add a mempool client for fee estimation

chain/fee_estimator.go

@@ -0,0 +1,21 @@
+package chain
+
+import "context"
+
+type FeeStrategy int
+
+const (
+	FeeStrategyFastest  FeeStrategy = 0
+	FeeStrategyHalfHour FeeStrategy = 1
+	FeeStrategyHour     FeeStrategy = 2
+	FeeStrategyEconomy  FeeStrategy = 3
+	FeeStrategyMinimum  FeeStrategy = 4
+)
+
+type FeeEstimation struct {
+	SatPerVByte float64
+}
+
+type FeeEstimator interface {
+	EstimateFeeRate(context.Context, FeeStrategy) (*FeeEstimation, error)
+}

mempool/mempool_client.go

@@ -0,0 +1,90 @@
+package mempool
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/breez/lspd/chain"
+)
+
+type MempoolClient struct {
+	apiBaseUrl string
+	httpClient *http.Client
+}
+
+type RecommendedFeesResponse struct {
+	FastestFee  float64 `json:"fastestFee"`
+	HalfHourFee float64 `json:"halfHourFee"`
+	HourFee     float64 `json:"hourFee"`
+	EconomyFee  float64 `json:"economyFee"`
+	MinimumFee  float64 `json:"minimumFee"`
+}
+
+func NewMempoolClient(apiBaseUrl string) (*MempoolClient, error) {
+	if apiBaseUrl == "" {
+		return nil, fmt.Errorf("apiBaseUrl not set")
+	}
+
+	if !strings.HasSuffix(apiBaseUrl, "/") {
+		apiBaseUrl = apiBaseUrl + "/"
+	}
+
+	return &MempoolClient{
+		apiBaseUrl: apiBaseUrl,
+		httpClient: http.DefaultClient,
+	}, nil
+}
+
+func (m *MempoolClient) EstimateFeeRate(
+	ctx context.Context,
+	strategy chain.FeeStrategy,
+) (*chain.FeeEstimation, error) {
+	req, err := http.NewRequestWithContext(
+		ctx,
+		"GET",
+		m.apiBaseUrl+"fees/recommended",
+		nil,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("http.NewRequestWithContext error: %w", err)
+	}
+
+	resp, err := m.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("httpClient.Do error: %w", err)
+	}
+
+	defer resp.Body.Close()
+	if !(resp.StatusCode >= 200 && resp.StatusCode < 300) {
+		return nil, fmt.Errorf("error statuscode %v: %w", resp.StatusCode, err)
+	}
+
+	var body RecommendedFeesResponse
+	err = json.NewDecoder(resp.Body).Decode(&body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
+	}
+
+	var rate float64
+	switch strategy {
+	case chain.FeeStrategyFastest:
+		rate = body.FastestFee
+	case chain.FeeStrategyHalfHour:
+		rate = body.HalfHourFee
+	case chain.FeeStrategyHour:
+		rate = body.HourFee
+	case chain.FeeStrategyEconomy:
+		rate = body.EconomyFee
+	case chain.FeeStrategyMinimum:
+		rate = body.MinimumFee
+	default:
+		return nil, fmt.Errorf("unsupported fee strategy: %v", strategy)
+	}
+
+	return &chain.FeeEstimation{
+		SatPerVByte: rate,
+	}, nil
+}