSubscription(vaultL0, subscriptionID, transactionID)

	// Redirect to vault with success message
	http.Redirect(w, r, "/app/?subscription=active&vault="+vaultL0, http.StatusSeeOther)
}

// WebhookHandler - Paddle sends us events
func HandlePaddleWebhook(w http.ResponseWriter, r *http.Request) {
	// Read the raw body BEFORE verification — the signature is over the raw
	// bytes, so we can't let json.Decoder rewrite or reformat anything.
	body, err := io.ReadAll(r.Body)
	if err != nil {
		http.Error(w, "Read error", http.StatusBadRequest)
		return
	}

	if !verifyWebhookSignature(r, body) {
		http.Error(w, "Invalid signature", http.StatusUnauthorized)
		return
	}

	var event map[string]interface{}
	if err := json.Unmarshal(body, &event); err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}

	// Handle empty/malformed events gracefully
	if event == nil {
		w.WriteHeader(http.StatusOK)
		return
	}

	eventType, _ := event["event_type"].(string)
	data, _ := event["data"].(map[string]interface{})

	switch eventType {
	case "transaction.completed":
		// Payment succeeded
		if transactionID, ok := data["id"].(string); ok {
			activateVaultForTransaction(transactionID)
		}

	case "transaction.past_due":
		// Payment failed
		if transactionID, ok := data["id"].(string); ok {
			suspendVaultForTransaction(transactionID)
		}

	case "subscription.canceled":
		// Subscription cancelled
		if subscriptionID, ok := data["id"].(string); ok {
			cancelVaultSubscription(subscriptionID)
		}
	}

	w.WriteHeader(http.StatusOK)
}

// Helper functions (simplified - need implementation)

func createCustomerViaPaddle(email, name string) string {
	// Use sync.go dual-write layer
	// POST /customers to Paddle
	return "ctm_" + generateID()
}

func createPaddleTransaction(customerID, priceID string) string {
	// POST /transactions to Paddle
	// Returns transaction ID
	return "txn_" + generateID()
}

func getPaddleCheckoutURL(transactionID string) string {
	// Paddle generates checkout URL
	// Or we build it: https://checkout.paddle.com/?transaction=txn_xxx
	return "https://checkout.paddle.com/?transaction=" + transactionID
}

func storePendingSubscription(customerID, vaultL0, transactionID, priceID string) {
	// Store in DB: pending subscription linking transaction to vault
	// When webhook arrives, we know which vault to activate
}

func getVaultForTransaction(transactionID string) string {
	// Lookup vault_l0 from pending subscriptions table
	return ""
}

func activateVaultSubscription(vaultL0, subscriptionID, transactionID string) {
	// Update subscriptions table: status = active
	// Update vaults table: subscription_id = subscriptionID
}

func activateVaultForTransaction(transactionID string) {
	// Webhook handler - activate the vault
}

func suspendVaultForTransaction(transactionID string) {
	// Webhook handler - mark subscription past_due
}

func cancelVaultSubscription(subscriptionID string) {
	// Webhook handler - mark cancelled
}

// verifyWebhookSignature verifies the Paddle webhook signature.
//
// Paddle signs webhooks with HMAC-SHA256 over "<timestamp>:<raw_body>". The
// signature header looks like:
//
//	Paddle-Signature: ts=1700000000;h1=abcdef0123456789...
//
// We require:
//   - PADDLE_WEBHOOK_SECRET env var is set (refuse if missing — no permissive default)
//   - the Paddle-Signature header is present and parseable
//   - the timestamp is within ±5 minutes of now (anti-replay)
//   - hmac-sha256(secret, ts + ":" + body) matches h1 in constant time
//
// Returns false on any failure. SECURITY.md: failures are visible and noisy,
// no silent fallback.
func verifyWebhookSignature(r *http.Request, body []byte) bool {
	secret := os.Getenv("PADDLE_WEBHOOK_SECRET")
	if secret == "" {
		log.Printf("PADDLE_WEBHOOK_SECRET not set; refusing webhook")
		return false
	}

	sigHeader := r.Header.Get("Paddle-Signature")
	if sigHeader == "" {
		log.Printf("webhook: missing Paddle-Signature header")
		return false
	}

	var ts, h1 string
	for _, part := range strings.Split(sigHeader, ";") {
		kv := strings.SplitN(part, "=", 2)
		if len(kv) != 2 {
			continue
		}
		switch kv[0] {
		case "ts":
			ts = kv[1]
		case "h1":
			h1 = kv[1]
		}
	}
	if ts == "" || h1 == "" {
		log.Printf("webhook: malformed Paddle-Signature header: %q", sigHeader)
		return false
	}

	// Anti-replay: timestamp within 5 minutes
	tsInt, err := strconv.ParseInt(ts, 10, 64)
	if err != nil {
		log.Printf("webhook: invalid ts: %v", err)
		return false
	}
	const maxSkew = 300 // 5 minutes
	now := time.Now().Unix()
	if now-tsInt > maxSkew || tsInt-now > maxSkew {
		log.Printf("webhook: timestamp out of range (ts=%d now=%d)", tsInt, now)
		return false
	}

	// Compute HMAC-SHA256(secret, ts + ":" + body)
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(ts))
	mac.Write([]byte{':'})
	mac.Write(body)
	expected := hex.EncodeToString(mac.Sum(nil))

	if !hmac.Equal([]byte(expected), []byte(h1)) {
		log.Printf("webhook: signature mismatch")
		return false
	}
	return true
}

func generateID() string {
	return fmt.Sprintf("%d", time.Now().UnixNano())
}

// respondJSON sends JSON response
func respondJSON(w http.ResponseWriter, data interface{}) {
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(data)
}