writekit/internal/billing/lemon.go

package billing

import (
	"bytes"
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
)

const lemonBaseURL = "https://api.lemonsqueezy.com/v1"

type LemonClient struct {
	apiKey        string
	storeID       string
	webhookSecret string
	httpClient    *http.Client
}

func NewLemonClient() *LemonClient {
	return &LemonClient{
		apiKey:        os.Getenv("LEMON_API_KEY"),
		storeID:       os.Getenv("LEMON_STORE_ID"),
		webhookSecret: os.Getenv("LEMON_WEBHOOK_SECRET"),
		httpClient:    &http.Client{},
	}
}

func (c *LemonClient) IsConfigured() bool {
	return c.apiKey != "" && c.storeID != ""
}

type CheckoutRequest struct {
	StoreID         string            `json:"store_id"`
	VariantID       string            `json:"variant_id"`
	CustomPrice     *int              `json:"custom_price,omitempty"`
	CheckoutOptions *CheckoutOptions  `json:"checkout_options,omitempty"`
	CheckoutData    *CheckoutData     `json:"checkout_data,omitempty"`
}

type CheckoutOptions struct {
	Embed bool `json:"embed,omitempty"`
}

type CheckoutData struct {
	Email  string            `json:"email,omitempty"`
	Name   string            `json:"name,omitempty"`
	Custom map[string]string `json:"custom,omitempty"`
}

type CheckoutResponse struct {
	Data struct {
		ID         string `json:"id"`
		Attributes struct {
			URL string `json:"url"`
		} `json:"attributes"`
	} `json:"data"`
}

func (c *LemonClient) CreateCheckout(ctx context.Context, req *CheckoutRequest) (*CheckoutResponse, error) {
	if req.StoreID == "" {
		req.StoreID = c.storeID
	}

	payload := map[string]any{
		"data": map[string]any{
			"type":       "checkouts",
			"attributes": req,
			"relationships": map[string]any{
				"store": map[string]any{
					"data": map[string]any{"type": "stores", "id": req.StoreID},
				},
				"variant": map[string]any{
					"data": map[string]any{"type": "variants", "id": req.VariantID},
				},
			},
		},
	}

	body, err := json.Marshal(payload)
	if err != nil {
		return nil, err
	}

	httpReq, err := http.NewRequestWithContext(ctx, "POST", lemonBaseURL+"/checkouts", bytes.NewReader(body))
	if err != nil {
		return nil, err
	}

	httpReq.Header.Set("Authorization", "Bearer "+c.apiKey)
	httpReq.Header.Set("Content-Type", "application/vnd.api+json")
	httpReq.Header.Set("Accept", "application/vnd.api+json")

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode != http.StatusCreated && resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("checkout creation failed (status %d): %s", resp.StatusCode, string(respBody))
	}

	var checkoutResp CheckoutResponse
	if err := json.Unmarshal(respBody, &checkoutResp); err != nil {
		return nil, err
	}

	return &checkoutResp, nil
}

func (c *LemonClient) CreateSubscriptionCheckout(ctx context.Context, variantID, email, name string, custom map[string]string) (string, error) {
	req := &CheckoutRequest{
		VariantID: variantID,
		CheckoutData: &CheckoutData{
			Email:  email,
			Name:   name,
			Custom: custom,
		},
		CheckoutOptions: &CheckoutOptions{Embed: true},
	}

	resp, err := c.CreateCheckout(ctx, req)
	if err != nil {
		return "", err
	}

	return resp.Data.Attributes.URL, nil
}

func (c *LemonClient) CreateDonationCheckout(ctx context.Context, variantID string, amountCents int, email, name, message string, custom map[string]string) (string, error) {
	if custom == nil {
		custom = make(map[string]string)
	}
	if message != "" {
		custom["message"] = message
	}

	req := &CheckoutRequest{
		VariantID:   variantID,
		CustomPrice: &amountCents,
		CheckoutData: &CheckoutData{
			Email:  email,
			Name:   name,
			Custom: custom,
		},
		CheckoutOptions: &CheckoutOptions{Embed: true},
	}

	resp, err := c.CreateCheckout(ctx, req)
	if err != nil {
		return "", err
	}

	return resp.Data.Attributes.URL, nil
}

func (c *LemonClient) VerifyWebhook(payload []byte, signature string) bool {
	if c.webhookSecret == "" {
		return false
	}

	mac := hmac.New(sha256.New, []byte(c.webhookSecret))
	mac.Write(payload)
	expectedSig := hex.EncodeToString(mac.Sum(nil))

	return hmac.Equal([]byte(signature), []byte(expectedSig))
}

type WebhookEvent struct {
	Meta struct {
		EventName  string            `json:"event_name"`
		CustomData map[string]string `json:"custom_data"`
	} `json:"meta"`
	Data json.RawMessage `json:"data"`
}

type SubscriptionData struct {
	ID         string `json:"id"`
	Attributes struct {
		CustomerID  int    `json:"customer_id"`
		VariantName string `json:"variant_name"`
		UserName    string `json:"user_name"`
		UserEmail   string `json:"user_email"`
		Status      string `json:"status"`
		RenewsAt    string `json:"renews_at"`
		FirstSubscriptionItem struct {
			Price int `json:"price"`
		} `json:"first_subscription_item"`
	} `json:"attributes"`
}

type OrderData struct {
	ID         string `json:"id"`
	Attributes struct {
		UserName  string `json:"user_name"`
		UserEmail string `json:"user_email"`
		TotalUsd  int    `json:"total_usd"`
	} `json:"attributes"`
}

func (c *LemonClient) ParseWebhookEvent(payload []byte) (*WebhookEvent, error) {
	var event WebhookEvent
	if err := json.Unmarshal(payload, &event); err != nil {
		return nil, err
	}
	return &event, nil
}

func (e *WebhookEvent) GetSubscriptionData() (*SubscriptionData, error) {
	var data SubscriptionData
	if err := json.Unmarshal(e.Data, &data); err != nil {
		return nil, err
	}
	return &data, nil
}

func (e *WebhookEvent) GetOrderData() (*OrderData, error) {
	var data OrderData
	if err := json.Unmarshal(e.Data, &data); err != nil {
		return nil, err
	}
	return &data, nil
}