Coingecko

.travis.yml

@@ -0,0 +1,19 @@
+language: go
+
+go:
+  - 1.11.x
+
+install:
+  - export GOMETALINTER_VERSION=2.0.11
+  - ./.travis/gometalinter-install.sh
+  - export PATH=$PATH:${TRAVIS_HOME}/gometalinter/gometalinter-${GOMETALINTER_VERSION}-linux-amd64
+  - export GO111MODULE=on
+
+cache:
+  directories:
+  - ${TRAVIS_HOME}/gometalinter/gometalinter-${GOMETALINTER_VERSION}-linux-amd64
+
+script:
+  - gometalinter --config=gometalinter.json ./...
+  - go build -v -mod=vendor ./...
+  - go test -v -mod=vendor ./...

.travis/gometalinter-install.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+set -euo pipefail
+
+readonly version="$GOMETALINTER_VERSION"
+readonly archive_url="https://github.com/alecthomas/gometalinter/releases/download/v$version/gometalinter-$version-linux-amd64.tar.gz"
+readonly gometalinter_dir="${TRAVIS_HOME}/gometalinter"
+
+if [[ -f "$gometalinter_dir/gometalinter-$version-linux-amd64/gometalinter" ]]; then
+    echo "gometalinter is already installed, skipping..."
+    exit 0
+fi
+
+pushd "$gometalinter_dir"
+curl -fsSLO "$archive_url"
+tar xvf "gometalinter-$version-linux-amd64.tar.gz"
+rm "gometalinter-$version-linux-amd64.tar.gz"
+popd

coingecko/coingecko.go

@@ -0,0 +1,81 @@
+package coingecko
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// CoinGecko is the CoinGecko implementation of Provider. The
+// precision of CoinGecko provider is up to day.
+type CoinGecko struct {
+	client  *http.Client
+	baseURL string
+}
+
+// New creates a new CoinGecko instance.
+func New() *CoinGecko {
+	const (
+		defaultTimeout = time.Second * 10
+		baseURL        = "https://api.coingecko.com/api/v3"
+	)
+	client := &http.Client{
+		Timeout: defaultTimeout,
+	}
+	return &CoinGecko{
+		client:  client,
+		baseURL: baseURL,
+	}
+}
+
+type historyResponse struct {
+	MarketData marketData `json:"market_data"`
+}
+
+type marketData struct {
+	CurrentPrice map[string]float64 `json:"current_price"`
+}
+
+// Rate returns the rate of given token in real world currency at given timestamp.
+func (cg *CoinGecko) Rate(token, currency string, timestamp time.Time) (float64, error) {
+	const timeLayout = "02-01-2006"
+
+	url := fmt.Sprintf("%s/coins/%s/history", cg.baseURL, token)
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		return 0, err
+	}
+	req.Header.Add("Accept", "application/json")
+	q := req.URL.Query()
+	q.Add("date", timestamp.UTC().Format(timeLayout))
+	req.URL.RawQuery = q.Encode()
+	rsp, err := cg.client.Do(req)
+	if err != nil {
+		return 0, err
+	}
+	defer rsp.Body.Close()
+
+	if rsp.StatusCode != http.StatusOK {
+		return 0, fmt.Errorf("unexpected status code: %s", rsp.Status)
+	}
+
+	var history = &historyResponse{}
+	if err = json.NewDecoder(rsp.Body).Decode(history); err != nil {
+		return 0, err
+	}
+	rate, ok := history.MarketData.CurrentPrice[currency]
+	if !ok {
+		return 0, fmt.Errorf("currency %q not found in market data", currency)
+	}
+	return rate, nil
+}
+
+// USDRate returns the historical price of ETH.
+func (cg *CoinGecko) USDRate(timestamp time.Time) (float64, error) {
+	const (
+		ethereumID = "ethereum"
+		usdID      = "usd"
+	)
+	return cg.Rate(ethereumID, usdID, timestamp)
+}

coingecko/coingecko_test.go

@@ -0,0 +1,21 @@
+package coingecko
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCoinGecko(t *testing.T) {
+	cg := New()
+	rate, err := cg.Rate("bitcoin", "usd", time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("current Bitcoin/SGD price: %f", rate)
+
+	rate, err = cg.USDRate(time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("current ETH/USD rate: %f", rate)
+}

doc.go

@@ -0,0 +1,3 @@
+// Package tokenrate supports query historical rates of tokens. There
+// are multiple implementations using different API providers.
+package tokenrate

gometalinter.json

@@ -0,0 +1,10 @@
+{
+  "Vendor": true,
+  "DisableAll": true,
+  "Enable": [
+    "gofmt",
+    "golint",
+    "vet"
+  ],
+  "Deadline": "5m"
+}

interface.go

@@ -0,0 +1,17 @@
+package tokenrate
+
+import "time"
+
+// Provider is the common interface to query historical rates of any
+// token to real worldp currencies.
+// **Experimental**: the token, each provider intepretered currency,
+// parameters differently.
+type Provider interface {
+	Rate(token, currency string, timestamp time.Time) (float64, error)
+}
+
+// ETHUSDRateProvider is the common interface to query historical
+// rates of ETH to USD.
+type ETHUSDRateProvider interface {
+	USDRate(time.Time) (float64, error)
+}