feat: port template-parsing logic from influxdb (#146)

pkg/github/normalize.go

@@ -0,0 +1,45 @@
+package github
+
+import (
+	"net/url"
+	"path"
+	"strings"
+)
+
+const (
+	githubRawContentHost = "raw.githubusercontent.com"
+	githubHost           = "github.com"
+)
+
+func NormalizeURLToContent(u *url.URL, extensions ...string) *url.URL {
+	if u.Host != githubHost {
+		return u
+	}
+	if len(extensions) > 0 && !extensionMatches(u, extensions) {
+		return u
+	}
+
+	p := u.Path
+	if !strings.HasPrefix(p, "/") {
+		p = "/" + p
+	}
+	parts := strings.Split(p, "/")
+	if len(parts) < 4 {
+		return u
+	}
+
+	normalized := *u
+	normalized.Host = githubRawContentHost
+	normalized.Path = "/" + path.Join(append(parts[:3], parts[4:]...)...)
+	return &normalized
+}
+
+func extensionMatches(u *url.URL, extensions []string) bool {
+	ext := path.Ext(u.Path)
+	for _, e := range extensions {
+		if strings.EqualFold(e, "."+ext) {
+			return true
+		}
+	}
+	return false
+}