first commit of restructured project

trahn-trade-backend/internal/external/coingecko.go

@@ -0,0 +1,58 @@
+package external
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/kjannette/trahn-backend/internal/httputil"
+)
+
+const coingeckoURL = "https://api.coingecko.com/api/v3/simple/price?ids=ethereum&vs_currencies=usd"
+
+type CoinGeckoClient struct {
+	httpClient *http.Client
+	retry      httputil.RetryConfig
+}
+
+func NewCoinGeckoClient() *CoinGeckoClient {
+	return &CoinGeckoClient{
+		httpClient: &http.Client{Timeout: 10 * time.Second},
+		retry: httputil.RetryConfig{
+			MaxAttempts: 3,
+			BaseDelay:   2 * time.Second,
+			MaxDelay:    10 * time.Second,
+		},
+	}
+}
+
+func (c *CoinGeckoClient) GetETHPrice(ctx context.Context) (float64, error) {
+	resp, err := httputil.Do(ctx, c.httpClient, c.retry, func() (*http.Request, error) {
+		return http.NewRequestWithContext(ctx, http.MethodGet, coingeckoURL, nil)
+	})
+	if err != nil {
+		return 0, fmt.Errorf("coingecko fetch: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return 0, fmt.Errorf("coingecko returned status %d", resp.StatusCode)
+	}
+
+	var data struct {
+		Ethereum struct {
+			USD float64 `json:"usd"`
+		} `json:"ethereum"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+		return 0, fmt.Errorf("decode: %w", err)
+	}
+
+	if data.Ethereum.USD <= 0 {
+		return 0, fmt.Errorf("invalid price: %f", data.Ethereum.USD)
+	}
+
+	return data.Ethereum.USD, nil
+}