package proxy

import (
	"net/http"
	"net/http/httputil"
	"net/url"
	"strings"
)

// NewReverseProxy builds a reverse proxy to target base URL with path rewriting:
// stripPrefix (/api/{alias}) + pathPrefix (/v1) + remainder.
func NewReverseProxy(target *url.URL, stripPrefix, pathPrefix string, setAuth string) *httputil.ReverseProxy {
	proxy := httputil.NewSingleHostReverseProxy(target)
	orig := proxy.Director
	proxy.Director = func(req *http.Request) {
		orig(req)
		p := req.URL.Path
		if strings.HasPrefix(p, stripPrefix) {
			rest := strings.TrimPrefix(p, stripPrefix)
			rest = strings.TrimPrefix(rest, "/")
			if rest == "" {
				req.URL.Path = pathPrefix
			} else {
				req.URL.Path = pathPrefix + "/" + rest
			}
			req.URL.RawPath = ""
		}
		if setAuth != "" {
			req.Header.Set("Authorization", setAuth)
		}
	}
	return proxy
}